01' XC 500 bogging off idle & surging on top end at WOT - Snowmobile Forum: Your #1 Snowmobile Forum
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Old 01-28-2011, 11:07 AM   #1 (permalink)
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01' XC 500 bogging off idle & surging on top end at WOT

I'm having a problem with my 01' XC 500 Edge (NOT the VES SP engine)

It pull starts & idles well (but not super strong, though most carb'd sleds don't in my experiance), and if you half choke it at idle it dies immediately so I assume it isn't too lean (I also played with the pilot fuel screw anywhere between the factory setting of 1.5 turns out, too 1 turn out & 2 turns out) but If you pin the throttle pulling out at idle it just bogs & shuts off.

If you bring it up to 2000 rpm & pin it, it stumbles then backfires through the exhaust, & then takes off when the rpms get up over 3000. If you ease on to the throttle "normally" when the clutch engages it pulls out pretty well & takes of good as the engine climbs up into the midrange where it runs very good if not fantastic.

Running over 3000 RPM at between 1/8-3/4 throttle in the snow (6-8"s), it continues to run fantastic till 77-8000 rpm where you'll notice a very slight REV limiter type "surge" OR you go to WOT - then it acts as if it's barely able to maintain the speed you were at plus develops a surge which feels like it's banging off some kind of REV limiter (which I don't think it has AND I'm pretty sure this engine is good for 8200 + rpm anyways)

Running half choke seemed to help a tiny bit with the bottom end hard take off bog, but definitely didn't fix it AND running half choke did nothing for the topend power loss & surge plus making the normally great mid range sound dull & un-responsive.

Another oddity is the symptoms at WOT + 8000 rpm changes when the engines loaded - in the yard in 8"s of snow it's very evident, but when on the super hard pack dirt road snow, the surge goes away almost completely and it pulls up through the gearing much better. But even on the road if you let up to 3/4 throttle it pulls harder, smoother, and faster.

I thought maybe the load on the engine wasn't high enough for it's RPM power range, so I knocked the secondary spring down to the first hole. After doing that, it does exactly the same thing as it did before, but it does it 200 rpm lower at WOT. Plus I later read the this engine is supposed to operate at 8000rpm +/- 200 and is capable of over 8400 if you push it hard.


I'm thinking CDI/timing at this point, but it's not possible to test a CDI as far as I know AND it's so expensive to replace them. As for timing, I don't know the first thing about checking that on these engines. And if it was base timing, why would it be acting up everywher but 3000-7700 at between 1/8-3-4 throttle?

Sooooooooo - any ideas?
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01' XC 500 - currently having a couple issues.
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Old 01-28-2011, 11:31 AM   #2 (permalink)
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I would try moving the spring in the secondary to the number 4 notch. this will help maintain higher RPM while under load. I did it to mine and it helped a bunch. Mine would run great on hard pack but stumble under load at WOT.Just watch for over reving on the hard stuff.
What do your plugs look like after you let it idle for a bit. I think you may be able to lean it out a bit but not sure.

Hope this helps
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Old 01-28-2011, 11:36 AM   #3 (permalink)
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Also check compression if you can.
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Old 01-28-2011, 12:07 PM   #4 (permalink)
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check your reeds sounds like broken pedals
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Old 01-28-2011, 12:14 PM   #5 (permalink)
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I would try moving the spring in the secondary to the number 4 notch. this will help maintain higher RPM while under load. I did it to mine and it helped a bunch. Mine would run great on hard pack but stumble under load at WOT.Just watch for over reving on the hard stuff.
What do your plugs look like after you let it idle for a bit. I think you may be able to lean it out a bit but not sure.

Hope this helps
I'm running a 380 main, which according to the polaris manual is good for -10 - +20

I'm gonna do a plug chop later today.

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Also check compression if you can.
Never checked it with a gauge, but it feels strong and the mid range is too strong to be a compression issue (my 88' Indy 400 only had 95 psi & though it was lazy in the bottom end, it ran great once you got the R's up)

