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post #1 of 9 (permalink) Old 09-12-2015, 03:13 PM Thread Starter
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Won't idle, backfires when decelerating

2004 Sportsman 700 Hard to start, takes full choke and then 3/4 choke to keep it running. Idles at 1750, backfires upon deceleration when hot and will run well after acceleration begins but runs rough until 5 MPH. I removed plugs, L one was wet with gas. This ATV has 50 hrs and actually belonged to a little old lady who drove it to a mailbox and got too old to get on it. Someone, did not care for it and it had mud in the aircleaner box, and signs of being run through soupy mud everywhere, never had oil or aircleaner changed.Any thoughts would be appreciated.
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post #2 of 9 (permalink) Old 09-12-2015, 03:29 PM
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take carb apart and clean. check rubber boot between carb and cylinder for cracks
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post #3 of 9 (permalink) Old 09-12-2015, 03:33 PM
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I would say aknawful pretty much nailed it.
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post #4 of 9 (permalink) Old 09-12-2015, 04:46 PM
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Ditto on the carb boot. They're rubber and tend to crack.
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post #5 of 9 (permalink) Old 09-13-2015, 07:02 AM Thread Starter
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k, Thanks Will do it. I hate working on Sunday but may start on it today. What about Seafoam? Good-Bad? I will drain fuel tank and use fresh gas. Thanks again
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post #6 of 9 (permalink) Old 09-13-2015, 09:54 AM
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Sounds like more than just one issue going on. Wet plug as you described could be a coil, plug lead, or dead plug. I would have a look at the plug connector to make sure it's got a clean contact with the wire. (Yours may thread into the plug wire which allows for corrosion.) If the connection is bad just snip off a 1/4 inch or so till you have clean wire inside and thread it back in. Check that the coil has a clean ground and is tight to the mount. If you find it loose then I would take it off and clean up the contact surface before tightening it back up. Inspect the wires feeding the coil. As for mud in your air box; did it have mud past the filter? Clean that all up and throw in a new air filter. Check that you haven't lost the plug out of the drain hose, allowing a reverse flow. Without it water will get sucked into the system. If your filter element is clean on the inside and you can not see any contamination that got through then your carb is most likely unaffected. You can check for cracks or leaks as mentioned with a solution like carb or throttle body cleaner and just spray the boot while the engine is running. Any leak will show with the increase in RPM or in your case may kill the engine due to too much fuel. I suspect the backfiring is due to excessive fuel because you're employing the choke as you referred to. What does the other plug look like?

I think you may find that you have at least three things happening here to make for a bit of confusion. First one plug isn't firing properly. Second is an fuel/air mix problem, and last is a possible unmetered air intake issue. The latter is fairly straight forward to solve and can be carried out in the process of tackling either the carb or the ignition problem. If this were my machine I would first work on the ignition system by inspecting and then checking resistance and continuity on the plug lead and coil connections as well as all related wiring. (Could have a chafed wire contacting the frame for example.) Unless I could see signs of the carburetor having been contaminated I wouldn't pull it before doing the aforementioned and running the engine. If someone had of swamped your carb, they never would have got the engine running without doing a thorough cleaning. All the mud you're seeing is quite normal simply by driving through large puddles at cruising speed. However mud in the air box isn't so making sure the drain plug and lid are sealing properly is a must.

When you install your air filter and box after cleaning give the connection points a little wipe with grease before tightening the clamps. Makes for a better seal and they come apart easy later. If you pull your carb I would go straight to the vacuum block and diaphragm and look for signs of dirt on the underside of the diaphragm and in the slide area of the carb body. Put before you do that, have a reach into the carb throat and give a push up on the vacuum block. You can quite often actually feel the dirt kind of chattering back at you as you lift the block and keep your finger tip touching the block as it travels back down.

Hope all this helps.
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post #7 of 9 (permalink) Old 09-13-2015, 03:42 PM Thread Starter
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Thanks for all the ideas. Found water was injested into the intake past airbox. Drain was completely
plugged with mud. The carb throat feels gritty but no signs of mud. Will remove rest of intake and see whats inside. Haven't pulled plug wire yet to test. Have air cleaner ordered. Wires look good, only 60 hr on machine but will test. I have this and 1000 things to do before the 24th then it's off to Co for a month.
Washed the intake and inspected boot. Appears to look new. This ATV belonged to a guys Mom and she rode it to the mailbox but he rode it in the mud. Since 2003 it has only had 4 new tires put on due to cracking and the plugs changed. Never washed or anything else.

Last edited by WupperAV; 09-13-2015 at 03:45 PM.
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post #8 of 9 (permalink) Old 09-14-2015, 03:55 AM
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The carb throat feels gritty but no signs of mud. Will remove rest of intake and see whats inside

Yah..good Call..


This ATV has 50 hrs and actually belonged to a little old lady who drove it to a mailbox and got too old to get on it. Someone, did not care for it and it had mud in the aircleaner box, and signs of being run through soupy mud everywhere, never had oil or aircleaner changed.Any thoughts would be appreciated.


Take the boot and hold it up to a bright light and bend it look for light coming in.
Plugged filter ..good enough reason..for problems like yours.

While your at it.. take of the CVT covers..chances are theres mud in there to ..

The grit will eat your belt and clutch fly weights.

Bestof luck with this.

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post #9 of 9 (permalink) Old 09-16-2015, 10:14 AM Thread Starter
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Thank You, Hoping a friends boyfriend comes by today, he owns 3 and is a mechanic. Will interrogate him. You guys are the best!
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