engine surging issues
- Thread starter keakar
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I would think a worn out cam would have more of a timing issue, causing sputtering and back firing.
ok thanks, just trying to wrap my mind around what the issue could be
i randomly get these engines that have no obvious external issues but refuse to stop surging
at least now i know i can rule out a bad cam being a possible cause
i just hate to junk running engines because of surging issues but at some point there are only so many hours worth putting into an engine before scrapping it and my OCD want to solve every problem so i hate giving up on them
bertsmobile1
Lawn Royalty
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Surging on a goverened engine is always cause by an air : fuel ratio that is too lean to maintain a constant speed.
For that to happen either the carb venturi is not passing enough fuel into the air stream or more air is entering after the fuel has been added.
IT has to be one or the other or if you are really lucky, both .
So you are looking at sources of induction leaks or fuel restrictions.
IT can be as obsecure as the carb mounting stud/ bolt causing the intake tact to crack or being drilled so deep it intersects the inlet tract.
A cracked head, leaking gasket badly worn butterfly pivots, cracked manifold, porous manifold .
For that to happen either the carb venturi is not passing enough fuel into the air stream or more air is entering after the fuel has been added.
IT has to be one or the other or if you are really lucky, both .
So you are looking at sources of induction leaks or fuel restrictions.
IT can be as obsecure as the carb mounting stud/ bolt causing the intake tact to crack or being drilled so deep it intersects the inlet tract.
A cracked head, leaking gasket badly worn butterfly pivots, cracked manifold, porous manifold .
A worn out cam in the ones that I have seen wouldn't reach full rpm on single cylinder engines and just no power on twins.. Since the valve wouldn't open fully it was creating it own governor effect . I have seen a couple that would surge from governor issues but those are really rare. I actually create a governor issue last week on a briggs twin after replacing the sump gasket. Got the governor arm to gear too tight i guess and it would surge badly. The tell was it wouldn't smooth out under mowing load.
no solution for the 15.5 hp engine, ended up scrapping it
but you were spot on with the 17.5 hp, it had an intake manifold crack that couldnt be seen until the barb bolts were tightened and that opened the crack to cause the surging. replaced the manifold and no more surging on that one.
i still need to investigate the 19.5 hp closer