When I’m trying to diagnose a suspected fuel issue, I try to test whether it is lean or rich problem. I’m not good enough to figure it out by intuition.
Testing for lean is pretty easy. Put the engine at the RPM where the rough running occurs. Add some sort of fuel (spraying something down carb) and see if it smooths out or gets worse. If adding the fuel smooths it out, I go searching for the cause of the lean condition.
If adding the fuel makes it run rougher, I presumably have a rich condition. Verifying rich takes a little more creativity. I’ve done it on small engines regularly but not on my Stovebolt. Either have to restrict fuel or create an intentional vacuum leak. Plan carefully as to not expose yourself to the lean backfire you might create. Someone here probably has a suggestion.
I am not altogether convinced you have a fuel issue. It’s easy to start throwing crap at the wall and seeing what sticks when you get into one of these frustrating diagnoses. I am still guilty of that approach even though I should know better. I get all confident I know what’s up and chasing rabbits down dead ends.
I would strongly suggest:
1) Verify that initial timing is somewhat close by the flywheel ball and rotor position. Dizzy might have moved and you didn’t know it. Might also run at idle with a dwell meter, if you have one. I get a better tune using dwell than I do with point gap.
2) Put a vacuum gauge on it at idle and report back with reading and needle behavior. Vac gauge can point out all kinds of goofy stuff. Sticky valves, timing, compression issues, all kinds of stuff.
Edit: Ignition issues can present themselves in all kinds of weird ways that can keep a guy thinking it’s fuel. My bet would still be on an ignition problem.
Last edited by JW51; 12/06/2023 6:31 PM.
