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Is it worth rebuilding a Rochester 4GC


DaveC6970

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Hello again, question for you all. My 63 has the original, as far as I can tell, Rochester carb on it. The previous owner told me when I bought the car he thought the carb needed rebuilt. When I test drove it I agreed something needed tuned but I wasn't sure it was the carb. The car runs rich and has bog when accelerating from an idle.

Once I got the car home I wanted to check the ignition system first, just to be sure it wasn't a timing/spark problem. So I've checked plugs, looked fairly new so I cleaned and reinstalled. Wires and distributor cap look new as well. Previous owner said he had replaced them. Checked the dwell on a meter, right at 30deg, that's good. Checked the timing, right on the 12 deg mark which is what manual says it should be. So I guess he was right, sound like it might be the carb.

I've been reading the service manual, not a lot of info about tuning the Rochester, unless I just haven't found it. My question is, would you rebuild the Rochester or just switch to the Carter? From the forum searches I've done it seems the Carter is the preferred carb. Would the cost of a rebuilt Carter be astronomical? I'm pretty sure I would just pay to have the Rochester rebuilt, I'm no carb expert.

Any advice appreciated, Dave

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If you have a basically stock engine and two original carbs, one a Carter, the other a Rochester AND you have both professionally rebuilt.

Then take the car to a mechanic, have he/she install one of the carbs, and not tell you which one, and seal the hood. Drive the car a 1000 miles. Then return it to the mechanic, who then installs the other carb. Seal the hood, and drive 1000 miles.

You will not be able to tell the difference in the 1000 mile drives. Good driveability, same mileage, same power.

HOWEVER:

If the engine is highly modified (big cam, headers, increased compression, etc.) you will find more individuals that can MODIFY the Carter (and it is somewhat easier to modify) than the Rochester.

Jon.

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Jon, so based on what you're saying maybe I'll just rebuild the carb I have. Now the only carb I ever rebuilt was a single barrel VW carb so it was pretty simple compared to the 4GC. I have been watching YouTube videos of 4GC carb rebuilds and I'm wondering if this is something I should try myself. What's a rebuild kit cost for a Rochester if I'm allowed to ask? Any advice for a first time rebuilder? Maybe no too try it? Thanks for your help -Dave

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The '63 Riviera came from the factory with a Carter AFB, carb number 3503S (or SA). Why would you NOT use the carb that the Buick engineers designed for this engine and transmission?

Which Rochester 4GC is it that you have? Does it have a number stamped on it? What is is from? Another full-size Buick with a nailhead?

It's not that hard to find a rebuildable Carter AFB. Why not get one, get it rebuilt, put the original air filter on it and drive away happy?

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Hi Jim, Thanks for the response.

I believe the Rochester is the carb my Riv came with, some did in 63 didn't they? The number is 7023143, at least that's the number written in my service manual, the tag is no longer on the carb. My car has the original air filter so I assumed it was the original carb, maybe I am mistaken.

I was just wondering if it was worth the cost of rebuilding the 4GC or should I skip the Rochester and go right to the Carter. The Carter is similar to the edelbrock isn't it? I have used them in the past with good results. Any tips on where to find the correct Carter carb for a 63? Maybe a want ad here? thanks again, -Dave

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Jim and I have had this discussion before. I have an AFB on my '63 now but it came originally with the 4GC. (I found a good AFB to install rather than rebuild the Rochester, and I had experience with rebuilding Carters on other cars I previously had.) There was no performance difference between the two. I just like AFB's because there are no gaskets (possible leaks) below the float level so you'll never experience leaking gas onto a hot exhaust manifold.

I bought the car from the original owner and got a complete service record with it. Had he changed carbs, it would have been in his service records. I'm with you, the Rochester is probably the original carb. The chassis manual specifies both Carter and Rochester carbs for the 401, and does not discriminate because of models.

