850 Carter Thermoquad flooding at low rpm
Congrats on using the best 4bbl carb ever made.
I doubt that you have excessive fuel pressure causing the problem; the superior design of Carter/ Edel 4 bbl carbs means that they can tolerate 10 psi pressure.
As others have suggested, leaking/worn needle & seats can cause erratic running. To check: warm up engine, engine idling, look for fuel dripping from boosters. Should be dry.
I have heard of Nitrophyl floats becoming fuel logged, have never seen one & doubt that is your problem. Float should weigh 7.5-8 gms.
If the carb has a lot of mileage, possible cause of rough low speed running:
- rubber o rings leaking
- pri main jet plastic cap leaking.
O rings. I NEVER use the Carter o rings, too flimsy. Instead but some fuel resistant O rings 7/16" OD, 1/16" wall thickness.
Plastic caps. They are expoxied at the factory & can leak if treated roughly. It does NOT affect idle [ unless the lower gasket leaks ], but it can cause a rich cruise condition. The fix is to carefully scrape out the old white expoxy out of the joint & fill with new epoxy such as JB weld. Be careful not to excessive bulging of the epoxy otherwise, the lower gasket will not fit.
Set float level to 24mm.
Unlike brand H & clones, you will not need gaskets if you are careful.
That cam is going to have low vacuum. Make sure the metering rod hangar stays down at idle, in gear if auto.
Cam will require higher than stock idle speed. Too much transfer slot may be exposed at idle, adding to the rough running.
Factory initial timing [ 10-15* ] is not going to cut it, will need at least 25-35* at idle for best performance, best idle quality. See below.
First thing to do however is to check out/fix the carb as detailed above.
Congrats on using the best 4bbl carb ever made.
I doubt that you have excessive fuel pressure causing the problem; the superior design of Carter/ Edel 4 bbl carbs means that they can tolerate 10 psi pressure.
As others have suggested, leaking/worn needle & seats can cause erratic running. To check: warm up engine, engine idling, look for fuel dripping from boosters. Should be dry.
I have heard of Nitrophyl floats becoming fuel logged, have never seen one & doubt that is your problem. Float should weigh 7.5-8 gms.
If the carb has a lot of mileage, possible cause of rough low speed running:
- rubber o rings leaking
- pri main jet plastic cap leaking.
O rings. I NEVER use the Carter o rings, too flimsy. Instead but some fuel resistant O rings 7/16" OD, 1/16" wall thickness.
Plastic caps. They are expoxied at the factory & can leak if treated roughly. It does NOT affect idle [ unless the lower gasket leaks ], but it can cause a rich cruise condition. The fix is to carefully scrape out the old white expoxy out of the joint & fill with new epoxy such as JB weld. Be careful not to excessive bulging of the epoxy otherwise, the lower gasket will not fit.
Set float level to 24mm.
Unlike brand H & clones, you will not need gaskets if you are careful.
That cam is going to have low vacuum. Make sure the metering rod hangar stays down at idle, in gear if auto.
Cam will require higher than stock idle speed. Too much transfer slot may be exposed at idle, adding to the rough running.
Factory initial timing [ 10-15* ] is not going to cut it, will need at least 25-35* at idle for best performance, best idle quality. See below.
First thing to do however is to check out/fix the carb as detailed above.
