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CH motorsports
CH motorsports, Technician
Category: Motorcycle
Satisfied Customers: 25
Experience:  Atv,motorcycle,sled mechanic for 10 years. Owned Small engine repair shop for 4 years
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1996 polaris 425 magnum. Idles great. Backfires through carb

Resolved Question:

1996 polaris 425 magnum. Idles great. Backfires through carb when you give it any gas. Cleaned carb and same thing. Air box is off so I can see slide moving so I take it the diaphram is doing its job. I also see a fire ball in the front of the carb when I give it gas. Seems like it is getting too much gas but the plug is bone dry. Choked it and same response. Should full choke kill it because it just seems to lower idle. Also I heard these had a habit of the cam getting flat.
Submitted: 7 years ago.
Category: Motorcycle
Expert:  CH motorsports replied 7 years ago.
Does it miss like it does when you are in reverse with out pushing the button?
Customer: replied 7 years ago.
Kind of but it seems to be worse than that. As soon as you give it almost any throttle it misses so bad it about kills it.
Expert:  CH motorsports replied 7 years ago.

When it is at full choke will it rev or no?

Customer: replied 7 years ago.

no

 

Expert:  CH motorsports replied 7 years ago.
Have you checked the valve clearence?
Customer: replied 7 years ago.

No. Could you give me a crash course on how to do that? Also how many turns should the fuel/ air screw be turned out?

 

Expert:  CH motorsports replied 7 years ago.
On the mag you need to pull the tank to gain acces to the valve cover. Once you have the cover off, pull the plug on the recoil housing,there is timming marks on the flywheel. Bring it to top dead center,there is also a timming dot on theupper cam gear.At this point all four rocker arms should be loose. You need to set the clearence at .006 int. and ext.If you look at the ext lobe[center lobe] of the cam it should be fairly pointed if it is rounded it is junk. Fuel screw should be about 1 1/2 turns from seated, but if the choke does not seam to help I doubt that the screw has any thing to do with your problem.
Customer: replied 7 years ago.
.006 on int .009 on ext
Expert:  CH motorsports replied 7 years ago.
According to my book they are both .006 but my book is for a 97' could be different but as far as I knew all polaris's are the same int and ext.
Customer: replied 7 years ago.
Could they be just out of adjustment on the exhaust? And if it was flat I take it that they would not open far enough or would the duration they are open be too long on a flat cam?
Expert:  CH motorsports replied 7 years ago.
It's possible that they are just out of adjustment but I doubt it. When the cams are wore out the valves do not open enough to let the ext. escape the cylinder.
Customer: replied 7 years ago.

Ate lunch and decided to take rockers off and take a better look. Exhaust rocker and cam lobe are both worn. Just got wheeler so maybe someone was in it before and adjusted them so they would open. Anyways, you have any last words of wisdom on cam replacement before I quit bothering you and hit the ole accept buttonm?

Expert:  CH motorsports replied 7 years ago.
Not much to reccomend other than make sure that your cam timming is on when you install the new cam. Check your rockers when the cam goes it usually takes them out also. In my experence the most common cam failures are do to some other type of oil than the polaris 0w50. Hope i've been of help to. If you need any thing else don't be afraid to shout.

Edited by CH motorsports on 12/29/2009 at 10:13 PM EST
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Expert:  CH motorsports replied 7 years ago.
If you don't need any more info please hit the accept button.
Expert:  CH motorsports replied 7 years ago.
1
Expert:  CH motorsports replied 7 years ago.

Please accept if there is nothing else.

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