Ed

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Dave - the 4GC is a larger carb than the VW carb, and has a few more pieces. On the other hand, the quality of the materials of the Rochester are far superior to those of the Solex, so doing a quality rebuild is much easier with the Rochester.

As to the youtube videos, cannot say, as I have not watched them.

The good news about the internet is that anyone can post HOWEVER

the bad news about the internet is that anyone can post!!!

There is sufficient Rochester material available if you look for it; as well as information in Buick shop manuals, Motors manuals, etc. that were written during the period when the carburetor was new.

If you doubt your ability to do the rebuild, find a knowledgable local that has done these carbs, and invite he/she over for a Saturday BBQ and carb rebuilding session. Nice to make friends, and learn more about your car.

Jon.

Edited by carbking (see edit history)
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I missed the part between removing the plugs and putting them back in where the compression was tested. If the valves and rings are shot, a valve is cracked, or a piston has a hole in it Nothing will smooth it out. That's the first step.

I have also found, possibly due to modern fuel chemistry, that plugs fouled by a car running rich rarely fire well after cleaning; replace them.

The 4GC is a friendly carb to rebuild. If you are learning you might want to buy two kits in case you have to give yourself class 101 over. Once you get the setting right be sure the choke heat tube works correctly. I did have a '56 Olds with a 4GC that I converted to an electric choke. It worked great.

If it is the wrong 4GC, then the correct carb should be installed.

Edit: I just had a brain fart. My AFB is one I rebuilt, first, in the early '80's. I remember having three carbs, the original, one from a '58 Lincoln that was larger, and some bits and pieces of others. I remember some of the Lincoln components were larger in bore, different metering rods, or something and I just used what looked good to me at the time. I redid it in the mid-90's and it still runs good.

Read books, be patient, and be willing to do things over, and read the books again.

Once my wife asked me why people paid me so much for fixing their cars. I told her to the best of my knowledge the other guys were fixing Buicks, Cadillacs, or whatever car based on the make history and anecdotal stories. I was fixing systems based on their mechanical principals. Read the books.

Bernie

Edited by 60FlatTop (see edit history)
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Dave, it was thirty plus years since I rebuilt my last carburetor on the kitchen table at my mom and dads house. That was before I rebuilt the Rochester 4GC on my 65. I got a kit for about $50, some carb cleaner, and a tray to do the work in. My wife would not let me use the kitchen table, but my work bench worked out fine. Take your time, follow the instructions, the Youtubes I saw were pretty detailed and did help, and take some pictures of the before carburetor. After you are done you will likely have extra parts, my kit did.

My car had the same sluggishness off an idle and after the rebuild that is gone, additionally the new accelerator pump doesn't leak like the last one (so no cleaning the intake manifold any more). I also found the rebuild that was done before I got the car had a few problems, the high idle cam was positioned incorrectly, and a gasket appeared to be from an incorrect kit and was causing a bad vacuum leak.

The rebuild didn't take long and was easy to do. After that a little tweaking of the idle jets and cam adjustments and your on the road.

Good Luck

gord

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Hi Jim, Thanks for the response.

I believe the Rochester is the carb my Riv came with, some did in 63 didn't they? The number is 7023143, at least that's the number written in my service manual, the tag is no longer on the carb. My car has the original air filter so I assumed it was the original carb, maybe I am mistaken.

I was just wondering if it was worth the cost of rebuilding the 4GC or should I skip the Rochester and go right to the Carter. The Carter is similar to the edelbrock isn't it? I have used them in the past with good results. Any tips on where to find the correct Carter carb for a 63? Maybe a want ad here? thanks again, -Dave

Ed is correct, you can use either carb. I prefer the Carter AFB. :cool:

The carb number you quote above (7023143) is listed in the Delco Carburetor parts list (Nov. 1971 printing) as for a "Buick 401 Late '63". Before it they used a 7023040 (which is the carb number in the shop manual). I don't know when they switched carbs. It is not mentioned in the service bulletins.

