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CARB PROBLEM


cornwall classics

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Hope someone can help. I have a 48 Dodge club coupe, 230 motor with a ball and ball carb on it. I am having problems with the carb and setting the idle speed. If i set the idle speed to slow the engine ticks over fine but when i press the accelerator pedal the engine does not pick up revs straight away and cuts out sometimes. If i feather the pedal  this helps and will usually then pick up revs.  If i set the idle speed to fast i do not have this problem and the car picks up revs ok.  The plugs are also getting fouled with black carbon so presume it might be running too rich Any help would be much appreciated. Graham

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1 hour ago, cornwall classics said:

It has had a carb kit installed including new accelerator pump. 

Have you checked the adjustments on your carb linkage to make sure it begins to open when you press the accelerator?

 

Have you checked the idle adjustment screw? That,and the accelerator rod linkage is where it all begins. You might need to get someone to operate your accelerator pedal while you are watching the linkage move under the hood to get a clear understanding of what you need to do.

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When the carb was apart, did you remove  or disturb the throttle butterfly valve? I had the same problem with a B&B C6E2.The engine would idle on the adjustment screw, but the mixture screw had no affect - it idled best with the screw all the way in. Poor transition off  idle - stumble, hesitation, stalling, fouled plugs. I tried everything I could think of - Installed a carb kit, checked fuel pressure, changed the float level, different initial timing, a different distributor, nothing helped. I finally read the rebuild instructions in an old Motor manuel. They stressed the importance of correctly centering the throttle butterfly making sure the transfer slot was completely covered. The C stamped in the butterfly visible from the bottom and toward the idle port. The C6E2 had been apart before. Sure enough, the transfer slot was partially exposed with the butterfly completely closed. This condition bypasses the the idle port/ mixture screw completely and dumps  air/fuel emulsion below the butterfly. It's only supposed to happen off idle to supply extra fuel until the main metering system has sufficient air velocity to take over. I was not able to adjust the butterfly correctly as I think it had the wrong butterfly. Luckily, I had a parts carb, swapped butterflies, and that butterfly adjusted perfectly and the carb worked fine. If the  shaft is loose in the throttle body, the butterfly may not center correctly. Hope this helps.

 

The first picture shows the idle port and transfer slot below it.

The second picture is the throttle butterfly closed and the transfer slot covered.

The third picture is problem butterfly that couldn't be centered to close enough to block the slot

DSC08847.jpg

DSC08852.jpg

DSC08850.jpg

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13 hours ago, rekbender said:

When the carb was apart, did you remove  or disturb the throttle butterfly valve? I had the same problem with a B&B C6E2.The engine would idle on the adjustment screw, but the mixture screw had no affect - it idled best with the screw all the way in. Poor transition off  idle - stumble, hesitation, stalling, fouled plugs. I tried everything I could think of - Installed a carb kit, checked fuel pressure, changed the float level, different initial timing, a different distributor, nothing helped. I finally read the rebuild instructions in an old Motor manuel. They stressed the importance of correctly centering the throttle butterfly making sure the transfer slot was completely covered. The C stamped in the butterfly visible from the bottom and toward the idle port. The C6E2 had been apart before. Sure enough, the transfer slot was partially exposed with the butterfly completely closed. This condition bypasses the the idle port/ mixture screw completely and dumps  air/fuel emulsion below the butterfly. It's only supposed to happen off idle to supply extra fuel until the main metering system has sufficient air velocity to take over. I was not able to adjust the butterfly correctly as I think it had the wrong butterfly. Luckily, I had a parts carb, swapped butterflies, and that butterfly adjusted perfectly and the carb worked fine. If the  shaft is loose in the throttle body, the butterfly may not center correctly. Hope this helps.

 

The first picture shows the idle port and transfer slot below it.

The second picture is the throttle butterfly closed and the transfer slot covered.

The third picture is problem butterfly that couldn't be centered to close enough to block the slot

DSC08847.jpg

DSC08852.jpg

DSC08850.jpg

Thanks for this info i will definitely check the throttle butterfly. I did not take it off but because the car has not run since 72 it might not be set correctly. Thanks again for the info.

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I'd also check your float level again and make sure it's not too high leading to the rich condition you describe. Additionally for the off idle stumble make sure there is no vacuum leak at the carb base by spraying some carb cleaner around it, there should be no change in idle.

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In the post with the screens showing the illustrations, note the different size of balls the check valves.  It is imperative that they are in the proper positions for the accelerator pump to work.  

The other item to check is the step up valve.  If it is stuck open or not getting its proper vacuum signal it will cause an over rich fuel mixture.  This will cause poor running, sooted plugs, low gas mileage, heavy gas smell in the exhaust, and sometime gas oder in the oil.

The valve and piston should move freely against the spring pressure.  A vacuum signal from the intake manifold passes through a passage through the carb to hold it closed at idle and cruise with high vacuum. If the signal is absent, the spring holds the piston and needle valve open at all times.

 

What plugs are you running??  Champions are notoriously poor quality these days.  Been running AC 45 for years with great results.  Just pulled one the other day, after 15000 miles it looked so good, 

I put it back in and have assumed the others look the same.

Edited by greg g
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