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Old 05-06-2012, 01:47 PM
wits-end wits-end is offline
Join Date: May 2012
Posts: 2
Most confusing lawnmower problem

This is more of a question to pick the experts brains here, because I'm stumped, so I'll give a small history.

I have a Craftsman 6.75 hp lawnmower, model 944.368300, and although it's 12 yrs old, it has run flawlessly til last fall, when it started to run as though it was a governor problem, speeding up and slowing down, but it wasn't a governor problem.

I replaced the plug, the gas, float bowl and cleaned the carb but still it made no difference. Then I bought a new carb and installed it. Problem is, I also noticed the gas line was cracked while replacing the carb, so I replaced it too. So, since I replaced two things, I'm not sure if the problem was the gas line or the carb.

My question: Is it possible for a gas line to be cracked, but not leak gas, yet allow air to leak in when the mower is running? I know this may sound silly, but when you think about it a bit, it seems to fit the symptoms and could mimic a governor problem. My mower now runs like new. I'm just curious which was the more likely culprit, the gas line hose or the carb.

I'll be happy to read any feedback or thoughts anyone may have.
Old 05-06-2012, 02:36 PM
excavating (for a mind) excavating (for a mind) is offline
Join Date: Nov 2010
Location: In a canyon, in a cavern
Posts: 1,176
My vote is for the carburetor as the original problem, since you replaced that and it fixed it. The gas to the carburetor line is a gravity feed, so if it was cracked through it would have leaked gas out, not air in. It was good that you replaced it, but I doubt the cracked gas line was the problem.

excavating (for a mind)
Old 05-06-2012, 02:36 PM
Mr. Duality Mr. Duality is offline
Join Date: Jul 2001
Location: The High Plains
Posts: 1,480
I've seen that happen with a snowblower. I have no doubt your cracked gas line was the problem.

Last edited by Mr. Duality; 05-06-2012 at 02:37 PM.
Old 05-06-2012, 03:02 PM
johnpost johnpost is offline
Join Date: Jul 2009
Posts: 12,056
there is good reason they are called infernal combustion engines.
Old 05-06-2012, 06:03 PM
aceplace57 aceplace57 is online now
Join Date: Oct 2009
Location: CentralArkansas
Posts: 22,989
Check the gas cap vent. If its clogged you'll get a vacuum and gas won't flow properly. engine surges etc. it can even kill the motor if its totally clogged.

Try blowing air through the cap with your mouth.

Last edited by aceplace57; 05-06-2012 at 06:08 PM.
Old 05-06-2012, 07:33 PM
Napier Napier is offline
Charter Member
Join Date: Jan 2001
Location: Mid Atlantic, USA
Posts: 8,935
My guess is carburetor, something to do with flakes of rust from water in the gas, which evaded your earlier cleaning.

In any case I don't see how the hose could let air in and not leak.
Old 05-06-2012, 10:08 PM
wits-end wits-end is offline
Join Date: May 2012
Posts: 2
Thanks for your replies. My vote is for the carb too, but I may never know. I'm just glad it's back to working as it should.
Old 05-06-2012, 10:35 PM
california jobcase california jobcase is offline
Join Date: Dec 2009
Location: S. GA
Posts: 2,938
The symptom is that of a vacuum leak. I vote for loose carb bolts or deteriorated gasket.
Old 05-06-2012, 11:51 PM
Gatopescado Gatopescado is offline
Join Date: Aug 2001
Location: on your last raw nerve
Posts: 18,156
You wanna know?

Put that original suspect hose back on with the new carb and see what she does. Unless you tossed it.

I'll just say that I've never had to replace a whole carb. I would guess it wasn't completely cleaned or a jet was plugged or a strange vacuum problem, like pointed out earlier. Heck, even a gasket can suck when you least expect it.

Screw it! It's workin' now, so mow happy!

Last edited by Gatopescado; 05-06-2012 at 11:51 PM. Reason: In other words, "I don't know"


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