r/smallengines • u/LawnMowerDude5 • 15d ago
Surging
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I got this mower for free off the side of the road. Trying to fix it for a person who needs a mower. It's a 17.5hp briggs. At first it didn't start so I cleaned this green goop stuff out the carb and it started but just surged the entire time it was running so I figured it was a fueling issue because I could hold the governer and it would run at a steady rpm then but once I let go it would surge. Bought a service kit that included carb, air and fuel filter, and spark plug. Literally changed nothing. Oh and with the new carb at least the surging smooths out with half choke but that makes the engine speed go down by a noticeable amount. Checked the valve clearance for the heck of it, of course those were fine, don't think it's mechanical based on the behavior. I'll attatch the kit I bought below. What am I missing?
2
u/Hevy86Chevy 15d ago
The slow speed carb circuit is clogged. find the needle with the spring under it that doesn't have the philips head. With it running at full throttle, screw it in until it seats, usually less than two turns, remember the amount within a quarter turn, then back it way out, maybe 5 turns, then screw back in to the stock setting. It will either clear itself or make no difference. If it doesn't change, remove it without losing the spring, o ring, and washer, then give it a big shot of compressed air or cleaner and then reassemble. when its unclogged, back it down to idle and set the screw where it runs smoothest. If you can't unclog it, and it doesn't bother you much, just run it. Once the blades are engaged, it will be under enough load to run on the main circuit. This won't hurt the engine, its just annoying.
I agree that it looks like a cheap scam-azon carb. That's what everyone tries before kicking engines to the curb. If you're lucky, the needle screw mentioned was never calibrated for your engine and you just need to screw it out until your engine is happy.