Have any of you had a cat that backfires when you let off the gas???
just got mine out of shop after rejet and new plug. old plug was black after 700 miles. ATV now backfires [like shotgun] when letting off accellerator. starts well, plenty of power/ acceleration in all gears, but going down hill it will backfire at idle until engine breaking gets speed slow.. Any solutions?
"Farting Cat" [img]i/expressions/face-icon-small-disgusted.gif[/img]

 

Sounds like your quad is running way to Rich. If your plug was black then your mixture was rich. The shop should have leaned the jet out some but they normally wound'nt do this to a stock quad. I'm assuming your valves were set prior to any carb adjustment. Did you pipe or openup the air cleaner? You could have a dirty carb with a float valve sticking. Example, drive down the trail while moving, shut the kill switch off pump the throttle and turn the kill to on.... the exhaust fills with fuel the spark ignites this and ....boom! It backfires loudly.

There is an air mixture screw that needs adjustment especially after jetting or valve adjustments. The screw is on the bottom of the front opening of the carb pointing down. The Liesureworld site has the parts listing that can help you with this. This adjusts the air/fuel mixture. This needs turned in or out a full turn.

The proper way to adjust this is to warm the quad and slowly turn the mixture screw in until there is a slight RPM drop then open (back off) one full turn. If there is no change then you have to turn the screw out until there is a drop in RPM then in one full turn.

Hope this helps! Let us know what happens.

 

I believe there is an electronic throttle control device attached to your throttle cable. Its purpose is to interupt ignition in the event the carbs throttle plate does not close when you release the throttle lever...a safety feature. If your cable is adjusted too loose it will cause the same condition...so when you release the throttle lever the control device interupts the ignition and as your engine is slowing down it is loading up and when it fires intermitiently it will cause backfiring. Try adjusting the throttle cable to specs and see if this solves your problem.

 

ya i have a question too, my ac 250 (01) backfires after it is warm and you shut it off, is this normal and is this bad for it?

 

Thankyou Newcatman and rws. I put a call into the second dealer in town and he brought up both the throttle cable and air/fuel screw. Throttle adjustment had little effect, air screw seems to do the trick. I am at a little more than half a turn IN, and it didn't bang. If you guys have maunuals for AC, there is a discrepancy between the two dealers for the proper Jet on the kehlin carb. Original dealer said it was a 145 stock, and second dealer rejetted to a 150. operational elevation is 1000-4000 feet now,and in the summer, 5000-7000 feet. Did Arctic Cat change specs after 500 was manufactured??? I now have a 150, 147.5, I found the 145 under the battery, and I have a 142.5. How much does hanging the jet affect power?> I think the machine was a little less peppy with air screwturned in. HEy!! and Have a Merry Christmas , TOO! [img]i/expressions/face-icon-small-smile.gif[/img]

 

NewCatMan said>>I'm assuming your valves were set prior to any carb adjustment.

I was told by the first dealer that it was done.... but I don't KNOW because I wasn't able to stand over their shoulder at the shop.
I hope they were done right. the machine backfired before and after they worked? on it. dusty

 

my kodiac is like that when i shut it off if its still reving so befor u shut it off let it idol for 15 or 20 seconds

 

Had the same problem with a brand new 250 last year,backfiring like a shotgun when i let go the throttle from wide open.My plug was almost white.Went from 130 to 135 main jet and45 to 50 pilot jet.That took care of most of my problem.Still too lean idle,will go to55 pilot next spring.Also you should clean that pilot jet (blow with air gun)often.The hole is so small it plugs up easy.Hope this will help.

 

I had much the same problem.I went to a 142 main and adjusted the mixture.I also turned up the idle a little and this had the biggest effect.[img]i/expressions/face-icon-small-happy.gif[/img]