Weird 1M Engine/compression issue. Help?

[chargerkid5]

So I was riding today on my 03 1M 900 AC. I had rode it about 15-20 miles from where we parked to a lodge. We stopped had lunch and left the lodge. About 1/4 mile down the trail all of a sudden I lost about half my power and when I stopped the engine sputtered to a stop (wouldn't idle).

I pulled it over and the engine had much much less compression than it normally does. I pulled the plugs. Everything seemed ok, jetting was about perfect, and when I held my thumbs over the spark plug holes and had my buddy pull it over (slow) it still blew my thumbs off.

We tried starting it for a while just to get it back to the lodge. It finally took off after a bit. I rode it back to the lodge and everything seemed fine again. It was running so well I went out in a close by field and clamped the throttle a couple times and power was good, rpms were good, everything seemed normal. I shut it down again and pulled it over and the compression seemed to be back.

I decided it was probably rideable back to the trailer at least. 3 hours and another 50 miles later it still was running like normal.

What's the deal here? A friend of mine said I might have a jacked up piston but where it ran fine for 3 hours I'm hopeful its not. Any help? Thanks.

ETA: Engine is bone stock. Not a single mod on the entire sled.

[whitewolf]

Use a tester, it sounds like you may have a bad piston. Have you taken a look inside the cylinders or looked at the pistons?

[akflyer]

sounds like you may have had a stuck ring. Carbon build up can do it, and maybe your WOT runs across the field cleared it up. Chances are you are OK now, but it would not hurt to pull the juggs and decarbon the pistons and ring groves.

[chargerkid5]

I was thinking at least pulling the head might not be a bad idea being its only a few bolts. Hopefully I don't have to do a rebuild. Thanks!

[John]

Do a compression test first. No point in tearing it down unless the compression is down. I wonder if your valves could have been stuck open too...that will make it seem real fat on the bottom and could also explain why it started acting normal again once they got unstuck?? Good luck, intermitant stuff sucks!

[Doc]

do a compression test, if that fails pull your heads....could have been a poor ground, worn wire, check wiring around rear mag side motor mount. wires tend to rub through there.

hell you coulda popped a boot off your plugs too

[HOBB-Z]

Everyone has sound advice, it could be just about anything. I'd compression check it and go from there.

[John]

Originally Posted by Doc

do a compression test, if that fails pull your heads....could have been a poor ground, worn wire, check wiring around rear mag side motor mount. wires tend to rub through there.

hell you coulda popped a boot off your plugs too

Another spot that can cause electrical issues is under the oil tank, very common for them to rub under there and cause all kinds of weird problems.