[sc2dave]

If i have an ex.leak right above one of the header tubes,would it cause that cyl to run richer? I took the gasket off and the ex. port on that cyl was way blacker than the rest.

[UTI4Life]

If you have a leak on only one tube, the exhaust isn't traveling the way it was intended (ie.: through the manifold). If its black around the gasket, couldn't that just mean exhaust is working its way around the gasket therefore leaving it blacker? The only way to change air/fuel ratio on one cylinder (in my mind) is if you had an O2 sensor on each exhaust manifold "tube". A very complicated setup i'd imagine.

More details would help also...
any cylinder head damage?
old, worn piston rings?
anything else relevant to this situation.

hope this helps

[sc2dave]

The whole exhaust port from the valve to the gasket on this one cyl was blacker than the other 3 cylinders.. It's on a 4cyl. engine.

[UTI4Life]

Just out of curiosity, have you checked valve train on the car? maybe cylinder compression checks? Id bet you got something else going on inside to make it that abnormally black. Leaky fuel injector even?

[sc2dave]

carbed ,22r engine. Double-checked valve clearance,recently did valve job.

[UTI4Life]

Id still be interested to see how a compression check goes... Thats the only other thing I can think of as far as causing the blackness. sorry couldn't be more help...

[sbchevfreak]

This blackness is likely due to air being drawn into the port on the low pressure pulse, through the leaky spot. You are getting some unburned hydrocarbons in your exaughst, and the leak is allowing air into the ex stream, and due to the heat and fuel and air there is incomplete combustion happening in the port. Not very likely that you have one hole running much richer than the others.

[UTI4Life]

Originally Posted by sbchevfreak

This blackness is likely due to air being drawn into the port on the low pressure pulse, through the leaky spot. You are getting some unburned hydrocarbons in your exaughst, and the leak is allowing air into the ex stream, and due to the heat and fuel and air there is incomplete combustion happening in the port. Not very likely that you have one hole running much richer than the others.

why is there combustion occuring outside the combustion chamber...?

have you checked your plugs? oil fouled maybe...

[sbchevfreak]

Originally Posted by UTI4Life

why is there combustion occuring outside the combustion chamber...?

have you checked your plugs? oil fouled maybe...

Easy. On any engine, especially a carb job, there is never complete combustion. It is the reason for HC's in the exaughst stream. When you have air introduced into that stream, that close to the point of ignition, it can and does make a combustable mixture, and the port temps are high enough to make it burn. It does not "explode" like it does in the chamber, but it does burn. It does not burn well, andf leaves a black carbon residue. Have you never heard an exaughst afterfire?