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2001 xcsp 600. im stumped. backfireing

11K views 14 replies 6 participants last post by  zobenv 
#1 ·
I think I've got a good one for you guys.
it is a 2001 Polaris xc sp 600 ves motor. bought off of crags list for a grand.
sled is absolutely spotless with 2500 miles. has electric start and reverse
two problems it back fires at idle, and reverse doesn't work.
1 fix motor
2 fix reverse
it still dose not idle vary well.
so fare I have replaced:
base gaskets
head O-rings
exhaust gaskets
fuel pump
carb boots
reeds
swapped cdi box
unplugged tors
cleaned power valves
inspected stator side crank seal and timing
inspected pistons, rings, and cylinders
o yea. cleaned and adjusted carbonators at least 5 times in the last 2 days trying to figure this out. each step I take it runs better but still has a random back fire to the carb and exhaust on the pto side.
jetting is all stock and correct for my altitude.

all that being said.... dose anyone have an idea what to try next.
the only thing I have noticed is one of my screw drivers was not magnetic until after I used it on the sled. but I don't know why or where it could have become magnetized.
Help -,-
never had trouble fixing a Polaris before.
 
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#4 ·
Reeds? If the petals are cracked or chipped, they won't seal well and the motor won't hold compression on the downstroke of the cylinder. It will cause it to backfire out through the reeds which makes the problem even worse.
 
#5 ·
The reeds that are in it right now came out of my 2002 600 exsp it is running what came off this 2001 and no change.
I have adjusted idle fuel screws already. on both sides to try to richen it up.
I have the mikuni 38mm flat slide rail carbs. and they are vary vary clean. neither idle fuel adjustment screw is broken off.

I'm going to call a friend today and barrow his old 2001 pro x 600 carbs to try on it. he tossed a rod in it last year so its a community doner sled. ^,^
 
#6 ·
update

I believe I have narrowed it down to carbonators. I have not got ahold of my friends to pick up his spare yet but according to the plugs it is happy on the stator side and extremely rich on the pto side.
Could a bad float case this and yet not flood the crank case?
the sled is at a half a tank of fuel.
 
#7 ·
It's technically possible, but not common. More likely is that there's an electrical issue.

Check the wire for that plug, check the inside of the cap, and check connection between the two - unscrew the cap, clip 1/4" of the wire off and screw the cap back in nice and tight.

If the metal inside of the cap looks blackened or even scored, there's a bad connection and the boot needs to be replaced.
 
#9 ·
If you swapped everything, including all of the wires, then it should rule out electrical altogether. Swap the plugs? Maybe one of the plugs is bad. Also, have you verified compression?
 
#10 ·
I put my top hat, coil, wires, on just plugged in to cdi box and popped on plugs. have three sets of plugs have tried all three and swapped left for right.
its still extremely rich on clutch side and back fires inside carburetor.

yes 124 psi clutch
127 psi stator
I reason I asked about the floats is when I removed them for inspection the o rings were a little worn. so I put Vaseline on them before assembling them. and it fired up and idled well for about a 60sec before it began to backfire again.
 
#11 ·
How many miles on the sled? If it has a lot of miles, the slides in the carbs may be worn, which will let air around the slides and cause issues. The plastic flat slides wear more than the older round slides, which were made of metal. It's something to check, especially if you have ruled out everything else.
 
#12 ·
review

I am working on a 2001 Polaris ex sp (2507 miles) equipped with a 600 liberty engine, electric start, reverse, in a short track.
it is rich on the clutch side. causing a back fire in to the carburetors at idle/ low rpm.

view list at top of forum for list of parts inspected/ replaced.


I completely disassembled the carbs last night and found nothing dirty, clogged, or showing any wear.

QUESTION. could the choke on that carb be leaking past. causing a rich mixture?
 
#15 ·
Sounds crazy but, check the air screw in the carb make sure it is all there. I have a Polaris that someone tightened the air mixture screw to tight and it broke off in the the seat. I did fix it some what by having a machinist make a fixture that goes in the space where screw goes and kept drilling until the small piece of brass fell out. And yes the sled was backfiring.
 
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