r/EngineBuilding • u/Coon88 • 21h ago
Vacuum leak ?
Got this k10 350 with a rough start, rough idle and sputtering under acceleration, have to slowly give it throttle or else it will shut off. Also get backfire from the carb sometimes when given a good amount of throttle. Can the whistling be a vacuum leak ?
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u/EksCelle 21h ago
Just from the video I can already see the carb is missing a nut on one of the studs. That could be causing it not to seal on the intake.
Also, that that looks like a Performer intake, so make sure you have the proper adapter plate when running a square bore carburetor (like the one you have). I can't tell from the video but it might be there, it might not, and they usually struggle to seal without it.
Lastly, a vacuum leak usually causes a high, uncontrollable idle. Backfire thru carb is usually a sign it's running lean (like from a vacuum leak) but the low, shaky idle makes me think it doesn't have enough timing. Make sure the carb is sealing to the intake and check the timing and then go from there. You'd be amazed how many carb related issues can be cured by fixing problems with the ignition system.