56 Buick

56 Rochester 4GC - buy kit or buy recond carb?

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Hi all

 

The car has a worsening idle and hesitation on acceleration. I have replaced almost all the ignition system and suspect the issue resides with the Rochester 4GC carb. 

 

I am interested to obtain opinions as to whether its best to buy a kit and rebuild the carb myself or buy a fully reconditioned unit?

 

I have also read of opinions regarding the Carter WCFB vs the Rochester. Are the 2 units interchangeable or require alteration of manifold and/or linkages?

 

Thanks

 

Drew

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Before making this decision:

(1) Have you done a compression check on the engine?

(2) Have the original points and condenser been replaced by an electronic whizbang? (If so, try points and condenser before throwing rocks at the carb). 

 

Both the Carter WCFB and the Rochester 4-Jet use the same mounting gasket, so would assume that nothing would need to be done to the manifold.

 

Both the Carter WCFB and the Rochester 4-Jet (opinion) are MUCH easier to rebuild than a Holley 4-barrel, and seems everyone is a Holley expert. If you have done a few carbs, see no reason why you shouldn't rebuild what you have.

 

As to a comparison of the WCFB vs the 4-Jet (you didn't ask, but extra information):

 

(Professional opinion) if both are professionally rebuilt, and you have a basically stock engine; you could have a mechanic install one and seal the hood, and drive it 1000 miles. Then have the mechanic change carbs, seal the hood, and drive another 1000 miles. At the end, you really would not have been able to tell the difference.

 

Jon.

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I would add that you may never get rid of the hesitation because there was a tech services bulletin that indicated some ways to lessen it. Which means it was prevalent when these cars were new and there was no sure-fire fix. 

However, you may want to try snugging the carb mounting bolts. Also how old is your gasoline and is it ethanol free?

 

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And if the carb does need work, get the kit.

 

"Remanufactured Carburetor" was, for a couple of decades at least, just a codeword meaning "horse puckey" or "someone else's problems". Unless you already have such a carburetor on your car, the one you would be giving away as a core is 10 times better than what you would be buying.

 

If you do not have the ability to overhaul it yourself, or don't want to, find a specialist who is very familiar with the 4gc to rebuild the one you have.

 

P.S. Carbking (2 posts above) has rebuild kits, very good ones.

Edited by Bloo (see edit history)
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Rebuild what you have.  The many times I replaced with a reconditioned carb off the shelf that did not work well I lost count.   Concerning hesitation,  I can attest to my rebuilding of the Rochester on the 1960.   The only item internally I replaced was the accelerator pump.  I used a can of carb cleaner to clean it up. Sprayed in the various orifices, etc.   I assured the floats were set as they should be.  I put the top back on with new gasket.  My rough idle is gone.  The best part, the hesitation was gone as well.   Entirely new running condition for the better.  

Edited by avgwarhawk (see edit history)
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The car may well have used ethanol fuel before I bought it and likely also sat without running for long periods. I have not used ethanol fuel but again the car csn sit for a while without starting.

 

The car has petronix electronic ignition but a reason I put that system on was that the engine was running rough when I bought the car. I did a compression test and the figures weren't fantastic - cylinders varying between 105 and 135 with majority around the 120/125 if I recall correctly.

 

The carb just seemed like the culprit as the rough idle has steadily been getting worse. One side idle mixture screw has quite limited responsiveness - I did try to blow out any sediment with compressed air but that had no effect. And it is dufficult to get engine to idle low unless I physically push the throttle linkage back against the stop despite the idle and choke settings being backed right off.

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13 minutes ago, 56 Buick said:

And it is dufficult to get engine to idle low unless I physically push the throttle linkage back against the stop despite the idle and choke settings being backed right off. 

 

That would suggest that the throttle shaft or bushings are worn out. If so it may need to go top a specialist. When you have it off of the car, pull the throttle arm in the same direction the return spring pulls it and close the throttle slowly. If a throttle plate is scraping the bore before it closes, the shaft or bushings are going to need work.

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Are the compression numbers from a current test, or from when you purchased the car?

 

Not horrible, but not good either. Would be nice to have numbers from a current test.

 

If you are in love with the electronic whizbangs, I will not attempt to change your mind; but (no offense meant) will not waste my time trying to debug a carburetor on a car with this conversion! If you absolutely must have the whizbang, an upgrade to an alternator is a necessity. A generator does not provide a stable voltage at idle, and can cause the whizbang to not bang correctly at idle.

 

And just for the record, I do NOT own stock in the companies producing points and condensers.

 

To add to Bloo's post above: the initial clearance from the throttle shaft to throttle body was 0.004~0.006 inch. 0.003 additional wear is acceptable. So, using a dial indicator, measure the clearance of the primary throttle shaft (the secondary will be fine). If it does not exceed 0.009 inch, forget about it. 0.010 or more, something to consider.

 

Jon.

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20 hours ago, carbking said:

Before making this decision:

(1) Have you done a compression check on the engine?

(2) Have the original points and condenser been replaced by an electronic whizbang? (If so, try points and condenser before throwing rocks at the carb). 

 

Both the Carter WCFB and the Rochester 4-Jet use the same mounting gasket, so would assume that nothing would need to be done to the manifold.

 

Both the Carter WCFB and the Rochester 4-Jet (opinion) are MUCH easier to rebuild than a Holley 4-barrel, and seems everyone is a Holley expert. If you have done a few carbs, see no reason why you shouldn't rebuild what you have.

