I have a trail blazer 97 ran great till month ago.. started back firing through airbox. Shut it off didn't want to start.. i pulled the carb cleaned it and put on and started up.. rode it for couple minutes started back firing through air box again.. any ideas what it can b..

 

Check for spark and do a compression check.

 

Has spark starts up.. what should compression be.. idles fine when u ride for a few minutes when it starts to pop back through the airbox..

 

Manual shows 100 psi to be bare minimum,but that's really cutting it close. Do a compression check cold and then again after it warms up and starts acting up. If it's lower than 100 psi then may be excessive piston and ring wear.

 

Checked the compression cold 105psi ... let it warm up to wear it acts up still 105psi..

 

Still getting down there,but if spark is good as you say then you could pull the carb, check for any cracks around the intake manifold,clean the carb jets and make sure the float level is ok. Here's the carb section from the manual that can help.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA If it still back fires through the carb then could be the old pesky crank seal behind the drive clutch.They're notorious for leaking,causing engines to either run lean,back firing like you mentioned or not run at all. Beyond that only thing left is to pull the top end and check the piston to cylinder clearance since compression is down close to bare minimum.