MY FRIEND IS HAVING A PROBLEM WITH HIS GRIZ. IF YOU CHOKE IT HALF WAY THE BIKE RUNS FINE BUT WHEN YOU TAKE THE CHOKE OFF IT BACKFIRES THROUGH THE CARB AND EXHAUST AT THE SAME TIME. ANY HELP WOULD BE GREAT. I TRIED TO GET HELP ON THE YAMMY SITE TO NO AVAIL, SORRY IF I OFFENDED ANYONE. I WARMED THE BIKE UP FOR 10 MIN. AND RODE IT FOR 5 BUT THE PROBLEM WAS STILL THERE.

 

I am guessing he is running lean. I might be wrong but the reason why it might be running fine with the choke is because it is running a little richer and when the choke is off it might be lean. You will probably have better luck with someone else but thats just my 2 cents.

 

Tell him to check for intake manifold leak if back firing through carb or exhaust manifold leak if backfiring through exhaust. If nither of these than check ignition system. I'm assuming that he hasn't been fooling around with the jetting or carb settings. My bet would be on an intake leak.

 

I would have to agree with wam. An air intake leak will act exactly this way. I've had this happen more than once on two wheelers. Check the intake boot between the carb and head. Spay some wd or carb cleaner around the area while the bike is running. If it stumbles then you have a noticeable leak.