 

As to a comparison of the WCFB vs the 4-Jet (you didn't ask, but extra information):

 

(Professional opinion) if both are professionally rebuilt, and you have a basically stock engine; you could have a mechanic install one and seal the hood, and drive it 1000 miles. Then have the mechanic change carbs, seal the hood, and drive another 1000 miles. At the end, you really would not have been able to tell the difference.

 

Jon.

Thanx 4 posting! Ive read that that quadra-jet carb was the closest thing to a computerised carb while still being mechanical becuz of its ability to be very precisely adjusted and its flexibility with regards engine size. I found one adapted with an aluminum plate to a 56 Cent 322 and was wondering what you might think about that modification? Thanx ahead for your input! Best Regards, Greg

Edited by 2carb40 (see edit history)

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1 hour ago, 2carb40 said:

Thanx 4 posting! Ive read that that quadra-jet carb was the closest thing to a computerised carb while still being mechanical becuz of its ability to be very precisely adjusted and its flexibility with regards engine size. I found one adapted with an aluminum plate to a 56 Cent 322 and was wondering what you might think about that modification? Thanx ahead for your input! Best Regards, Greg

 

The short answer is: DON'T DO IT!

 

The Rochester Quadrajet (opinion) is an excellent carburetor (although probably no better than the Carter Thermoquad). BOTH REQUIRE AN INTAKE MANIFOLD DESIGNED FOR A SPREAD-BORE CARBURETOR!

 

You could always remove the hood, and hire a 15-year-old to sit on the fender and pour gas into the engine out of a leaky boot! Would probably work better than the adapter!

 

Jon.

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2 hours ago, carbking said:

Are the compression numbers from a current test, or from when you purchased the car?

 

Not horrible, but not good either. Would be nice to have numbers from a current test.

 

If you are in love with the electronic whizbangs, I will not attempt to change your mind; but (no offense meant) will not waste my time trying to debug a carburetor on a car with this conversion! If you absolutely must have the whizbang, an upgrade to an alternator is a necessity. A generator does not provide a stable voltage at idle, and can cause the whizbang to not bang correctly at idle.

 

And just for the record, I do NOT own stock in the companies producing points and condensers.

 

To add to Bloo's post above: the initial clearance from the throttle shaft to throttle body was 0.004~0.006 inch. 0.003 additional wear is acceptable. So, using a dial indicator, measure the clearance of the primary throttle shaft (the secondary will be fine). If it does not exceed 0.009 inch, forget about it. 0.010 or more, something to consider.

 

Jon.

The compression is low...should be closer to 170 (HERE).  Either that engine is real tired or was rebuilt with low compression components.  A leak down test may be in order...leaking intake valves will cause stumble.  A vacuum gauge may help diagnose also.

I you insist on running the Pertronix:  Use an alternator as noted above; use resistor plugs along with suppression wires; new cap and rotor and then to check for electronic interference tune the am radio between stations and anything other than constant static with the engine running (like popping) needs to be checked; use a stock coil and DO NOT bypass the ballast resistor... the rotor on 322's is unique as it has a carbon rod between the center and tip and if a hotter spark run it will arc and even catch fire.

Remember:  ignition problems come on suddenly and carburetor problems develop slowly.

If you do service the carb, study the diagrams and understand the function of the various parts as outlined in the service manual.  Then pay attention to the fuel passages in the base or throttle body section above and below the throttle plates; then follow up into the base to be sure all passages associated with idle and transition are open.

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And do not over look a repeat compression test.  Chances are the low cylinders are on the right side bank, towards the back, and there be burnt or cracked valves. 

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Your car should show a lot on a oscilloscope. You may have to hunt to find one. In the 1990's I had an obsolete Allen diagnostic center and once I learned to read the waves there was a ton of information on each cylinder that could be gleaned. It was a large unit with an over car swing arm that had more functions than I needed and took up too much space so I sold it off in pieces.

Today I can do similar diagnostics with a vintage Sears unit that has an inductive high voltage plug wire lead. It is not the same degree of analysis as the O-scope, but I can compare voltages on each cylinder and, if necessary, match the intake manifold runners to the cylinder readings to see what internal sections of the carb may be running rich or lean. Or locate a vacuum leak internal (valve guides) or external to the cylinder.

 

There is a lot of good diagnostic equipment out there that still works fine and about $30 is the top money, even up into the OBD1 cars.

 

Great reason to buy more tools!

Bernie

Edited by 60FlatTop (see edit history)
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3 hours ago, 60FlatTop said:

 

Great reason to buy more tools!

Bernie

 

I do not really need a reason.  I just want more tools. Guess that is reason enough.    

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"Reason to buy tools" and a place to keep them, if available.

 

www.halifaxshops.com might be one source of used Sunn diagnostic equip.

 

At work, at one time, we had one of the BIG Sunn roll-around units.  Had the sniffer for emissions readings, until one tech used that rubber line to check for a possible head gasket leak.  It inhaled coolant when he got it too close.  OUCH!  By that point in time, it was taking up space in the shop, so it "went somewhere else".

 

NTX5467

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I found this piece of equipment at a local garage that was closing down.  Cost me $ 50.  It works but the one cable looks like it has been caught in a fan blade one too many times.

I found a replacement and its on its way. I also found a place that has a ton of books on this and also on how to read the waves on the scope. Seems like black magic to me, but I am going to try.

 

 

IMG_2865 (1).jpg

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7 hours ago, Bill Stoneberg said:

Seems like black magic to me, but I am going to try

 

If you are comfortable with Mirror Magic you should do OK.

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