my blaster has backfire and overheating

[Alan_76]

Hello all ,i have a 2003 blaster with 98mm wiseco pistons, a couple of weeks ago i make the full bottom end rebuild all brand wiseco ,and it runs great before that but sometimes when i kick it make one low backfire and then when runs 10 mins it starts to overheating ,i can feel the heat on my leg ,the carb and air filter are clean, there are no oil lakes from the crankcase
i dont know what to do to fix this trouble please help!

 

[Blasturd]

Thats a big piston!

 

[Blaaster]

Did you leak test the engine before you started it?

Did you do heat cycles then re tension the head and cylinder bolts?

 

[Alan_76]

jejeje sorry its 68mm piston ;
i just check the crankcase leak and it is fine there are no leakes

 

[Blaaster]

How long did the engine hold the pressure?

Did you heat cycle?

 

[Larry's Shee]

Other than the 30mm overbore , list all mods and jetting you know of.

 

[Alan_76]

i found this mark inside the piston (this is the old piston but it still be on the new one),i never seen that before the overheat ,and the leak test i didnt check it with air pressure but it has new cyliner ,head and reed gaskets

 

[Larry's Shee]

A proper leakdown test is the ONLY way to insure the engine is leakfree. Ya, there are some quick and dirty ways to check, but are no where near as reliable, and are very limited in application.

Carbon on underside of piston is normal. Tho heavy deposits or if it is more ash like is a sign of trouble.

FYI, new parts are no guarentee of leak free assembly.

 

[Alan_76]

you were right i went with an mechanical , he made the leaktest and found a big leak on the head ,i think it was the cause of the overheat because the heat air doesnt allow the right cooling ,let me test it and see how it runs

 

[jus_me]

^^ yes,, the air leak created a lean condition which in effect caused over heating and eventually would have caused a seizure and or worse.

While things are apart, it would be a good idea to check bottom end crank play, and you also may want to change the top end/wrist pin bearing. They don't like excessive heat..