I have a kohler ch25 engine on a toro zero turn .. was reading thought some posts it is like the one bear369 posted runs very rough both coils are firing.. did a compression test both cylinders have about 150 psi on them .. has a lot of crankcase pressure it will blow the cap off the oil filler tube if you loosen it.. reminds me of a diesel motor with blow by a bad head gasket .. love some help on this one..
I have a kohler ch25 engine on a toro zero turn .. was reading thought some posts it is like the one bear369 posted runs very rough both coils are firing.. did a compression test both cylinders have about 150 psi on them .. has a lot of crankcase pressure it will blow the cap off the oil filler tube if you loosen it.. reminds me of a diesel motor with blow by a bad head gasket .. love some help on this one..
150 psi (if accurate) is actually very good (most motors). What obviously is very abnormal by your description is the crankcase pressure. What does that motor have for crankcase venting ? Is your muffler/exhaust plugged up? are all valves moving appropriately?
I don't use the pull the oil fill cover/ cap to determine a small engine has an issue with excess blowby. Why? because these small engines don't have very much crankcase area displacement like vehicle engines. Aside from that, if you had excess blowby, you would not be reading 150 psi compression.
It is rare for a crankcase vent valve to go bad because they are such a simple design.
The most common issue with many small engine applications starts at the fuel tank and up into the carburetor. It may take weeks or even years, but moisture, dust and dirt collect very gradually in the fuel system by way of the fuel cap vent and fuel containers that sit around.
The most overlooked and often avoided is the fuel tank and the supply lines. The fuel tank is likely well covered/hidden on this machine and it takes work to get it out for a good washing out and drying.
Clean out the fuel system all the way to the carburetor, then pull the carburetor off for a good cleaning.
From there, verify the spark plugs are correct and properly gapped at .030 inch.
To verify both cylinders are producing power, spray a little water on each exhaust tube to see if the water quickly burns off while running. If not, you have coil issue, or the coil kill wire is bad. The top cover will have to come off and the kill wire disconnected at each coil. Then run and test again with the water to see if both sides now burn off the water quickly.
The engine will have to be choked to shut it down.
There have been a lot of mowers scrapped, parked and abandon because of a simple bad kill wire diode assembly.
Hope this information helps.
Teryl fixes all on You Tube has some good repair videos, even though he tries to be a clown with "skits" to keep it interesting, the guy knows his stuff when it comes to small engine equipment.
I worked on a friend's Kohler engine for their ZT mower that acted like this about 15 years ago.
It ran rough and was down on power.
Going from memory.
Yes, both cylinders were firing, but ONE of them was firing at the wrong time.
I found this out when I tested each cylinder with a timing light.
Though there were two magnetic pickups (one to fire each cylinder at the correct time), I found that both plugs were firing at the same time.
i.e. one was firing at the wrong time.
When I checked the wiring of the magnetic pickups, I found that on one of them, the connections looked OK but were flaky.
I cleaned up the connections, and reconnected them.
AFTER that the engine ran smooth, and when I connected the timing light to each cylinder, they were now firing at different times.
For some reason, with one of the magnetic pickups having flaky connections, the ignition system was using the one pickup with a good connection and firing both cylinders off of it, with one cylinder firing at the wrong time.
The engine has run fine ever since.
WHAT CAUSED me to look at the ignition connections was, the Kohler engine service manual said
"Reported ignition problems are most often due to poor
connections.".
And on THIS engine that was the problem.
YMMV
thanks to all that have replied... a little history on this engine two years ago a shop replaced both cylinder heads new gaskets and valves.. both coils were replaced at that time to ..it has a front crank shaft that runs the hydraulic pump on it shop told him it was cost effective to replace them at that time.. the engine burns no oil .. checked the crankcase oil no smell of gas in the oil normal level of oil in it.. this mower is used daily to take dad around the farm and too the mail box.. wish he was closer to me on Tuesday will drop by and look at it again.. love any help you guys can give...