A full description of your carb is in the shop manual beginning on page 3-45. Rebuild instructions start on 3-50, including all internal and external settings. There is no reason why you can't follow them and rebuild it yourself.

I will be in LA on Monday May 19th with nothing to do during the day. If you want to rebuild it during the day (not in the evening, not at night) I will walk you through it in person. I seldom make this offer. :rolleyes: If we determine that there is any reason to not rebuild this carb, then you can look for an AFB to replace it if you want. Otherwise just rebuild it.

The new Edelbrock being sold is a modern version of the AFB. The main issue with it that I have seen is that the stock air filter housing does not fit the air horn by a small amount. I also don't know how they have jetted it. I prefer to stick to the original parts and know what you have.

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Ed is correct, you can use either carb. I prefer the Carter AFB. :cool:

The carb number you quote above (7023143) is listed in the Delco Carburetor parts list (Nov. 1971 printing) as for a "Buick 401 Late '63". Before it they used a 7023040 (which is the carb number in the shop manual). I don't know when they switched carbs. It is not mentioned in the service bulletins.

A full description of your carb is in the shop manual beginning on page 3-45. Rebuild instructions start on 3-50, including all internal and external settings. There is no reason why you can't follow them and rebuild it yourself.

I will be in LA on Monday May 19th with nothing to do during the day. If you want to rebuild it during the day (not in the evening, not at night) I will walk you through it in person. I seldom make this offer. :rolleyes: If we determine that there is any reason to not rebuild this carb, then you can look for an AFB to replace it if you want. Otherwise just rebuild it.

The new Edelbrock being sold is a modern version of the AFB. The main issue with it that I have seen is that the stock air filter housing does not fit the air horn by a small amount. I also don't know how they have jetted it. I prefer to stick to the original parts and know what you have.

Hey Jim, you bet I'll take you up on that offer. I'll order the rebuild kit and just let me know anything else I might need. Honestly I did want to try this myself but having an experienced person guide me, that's just awesome. Thanks so much! -Dave

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On the V8Buick forum, a couple of guys have taken the Edelbrock's AFB and swapped out the top fOR the OE Carter's AFB top so that the original air cleaners will fit properly. I guess you'd have to switch the linkage as well to work either the '63's manual kickdown or the '64 - 65 kickdown switch. I've not done this, only reiterating what I've read. One thing this would allow you to do is to run the Edelbrock AFB with the 750 cfm rating rather than the OE Carter AFB with 625 cfm. You would have to make sure that the intake manifold ports are large enough for the larger secondary butterflies to open fully if you wanted to take advantage of the additional cfm's

Ed

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On the V8Buick forum, a couple of guys have taken the Edelbrock's AFB and swapped out the top fOR the OE Carter's AFB top so that the original air cleaners will fit properly. I guess you'd have to switch the linkage as well to work either the '63's manual kickdown or the '64 - 65 kickdown switch. I've not done this, only reiterating what I've read. One thing this would allow you to do is to run the Edelbrock AFB with the 750 cfm rating rather than the OE Carter AFB with 625 cfm. You would have to make sure that the intake manifold ports are large enough for the larger secondary butterflies to open fully if you wanted to take advantage of the additional cfm's

Ed

I helped a friend over in Austin a few years ago where the Previous Owner blindly connected all the linkage on his '63 to a new Edlebrock AFB clone. My friend thought it ran well, but as soon as I saw how it was all connected, I could see that the kick-down linkage prevented him from opening the throttle much past half way. I temporarily disconnected the kick down and we went for a test drive.

He was thrilled. For the first time he experienced the full power of the nailhead! We went screaming down his street with the Dynaflow in Low. Then we went out on the Interstate in Drive. When he got it over 100 MPH, I asked him to please back it down! He had never been there before with this car. He was grinning from ear to ear the whole time! :D

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One thing I did notice this morning when out in the garage, I don't think the choke on this carb is working. When the engines cold that choke should be shut, right. Something is not right, I can't make it shut moving any of the linkages. Also, if the carb had a vacuum leak would that cause the rich condition and rough running? -Dave

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If adjusted correctly, on a cold engine, the choke butterfly should snap shut when you open the throttle even part way.

