# 1974 John Deere 140 H3 engine problem



## Corvette guy (6 mo ago)

I was mowing for about an hour when I detected a slight backfire and decided to shut it off and try to figure out what was causing the backfire and and loss of power. After I shut it down, it dieseled for a bit and finally the engine stopped running. I wasn't able to initially find anything wrong and when ever I tried to to restart it, the engine backfires extremely loudly through the exhaust. However once it had cooled down it did restart once and I did turn it off right away. Since then it has never run again. After reading the trouble shooting guide in the manual I decided that it was probably a blown head gasket. I could only get my compression tester hose to screw into the spark plug hole a few threads because of the shielding being in the way. at that point it had 33 psi of compression. I removed the head and with the discoloring on one section of the gasket, I assumed that my diagnosis had been correct. Once I got it back together with a new gasket, it still has the consistent backfiring through the exhaust and it will not run. I would appreciate any thought and/or advice. Thank you.


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## BigT (Sep 15, 2014)

Hello Corvette guy, welcome to the forum.

Low compression coupled with backfiring out the exhaust indicates a stuck / not seating correctly exhaust valve.


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## Corvette guy (6 mo ago)

Hello Big T
I was thinking that I would find a stuck valve or carbon on the valve or seat. The valves seem to work properly and surprisingly there was very little carbon on the head or valves. I scrapped and wire brushed the valves and seats just in case. I figured the culprit was the head gasket and I know now that I should have taken another compression test when the shield was removed. I will now try it again. Didn't i read in the manual that there is some sort of automatic compression release for starting purposes? Thanks.


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## BigT (Sep 15, 2014)

Taking the cover off is not a big job. You need to confirm compression. 

Have you checked the points?? The point gap should be .020".


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## Corvette guy (6 mo ago)

BigT said:


> Taking the cover off is not a big job. You need to confirm compression.
> 
> Have you checked the points?? The point gap should be .020".





BigT said:


> Taking the cover off is not a big job. You need to confirm compression.
> 
> Have you checked the points?? The point gap should be .020".


Big T
I just wanted to let you know that I got my 140 running and did a little mowing with it today. It turned out to be a carburetor problem. I began to think that it might be allowing too much fuel in and it was building up in the muffler and then igniting. I pinched off the fuel hose with vise grips and gave the carburetor a shot of ether and the engine started right up. So then I removed and cleaned and reassembled and adjusted the carb. It all worked fine after that, however when I return the throttle to idle the engine continues to run for a while at a very low RPM. It is not like it is dieseling, it just runs normally and very slowly. 

Thank you so much for all of you advice. Let me know please if you have any thought on why it doesn't shut down when the key switch is turned off.

Corvette guy


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