Any thoughts on this engine issue

73AbodEE said

this is a mystery and i will not rest until this is solved. if you have exhausted and replaced everything outside the engine, its time to dig in. i would start right at the timing cover.

what causes a surge?

vacuum leak (s)
a stretched chain or timing has jumped
any kind of fluctuating fuel pressure

because you have eliminated the fuel pressure and any vacuum leaks , that really leaves only the timing. everything is coming back to the timing. you say it is jumping around?

are you sure the mufflers are full of mud? lol

Click to expand...

Being that the engine was built 100% with all new parts -- NOTHING USED except the crank and rods, and they were all handled and the engine builder... Which I am not...So I have a hard time seeing how the steel chain would have stretched with just idle time on it. Only actual driving time was about 40ft to put it on a trailer 4 years ago... Since then its only been pushed...

The only place it could be leaking vacuum would be under the intake were we can not get to.... and the puzzling part is when we un cap the vacuum for a direct leak at the carb it runs a little better. Doesn't eliminate the issue but does run better.

Fuel pressure is solid right in the range of the pump. Pump is 5.5-6.5 psi rated and the gauge reads 6psi all the time.

Definitely confused.... But I'm not engine guy either..so it didn't take much.