A new problem that has popped up.
Went for a 70 mile ride on saturday.. Temps in the low 70s, no mud just flat trails.
Halfway thru the ride, the quad started giving me grief.
We were cruising along at 25-30 MPH AND I started noticing that there was no mid throttle response.
Bike would go like jack the bear if I went wide open throttle and idle fine but there was nobody home in between.
It would sputter but not backfire.
You can hear it trying to suck air thru the air intake like a low growl... and constant missing but would smarten up on wide open throttle.
At some points it would be ok... then start bogging again.
Based on my past experience , if it was a lean condition, I would hear a backfire now and again... not once did it backfire.. just no *****.
Now, I did raise the needle one notch back in March because I thought it was a little lean on the higher rpm. And it seemed fine until saturday.
I've ran it in warmer Temps and not had a problem like this!
I do have a fuel filter installed so I don't think I've got crap in the carb.
It's acting like the pilot is plugged.
I'm 400 miles from home and don't really want to pull the carb off..... but if I have to i will.

Any logical direction I should take ?

Thanks in advance.

 

I'd eliminate the carb as the source of the problem and pull it off. If you're going to do that I'd install a new carb kit. No sense in having to go into one more than once.Carb Carburetor Rebuild Repair Needle Gasket Kit Polaris Sportsman 500 HO 01 13 | eBay

 

I'm still having the same problem.
Rebuilt carb, new plug, checked fuel filter, checked fuel pump.
Starts fine idles fine.
if you run along slow it will be ok, once you try to accelerate or climb an incline it starts missing bad and will almost come to a stop. If i feather the throttle I can get it back, somewhat. once in a while if you go wide open, it will go like jack the bear, then dead in the mid throttle range again.
It makes no difference if the air box is on or off.
I can see the carb slide moving up and down with throttle action but very jumpy.
Would a worn cam cause a vacuum issue with the slide?
I've taken the carb off 3 times and checked for debris... always clean!
Tried running with the choke on too.. no change.
So its either fuel or spark related.
Never heard of a coil slowly going bad.. either they work or they dont! and I've checked the sparkplug wire as well.

 

If you can determine it's not a fuel or carb problem,I'd check valve clearance just to be on the safe side. Cams shouldn't be a problem on this model,especially if it runs good wide open. My sneaky suspicion is that it could be another ecm module causing problems. On that I'd at least eliminate the electrical system trouble shooting checks and tests in the manual on the ignition first.2008 Polaris Sportsman 500 Service Manual PDF Download
4011568 CONTROL-MODULE,SINGLE,CARB $181.60

 

Well, I'm still stumped! Took the carb off again.. checked, cleaned, blew out every single orfice in the damn thing! still doing it!
A while back, I had the recoil fly apart inside the cover.
I cleaned all the debris out and replaced all the parts with new.
I didnt check to see if the pulsar coil got damaged or moved when all the parts ran through there like a shredder!
could something like too much air gap cause this type of issue?
it almost seems like its a spark issue since its getting all the fuel it should.
And again.. the more fuel in the tank, the worse it is (as odd as that sounds)

I've been messing with 4 cycle and 2 cycle engines for close to 40 years, this one has me stumped!

 

If pick up coil gap is more than .040 from the flywheel or if the bracket is bent,that could possibly have something to do with it.Wouldn't hurt to check ohms resistance also. Should be somewhere around 97 ohms +/- 20%. If its weak,outside of the allowable range,replacements are on ebay. You may just need to move the bracket inward and see if that helps. Kinda like what this guy came up against when his rope broke,but he didn't have spark with the starter.no spark to plug when using electric starter - Page 3 - ATVConnection.com ATV Enthusiast Community

 

Well , a long awaited update. After many carb inspections and changing parts, I've given up on the original carb. I installed the 2002 sportsman carb on my 2008 and it runs like a champ.
The problem I was having is no idle quality and no power mid throttle. I know its in the pilot circuit of the carb but I cannot find any blockage or reason for this to happen. Finding a used carb is hard, and a new carb at $500 US isn't really the direction I want to go. I would leave the 02 carb on but I don't think the little lady will want a quad sitting in parts in the garage.
I can get a Caltric carb for $83 US (in total about $170 CA delivered)
Are these knock off carbs any good? would it be a waste of money or worth the chance.

 

Have you removed the block off plug for the pilot screw adjustment/replacement for the repair kit parts? As far as those Caltric carbs they lump all year models together. Up until 2000 the Sportsman used a Bst34 carb,afterwards the 40 mm bst40. I don't know if it'd fit the 40mm intake manifold correctly or not.

 

Yes I have and I have tried running it at different adjustments. anywhere from 2 to 3 turns and all in between. changed pilot jets, changed clip positions... float heights . many things.
The 02 runs the BST40. identical carb except the choke plunger and choke nut.

 

Did find this one that's supposed fit the later models other than the Zoom-Zoom or Caltric carbs.New Carb Carburetor Assembly for Polaris Sportsman 500 2001-2013 3131453 3131567 | eBay I'd make sure whatever carb you got that you'd open it up and blow out every orifice and check jets with the oem carb.Supposedly interchanges with your Mikuni 3131453 carb as well as later numbered carbs.