The most common cause of this not happening is the little choke piston is frozen in the bore inside the choke unit.

A common cause of this happening is that the hot air tube that passes through the passenger side exhaust manifold has rusted through and raw exhaust gases are flowing into the choke coil area instead of filtered hot air. You will find all kinds of carbon build up in there if this is the case. So you can see how one problem leads to another. You can rebuild the carb but it will give problems if you don't fix the hot air tube.

Or the little piston might just be stuck in there from not being driven for a long time. Try opening the throttle and then working the choke butterfly with your fingers to loosen up the little piston.

What you don't want is for the little piston to stick in the closed position... that will make it run very rich. You used to see cars going down the road pumping out a thick cloud of black smoke. This was often a stuck automatic choke.

A vaccum leak makes an engine run lean (lean = too much air, not enough fuel). It can make it run rough.

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Jim and I have had this discussion before. I have an AFB on my '63 now but it came originally with the 4GC. (I found a good AFB to install rather than rebuild the Rochester, and I had experience with rebuilding Carters on other cars I previously had.) There was no performance difference between the two. I just like AFB's because there are no gaskets (possible leaks) below the float level so you'll never experience leaking gas onto a hot exhaust manifold.

I bought the car from the original owner and got a complete service record with it. Had he changed carbs, it would have been in his service records. I'm with you, the Rochester is probably the original carb. The chassis manual specifies both Carter and Rochester carbs for the 401, and does not discriminate because of models.

Ed

My edition of the `63 service manual specifies the referenced 4 GC carbs for 4400 power pack-4600-4700-4800 Those models are the LeSabre with 4 barrel/dual exhaust, the Wildcat, Riviera and Electra. The 401 Rivs definitely came from the factory with 4GC carbs, I have seen MANY. As a matter of fact, the first carb i ever rebuilt (4 barrel) was on the first Riv I ever owned and it was a 4 GC. That was a looong time ago when the first gen cars were just cheap used cars.

It`s not a hard carb to rebuild. As Gordon has referenced be sure the gaskets match the carb body when you assemble it. There will be several choices in the kit. Good luck!

Tom Mooney

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Attached below is a pic of the choke inside(s) when I took it apart. Would you call that carbon-ed up? I would. The piston was froze just like Jim said it might be, but with minimal effort freed right up. I cleaned the inside with carb cleaner as best I could with the carb in place. Everything now moves freely. I also adjusted the fast idle linkage that was connected to the choke per the manual, this was way off. Reset the choke spring tension and tightened everything up being careful not to over tighten the choke screws. Guess what, with the choke working the car starts right up, funny how that works. I let the car run till it warmed up and the choke opened as it should. Also when I blip the throttle it doesn't appear to bog. It is still running a bit rich and has a miss that I can't track down.

I installed a set of new plugs, AC45S, per Bernie's suggestion. Checked the distributor cap for cracks, could find none. Checked all the plug wires for continuity and resistance, none were broken and the highest resistance I got was 12K ohms, these should be OK? So I'm down to the compression check, I have to admit I have never done this before. I went to the local AZ and bought the nicest gauge setup they had (Actron), figured it was worth the investment for future use too. I have read a couple of different methods for compression check, is one any better than the other?

thanks again for all the advice, you can learn so much on this forum. -Dave

post-97368-143142474449_thumb.jpg

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Attached below is a pic of the choke inside(s) when I took it apart. Would you call that carbon-ed up? I would. The piston was froze just like Jim said it might be, but with minimal effort freed right up. I cleaned the inside with carb cleaner as best I could with the carb in place. Everything now moves freely.

<snip>

That's looking pretty crusty. You may be better off finding a rebuildable carb in better condition.