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check your reeds sounds like broken pedals
I though the same, but if they were broken (or even bent for that matter) why the strong mid range & decent idle?
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01' XC 700 SP - YeeHaw!!!
01' XC 500 - currently having a couple issues.
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Old 01-28-2011, 12:53 PM   #6 (permalink)
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sometimes it will only effect your top end and cause backfiring issues.what does it have for carbs does it have the mikuni flatslides?definatly check the reeds.usally from idle if you pin it and it falls on its face its to lean and if it has the flat slides you have to adjust your fuel screw one with white noob turn it out for more fuel.your air screw is a brass flat head by the mouth of the carb turn in to richen out to lean.also if your in deep snow it puts more of a load on the engine which makes it run hotter which will put it in limp mode and your temp light will not come on for it to do this.a 121 500 is geared to high and clutched all wrong to run in deep powder.if the sled is cool and you run it in powder and it runs good them after a few minutes it starts to act up then you know its getting to hot and going into limp mode.if it does it all the time and your carb settings are stock then it could be reeds,week spark,low compression or week clutch springs.springs should be replaced every one or two years.week spring will cause it to upshift to fast and not backshift fast enough causing a bogg
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Old 01-29-2011, 04:56 PM   #7 (permalink)
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I have a 1999 xc 500 non ves, so the engines should be the same. Your clutch should not engage until about 4500 rpm. I am at sea level up to about 750' abouve sea level, I had stock 370 mains, I dropped a size to 360 really cleaned up wotIdon't know much about clutching so I can't tell you how to correct the problem. I also raised the clip on the needle to clean up the mid range. That endune make 92 hp at 7700 and drops off quickly, by 7900 there is a large drop in hp.
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Old 02-14-2011, 12:51 PM   #8 (permalink)
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Things I've tried;

New reeds (V-Force) = same thing. Also roughly checked crank phasing while the reeds were out, looked to be 180 from each other (Or REALLY close) like they should be.

Took a compression check, exactly 105 psi in both cylinders - definitely could use an over haul, but can't see that being my issue either. (Had other sleds with clean down to 94 psi and they were lazy, but they didn't do any of this)

Sprayed crank seals with Berkible 2+2 while idling and saw no change in rpm or sound. (plus it starts pretty good and idles decent)

Tried the CDI off my 01 XC 700 SP = No change

Pilot jet was a 35, went up to the factory size of 40 and reset the fuel screw to 1.5 turns out. Seemed to idle better, but still bogged/backfired when coming of idle without feathering. Moved clip down (needle up) one more clip (was dead in the middle instead of factory setting of #2) and it's almost tolerable now, but it isn't really "fixed" either. Moving the clip down (needle up) seemed to make it run really good at about half throttle too, actually went faster up hill at half throttle (by almost 10 mph) than at WOT!

Half choke seems to help off idle bog/backfire even more now, but it def won't idle with the choke on, so that tells me it isn't the actual pure idle circuit seeming lean, it's more the off idle portion of the circuit which is controlled with the slide cutaway and needle's upper profile acting along with the pilot & air jets correct?

Choke still makes no difference on WOT issue.


Next steps;

Ordered new exhaust gaskets to fix a little seepage at the exhaust port and allow me to check the exhaust port, piston, and pipe for issues

I think I've figured out how to check the base timing to make sure it's set right

Gonna try the carbs (or at least main needles) from my 700 on the 500 to see what happens (Also have the option of trying a buddy of mines VM34mm carbs off his '02 550 fan)

Also ordered a couple size smaller main jets to try and see if that helps my WOT surge/power loss (none of the changes listed above has had any result on my WOT issues)
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01' XC 500 - currently having a couple issues.
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Old 02-14-2011, 05:01 PM   #9 (permalink)
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try checking you tps maybe it has a dead spot in it or out of adjustment.
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Old 02-15-2011, 04:22 PM   #10 (permalink)
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Originally Posted by ppolaris1010 View Post
try checking you tps maybe it has a dead spot in it or out of adjustment.
'01 XC 500 (w/o SP, w/o VES) didn't have a TPS. But thanks for the suggestion anyways.
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01' XC 500 - currently having a couple issues.
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Old 02-15-2011, 04:43 PM   #11 (permalink)
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This may sound dumb but check your choke cable tension. It can get fussy. Also make sure the cable moves well and isn't sticking.
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Old 02-15-2011, 07:09 PM   #12 (permalink)
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what do you mean by backfire.if its backfiring it would seem to point in the direction of electical more than carbs.if your carbs are at the factory settings it wouldn't backfire.have you tried unplugging the black wire by your stator to bypass all you shut offs and saftey switches just to rule out bad safety shutoff.i would definatly check your timing the dial indicator way.backfiring could also be your crank phase it doesn't take much to through it off really have to do it with a degree wheel and dial indicator.
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Old 02-23-2011, 02:48 PM   #13 (permalink)
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I think I'm getting to the bottom of it.


The jetting seems to be majorly whacked out, too rich on the bottom, too lean just off idle, and too rich at WOT. But midrange seems great.


Gonna lean out the pilot system, richen off idle with a thinner main needle, and play with WOT a bit to get it to pull smoothly then do a plug chop and see what happens.

It's gonna get a rebuild too, but I just can't see the low compression being the major culprite here.
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1988 Polaris Indy 400 - sold
1996 Polaris Indy 500 - sold
01' XC 700 SP - YeeHaw!!!
01' XC 500 - currently having a couple issues.
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