[AKCheese]

OK I've been having problems with my sled (2000 RMK 500) getting 4 MPG all winter

Carbs are clean, fuel pump rebuilt, jets are correct, new floats, choke is working properly, checked the reeds.... they look great, track is nice and loose (to spec) clutches are aligned to spec and it's NOT leaking gas anywhere.......carbs are synced ..... compression is good in both cylinders

I was out camping and riding for 4 days (check this out if you have a chance!! http://www.arcticman.com/welcome.htm ).....so I had a lot of time to monkey with it along with a Polaris mechanic..... he even used some kind of "venturi meter" to check the carbs and they were "fine"

Besides the 4MPG .....the PTO side plug looks textbook, the Mag side is wet and not black or brown or anything......it's just wet

we changed the spark plug cap and it seemed to be getting better spark and in fact the plug started turning black and even at one point chocolate brown but at the end of the day it was back to clear and wet and 4MPG.......

I think the Mag side is not getting as strong a spark as the PTO side and a lot of gas is washing past at low RPM and on and off throttle riding (the last mile or so back to camp is badly moguled up so you're just thumping over bumps the whole way at a few miles per hour on and off the throttle contantly)

and the cap we used was still a little loose so with the weaker spark and the looser cap I'm thinking that was adding up to a LOT of unburned gas which washed the plug darn near clean by the time I get back to camp.......

Would replacing the voltage regulator and new caps fix this? (I already did new wires) or would I have to go all the way back to the magneto???

He told me the belt is also really loose in the primary clutch and I can fix that with the shims so that's why it's taking a while to engage.......

Could this be "most" of the mileage problem?

Bottom line is my son and I are going mostly the same places on our sleds although he's off in the powder a LOT more and goes maybe 4 or 5 miles more overall........

I take 7.5 gallons and he takes 4 in his 700 RMK........

I'm pretty much out of other ideas but if you have them I'd love to hear them!

 

[tifa_5_2000]

can you check if your pulse line to the crankcase has gas in it?

 

[tifa_5_2000]

backwards powervalves? or valves not opening.

 

[tifa_5_2000]

did the mainjet come loose and fall out?

 

[63November]

New, sound plug caps might help, especially since resister types can "fail." The voltage regulator has nothing at all to do with engine performance. (The machine has two electrical sides; one powers the engine and is unregulated, the other the lights and everything electrical not part of the engine.)

How is compression? Are the VES valves clean and fully operational? Could be fuel system too as has been suggested. Does it ever flood, especially on one side only?

 

[AKCheese]

OK I'm going to have to find out about VES valves or power valves as I don't know what those are

I do know the reeds looked good

Also not sure what the pulse line is to the crankcase is so I'll look at that

A guy here are work said the coil could be bad on one side so I should replace that which will also give me new spark plug wires and caps

The main jet was definitely OK as we checked that several times (along with the clip position)

Thanks for the help so far and any more you've got to offer.....!!!!

 

[Beaxch]

You might try switching the plug wires and ride it that way for a while. And by that I mean, only switch the wires at the engine, leave the other end of the wires connected as normal. Both spark plugs fire at the same time so the plug wire order does not matter. Then check your plugs. That way if the same plug is wet after you have swapped wires you can eliminate the spark as the problem. If the wet side switches when you switch wires then you know what's happening.

The belt being too loose does affect your shift ratios negatively, so the engine may be working hard especially if you're going slow, stopping and starting a lot.

There is another issue that may be affecting your mileage, but I'm really not sure. That is the 2000 500 RMK is geared at a 18/41 ratio stock, which is very very low. This is so you can have good performance in powder and on hills (off trail stuff, that's what an RMK is supposed to be designed for) despite the small engine. But you lose top speed as a tradeoff. By my calculation your top speed is 73.55 MPH. Most polaris 500 engines are in trail sleds and are typically geared more like 21/39 or 22/41 (90MPH). So if you're on the trail all the time pushing your top speed this can be like being in 3rd gear on the freeway instead of 5th. This example isn't perfect because the CVT in the sled tries to shift effeciently, but I would not be surprised if the gearing has something to do with it especailly if you're trying to approach or exceed your top speed. If you're going really slow all the time that gearing should actually give you better mileage because the sled has to do less work to reach the same speeds.

I should say that my wife's 92 500 SKS EFI is geared 18/39 and seems to use very little gas, but you're geared down quite a bit more than that. Also she does not try to go very fast on the trail. I'm pretty sure your sled has exhaust valves where my wife's does not (I can't tell from the parts diagram)...stuck exhaust valves are common so don't overlook that.

But here's probably the most important point.

The fact that one plug is clean is very likely a coolant leak, coolant getting past the head gasket and into the cylinder. It will literally steam-clean your piston. My wife's sled had this problem on both sides, but it didn't even need a new gasket, just the head bolts hadn't been retorqued after the previous owner had the engine rebuilt and broken in. It had super clean plugs (impossibly clean) and intermittent foam in the coolant, but generally as the engine got hot it would mostly seal itself up and stop foaming, and the performance was fine, so at first I didn't realize it was the head. Once I got the bolts properly torqued the problem went away entirely and the plugs were never clean again! I would say that an impossibly clean plug is most likely a coolant leak and you should take it seriously. Just running gas through it without spark, in my opinion, won't clean it off as thoroughly as you are describing. It takes the heat of combustion and the steam to do what it sounds like you are describing. Unfortunately I don't know how to further diagnose that. You could still be getting very good compression if the leak is very small. Again if you are very very slowly loosing coolant or if you can see foam floating in the reservoir then I would feel confident in saying that's at least part of your problem. Borrow a decent torque wrench or buy one at harbor freight (and make sure you know how to use it), find your head bolt specs (mine was only 17-18 lb/ft) and make sure those bolts are tight enough. I wished I'd done that months before because it was so simple and I spent so much time scratching my head over it.

Sometimes bad performance has more than one cause. Good luck to you.

 

[AKCheese]

Thanks for all the replies!!

I'm going to check out all of the items you suggested and hopefully when I take it out next winter it'll be sipping gas!!!

Thanks again for all the specific ideas of what could be wrong and how to fix them!!