Hey everyone. I have a 2000 AC 250 2x4 and as of today is backfiring compression and fouling spark plugs left and right. In the past when I fouled spark plugs my values were out of adjustment. And my last adjustment got my top end rebuilt cause ac said my 250 had a bad batch of values in it. They said the metal was too soft and warped when the motor was started. I got the whole top end rebuilt and havn't needed adjustments in 2 years now. Now Its back to the same old same old and I am thinkin the values are going out of adjustment again. Does anyone else think this is the case. Would hate to bring it to the dealer and have them say there is nothing wrong.

THX
Extreme

 

Sounds like it needs carb adjusting more than valve adjusting. Im not sure, that out of spec valves would foul plugs.
What are the circumstances where it backfires? Coming off of wide open throttle? Opening the throttle just past idle? Only when its cold? All the time? When its cranking?

 

Hondabuster is right, it isn't the valves. It got to be the carb. High float setting or pilot adjustment way rich. Then again I had a spacer on the needle in the slide missing that cause the same problem. But that would be the last thing I would check. Plugs foul for one of two reason; oil past the valves or rings or to much fuel. The backfire in the exhaust is a fuel issue so I would doubt and oil problem. You are gonna have to pull the carb and check it out.

 

my 2001 ac 250 2x4 did the same thing, but we cleaned the carb and it still did it. then we broguht it to a mehcanic and he asid it was the intake valve, it was to tight.

 

Okay heres what I did so far. I ran the bike quite cold out today around 15-20. It idled fine on choke and all that good stuff. Took it off choke and idle was low and it was stalling uncontrollably. I checked the plug and yea it was fouled. Put a new one in it and started it up. Idled okay for a few minutes then as I brought it back into my driveway I hit the gas and she was sputtering and backfiring then began backfiring compression. Hondabuster in reply to ur question I was just getting back onto the gas when I noticed it. Checked the plug again and she was fouled again. I am gona take the carb out tomorrow and see what it looks like. It quite odd because when my valves went out in the pass I lost all power and it couldn't accel past 20 mph. My carb has been set the way it has been set since new I don't know if that means anything. When I first got the quad brand new I had value problems all the time and the carb was considered the issue until they found bad top end and the carb idea went away. Maybe it is a problem in the carb that was never noticed cause they jumped to conclusions sayin it was only in the top end.

EXTREME

 

The fuel now days is junk, it goes bad fast and has a lot of impuities in it, plus alcohol which collects water and leaves it in the float bowl. It also can screw up your settings by plugging passages etc. The problem you are discribing, is a carb problem. Valves can't foul the plug. I was a pro mechanic for better than 25 years, you have a fuel problem.

 

Sputering and backfire on the throttle ...too lean. Air leak in intake, carb circuit plugged, bad gas, air box lid off or no filter....
Drop the float bowl, and look for crud inside of it. My guess, is youre gonna find little floaties, and some hardened crap. If you do find these, then youre gonna need to clean out the jets and passageways of the carb.
I think the valve adjustment is pretty straight forward, on that motor, and shouldnt take too long to check. Or if you have a compression gauge, do a compression check, if your valves are out of adjustment or shot, itll show up on the compression test.
Theres are many circuits in a carb, starting , pilot, midrange and main. Anyone of them could be lean or rich...independant of the others. So having symptoms of lean (backfiring and stumble), and rich ( fouling), can happen.
Id start with a carb cleaning.
Look over the rubber intake, for rips or holes, or loose clamps or bolts.

 

try putting dry gas in her and it will fix it, my ozark had the same problem. when did it happen last because if it is winter time than it is condinsation build up

 

If you want to keep the water out of your gas use a fuel drier regularly. However never us any alcohol other than isopropal as etheno and methenol both are corrosive and have on other nasty habit. When there is to much water for them to hold in solution, they dump all the water back into the bottom of the tank. You end up with a layer of water at the bottom, then a layer of alcohol and then gas. Makes a bitch for your engine to run on water or alcohol. Isopropol just ignores any water it can't hold in solution, so you get a little water at the bottom of your tank, not all of it. BTW, any alcohol will pull moisture out of the air so burn your gas soon. NAPA sells a bottle of almost pure isopropol alcohol. Isopropol is the same as rubbing alcohol, except what you buy at the drug store already has 60 to 70% water in it, don't go there.