My S8D will idle well however in the upper rev range to full throttle it has a minor misfire, just enough to seem like a surging engine however it is not that. It also requires petrol tipped down the air intake to start but starts on its own after that satisfactorily.
What I have done to date on this motor, not all to cure this problem just a list of work:
New Spark Plug - Have tried with a 2nd new plug as well.
New Points and condenser, gapped correctly
Cleaned gas tank and replaced fuel line
Had carb professionally rebuilt - new gaskets, needles, float etc.
New Air Filter
Fresh SAE30 oil
Removed cowling and cleaned fins
Have verified correct valve lash and movement.
It will idle happily all day long, perfectly smooth, however under load and predominantly at throttle it putters around no problem but has a steady misfire.
Any help much appreciated, have exhausted my expertise on it.