99 500 WOT Bog...ideas?

[Rain Man]

Cleaning up for an in-law who lacks snowmobile smarts. About 1500 miles of light to moderate rider. Obvious good shape and not ridden hard by any means, ugly varnished fuel however, so I thought this was going to be easy, right.

Carbs gone through multiple times, cleaned with carb cleaner and air, set to stock for altitude, +10 to-20 jetting, pilots, needles #3, set air screws. Went from draw tube to carbs, replaced fuel filter. Carb vent lines check, some replaced. Intake box to exhaust pipe exit cleaned, no restrictions. Drained old fuel, replaced with 91 oct non-ethanol and run through system completely.

Stock clutching for local altitude, swapped primary spring for troubleshooting, checked bottons, rollers. No secondary to swap to troubleshoot, but spring looks new, #2 hole in secondary, cleaned. Tried multiple belts.

Track tension set, ok.

Runs great up to last 3/4, maybe closer to 7/8 of throttle, as soon as you tape it to the bar, goes from 8k'ish to 7000 like a switch. Can do it riding or on stand. Back off, back up to 8k'ish and goes great again. Run WOT to bog, shut down with kill switch, plugs look acceptable. Run with choke on at bog, stumbles and no noticable improvement.

Haven't ridden this sled in length, just test runs, so it may have had this problem and in-law might not have noticed, but I do and bugs me. May try bring it to the lake for futher testing. Running out of ideas???

 

[X2Freeride]

When you drained the fuel out of the tank what was it like? You might have to take the tank off and clean it out good there is actually a small filter on the line inside the tank. If there is a bunch of crap in there when it goes to pull a lot of fuel at WOT it might be too restricted to pull enough fuel.

If the tank has a bunch of crap in it take it off the sled and power wash it out. old crappy car washes work good for stuff like this.

If that doesnt work well will keep going. I've got a couple more ideas.

 

[Rain Man]

I pulled the draw tube and checked it, metal screen on it was clean, no debris noted. The tank looks clean as best I can see in a black tank, so was the fuel that was in it even though it was varnished. There was some sediment in the fuel filter it appeared, could still get good flow, then replaced it anyway as it was cheap. Was thinking along your same lines so pulled the carbs again, checked the float settings, seemed to have a slight restriction in one of the float needle valves, so replaced it also, with still no success. Won't get to work on it again for a couple days but will pull draw tube completely off and re-check again, as well as inspect the tank. I'm convinced it's not the carbs for as many times I've been through them. I'm familiar with many types of carbs and do all my own work, changing for temps, altitude, and pre-post storage, with good results, yet this acts like it's a fuel delivery problem and I've been unsuccessful here? Oh yea, pulled fuel pump apart and inspected all diaphrams etc, forgot to mention, looks good. Would like to swap with another for troubleshooting purposes but too $$$ to not have it work. Only other one I have is a Walbro and this is a Mikuni pump, don't know the spec differences but I guess wouldn't hurt to try? Thanks!

 

[X2Freeride]

The Walboro pump should flow close to the same gallons per hour so it shouldnt be a problem most fuel pumps flow very similar specs and as long as its not a lower flow rate that stock which im sure its not it should be fine.

Only other thing I could think of would be that its a problem with the helix or spring in the secondary and its back shifting too soon. Either that or its geared to low. It sure sounds like you've covered basically everything else and if changing the belt out didnt help it would have to be the secondary or the gearing. Even though the secondary spring looks new it can still be shot. i mean the sled is what 12 model years old thats a pretty old spring even with the low miles, they lose tension just like a primary spring does. personally I change them out every year.

 

[retiredpop]

At approximately 7/8 throttle position the jet needle is pulled high enough from the needle jet tube so that it no longer restricts fuel flow from the main jet. Therefore you get maximum fuel flow from the main jet. Because it runs good until you reach this point I would say the main jets are too big. Either that or you have some sort of restriction in the air box which does not allow maximum air flow to the carburetors. Did you dismantle the air box so you could look inside?

 

[Rain Man]

I wondered that about the secondary, have been over it several times, cleaned the helix with emery cloth. I don't have another gold, or any other color spring to troubleshoot except from a TEAM off my Escape. I'll see if I can come up with one to troubleshoot at least, or even just buy one, like you said needs it anyway probably. I did switch from #2 to #3 hole in the secondary for troubleshooting purposes and didn't notice any difference in my limited tests areas. (Local road and ditch) May have to take it out to the lake where there's less restrictions, and run it further to see if it's exhibiting other symptoms that I have yet to find. I do like your changing spring idea however, and will focus on that next. If no luck there I'll swap with the Walbro pump I have next.

The main jets are stock set-up for local area so I don't think there's a problem there, and I verified with the manual. Put the carbs to complete stock settings for here and besides being a little fat for Polaris's safety as usual, should be good. I did take apart the airbox and clean completely, reassemble, and verified a few times as I wondered about that. Even checked exhaust as I thought maybe a mouse or something would block the pipe at high flows, but it's clear. Stock gearing, never modded, so the shifting with secondary would be next logical after carbs/airflow is ruled out. Thanks for the suggestions, may get back to it in a day or two hopefully.

 

[Rain Man]

Well rule out the secondary. I pulled my complete secondary off my 700 SKS and tried that on it, same result. Only difference is it had a silver/blue spring instead of gold.
Going to try inspect the carb intake boots for cracks or air leaks next I suppose. Probably pull the fuel line completely out of the fuel tank completely and inspect. I'm not smart with the CDI but could that be anything? What difference does it make if it's WOT or running at idle, a spark is a spark, but I don't know??? I did inspect the CDI wires noting some spots where it wore through the outer insulation, but the inner main wires were all fully insulated still, then electrical taped the wires where worn. Ruling out clutching and as much as I've looked at fuel and intake, maybe electrical somewhere? I did already disconnect the throttle safety and kill switches with no improvement....what next?????