Kohler KT735 on Hustler Raptor running rough/losing power

sl10002001

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Hi All,

I have a Hustler Raptor with only about 80 hours on it, with a Kohler KT735 engine (with the smart choke). Spec is PS-KT735-3051.

About a month ago it started running like it was running out of gas or bogging down in the middle of mowing. Checked the deck for obstructions, everything was clear there. Replaced the oil/oil filter/fuel filter/air filter and plugs. Same thing.

Took it to the dealer who checked for water in the fuel plus everything I had already checked and deemed it ok; they cleaned the carb and mentioned something about a main air line being clogged (sorry I don't have the paper I got back then so i don't remember the exact wording). It ran great for about an hour after i got it back then started the same thing.

It starts and idles fine. Once you get to about half throttle it will start surging a bit, or skipping sometimes. When you engage the deck it gets much worse and if you hit any sort of heavy grass it sounds like it wants to die. The engine will bog down and sputter then surge back to speed and when it does this i sometimes notice a smell of gas. Disengaging the deck will make it run smoother but not as it should at anything above an idle. I can see the linkage for the choke moving up and down slightly as it compensates (I think) for the need for fuel.

I cleaned the carb again (and again, and again) and each time it would run for about 15min ok then start again. I was convinced this was due to the outside carb gasket i noticed was coming apart and thought pieces were getting in the carb. I ended up putting a brand new Walbro carb and gaskets on...and it is doing the same thing.

I unplugged each spark plug while it was running and heard the motor degrade but didn't stall each time. I've run a long fuel hose directly from the fuel pump onto the tank to rule out the inline filter (which is new) or anything blocking the in-tank hose. Still same thing. Finally i've replaced the fuel pump just because i had a spare one and its still running like crap.

If anyone has any suggestions or more ideas please let me know. Its so strange that it would run well for a short time after cleaning the carb, but now with a brand new carb its not any better. My dealer is at a 14day wait now and the other local guy told me 30 days since i'm not a customer. I don't want to mow my 3 acres by push mower!

Thanks in advance for any info or advice.
 

Hammermechanicman

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Have you pulled the fuel pickup tube out of the tank and checked it?
 

sl10002001

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
I did not because i ran a separate fuel line directly into the tank to the fuel pump (bypassing the pickup tube and inline filter) so i thought that would rule out the pickup tube/inline filter?
 

Hammermechanicman

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Grass and debris can clog the pickup in the tank than can restrict the flow.
 

sl10002001

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Yep I had read i should check that. But I had a spare 5ft fuel line so i ran a separate fuel line from the filler cap directly to the fuel pump. So this totally bypassed the pickup in the tank. It may very well be blocked but the motor still ran the same when I had totally bypassed it.
 

Samsungjle

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Yep I had read i should check that. But I had a spare 5ft fuel line so i ran a separate fuel line from the filler cap directly to the fuel pump. So this totally bypassed the pickup in the tank. It may very well be blocked but the motor still ran the same when I had totally bypassed it.
Having the exact same problem have replaced everything but the choke assembly dealer could not find anything wrong stops getting gas after about 10 to 15 Mnutes run time
 

Samsungjle

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Was there any answer to the raptor fuel problem
 

StarTech

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Not familiar with this setup using an electric thermostat choke. But have tried crippling the choke to see if the electric thermostat is working or not. It might be bad electrical connection or voltage supply to it.

Basically warm up the engine, shut down, tie the choke open, and give it a test run. Also check for a mouse bed under the engine shroud that might blocking air flow to the air vane that opens the choke.

Fuel supply problems are harder to troubleshoot on a ZTR as mounting an external tank is problematic but maybe a path to check things.

As OP did I recently had to troubleshoot a fuel supply issue on a JD Z540. The root cause was determined to be a honey bee and a yellow jacket wasp in the fuel tank. And I have seen once in the last year for a vacuum fuel pump to fail in such a way that it worked off load but failed under engine load.

Even fuel lines can cause fuel supply problems.
 

VegetiveSteam

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  • / Kohler KT735 on Hustler Raptor running rough/losing power
Hi All,

I have a Hustler Raptor with only about 80 hours on it, with a Kohler KT735 engine (with the smart choke). Spec is PS-KT735-3051.

About a month ago it started running like it was running out of gas or bogging down in the middle of mowing. Checked the deck for obstructions, everything was clear there. Replaced the oil/oil filter/fuel filter/air filter and plugs. Same thing.

Took it to the dealer who checked for water in the fuel plus everything I had already checked and deemed it ok; they cleaned the carb and mentioned something about a main air line being clogged (sorry I don't have the paper I got back then so i don't remember the exact wording). It ran great for about an hour after i got it back then started the same thing.

It starts and idles fine. Once you get to about half throttle it will start surging a bit, or skipping sometimes. When you engage the deck it gets much worse and if you hit any sort of heavy grass it sounds like it wants to die. The engine will bog down and sputter then surge back to speed and when it does this i sometimes notice a smell of gas. Disengaging the deck will make it run smoother but not as it should at anything above an idle. I can see the linkage for the choke moving up and down slightly as it compensates (I think) for the need for fuel.

I cleaned the carb again (and again, and again) and each time it would run for about 15min ok then start again. I was convinced this was due to the outside carb gasket i noticed was coming apart and thought pieces were getting in the carb. I ended up putting a brand new Walbro carb and gaskets on...and it is doing the same thing.

I unplugged each spark plug while it was running and heard the motor degrade but didn't stall each time. I've run a long fuel hose directly from the fuel pump onto the tank to rule out the inline filter (which is new) or anything blocking the in-tank hose. Still same thing. Finally i've replaced the fuel pump just because i had a spare one and its still running like crap.

If anyone has any suggestions or more ideas please let me know. Its so strange that it would run well for a short time after cleaning the carb, but now with a brand new carb its not any better. My dealer is at a 14day wait now and the other local guy told me 30 days since i'm not a customer. I don't want to mow my 3 acres by push mower!

Thanks in advance for any info or advice.
Do you have to be mowing with it for it to act up or will it act up just sitting and running?
 
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