engine miss

My B has a high speed engine miss. Is it more likely to be fuel or igntion ? My plugs are very black from my time getting the carb " right" - could that be it? NAPA sold me NGK plugs ( all they had) - I wanted autolite 295's.

It idles fine

Thanks for your thoughts
 
Pull one plug wire at a time and see which cylinder has the miss. Then move spark plugs around and see if the miss goes with the plug
 
Agree with what has been said below. Listen close to the exhaust for a slight hiss sound. You would get the with a leaking valve. After spark plug test as done like below it need to have a compression check if plugs are not the problem.
 
I just went back and read that you had a (new) head. If the (new) head had a good valve grind you could have a tight rocker arm to valve clearance. If you don't have a feeler gage a single edge razor blade will work for clearance on this engine.
 
now this is a stupid question... I take one spark plug wire off at a time and it just seems to drop the rpms of the motor ( it may not be it but it runs rough). How do you tell if the miss is gone when removing each wire if it runs rough with a wire removed??

I hope that made a little sense.. THANKS
 
If you have a plug problem when you remove the engine sound changes when you remove a plug wire until you remove the wire from a bad plug and then you do not have a change in the sound. Switching plugs to different cylinders will have the problem follow a bad plug from one cylinder to another cylinder. If the problem stays at the same cylinder you can probly assume a leaking valve. Could be a head gasket.
If you have done this and could not see any change it sounds like time to check the valve clearance. .010 is what the book calls out for valve clearance but I use .012. If the clearance is all good I would do a compression check as it would point to a weak seal on a valve or two.
 
I will start checking - thanks for the info

I did a bad job of describing the sound it is like "small hicupp" that occurs ; almost like a "huff". Only does it a high idle. I did run the valves but I think I need to check again. Did a compression test and all were slightly over 100psi..

The plugs are pretty black from my carburetor adjustment so I think I will change those. I have NGK as they did not have automate . Going to put Autolite 295's

Does this sound like a direction??

Thanks again for your help
 

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