You need to see if exhaust gases are coming up that hot air tube. On a cold engine, see if the tube through the exhaust manifold is burned through by blowing in one end while plugging the other end. I think there is a repair kit available for this if it's burned through.

Ed, if you convert a Carter AFB to electric choke, can you remove and plug this hot air tube? I've not done an electric choke.

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Dave,

Yup that is a bit of carbon build up. Even with the good results seen so far, I would still rebuild the carb. You will know for sure when it was rebuilt last and that it was done right, you will get some up close and personal time with another piece of your Riv (you will probably get familiar with every nut, bolt and screw with your car before you are done) and it sounds like you will have some bonding time with Jim to boot.

A quick compression check while Jim is there may be in order too. They don't take too long (less time without an AC compressor in the way of #1). I think it is easier with two people, I actually had some one-on-one time with my wife and the Riv when I did it last. A baseline straight dry compression check would be in order first. If you find some differences between cylinders or problems with any of them, a wet test or a leak down test may be in order.

Sounds like you are having fun.

gord

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It definitely appears as though raw exhaust gas is entering the choke housing thru the hot air tube. This situation needs to be corrected as soon as possible. The tube is pressed into the exhaust manifold so replacing it requires removal, etc. At that point you are faced with finding a suitable replacement, etc.

One alternative is an aftermarket "heat stove" which I have used several times over the years. It is a small half barrel that clamps to the manifold and accumulates hot air which is then drawn into the choke housing. It is a little slower than the factory system but does work.

Your other alternative is an electric choke conversion. It is advisable to wire it so voltage is sent to the choke housing only when the engine is running. There is an oil pressure switch which GM used in such applications in the `80`s. Search this forum for specifics, you should have no problem finding the info.

Nothing needs to be addressed regarding plugging the old hot air tube, etc. The only vacuum that is present in the system is applied to the stock choke housing, thru the carb, to promote hot air flow. This small vacuum signal will be cut off when the electric conversion is installed. Good luck,

Tom Mooney

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So I'm down to the compression check, I have to admit I have never done this before. I went to the local AZ and bought the nicest gauge setup they had (Actron), figured it was worth the investment for future use too. I have read a couple of different methods for compression check, is one any better than the other?

thanks again for all the advice, you can learn so much on this forum. -Dave

Remove all the plugs, disconnect coil wire. I like to number the plug wires with some tape. On a piece of paper list each cylinder 1-8 per the firing order. Install tester in cylinder 1 and crank engine for a few seconds so it makes at least 4-5 revolutions. Record reading on paper and move to next cylinder. You can do them in any order but I follow the firing order to help keep track. Depending on what kind of numbers you get will determine if you need to do further testing to determine a low reading cause is rings or valves.

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During the compression test you should ground the coil wire. The coil will put out as much voltage as is required to overcome the resistance of the secondary circuit. That means with the wire just hanging you could overtax the coil and maybe burn it out. By grounding it the resistance is minimized and the output is very low.

Be sure to open the throttle plates while cranking so an unrestricted flow of air goes into the engine.

In your picture that rusted plate in the back of the housing is supposed to come out in one round piece. It is a baffle plate.

post-46237-143142475316_thumb.jpg Its on the right.

To check the heat exchanger and sensing tube, disconnect the tube at the choke housing and start the car. There should be no exhaust flow through it.

Bernie

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Just food for thought:

An electric choke goes off by time.

The hot air choke goes off by engine temperature.

If one has an older automatic transmission, and tries to use the vehicle when the temperature is below maybe 50 degrees; one backs out of the driveway, stops at the stop sign 3 blocks from one's house, where the engine stalls, AND WILL NOT RESTART!

The solution(s):

(A) After starting the engine in the morning, go back in the house for your second (and maybe third) cup of coffee.

(B) Don't try to use the vehicle in cooler weather.

© Convert to a standard transmission.

(D) DON'T convert to the electric choke.

If the heat stove is burned through, here is a solution:

http://www.thecarburetorshop.com/Heatstovefabrication.htm

Jon.

