Long story, hopefully to catch follow-up questions and find the underlying issue.
This summer I picked up a 1994 Max II with a 2012 Briggs Vanguard V-Twin 23hp (non-EFI, 386447-1138-G1) installed. Looks like original skid-steer installed. It started kinda funny, ran okay but overheated quickly and all the power would disappear. I thought perhaps it was the Seattle area heat waves. Oh, and the tub had lots of oil, grease, grime everywhere. It seemed like the exhaust manifold was leaking vapors where it joined the muffler -- I tried sealing that up better but to no avail. I cleaned up the engine and tub some, but it always got dirty quickly, and always accumulated fumes.
Eventually I discovered the main crankcase seal was leaking -- that point was when it sucked inward so much that the engine held no pressure anymore and it started spraying oil vapor all over the place. I have to admit, it sprayed some gasoline too, because in my frustration trying to start it many times with occasional teases of success, I overdid it way too much. The cylinder heads had saturated with gas, and ended up flooding the crankcase compartment with gasoline.
I pulled, drained, and rebuilt most of the engine. The only thing I left untouched and in-place were the valves, the pistons and their rings, and the starter. I kept the alternator, charging rectifier, kill diodes, and vacuum-actuated fuel pump. I replaced every gasket and seal, except the metal breather reed which seemed okay (and no replacement online that I could find). I fully disassembled the carb, thoroughly soaked cleaned and probed all passages, replaced all rubber seals, checked the float doughnut was fine, and had to replace the brittled fuel transfer tube after dropping it )-: New oil filter, air filter set, fuel filter, and new Champion spark plugs as per Briggs repair guide. Half of my time was spent just de-griming every nook and cranny. Gas tank drained, verified clean, and filled half-way with fresh 91 octane ethanol-free fuel. I reinstalled the engine with a new Dayco HP3003 belt and new Duracell Miata AGM battery. I had to slide the engine mounts inward a little to squeeze on this new belt. It starts immediately and smoothly by turn-key, and the pull-cord now actuates everything with ease. The belt tension is a little tight, I can only make the transmission pulley stop if I push on its rim sideways firmly with a stick. The belt has good grab right now after I had lightly sanded the crank pulley radially and then graphite lubed only a little bit.
One problem still persists though. I can adjust (bend) the governer tab so that the engine idles about 800-900 RPM, or 1200-1300 RPM, or anything between, and it will idle okay, cycling up and down over time. If I set a low ~850 RPM idle, it will not stay there for more than a minute. Eventually it cycles up to 1200 or so and then drop back down to 800. Infrequently in its idling down to the bottom end, I hear the governer flyweights click out and then it revs up again without issue. But from any of these speeds, when I actuate the throttle, the engine will immediately stall with a hollow sputter-out. The only way I can get it to rev is to very slightly creep the throttle open over about three seconds until the engine hits about 1700-1800 RPM, and then I can go wide open without any issue besides a single backfire if I just blip it open and then let off. This behavior persists whether the transmission is in neutral, or drive with the sticks pulled back or floating.
This engine has a Nikki 845191 carb with no visible adjustments on it (the Briggs manual confirms this). The only way I can completely avoid a stall is to bend the governer tab to idle super high like 1600 RPM.
I've just got in a replacement fuel pump (it could have overheated with all that gunk on the engine), and better NGK 5464 BKR5EIX-11 Iridium spark plugs, they seem to be a cross-compat fit. If I go outside tomorrow and put these in, and it still stalls out, what should I try next? Literally the only thing after this is to replace the throttle cable, which is sticky at the idle squeeze, but smooth after it gets going. Pulling the throttle cable at the engine proves it's the cable, not the engine, but this shouldn't be the real cause of the stalling problem.
Wow you got to the end! thanks for reading it all. --neveroddoreven
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Originally Posted by neveroddoreven
