my buddies 1991 300 honda fourtrax and it backfired and blew black crap almost 3 ft out the exhaust , so i was wondering why they backfire and if it is hurting the 4 wheeler thanks

 

i would clean ouy the carb; make sure all the jets are clean with no trash in them. then do a spark plug test. if its running well, warm it up then go for a ride all the way threw the gears. once your in top gear about full throttel hit the kill switch. stop and check the clolor of the spark plug. black is too rich, white is too lean. your wanting ideally a marshmallow brown.

if your carbs clean and your plugs not too rich, then its probbly just built up carbon n crap from your tail pipe.

hopr this helps

 

You have a 99' 300 fourtrax i agree with cherokee99 cleaning the carb and doing the plug check , i would also suggest that you remove the spark arrester from the muffler and start the engine and rev the engine to blow out the carbon thats builtup in the exhaust ; this is a proceedure that your Honda Service manual calls for after so many miles then reinstall spark arrester !

You should also make sure your airfilter is cleaned and reoiled to ensure you're not starving for air , especially if you are running the stock air filter and you're not sure when it was last serviced ; hope this info along with cherokee99 has suggested and welcome to the forums !

Oh and one other thing to check is your valve clearance specs to insure they are within specifications , good luck and be safe when riding ; the life you save could be mine or cherokee99's !........