Edited by carbking (see edit history)
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It definitely appears as though raw exhaust gas is entering the choke housing thru the hot air tube. This situation needs to be corrected as soon as possible. The tube is pressed into the exhaust manifold so replacing it requires removal, etc. At that point you are faced with finding a suitable replacement, etc.

One alternative is an aftermarket "heat stove" which I have used several times over the years. It is a small half barrel that clamps to the manifold and accumulates hot air which is then drawn into the choke housing. It is a little slower than the factory system but does work.

Your other alternative is an electric choke conversion. It is advisable to wire it so voltage is sent to the choke housing only when the engine is running. There is an oil pressure switch which GM used in such applications in the `80`s. Search this forum for specifics, you should have no problem finding the info.

Nothing needs to be addressed regarding plugging the old hot air tube, etc. The only vacuum that is present in the system is applied to the stock choke housing, thru the carb, to promote hot air flow. This small vacuum signal will be cut off when the electric conversion is installed. Good luck,

Tom Mooney

This is the choke stove repair kit I referred to in my previous post. Surprised it is still available.

http://www.jegs.com/p/Dorman-Products/Dorman-Choke-Stove-and-Heater-Tube-Kit/2395067/10002/-1

Good luck,

Tom Mooney

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I found time to do the compression check this evening. I had one cylinder (no.1) that was more than the 10% average compression. My averaged result was roughly 180 and no.1 was 200. Not much more than 10% but a little more. I came back and did no.1 again at the end just to be sure, result was the same. Results were as follows: 1=200, 3=180, 5=175, 7=180, 2=180, 4=180, 6=170, 8=170. Also the engine was cold when I did this and I did not add any oil to the cylinder before cranking.

I also attached a picture of the spark plugs, some are really dirty considering they were brand new yesterday only ran for about 10 minutes or so. Looking at the picture, the adult beverage cap would be the front of the car. It seems the plugs towards the front on either side are much dirtier, is that just coincidence?

What do you guys think, anything to be concerned about? Thanks -Dave

post-97368-143142475995_thumb.jpg

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When analyzing plug condition the distribution through the manifold will help identify a barrel of the carb that might be rich or spilling over.

Here is the nailhead arrangement:

post-46237-143142476649_thumb.jpg The fronts are fed by both barrels, looks like there is still a choke problem.

Bernie

Edited by 60FlatTop (see edit history)
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I found time to do the compression check this evening. I had one cylinder (no.1) that was more than the 10% average compression. My averaged result was roughly 180 and no.1 was 200. Not much more than 10% but a little more. I came back and did no.1 again at the end just to be sure, result was the same. Results were as follows: 1=200, 3=180, 5=175, 7=180, 2=180, 4=180, 6=170, 8=170. Also the engine was cold when I did this and I did not add any oil to the cylinder before cranking.

I also attached a picture of the spark plugs, some are really dirty considering they were brand new yesterday only ran for about 10 minutes or so. Looking at the picture, the adult beverage cap would be the front of the car. It seems the plugs towards the front on either side are much dirtier, is that just coincidence?

What do you guys think, anything to be concerned about? Thanks -Dave

There is nothing wrong with your compression numbers, considering they were taken on a cold engine. If the engine was still hot when it was tested, the numbers would all be higher and probably closer together.

If these spark plugs only have 10 minutes of run time on them, then I'd say your problem is ignition and #3 is missing big time.

What is the condition of the points and condenser? I don't remember, are they recently new? If new points, did you lube the cam?

I know you were talking about putting new spark plug wires in the engine. You can get a universal set and cut them to proper length:

[TABLE]

<tbody>[TR]

[TD]#1 (bent end at plug)

#2

[/TD]

[TD]

32 inches

[/TD]

[/TR]

[TR]

[TD]#3, #4, #5[/TD]

[TD]25.5 in.[/TD]

[/TR]

[TR]

[TD]#6, #7, #8[/TD]

[TD]22.5 in.[/TD]

[/TR]

</tbody>[/TABLE]

(Source: 1963 Buick Master Chassis Parts book)

Put a small ring of silicon tune-up grease in each boot before you snap it over the plug. After you snap it on the plug, rotate the boot on the plug 1/4 turn each way to spread the grease out. This will make getting the boots off much easier in the future.

