Hi,
I have a 2000 polaris xpedition I bought none running. I cleaned the carb very well, flushed and changed the fuel. now it runs but spit's fuel back out of the carburator, if you rev it up and let off it backfire's and spit's more fuel back out of the carb. any idea's on what is wrong and how i can fix it? thanks

 

Air box and filter have to be on or it will run lean and can backfire. If you do have the air box on,pull the cam cover and check valve clearance. .006 intake and exhaust. Basically the same top end as the Magnum 425 and early model Sportsman 500s.All three used the same cam (3086212) that a lot of people had problems with on the exhaust lobe wearing down.Same symptoms on back firing,couldn't take throttle. This could also be the cause. Look closely at the cam lobe,if it looks similar to this one,replacement cams along with the exhaust rocker arm are available on ebay. Hope it's something simple. Bad Cam Pic - ATVConnection.com ATV Enthusiast Community
http://www.ebay.com/itm/BRAND-NEW-POLARIS-400-425-500-CAMSHAFT-CAM-ROCKER-ARM-GEAR-GASKET-KIT-SET-/321679786960?pt=Motors_ATV_Parts_Accessories&hash=item4ae59c03d0&vxp=mtr

 

The Cam is Definitly bad. thanks for your help. I have never changed one before, Do you have any advice on the job?

 

Here's what I did on changing cams. Didn't go by the manual as it's quicker,BUT you have to be careful and not move the crank shaft.


"The originals weren't heat treated properly for a bunch of years.Some failed,some didn't.If the cam is cheaper than oem and they guarantee it,get this cam along with ordering a new exhaust rocker arm. Unusual for a 2001 to flatten a cam,but anythings possible. The easy way at least for me was to have the cam at tdc that is with the sprocket index pin straight up,center of the head.Make a mark on the head as the reference point. Remove the tensioner,thermostat housing(you have to remove it to access cam removal cover) Without moving the crank shaft remove the three cam sprocket bolts(impact gun allows you to do this without moving the crank!)Let the sprocket and chain drop down into the head cavity out of the way.Remove the cam rocker supports,rocker arms,then remove the cam cover and slide the old cam out. Install the new cam with lobes down,make sure the detent spring and lever are correct,pull up the cam sprocket,and install on the new cam. If you have to move the sprocket inside the chain or even jump teeth on the lower crank sprocket to align the index pin correct this is okay,just DON'T move the crank shaft! Once sprocket is on,replace the cam removal cover,thermostat housing,rocker arms and support blocks.Then replace the tensioner and bolts with the plunger pushed all the way back in(it will self adjust later) adjust the valves,then slowly pull the recoil. The tensioner will then adjust slack on the chain,then you can replace the top cam cover after adjusting valves. Top off the coolant you lost from the thermostat housing removal and leave the radiator cap off.You also need to clean the screen in the oil tank,replace oil and filter,clamp off the tank vent line and crank it up. Let it idle several minutes,then remove the vice grips from the tank vent. You may or may not hear a "hiss" of air when you do this. Also make sure you run it again to make sure any air is purged from the cooling system. If you don't like this way you can try to keep the tdc mark on the flywheel with the mark on the recoil cover and time it up,kinda hard to do, OR as you do when you rebuild one,remove the recoil,flywheel,stator,align the lower crank sprocket mark up with the engine case mark along with having the cam sprocket index pin dead center of the head,then replace the stator,flywheel,recoil,etc. Several different ways to change a cam. This way just the easiest for me. Plus don't pay any attention to the cam chain plated links. These three links were just for ease of install with the stator off and once the engine turns over the links don't line up again.."
If this all Greek to you, this cheap 5 buck manual can help explain step by step. DOWNLOAD 1999-2000 Polaris ATV Repair Manual ALL MODELS - Download ...

 

Hi, thanks for all your help. I installed the new cam and it runs a lot better but I am not sure I have the valve's tuned correct. do you have any advice in this area?

 

From the manual.



VALVE CLEARANCE
Inspect and adjust valve clearance while the engine is cold
and the piston positioned at Top Dead Center (TDC) on
compression stroke.
1. Remove the seat.
2. Remove body panels and fuel tank as necessary to
gain access to valve cover.
3. Remove the spark plug high tension lead and remove
the spark plug. CAUTION: Place a clean shop towel
into the spark plug cavity to prevent dirt from entering.
4. Remove rocker cover bolts, cover and gasket.
NOTE: It may be necessary to tap cover lightly with a
soft-faced hammer to loosen it from the cylinder head.
5. Remove timing inspection plug from recoil housing.
CAUTION: Failure to position the crankshaft at TDC on
compression stroke will result in improper valve adjustment.
6. Rotate engine slowly with recoil rope, watching the
intake valve(s) open and close.
NOTE: At this point watch the camshaft sprocket locating
pin and slowly rotate engine until locating pin is facing upward,
directly in line with the crankshaft to camshaft center
line as shown. The camshaft lobes should be pointing
downward.
7. Verify accurate TDC positioning by observing the “T”
mark aligned with the pointer in the timing inspection
hole. In this position there should be clearance on all
valves.

INTAKE VALVE CLEARANCE ADJUSTMENT
1. Insert a .006″ (.15mm) feeler gauge between end of
intake valve stem and clearance adjuster screw.
2. Using a 10 mm wrench and a screwdriver, loosen
adjuster lock nut and turn adjusting screw until there is
a slight drag on the feeler gauge.
3. Hold adjuster screw and tighten adjuster lock nut
securely.
4. Re-check the valve clearance.
5. Repeat adjustment procedure if necessary until
clearance is correct with locknut secured.
6. Repeat this step for the other intake valve.

EXHAUST VALVE CLEARANCE ADJUSTMENT
NOTE: The exhaust valves share a common rocker arm,
and must be adjusted using two feeler gauges.
1. Insert .006 feeler gauge(s) between end of exhaust
valve stem and adjuster screw(s).
2. Loosen locknut(s) and turn adjuster screw(s) until
there is a slight drag on feeler gauge(s). NOTE: The
feeler gauge(s) should remain inserted during
adjustment of each valve. The Valve/Clutch Adjuster
(PA--44689) can be used to adjust the 500 engines
valves.
3. When clearance is correct, hold adjuster screw and
tighten locknut securely.
4. Re-check the valve clearance.
5. Repeat adjustment procedure if necessary until
clearance is correct with locknut secured. P.S. on adjusting exhaust valves make sure to use two .006 feeler gauges so the rocker arm doesn't get cocked.Loosen both exhaust rocker arm 10mm nuts,loosen adjusters if needed,slip in both feeler gauges,then adjust one at a time.This just keeps the one side of the forked rocker arm close to the clearance of the other.Older type rocker arms like this used on street bikes if not adjusted correctly,could put pressure on one side and knock valve keepers out and destroy heads and pistons. Even a possibility on the 425/500 engine if not adjusted correctly,but don't remember seeing this happen.