Bombardier ds90 dies out after a few minutes of riding*Please help*

[jm_middleton07]

I recently rebuilt the top end on it because it wouldn't start at all. The rings where worn bad but the rest of the top end looked good. It will sit and idle forever but if you take off on it a few minutes later it dies. Like you cut the gas off to it. I changed the fuel lines to clear one so that I could see the fuel. I've had the carb off a million times. I soaked it in mean green and then washed it off. Then cleaned it with carb cleaner. Everything seems clear and open. The air fuel screw has to be set about 1/2 a turn out for it to idle the best. Anything out more and it dies. I'm guessing I need a larger pilot jet. Does anyone know what is in it now? It has the mikuni carb in it. I have two of these atv's. A 50 and this 90. Seems like both has to be set with the air fuel screw about the same to run. You would think with both of them being stock that the pilot jet would be ok.

[LT80]

Please explain what you did to the top end.

[jm_middleton07]

Please explain what you did to the top end.

The piston and cylinder looked good. No gouges nothing. Took the cylinder and had it honed. Kept the piston and put on new rings. I'm in the process of making a leak down tester to see if I have any air leaks.

[LT80]

Did they measure the piston to bore to see if it was in spec. (.007- .008 max). Do a comp test?
I've never been a rings only guy. Usually for another 25 bucks you can get a new piston.

[jm_middleton07]

No I just had them clean up the cylinder. Kicking starting it I never get a real high static compression. I could kick it a 30 times and it would never move over 60psi before or after the rings. I checked the diameters and other dimensions just so I would know if I decided to order other parts not from canam. I have two diameters wrote down. 49.8mm and 49.3mm. I'm assuming the larger is the bore and the smaller one is the piston. These where both taken with digital calipers.
I'm down for starting all over if that is the issue. Yesterday I adjusted the float because it would go .375" up into the carb before shutting off the gas. Thought maybe the bowl was getting too full. I have it adjusted now where the float is level with the housing when the fuel is off. When I test rode it I was able to keep it running when it went to die but it wouldn't take any gas. If you cover up the hole on the air filter box a little it will allow you to take back off. Then it will try to die again in a few seconds or a minute.

[LT80]

Well that would explain alot. The leak is between the cylinder and piston. LOL
I read that as .0195 clearance (.5mm). Way too much. Dang near 3x too much.
You need a new piston and the cylinder bored to the piston.
I'm unsure if a .5 over piston will be enough. You may need to go to 1.0 overbore.
I like stock pistons and parts.

[LT80]

How you make out?

[LT80]

How did you make out?