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bob
05-04-2007, 06:53 PM
I have a Grasshopper 725 with the Kubota gas engine. When I put the throttle to idle the engine dies. At half throttle the engine rpm's go up and down. I took the carb off and cleaned the jet needle, put a new fuel filter on, new air filter and changed the spark plugs. One thing I noticed was the fuel filter (its clear) is never more than a 1/4 full of gas. Could it be the fuel pump? The mower use to have a back-fire when I would shut it off. It doesn't do that anymore, it just idles real low until it dies.

Bill Kapaun
05-04-2007, 08:07 PM
How does it run at full throttle under load.
If it runs good then, that pretty much eliminates any fuel delivery issues.

I'd look for loose carb mounting/intake bolts etc. that might allow an air leak.

Restrorob
05-04-2007, 08:19 PM
Start the engine and put the throttle at half where it starts going up and down, Slowly start applying the choke. If it smooths out then it's running lean, Most likely a blockage in the low speed circuit.

Sounds like you need to go back through the carb. again, Spray carb. & choke cleaner with the straw through ALL ports, passages and jets. If you have a air compressor follow with that then re-assemble. Check your fuel tank for trash/water.

khouse
05-04-2007, 09:43 PM
I second the motion to revisit the carb!

diagnostech
05-05-2007, 12:01 AM
:weightlifter: yea check all intake gaskets, easy check is start it set where it runs rough, spray carb cleaner ( or start fluid)around outside of carb and manifold, if engine picks up or changes tune you have found aleak.