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55 century carbissues


gmeyer316
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The OP is gone.  He wants it to be a carb issue that is fixed externally.  From his introduction post, this car is new to him, pictures show a newly painted engine with lots of rigging and omissions.  No way to tell what was done inside or outside and apparently he wants no guidance to find out.

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I just got a look at this thread. "If the car was mine" I would start it and bring it up to the temperature where it cuts out and let it die. Then real quickly remove the air horn and float bowl cover.Allow that the fuel will be lower when the floats come out and look in all the chambers of the carb to see where fuel is missing, but should be there. Play attention to the accelerator pump well as well as the other little nooks and crannies. Once you have looked everything over and made your mental notes, put the float cover back on,tart the car and shut it off quick. Uncover the guts again and snoop around. What ain't right? Where are the vapors rising from? Is the pump well empty?

 

This is stuff I have actually done on these untenable problems. What I would be looking for is a fuel chamber adjacent to a vacuum passage that may have developed some porosity over the past 60 years. When you say "Hey! There's supposed to be gas in there." You may be on the track. I had it happen on a 4GC Rochester, but they are all made out of the same cheezy metal. I replaced the bowl and lived happily ever after. I was always going to coat the area I deemed porous with expoxy and test it. More pressing stuff came up.

 

It's worth a try. Always remember "The level of perfection one can achieve is directly proportional the the number of times they are willing to take it apart and do it again."

Bernie

Edited by 60FlatTop (see edit history)
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Well Im back been gone a few days, I wasn't ignoring any of you guys and I appreciate any help any of you can given me. Yes the car is new to me and its been years since I messed with these old engines. I got it from a guy who is familiar with these old Buicks with lots of rebuild experience, and I am indeed interested in your ideas and advice in order to solve this dilemma. I don't care what kind of issue it is and would like to solve it whether it be internal or external. Im just an old biker who cant ride any more because of arthritis in my hands so I thought I would try classic cars and I really like these old Buicks. I used to work on the old forties and fifties Chevys when I was young, I just need to refamiliarize myself with this fabulous old iron.

Now, I checked out the points and they were pitted beyond recognition so I replaced them and the condenser, the dwell is now 29, the book says 28-32 and the timing is right on. I have eliminated the vacuum line to the wipers so no leaks there now the only vacuum line is the one from the pump to the manifold. .

It started cold better than it has been and ran smooth till warmed up, once warm, idle fluctuates a bit and when put in gear dies almost immediately. I have no doubt that it is a carb problem at this point was just hoping it might be something easier.

I realize there is a wealth of experience knowledge and wisdom here, that's why I came here in the first place.

I thank all of you for any help you have sent my way and hope to continue a friendly dialogue with all of you.

Thanks Bernie

Greg

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Assuming that it was running/driving when you got it. I think what might help everyone here is if you could list out what changes and adjustments you made since you've had it. Preferably in order of how you made the changes and adjustments.

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That might help Paul, lets see what happens.

 

Still looking for 1) vac gauge reading at idle if possible to verify Mikes hunch, 2) rpms at hot idle in N and D and 3) rpms when timing was taken. 

 

Getting to idle under 400 rpms hot to let off the vac advance and allow an accurate timing measurment would seem pretty tough given the symptoms unless the advance was unplugged during the measurement.

 

A vac leak to kill the engine in D would have to be pretty big (and audible). And it would really be stumbling in N - hard to not notice.

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Hopefully, too, the timing was set/adjusted AFTER the points were installed and adjusted as point dwell change has a direct affect upon ignition base timing.   Points, then base timing, then hot idle speed, then idle mixture adjustments/tweaking, recheck idle speed and adjust idle speed and mixture until all is "in spec" and the engine operates "nicely".

 

If everything else has been done "to satisfaction", then it just might need a little more (hot) base idle speed to keep running reliably?  In some cases, especially with older vehicles and older (used) engines, the "factory specs" can be a good starting point for things, but if a little more idle speed might make things work better, then that's what the car is telling you it desires (like an additional 50rpm or so).  Once the idle is solid and reliable (in gear and in Neutral/Park), THEN you can worry about the apparent issues with the accelerator pump and related items.

 

It looks like things are progressing in the right direction (chasing vac leaks and such).  Please keep us advised of your progress.

 

NTX5467

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Looks to me that you need to start over with the idle mixture screws. See what the book says as a starting point to back them off. Bottom both screws and make a note how far each one was out from lightly bottomed. Back them both out equally to book specs, maybe 1 1/2 or 2 turns each and adjust from there for max vacuum or rpm. Adjust idle speed screw for 450-500 in park, some readjust of mixture screws may be required if idle was too high.

Sorry if I missed that you already adjusted idle mixture by the book, That is always the recommended procedure.

