98 450 es backfires when deaccelerating.how do you cure this problem.

 

Likely running lean. Could be air leak in the intake manifold, or if you've changed muffler or whatever and didn't change jetting...

Otherwise, you might bump up idle mixture slightly.

My 500 will pop from time to time on a really steep downhill, but it has since new and it runs fine otherwise, so I'm not inclined to mess with it.

 

Thanks for the info.that could be what it is.i turned the ide way down the other day.i'll boost it up again and try it.thanks again.

 

Could be a gummed up idle (slow/pilot) jet, leaving you lean. As mentioned, an air intake leak somewhere is likely as well.

 

On the 450, if the air fuel mixture screw is not adjust out far enough, it will backfire. Turn the fuel air mixture screw out 1/2 turn ride checking for improvement.

A few other issues that will cause this is if a float valve needle is not seating completely. When decelerating the over abundance of fuel from a high fuel level in the bowl will not completely burn in the combustion chamber and the mixture will explode when exposed to hot exhaust system.

An air leak in the exhaust system will also cause backfiring under decel.

A tight exhaust valve or faulty decompressor on the camshaft will cause a backfire

A carb primer diapram with a hole in it will leak too much fuel into the carb and cause the backfire

Most likely the first mentioned air fuel screw adjustment is off. The 450 likes to breath with this screw set at around 3 turns from seated position. How yours is set, it may need to backed out 1/2 to 1 turn to cure the issue

Also make sure your spark plug is not carboned up. Too much soot build up will give the plug the wrong characteristics for it's heat range.



----- Gimpster -----