Mystery stumble/stalling - SOLVED

I need some input... I just put a brand new Weber 32/36 on my 86 wagon. It runs great, except from 3-4K at part throttle in higher gears, it stumbles, backfires through the carb, and falls flat / stalls. If I downshift it recovers, or if I floor it she usually straightens right out and goes. Basically, I can cruise up to 45-55 without a problem on flat ground, but if I hit a hill or want to go 60 or more I am stuck alternating between full throttle and very light throttle.

AFAIK everything is connected correctly, the plugs/wires/cap & rotor are fine. Timing wasn't changed when I swapped out the hitachi, but I played with it and found only very slight improvement with significant retard, so it's currently back to its original setting. I've flow tested the fuel system and have a pressure reg on it at 2.5 psi. double checked the float and fuel inlet. I've searched all over and the only clue I've seen is a blog post showing messed up aux valves and gunked up aux chambers. I've got a cheap scope on the way so I can check that without pulling the head, and a jet kit coming so I can try that, but looking at tuning manuals I can't make sense of why it would have such a huge problem under such specific conditions caused by jetting.

Anyone else ever have this problem? I had an 86 with a Weber on it and it was perfect.


  • I would let it stumble, shut it off immediately, and check the plugs. Hard to say, but it appears to me as a fuel issue. I would move my PSI around from 1.5 to 3.5 on that carb based on what the plugs are telling you. If that does not change anything, you may have something going on with the carb itself. Or, possibly, an ignition issue.
  • solved! I did a plug check run but it looked to my eyes like the jetting was just right, though I wasn't sure what I was looking at, so I bumped the jets.... after putting richer jets in and driving it a bit hard, I looked at the plugs again (richer jets made it worse) and one of the ground electrodes had melted :nightmare: ! turns out I couldn't read the plugs because I was looking for jetting... not plug heat range. That'll be the last time I trust the parts store to pull the right plugs for me... they had given me champion RN14YC plugs, which are crazy hot! swapped them for ngk BR8's and viola! purrs like a kitten. shoulda been more thorough on checking the basics, I guess. One more reminder to double-check everything and not make assumptions (like assuming the parts store would give me an appropriate part...) thanks for the suggestions, y'all.
  • Glad to see you got this solved thaddeusss!
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