The reason you need the idle lower than 450 to set timing is to be certain the mechanical advance is out of the picture and not affecting timing.

OOPS! NTX5467 AND I WERE BOTH TYPING AT THE SAME TIME.

Edited by TexasJohn55 (see edit history)
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Thanks to you all. Lets see, first off I cant seem to get it to idle any slower than about 800. The first thing I did was to bend the accelerator pump rod straight, then eliminated the vacuum line to the wipers, then I tried timing, was a little advanced so I brought the lines back together and it idled a little better, that is when I checked the points and replaced them, set them at .016, that brought the dwell from 21 to 29, had the vacuum advance disconnected at the carb and the hole on the carb plugged during timing, again idled a little better but still dies is gear, I don't have a vacuum guage. Im thinking I need to pull the carb and go through it myself.

Greg

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Hmm, before pulling the carb, just for kicks, adjust the timing 'by ear' if you can. i.e. bring it back where you have a slow/smooth idle. It could very well be that the dist is off by one gear when it was installed and when timing by the marks it's not matching up to what it's supposed to be.

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When troubleshooting something like this it is best to say "I have a problem with my car." Pulling the carb is like "taking it out of context". Do you know how much trouble is caused by taking things out of context?

Bernie

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Did you verify that the vacuum advance is working?  Also check the sparkplugs.  Whoever neglected to change the points may have done the same with the sparkplugs---or---they installed platinum plugs that will absolutely not work in a carb engine.

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You must get the idle back down before you can adjust anything, back off the idle screw.

X2.

Let's work with what we know is wrong. The idle speed is twice what it should be to take an accurate timing measurement and the speed screw is bottomed out.

You stated that you brought the marks back together. At what idle speed? How about putting a timing light and tach on the car. Drop the idle rpm from 800rpm in 100 rpm increments and monitor the timing and try to get the timing back to base 5 deg at 400 rpm or less.

My interpretation of the findings in the post is if the timing is "right on" at this high of an idle , given it is difficult to idle below 800, then cranking the idle down is retarding the timing to the point of not running as the advance comes off. Maybe advancing the timing incrementally as the idle comes off of 800 will do it. Let's see how low we can get it to idle in P before it dies.

Don't pull the carb yet. There's a few more easy checks before we disturb the carb. One thing at a time. Pick someone's advice on this thread one step at a time and go from there. Do each step accurately so we get good information. If you did do any changes since it was running right and "just started acting up" tell us back to Paul's point.

Stay on it.

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I'm not familiar with the distributor's advance curve on the Nailheads of that vintage, but I know that for a middle-60s era motor, the centrifugal advance usually starts at about 1000rpm, but then idle speeds were usually about 550rpm in gear, or thereabouts.  I'll have to see if I can find an older service manual online, just for general information.

 

Platinum plugs in a carbureted engine?  I've been doing that for a good while, even Iridium (which has superceded platinum in many spark plug applications--even Buick 3800 V-6s OEM).  I'm not sure what issues Old-Tank might have had, though (which I'm interested in finding out).  Be that as it may.

 

You DO need to get it to idle at the factory spec rpm FIRST.  Point dwell WILL change with increasing rpm, too, which again, affects distributor spark timing.

 

WITH the engine at specified base idle rpm, is there any sensitivity to the adjustment of the idle mixture screws?  One or both?

 

Getting back to the "flow of fuel in the idle system" (mentioned in my earlier post), the FINAL point of calibration in the idle circuit is the idle mixture screw.  This screw seats against a hole in the throttle body, even might stick out of it a little.  The SIZE of the hole is important in how rich you can make the mixture with the screw.  In about 1971 or so, for example, GM/Rochester decreased the size of that hole from its earlier size so that you couldn't make the mixture richer than a certain level (for exhaust emissions reasons).  In this case . . . it's the manifold vacuum which is acting upon the idle system to pull fuel from the float bowl, into the venturi cluster, and then down to the idle mixture screw level AND the transition slot in each throttle bore.  IF those holes might have a little corrosion on/in them, even if everything else is "as designed", it would make the idle too lean and could result in the "dieing" described.  Something else to check when you disassemble the carb.

 

Also, on the pointed end of the idle mixture screw, the pointed end will be smooth before the threads start.  Check for the smoothness of that pointed surface, where it seats against the carb throttle body.  Sometimes, the screws can be tightened too much in seating them for the initial "turns-out" mixture setting, which can affect how things work a little bit.  A "shiny line" is acceptable, but an "indented line" would be marginal or need some attention.

 

Hot base idle to specs, then base timing setting, then dwell (already done), then adjusting the idle mixture/speed for "best lean idle" and "highest manifold vacuum".  "Best Lean Idle" is an emissions' era orientation, but can work on most anything.  When the idle speed and mixture are optimized, to verify that, you can turn the mixture screw in to get a 20rpm drop, then return it to what it was . . . on each one.  The manifold vacuum should not change that much, if any, but this ensures that an "over-rich" idle is replaced by a "cleaner idle".

