# Backfireing Carb



## Scott Jones (Mar 27, 2009)

I have a 02 660 Grizzly and it backfires through the carb. but only at low rpm. It will ONLY idle at around 1500 rpms or higher and only with the choke on. if i turn the choke off the bike will die unless you hold the rpms up to about 2000 rpms manually with my thumb on the thumb throtle. It recently backfired really loudly, and i mean louder than a normal backfire, thought the exhaust and died. when i finally got it cranked this problem has now occured. From 2000 rpms to full throtle the bike runs great with no missing or backfireing of any kind. only at low rpms


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## RDs Neighbor (Jun 24, 2009)

Sounds lean on the low end. I am sort of tuning for the same thing. You may want to try to adjust your air fuel mixture first. You may need to up size your pilot jet. Did you recently make a mod to allow more air in. Snorkels can have that effect if you use large pipe. If you use smaller pipe it ususally does the opposite.

It is common to have a bike run great on the high end and poorly on the low or vice versa. There are independent fuel circuits in the carbueator. You should search all of the key words involved with the symptoms you are having and read up. There is a lot of info here.

You may find a copy of the manual in the download section that would help you identify the components of the carb if you are not familiar with it.

Keep us posted if you have any luck. Or is adjusting the AF screw doesn't help.

Good luck :bigok:

Keep us posted.


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## Scott Jones (Mar 27, 2009)

Thanks for the info RDs. no i have not made any mods. the bike is bone stock with scock pipe. i just had the intake valve close up on me a little bitl i had a mechanic go in and adjust the intake valve and that got it back running again. i will try the air/fuel mixture first. i do seem to remember messing with it a few weeks ago while trying to get it to crank (before i took it to the shop) and didnt change it back.


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## PolarisEmtFirefighter (Nov 4, 2009)

heck just to throw it out there i know when my sportsman started doing this it was my cam . ive also heard it could be bent valves


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## jbart (Jan 21, 2010)

My 05 Brute 750 was doing the same thing. I removed and cleaned both carbs, twice, finally got all the circuits clean. Runs great now, idle's like a champ. Still a little sluggish and backfire on the low end, but I'm thinking that is the air/fuel mixture. My Brute has sat a lot over the last six years, just got junk built up in the carbs.


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## novass (Sep 25, 2009)

put some seafoam in the gas tank and drizzle some in the carbs


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## papaslim (Sep 30, 2011)

*backfiring*



Scott Jones said:


> Thanks for the info RDs. no i have not made any mods. the bike is bone stock with scock pipe. i just had the intake valve close up on me a little bitl i had a mechanic go in and adjust the intake valve and that got it back running again. i will try the air/fuel mixture first. i do seem to remember messing with it a few weeks ago while trying to get it to crank (before i took it to the shop) and didnt change it back.


I got an 09 brute with similar issues I was told to run a higher octane because of the compression it makes. backfiring can lead to more problems like blown injector gasket running hot and it will get worse if continued. thank god for high octane


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## wyo58 (May 13, 2011)

Its way lean on the idle circuit, no question. Two things can cause this 1. idle circuits in the carb are blocked up. 2. intake leak somewhere between the carb and the motor. Good luck, keep us informed.


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