Do you have the little plastic spark plug wire spacers mounted on top of the valve covers? Look in the shop manual and run your wires through them as shown to prevent cross-fire.

I know you mentioned a miss and perhaps a vacuum leak. I'd say it is ignition.

Not to say you don't also have a vacuum leak somewhere!

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Guest Coupfive

I just rebuilt my 4GC, the kit was $40, but I had to get some other gaskets that weren't in the kit. I took pictures and video of the dismantle so that I wouldn't miss anything when putting it back together.

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I seem to recall that the 4gc had a bit more flow than the afb and that with the 4gc two float bowls-one was for primary and one for secondary. The afb has one for a primary and secondary and the 2nd bowl for the other primary/secondary. The result was that a 'gramps' driven 4gc car where the secondaries never/rarely opened, got a gunked up bowl/float

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Guest Coupfive
Coup,

What kit did you use and which gasket was not included? Was it the gasket between the cover and carb body? Where did you get the proper gasket? Thanks,

Tom Mooney

I don't know my carb # because of missing tag, but was able to get the right parts and a copy of brass float measurements. Rochester 4GC.PDF

I got a Napa Echlin kit 2-5394 but it was missing two gaskets I needed. This kits are kind of funky but the ball bearings, and needles, etc. worked. I then had to get some additional parts from Quadrajetparts.com

1. Q1662E Throttle Body Gasket

2. Q1616C Bowl Cover Gasket

3. Rochester 4G Accelerator Pump Assembly, 3/4" Ethanol Resistant (OAL: 3.050") The one in the kit was 1/2" (too small).

I also got a Federal Mogul carb mounting manifold gasket Fel-Pro #9803

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The next time any one wants to rebuild a carb, give Jon at The Carburetor Shop a try for your kits. He makes his specifcially for THAT ONE carb you're overhauling. No universal 'zip' kits. He's on this forum under the handle of Carbking. If you check his website, you'll see that he makes a different 4GC kit for the '64 carb as compared to the '65 carb. There are differences and Jon's the one who knows what they are.

When I cross reference the Echlin part number you posted it says that it's for a Pontiac or a Studebaker.

www.thecarburetorshop.com

Ed

Edited by RivNut (see edit history)
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Thought I'd post an update, tonight I found some time to try and diagnose this carb/ignition issue again. I went to the service manual and found the section about tuning and setting idle mixture. So I set the mixture screws at 1 full turn out after gently screwing them in till they stopped. I started the engine, let it warm up, and started the process of screwing them back in till the engine stumbled according to the procedure. Well, nothing happened at all on the DR side screw, I could screw it in completely and the engine never changed one bit. The Passenger side would begin to run rough when you screwed it in but not the DR side. This barrel is also the one that feeds no's 2 and 3, based on the diagram above, which are the most fouled plugs from my pic, coincidence? -Dave

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On a four barrel carburetor, you have one primary that feeds four cylinders and one primary that feeds the other four. Then when you push down far enough on the throttle, you open the secondaries. Once again, one secondary feeds 4 cylinders and the other secondary feeds the other 4 cylinders. It's a dual plane intake. One plane for four cylinders, and a different plane for the other four. There is no single venturi that feeds just two cylinders. If that were the case, you'd only be supplying fuel to four cylinders on the primary venturi until you mash the throttle to open the secondaries to the other four. The left (driver's) side venturi - primary and secondary- feed cylinder #'s 2,3,5, & 8. The passenger's side venturi - primary and secondary - feed cylinders 1,4,6,& 7. Two even and two odd cylinders from each side of the carburetor.

