Kohler engine has me stumped

aloha

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Aug 31, 2011
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This was originally posted in the Scag forum, but because of the greater activity in the engine repair forum I am duplicating the post here.

I have a Scag Turf Tiger ZTR with the 27 h.p. Kohler CH740 engine that has died and defies troubleshooting. The grass is growing and I am desperate for suggestions.

The Scag is 6 years old, 560 hours, and has been completely reliable up until now. 3 days ago I had just started mowing, and about 3-5 minutes after having started the engine the engine backfired very loudly and immediately died. (I had just started a right turn after having mowed a straight line for about 2 minutes when it happened, probably just a coincidence, but it did happen at the instant I started the turn.) When I looked at the engine the air hose from the air cleaner was off the carburetor, presumably blown off by the force of the backfire. When I crank the engine it fires and sounds as if it is going to run, but when I release the key from the start position the engine it dies.

I have confirmed fuel is being pumped and the carburetor fuel shutoff solenoid is operating correctly. I pulled spark plugs and one was damp with a gas odor. Visual inspection of the carburetor shows nothing amiss, linkages are working correctly, although the throttle valve moves little from the full open position, which is where I normally run it. It appears that the fuel supply is not the cause.

I have checked that there are no obstructions to the air flow and attempted starting with the air cleaner removed. I find no problem with the air flow.

I have replaced both spark plugs. I have used a spark plug tester that shows both cylinders are sparking.

The local Scag guy said he has seen similar symptoms with a broken valve push rod. I pulled the valve covers and all push rods appear sound and straight. Pushing on the rocker arms showed all valves moving freely.

I have gone through the troubleshooting steps in the engine service manual, http://www.kohler-engine-parts.opeen..._REV1010EN.pdf, and find no clues in those things I can do without special tools and which seem even remotely possible. I'd like to get a timing light on it, but it appears that would require pulling the engine from the Scag to get access to the timing marks, and with the engine not running except by the starter turning it there might be little to be learned.

The local Scag guy has 2 to 3 weeks of repairs backed up, so I am pretty much on my own. And having determined gas apparently ok, air apparently ok, spark apparently ok, and the main mechanical components apparently ok (at least those that can be seen without seriously tearing into the engine) I have run out of ideas.

So, someone please show me that I am an idiot and have overlooked something easy. Or even something not so easy. All ideas are welcomed. Thanks.
 

Giles

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Mar 22, 2011
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It would be my guess that you have a fuel problem. Just because carburetor seems to be ok dosen't rule out carb. internal problems.
If you have GOOD FUEL--Compression--and spark (at the right time) the engine should run.
I always like to check the simple things first.
(1) Compression check?
(2) You said you have spark--If it is strong enough, you will get a spark from the center electrode to the threaded area of the spark plug---(After removing the ground electrode)--. Make sure you have a good plug---at least before removing the ground electrode.
(3) Now for fuel---remove air cleaner and be sure choke is off. While spinning the engine over, a small squirt of starting fluid should give a start--die result.
If you don't have starting fluid, find a way to SAFELY squirt or spray gasoline instead of SF.
If results are positive, with this test, you most likely have a stopped up circuit in your carburetor.
(4) Remove and thoroughly clean carb. along with flushing the fuel tank and replace with new fuel.
I can't begin to explain some of the problems I have encountered with todays JUNK gasoline.

It sounds like you have a jet blocKage problem or poor quality gas--DON"T assume gas is good!!!
 

KennyV

Lawn Pro
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I'm with Giles... Try the starting fluid... ether will light up no matter if there is spark... :smile:KennyV
 
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