Ok we have 2-2002-250 trailblazers both are doing the same thing .when you fire it up and ride it or just let it idle for a while then shut it off, it will not start , let it sit for 15 mins or so it will fire up, also it seems sometimes when it will not start with the key, if you use the pull start it starts. when it is running it runs great ,feels like it has all the power its ever had.

 

mine did the same thing, after I went & checked a ton of little things, I went & did a
compression test on it & it read about 98psi., it should be 115psi. I went & did a top
end job on it & that put it back to 118psi. & it would start great!! when the compression
drops they get harder to start. I would check your compression on both of the bikes
first & see if one or both might be low, if not then there are lots of other things to check.

 

DITTO on the compresion.

 

Well I checked compression ,one has 90 the other 115 pounds they were checked when motor was cold.so what do we think here guys the 90lb. just put in new rings if cylinder looks good or do you think it should be bored out,really dont want to bore it unless it has to be.

 

You need to mic the cylinder. Find the original bore and compare. If the cylinder is worn enough, then I'd go ahead and put .25 over piston kit. Your bore should be 72mm. Rings are about 18 dollars or you can get a weisco kit .50 over for 93.31 on hyperparts.com. The only problem there, is they don't have a gasket set for that model. And on the other bike, It is reccomended to get the bike to normal operating temp to check the compression. This allows for the cylinder to expand with the heat. Hope some of this helps.

 

Take the cylinder and piston to a shop and get them miced.If it needs bored get the piston from the shop that is doing the bore job along with the gaskets and piston pin bearing.