 

As mentioned, too, the vacuum advance needs to work for best drivability and cruise fuel economy.  Typically, it is hooked to a "ported vacuum" source (significant vacuum happens when the throttle valve is opened, with a very small amount at base idle, if any).  Vacuum advance usually needs about 5" Hg to start things moving .  .  . separate from the mechanical advance system.

 

Thanks for the updates.  Please keep us posted . . .

NTX5467

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Sorry Bernie, Im just trying to take all this in, so many ideas Im not sure where to start, gonna check mixture screws for scoreing and make sure the plugs are good, I think Im finally catching on, been a lot of information to process, will do my best to lower the idle speed using all of you guys ideas, and then take it from there, I sincerely appreciate all the time all of you are investing in order to help a stranger solve his problems. I haven't messed with engines for years except Harley engines, Im trying to catch up.

One question, the vacuum line from the carb to the distributor is made of steel and is very very small, Ive always seen much larger rubber hoses used there, could that be an issue. Bare with me Im not totally clueless but I have much to learn.

Thanks again for all of you guys time.

Greg

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Ok,sorry Bernie I am kinda overwhelmed with ideas from a number of directions, anyway I figured start over with the easy stuff first. Finally got it to idle just a little under 500 if you can call it idleing. it barely keeps running but seems to be pretty smooth. the vacuum advance is disconnected with the carb hole plugged, timing is advanced about a degree, starts to lag if moved either direction, adjusted idle screws according to the shop manual, dwell is at 29. Is it supposed to keep running is gear at 450 rpm just putting it in gear drops it 100 or so. None the less I think we re headed in the right direction

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Update, I finaly got it to idle nice at 500 timing a tiny bit advanced dwell 29-30, took it on a road test couldn't hear it running while at a light, was nice and smooth, only problem now is a slight hesitation when you first give it gas. Maybe accelerator pump issue?

Thanks to everyone who helped me struggle through this. Got plenty more I want to do to this car and will come to you guys when I need help.

Greg

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Thanks for that update!  Sounds like things are coming together!

 

You can check the accel pump "shot" by operating the throttle . . . engine OFF . . . and looking down the primary throttle bores.  Might need to verify that the pump arm is shaped like it needs to be, for good measure.  From my experiences, Carter 4bbl pump shot always seemed a little "lazy" compared to a similar Holley 4160-style carb.  But no real issues with tip-in "sags".  Adjusting the pump volume is what the extra holes are for in the accel pump arm.

 

Some of the older 4bbls used a leather accel pump plunger, rather than a more modern neoprene pump cup.  Leather can shrink with age, just as the accel pump bore can wear from use.  Might need to pull the pump plunger out and roll it backwards to get it fluffed-up some.  Some prefer the leather to the neoprene in those older carburetors.

 

Keep us posted, please.

NTX5467

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Try fine tuning the mixture screws as NTX suggested.  On todays fuel they may be turned out about 2-21/2 turns - least thats where mine cooperates best.  Some of Carter WCFBs have a bit of a flat spot in them coming off idle.  If its not too bad consider leaving well enough alone.

 

Good job.

Edited by KAD36 (see edit history)
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another update, I think I solved the accelerator pump issue, I noticed that the bend on the arm was so that it was keeping the pump arm from returning all the way down to rest position, making it so the pump was not getting a full stroke and the stroke was starting in the middle instead of the beginning or bottom. Make any sense, seems to have improved, much less hesitation.

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A comment on the mixture screw setting:

 

There is a MAXIMUM setting beyond which no further good is accomplished. Check the original manufacturer's literature for a range. On carburetors built prior to 1968, over 1 1/2 turns generally is futile, but there are a few exceptions.

 

What happened in 1968??? Smog emission. So, the angle on many idle mixture screws was changed; as for smog emissions, it was desirable for finer tuning with the screws. Some carbs in the early 1970's still have adjustment at more than 3 turns.

 

Contrary to what many believe, the idle mixture screws do not adjust the idle mixture! Rather, they meter the preset mixture. The mixture is preset by the diameters of the idle jet, idle air bleed, and idle air bypass.

 

If it seems impossible to acquire sufficient mixture within the manufacturer's range on pre-1968 carburetors, remove the idle jet(s) from the carburetor and drill them oversize. Start with 0.002 inch and then in an increment of 0.001 until a good mixture is acquired OR a maximum of 0.005 inch. Making this modification on 1968 and newer carburetors being used on licensed vehicles is probably unlawful under the 1966 Amendment to the Clean Air Act.

 

Jon.

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