Tecumseh OHSK130 Misfiring - Snowblower Forum : Snow Blower Forums
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post #1 of 13 Old 01-04-2020, 06:37 PM Thread Starter
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Tecumseh OHSK130 Misfiring

This one has me a bit puzzled so I wanted to get advice before proceeding down a blind alley.

This is a Cub Cadet 1333SWE with a Tecumseh OHSK130 (223813B spec number) with a 1998 DOM. From the video link, you can hear and see it intermittently miss, pop and puff smoke from the carb. It does this at idle and full throttle regardless of engine temperature.


It's far less likely to happen at 3/4 choke so I initially thought it was a fuel related problem. I went through my usual carb cleaning processes without success. I replaced it with a new Chinese carb, replaced all the fuel lines, installed a new spark plug, adjusted the valves to factory specs, drained fuel and replaced with fresh non-ethanol .....same outcome. I did not replace the carb gasket or the fuel shut-off valve since they looked good. I did spray carb cleaner around the gasket and it does not seem to have an air leak. I haven't tested RPM yet but idle and full throttle sound normal to my untrained ears.

I gave up for today but my plan is to install my inline spark tester with a thought toward a faulty coil. It still seems like a fuel issue but I'm not sure what I'd try next on that level. Any suggestions would be greatly appreciated!
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post #2 of 13 Old 01-04-2020, 06:50 PM
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Seems like a classic timing issue. Intake valve staying/sticking open during part of compression cycle. Bad valve spring or guide or seat or cam?
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post #3 of 13 Old 01-04-2020, 06:50 PM
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Garage
Sucking air somewhere if it runs good choked. Betting on the carb gasket that looked good...

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post #4 of 13 Old 01-04-2020, 08:52 PM
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Quote:
Originally Posted by Seeb02 View Post
Seems like a classic timing issue. Intake valve staying/sticking open during part of compression cycle. Bad valve spring or guide or seat or cam?
That seems reasonable. rod330, does it behave differently at high RPM vs low? If the intake valve was slow to close, maybe it would happen more often at high RPM.

Does it have good power?

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Originally Posted by Brent Holm View Post
Sucking air somewhere if it runs good choked. Betting on the carb gasket that looked good...
Certainly not a bad thing to replace. But spraying around the carb/engine interface should have helped test it for leaks.

I'm certainly scratching my head. Valve adjustment was my first thought, but you did that. I'd do a compression test if it were me, just to see what that shows.

If you had the ability to do a leakdown test it might reveal an intake valve that isn't fully sealing, even when it's just sitting there, as air leaking out through the carb. Could be a chunk of something sitting on the valve seat, or a worn valve and/or seat.

I don't have a leakdown tester, but apparently you can modify a spark plug and add an air fitting, and then use that to pressurize the cylinder. You won't get any leakage gauge readings, but you'd be able to listen for air coming out of different areas (carb, muffler, or oil fill tube). Or maybe you can buy a commercial fitting that would allow attaching an air line. Some compression tester fittings might help with this, for instance. I've never tried to rig something up, but it's probably something I should investigate before suddenly needing it.

If it was a valve that was sticking a bit, I wonder if adding some 2-stroke oil to the gas might help give a bit of extra lubrication, as the fuel mixture flowed past? It probably wouldn't hurt anything, at least.

It's a long shot, and seems pretty unlikely. But I've heard that really-excessive carbon buildup in the cylinder can cause pre-ignition. Little areas of that carbon can stay hot enough to light off the next fuel charge. It may be possible that, when you add choke, things run a little cooler, and you're less likely to get bad hot-spots. I'm sure this is a reach. But I'm just trying to think of anything that might be consistent with what you're seeing.

I'd certainly do the ignition test. But I don't think I get action out of the carb when I turn off my OHSK100 ignition, which would be somewhat similar behavior to the coil suddenly not firing.

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post #5 of 13 Old 01-04-2020, 09:34 PM
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Did you check the flywheel key? I would do that before a leak down.
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post #6 of 13 Old 01-04-2020, 09:48 PM Thread Starter
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Quote:
Originally Posted by RedOctobyr View Post
Does it behave differently at high RPM vs low? If the intake valve was slow to close, maybe it would happen more often at high RPM.

Certainly not a bad thing to replace. But spraying around the carb/engine interface should have helped test it for leaks.

Valve adjustment was my first thought, but you did that. I'd do a compression test if it were me, just to see what that shows.

If you had the ability to do a leakdown test it might reveal an intake valve that isn't fully sealing, even when it's just sitting there, as air leaking out through the carb. Could be a chunk of something sitting on the valve seat, or a worn valve and/or seat.

I'd certainly do the ignition test. But I don't think I get action out of the carb when I turn off my OHSK100 ignition, which would be somewhat similar behavior to the coil suddenly not firing.
The problem occurs at low and high RPM but it does run better at full throttle; that kind of makes me think it isn't related to the intake. I wish I had measured valve clearance before I started adjustment but both intake and exhaust were way out of tolerance.

Replacing the carb gasket will take just a few minutes so I'll begin there when I can get back to it next week.

Thanks so much!
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post #7 of 13 Old 01-04-2020, 09:50 PM Thread Starter
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Originally Posted by AriensProMike View Post
Did you check the flywheel key? I would do that before a leak down.
Ahh...another great suggestion...I'll add that to the list.

Thanks guys!
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post #8 of 13 Old 01-05-2020, 09:55 AM
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It may be a good idea to check the coil gap.... BEFORE pulling the flywheel. Only takes a couple minutes to get the cover off to check. Also, try spraying the ignition coil, wire and boot with water from a spray bottle & checking for flying sparks. Helps to look in a darkened garage. But I think you may find a bad Ignition coil causing your misfire.

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post #9 of 13 Old 01-05-2020, 12:30 PM
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its valves and /or timing, my bet is valves, valves arent seating fully so need to be reseated , most likely intake, or valves clearances are out of spec

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post #10 of 13 Old 01-10-2020, 05:38 PM Thread Starter
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Once again, thanks for all of the valuable input. I haven't had a chance to work on the Cub until this afternoon.

I verified the valve lash, replaced the carb gasket and reset the ignition module air gap. No luck, same outcome.

I ordered a new ignition coil just to eliminate that possibility and then I'll check the flywheel key. If it boils down to a valve problem, I'll be venturing into uncharted territory.

Last edited by rod330; 01-10-2020 at 07:00 PM.
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