Here's the story, tell me what you think . . .

Two winters ago my 1994 ZR 700 seized up. I took the motor out to find the bolts holding the oil pump to the crankcase had come loose, causing no or not enough oil to be injected into the mixture. Last fall I rebuilt the top end. I had both cylinders cleaned up and prepped at local dealer. They did not have to be bored, just some aluminum had te be cleaned out with acid, and then they were surfaced for new rings. I put all new gaskets and seals and o-rings in, tightened to torque specs. I made sure to align rings correctly (and pistons). I bought new carb boots also to be sure there were no leaks there. There was not a lot of snow here last year so I only had time and snow to ride 3 or 4 times. I ran double oil (injected and mixed in tank) and it seemed to be working fine. Started right up, full power, etc. After running at moderate rpms for the first 2 hours a few weeks earlier, I took off and rode for about 90 minutes one day. I rode normally letting the revs come up to full throttle but only for short bursts. All was well until on the way back to the house, just as I pulled in the engine ticked a little (rattled?) and as I came to a stop so did the engine. This was exactly what it had done the previous year when the oil pump had stopped working. I was sick. It was pretty cold out and I just walked away for a few minutes. I later opened the hood and noticed one carb was loose and almost out of the carb boot (barely hanging). My guess is air got through here, just enough to lean it out. I never did get a temp light on though. The oil pump is securely attached and so is the cable, so I don't think that was the cause. And I had oil mixed in the gas also. About 4 hours later I got the sled started and drove it up onto my trailer and brought it home where it has sat until yesterday when I checked to see if it would start up and run. And here's the thing. It did. Started on fourth pull. Runs normally. Revs up normally (to 4,000 RPM - still on trailer). Idles smoothly. I only ran the engine for maybe 2 or 3 minutes since its hot outside, but when it ran it ran good.

Sorry to be so long winded, but I wanted to get the details out there. Now the question - is it possible for an engine to seize like that and cool off and still be ok? Or will I need to tear it apart again. Is there any chance at all I can run it as is (if I make damn sure the carb stays connected)?

I have so much going on these days I was hoping maybe it would be ok without a tear down. What would you all suggest?

Thanks in advance for any help.

I think I am tired of messing around trying to fix an old snowmobile. Maybe I will read the magazines until I can afford a new one.

RT my guess is you will need to pull your motor apart again. Years ago a had a 700 Cat Race Motor that seized a number of times and I finally figured out it was the Waterpump seal in the crankcase. The seal was allowing antifreez to access the motor. 2 strokes do not like to burn antifreez. Once I changed the seal it ran perfect.
Riley

You do not get a signal from the temp light before a lean burndown. You can check the piston condition by looking through the spark plug hole with a "bend-a-light" and then you'll know if you have any damage to the piston crown. You can also pull the exhaust off to look at the piston skirt and rings through the exhaust port to check the condition of those.

You didn't say if the engine wouldn't turn over when it stopped at the end of your ride, so it is not clear if the engine actually seized, or just stopped running. You also didn't say if the oil pump is working properly, but with pre-mix in the fuel tank, lubrication should not be the issue.

If the air leak at the carb flange leaned it out enough to cause damage you will see that at the edge of the piston on the exhaust side. If any melted aluminum smeared onto the rings you should be able to see that through the exhaust port. It sounds like the rings are free because it seems to start and run well, but a compression test might be worthwhile too.

Thanks for the helpful reply. You asked if the engine would still turn over after it shut off, and the answer is yes it did. I pulled it over with the key off. I didn't want to run it any more so I just pulled it over to see. I have been busy and on vacation the last week and a half, but I will take a closer look as you suggest and post a message as to what I find. A few more months and the weather will be getting cold again. Guess I better get busy.

I would take the top of the motor off, I would want to see what the pistons and cylinders look like, also look for antifreeze in crankcase.
My guess you leaned it out and may have some piston damage.

pics of the pistons would be very helpful in giving you an accurate diagnosis.

I don't think it is too surprising that the engine quit just as you came to a stop with one carb hanging. It could be possible that you had some overheating on that side too. Maybe not. I would look into the exhaust port and at the piston crown. You also want to see compression nearly equal with the other cylinder. If there is more than minor scuffing or any sign of piston crown sag, then I'd open her up.