Robin Engine Problem

[larrydman]

Hoping to pick you guy's brains again. My 425 died on me and won't restart. I changed the fuel filter and cleaned and then replaced the air filter. Then I checked the plugs and was getting fire on both plugs. I mistakenly tried to start it without reconnecting the right plug and it started and would run on the left cylinder but won't run on the right. I've got about 1700 hours on it. I am already past the extent of my mechanical skills. Sound bad?

 

[MossRoad]

If you're getting a good spark at both cylinders,
and
it'll start and run on the left cylinder, but not on the right
then
I'd suspect NOT timing, because the left runs, so the right is in time.
then
I'd suspect compression on the right cylinder next.

Compression can be bad, like blown cylinder, bad head, etc...

however,

Have you ever checked the valve adjustment on that engine? I seem to recall more than a few PT owners that have had similar situations and a valve adjustment took care of it.

Find a maintenance manual for that engine and adjust the valves on that cylinder before you worry about doom and gloom.

 

[larrydman]

Thanks, David. Like I said, I'm no mechanic, and I have absolutely no idea of how to check the valve adjustment. My brain just kind of fogs over with things like that. I haven't been able to find a mechanic locally willing to come here and the darn thing quit on the opposite side of the yard from the driveway. I was thinking of trying to tram it on one cylinder enough to get it around the house where I can load it. Would that hurt anything? I see yours is 17 years old, how many hours you got? One thing, if I can get it loaded, I'm only an hour and a half from Tazwell.

 

[MossRoad]

If it runs, you won't do any damage to the hydraulics by moving it with the poorly running engine. If it doesn't run, then you'll have to open the tram port before you try to move it by pulling/pushing it, or you risk damaging the hydraulics. Specifically, the tram pump.

I only have about 700 hours on mine. It's the Kohler engine.

 

[larrydman]

Yea I called Tazwell yesterday and the guy said the same thing about tramming. He was guessing my problem was the coil.

 

[MossRoad]

The reason I went with valves over coil first, was because there's a good spark at both cylinders, indicating good coil for both cylinders. However, that doesn't mean it isn't the coil.

Adjusting the valves is free. That coil isn't.

 

[cqaigy2]

Somebody else here had similar problem that turned out to be one of the coils. Coil wasn't open so it produced spark in open air, but apparently not enough to jump the gap with gasoline vapor added to the mix i suspect the insulation was breaking down inside the coil. Like Moss said, valve adjustment is only an investment of time and coil replacement is both time and materials. You may want to check the valve adjustment while you have the engine where you would replace the coils.

 

[larrydman]

I thought the same thing about the coil and getting a spark, but I don't understand why it will run on one cylinder with the other unplugged and won't run if you plug em both up. On the valve adjustment, it makes sense to adjust something before you replace something, but how to go about adjusting valves inside an engine is way over my head. I may just take it back to Tazwell and let them handle it.

 

[BobRip]

I had this problem. It would start on one good coil, but.not start if both coils were connected to the plugs. Once it was running on the good coil, I could connect the bad coil and it would run ok. I replaced the bad coil and that fixed it. I suspect that the bad coil was firing early while cranking. This caused some backfire through the carburetor while cranking. Once running the early firing was normal. One way of looking at it was the coil firing was stuck on advanced timing.
So if it starts on one coil only and runs ok with two, and backfires through the carburetor when cranking then the is the same problem I had. My engine had about 1200 hours on it. I have a thread on this. The coil was about $250. It is good to check your pushrods as well.

 

[larrydman]

That sounds about what it's doing. It won't start with both plugs, it just sputters and backfires through the carburetor, like it wants to start but one cylinder is firing against the other and then it quits as soon as I let off the starter. I think this is over my head just like my grass is by now. I'm gonna haul it to Tazwell, there's a couple other things I talked to them about, and just let them give it a good going over. I might be tempted to come back with one of them new ones with the Kohler engines.