I know it's been asked before, and I've read the responses, but I'm still at a loss.
My 83 Brat has an intermittent problem of stumbling upon acceleration. It occurs whether the car is warm or cold. It seems to stumble only with slow acceleration and if I step on it, it surges and opens up, feels smooth. Doesn't seem to lack power overall and idles decently enough once it's warmed up. Stock Hitachi carb.
So far, in attempt to fix this issue and just because it needed it, I have replaced both fuel filters, air filter, spark plug wires, spark plugs(with new NGK, properly gapped), new distributor, put a bunch of heet and seafoam through it to clean out any gunk or water and checked for vacuum leaks by spraying starting fluid around the intake manifold and vacuum hoses (no change in idle speed noted). I also only run 89 octane or higher fuel.
Im thinking it could be a partially clogged jet in the carb. Maybe some other jet opens up with more throttle and thats why it only occurs at low throttle. I haven't opened up a hitachi, but I would be willing to rebuild it if that would help. And no, I'm not getting a Weber. I've gotten 31 mpg with the Hitachi properly tuned.
Any advice would be appreciated. Let me know if more info is needed. Thanks yall.