A buddy of mine has an AC500 ( I think '97 or '98). He has experienced some strange behaviour almost from day one that seems to escape local dealers.

If he is driving full throttle and lets go of the throttle quickly, he gets a nasty pop, and flames, out of the exhaust. His brother-in-law has a 454 with same symptoms. If the throttle is let of slowly, all is OK.

Has anyone seen this, and can suggest a remedy before a muffler is blown off.

 

He is running to lean with the carb.====BILL

 

Bill , How can that be.

By all logic, if you quickly back off a throttle, you would think that the timing is off and allows unburned fuel to be dumped into a hot exhaust, thereby creating the back-fire condition.

I am not too versed on ATV mechanics. I know that ATVs don't have computer like cars and most probably rely on systems cars used to have for advancing and retardnig the timing to avoid this situation.

I just found it ironic that two model years and different motors (i.e. 454 & 500) have the same symptoms.

 

I suppose you could be right as well.Im basing my thoughts on my quad.The same thing happened,and the mechanic richened up the carb somewhat and all was ok.===BILL

 

a slight pop is normal but flames are from running lean.pull the carb clean out the bowl the jets and the emulsion tube check the float level,make sure the c-clip is on the 4th notch from the top on the needle valve.give that a shot see if it helps.

 

I have the same porblem with my Cat except it's not very loud and there are no flames shot out.

Jetting is the problem.

PS. I talked to an Arctic Cat Mechanic and he told me that running 400 and 454 with a 150 main jet makes them run ALOT BETTER he said he could not tell the difference form the 454 to the 500 whit the 150 jet in it.

 

My 454 will still backfire after running full throttle then letting off quickly. the first few weeks I had the bike it experienced the same symtoms you described. As Boner said the jetting was wrong and was causing this. Since rejetting it I have found it to be less loud and less often that it occurs.

 

Lots of cats come with too rich of a carb setting, and sometimes a hotter spark plug can help. This loser above me had that same problem. Fixed the carb adjustment, put in a different plug, and it runs like a scalded mule with no ill effects whatsoever. Its amazing what a difference a few minor adjustments can make.