Cub Cadet 125

dhermesc · Jul 18, 2022

I have a 125 cub cadet - for what ever reason this is one that always backfires on shut down - and it is the loud - was that 12 gauge- backfire. No amount of cool down idling before shut off or adjusting the timing would make a difference. This engine was overhauled shortly after I bought the cub so I know it isn't carbon built up. Now after a few years of light use the engine is extremely low power until it warms up (5- 10 minutes of running) then it seems to run OK. Has the back firing ruined the exhaust valve to where it doesn't seal up until its hot?

Does anyone know where you can order a gas cap with the fuel gauge for a 1450?

steve_in_mo · Jul 18, 2022

I'd look at rings and cylinder condition before I'd look at valves.
That valve or the compression release might be stuck, leaving the
valve open a bit until it warms up.

You can do a compression check on one of those engines with a rope
wound around a pulley to rotate the engine backwards - if there is
a pulley on the tractor.

dhermesc · Jul 18, 2022

What is good compression on a 12 hp flathead?

steve_in_mo · Jul 18, 2022

80 or above.
You can download the service manual for free from the Kohler website. Look under classic engines.
The same manual works for all the single cylinder K series. The manual describes a leakdown test
to further diagnose a low-compression situation.

Phil B. · Jul 18, 2022

The backfiring after shutting down is known to bend the decompression tab. This causes slow cranking. You might have blew out the head gasket or broke a ring.
You can get a new gas cap here with the gauge.
Gas tank and accessories

T.R.K. · Jul 19, 2022

What you have is a hot spot in the muffler that is setting off the fuel mix that gets blown on through the engine after you cut off the spark.

Is your muffler in good condition? If the baffle inside isn't pretty good, nothing else you try will probably work.

Try making your fuel mix a little richer-open the mixture screws and adjust so it runs on the richer side of 'good running' if that makes any sense.

Also, try: Don't throttle down. push the throttle close to wide open, then cut the ignition switch. This is what we tell customers to do on their late model engines that have to run with a very lean fuel mixture and are prone to backfire. What we are trying to do is to blow any un-burnt fuel through the muffler before it gets a chance to explode.

T.R.K. · Jul 19, 2022

A Cub Cadet 125 is supposed to have a compression release mechamism on the cam. I am under the impression that you can't accurately test the compression on an engine with compression release. Unless you are planning to disable it somehow.

steve_in_mo · Jul 19, 2022

In my earlier post I discussed the practice of winding a rope around a pulley on the crankshaft so the engine could be rotated backward. The compression release does not work when the engine is rotated backward.

dhermesc · Jul 20, 2022

I'll check that out. Nothing else has worked.

DoubleO7 · Jul 22, 2022

We had a 125 bought brand new and used it for at least 25 years.
When it started to backfire on shutdown Dad would have a valve job done on it.
Nothing more at all, just the valve job.
No backfiring for another five to eight years and then do it again.

Cub Cadet 125

dhermesc

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steve_in_mo

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dhermesc

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steve_in_mo

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Phil B.

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T.R.K.

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T.R.K.

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steve_in_mo

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dhermesc

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