I would venture to guess that if the idle screw does nothing to affect the idle mixture, that the butterfly is not fully closing and the fuel is going through the main fuel delivery system and over-riding the idle circuit. Make sure that the fast idle screw set against the choke step is not holding the butterflies open when you're trying to tune the idle circuit.

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Thought I'd post an update, tonight I found some time to try and diagnose this carb/ignition issue again. I went to the service manual and found the section about tuning and setting idle mixture. So I set the mixture screws at 1 full turn out after gently screwing them in till they stopped. I started the engine, let it warm up, and started the process of screwing them back in till the engine stumbled according to the procedure. Well, nothing happened at all on the DR side screw, I could screw it in completely and the engine never changed one bit. The Passenger side would begin to run rough when you screwed it in but not the DR side. This barrel is also the one that feeds no's 2 and 3, based on the diagram above, which are the most fouled plugs from my pic, coincidence? -Dave

You probably have an obstruction in the idle circuit passage that is not responding. While the engine is NOT running remove the idle mixture screw and use a rubber tipped blow gun to blow compressed air into the idle screw hole. Do this gradually and be careful. NO sources of ignition should be in the area like a lit cigarette, etc....What you should observe happen is the compressed air will blow thru the mixture passages including out of the vent tube at the top of the carb. If that does not happen the obstruction still exists. I have used this quick fix MANY times for an engine that is only running/idling on 4 cylinders. Good luck,

Tom Mooney

Edited by 1965rivgs (see edit history)
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  • 4 weeks later...

Thought it was about time for an update on the 4GC.

Last week Jim Cannon was in the area and gracious enough to come by and lead me through the carb rebuild. (Thanks again Jim!) We disassembled the carb, soaked the pieces in carb dip, cleaned everything real good, and reassembled using a kit from Jon "carbking" at The Carburetor Shop. (Very nice kit by the way). Having never rebuilt a larger, 4 barrel, carb it was a little intimidating but also kinda fun. Having someone who had done this before was a huge plus, the factory service manual is a must too. Now I wouldn't hesitate to rebuild my next carb.

The results were excellent, the car starts, idles, and runs so much better. The bog/hesitation when accelerating from a stop is completely gone. Also the previous miss I was feeling may not have been a miss at all, but that's a story for another thread.

I do have a question though, I noticed today that the upper carb gasket has wicked some fuel. Not leaking just damp with fuel. Is this normal? It may have been doing this before but I never noticed, now the carb looks like new so it's kind of obvious. I guess when you think about it, there's no way to keep it from not wicking, it has to be getting splashed with fuel from the inside.

Finally, to answer the question I started thread with, it was worth rebuilding the 4GC. Very well worth it!

Thanks again for all help and advice, Dave

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Dave - I am glad you your issue is now solved (and also glad you liked our kit ;) ).

Sometime if you take a carburetor bowl, clean it, and place it on your workbench in an upright position; then fill it to the normal fuel level with modern fuel and observe what happens. You may be surprised to find the fuel actually "climbs" the wall of the bowl right up to the top. So while "sloshing" certainly occurs, the fuel would get to the gasket surface even if the vehicle is sitting in your garage.

You will note that one of the mating surfaces will normally have a "sealing ridge" (see picture): http://www.thecarburetorshop.com/Rochestersealingridge.jpg

This is a picture of a new old stock casting. Note that the sealing ridge does have some imperfections (these things were mass produced, not individually machined).

The purpose of the ridge was/is to "bite" into the gasket and seal as well as possible. But even a new casting will, to use your term, "wick" fuel. The wicking can become somewhat worse as the zinc alloy develops minor surface cracks over time, and MUCH worse when some mis-guided individual attempts to correct a warped surface by filing it flat (thus removing the ridge).

In a nutshell:

If it is a "driver", the fuel seepage is quite normal.

If it is a "showcar", a toothbrush can be a useful cleanup tool right before the show.

Jon.

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