12 RMK 800 won't pull more then 7200 RPMs

Hopfarmer · Dec 13, 2013

A friend of mine I ride with has 12' RMK 800. He turned up his oil pump to 40:1. This is the only change he has made. But while climbing he is only getting 7200 RPMs. He's losing @ 800 RPMs. He changed spark plugs and changed his belt. But neither of us know enough to drive into this problem. I'm thinking he might need to adjust his clutch weights? But the question is would turning up the oil cause a reduction in RPM ? If not, what would ?

mtproride · Dec 13, 2013

what elevation is he riding in?

mountainhorse · Dec 13, 2013

Turning up the oil would not have that efffect.. at least not untill you got down below 20:1.

What is the belt side clearance measurement in the primary at rest?

Did you set your belt deflection according to the owners manual supplied with your sled?

How many miles on the sled?

.

wellfed777 · Dec 13, 2013

need more info sir
did he turn up oiler before he rode it this season ? how does he know he's at 40:1 ? motor mounts ? sacked out clutch springs from last year ? worn clutch causing some binding ?
how many miles? answer these Qs and folks will probably be able to hep out

let it snow

PMSPOLARIS · Dec 14, 2013

Blow by on the piston rings! Your motor is on the way down!

Just a guess! but we have rebuilt a ton of these motors when people bring them in complaining of loss of RPM. What we find is that the rings have so much blow by, so the fix kit by MTNTK is the only thing we have found to fix this issue.
PS this kit gives the motor 5 extra horse in the mid range.
Hope this helps .

Murph · Dec 14, 2013

Broken primary spring?
Bad rollers in clutch?
Sacked out secondary spring?

The Fourth Wolf · Dec 14, 2013

PMSPOLARIS said:
Just a guess! but we have rebuilt a ton of these motors when people bring them in complaining of loss of RPM. What we find is that the rings have so much blow by, so the fix kit by MTNTK is the only thing we have found to fix this issue.
PS this kit gives the motor 5 extra horse in the mid range.
Hope this helps .

How many is a "ton" exactly?

Yeah...don't troubleshoot your sled or anything, just slap down a grand for phase one of the dartboard approach to solving performance issues.

locknload · Dec 14, 2013

Is it possible you could have bent something turning up the oil pump not allowing the throttle plates not to open all the way? If they are opening I would pull clutches, clean and inspect and replace clutch springs.

OuraySledder · Dec 14, 2013

I agree that turning up the oil should have zero effect on the rpms. I would be checking compression and taking a look at the rings.

I also have zero faith in a "fix kit" that uses a spacer between the case and jugs. Personally I would buy a set of pistons from the guy who had them properly engineered to solve the problem without a spacer.

Hopfarmer · Dec 14, 2013

So he knows it's 40:1 because he measured the gas to oil use after a couple of rides. His sled only has about 500 miles on it. We have not checked motor mounts but after only 500 miles I would be mighty disappointed if they were worn out. Surprised "NO" but disappointed "YES". Still need to check belt deflection.

rmscustom · Dec 14, 2013

Hopfarmer said:
So he knows it's 40:1 because he measured the gas to oil use after a couple of rides. His sled only has about 500 miles on it. We have not checked motor mounts but after only 500 miles I would be mighty disappointed if they were worn out. Surprised "NO" but disappointed "YES". Still need to check belt deflection.[/QUOTE]

First thing that needs to be done. Cant count how many sleds I've seen with running issues that are either fixed with a new belt or setting the deflection.

Kirklan · Dec 14, 2013

I'm Hopfarmer's buddy with the RMK 800. Just got the sled unthawed and took a look at the clutch spring, sure enough, it's broken in half. I plan on replacing it myself, but I have zero experience working on snowmobile clutches. Dirt bikes, tractors, and farm equipment, yes, but sled clutches, no.

I'm assuming I can just undo the 5 or 6 bolts there and pop the broken spring out and install the new one pretty easy? Seems like a no brainer, but sometimes it's better to ask first.

Dartos · Dec 14, 2013

Primary clutch spring is straight forward. I loosen the six bolt evenly, remove clutch cover. Remove spring and install new spring. You will need to push the cover in to compress the spring and start a few bolts back in the cover.

There is an X on the clutch cover. Make sure you line it up with the X on the spider to keep balance of clutch proper.

Tighten down six bolts.

Kirklan · Dec 14, 2013

Thanks for the help everyone, it is much appreciated!

Mr.Blizzard · Dec 14, 2013

check for a torn diafram on the power valves a common problem for loss of rpm

AKSNOWRIDER · Dec 14, 2013

While you have the clutch cover off, look into the spider and you can see the weights and the rollers the weights ride on, roll the rollers and make sure none of them have any slop, they should roll smooth with almost
0 slop......and have no flat spots on them.

granto · Dec 14, 2013

X2 on the primary clutch spring this happened to my 12 as well. It would barely pull over 7000 rpm. When i changed my spring i also put washers on each side of spring to stop it from digging into the aluminum and binding.

milo303 · Dec 14, 2013

PMSPOLARIS said:
so the fix kit by MTNTK is the only thing we have found to fix this issue.

Oh c'mon now...

AndrettiDog · Dec 14, 2013

It really sounds like you issue is clutching. So before you go buy some kit, spend some time on clutching. How many miles on the sled? I'd replace the primary spring, it's not that expensive. As other stated, check the rollers. Also make sure that the clutch is not cracked. Sounds silly, but I rode around for a couple rides and couldn't figure out why I lost about the same RPM's. Come to find out I had a bad clutch that cracked and was just about to go. Make sure your secondary is aligned right. SLP makes a tool that is cheap to help establish this. If you change a belt you need to check the sheave adjustment on the secondary. It should be tightened to the point where it almost whines. Usually a new belt won't lose RPM's but will gain a few depending on the belt. Old belts slowly wear and eventually lose a few RPM's. Also...you should be shooting for 8250 RPM's. Your post mentioned that you lost 800 RPM's and were at 7200. That is only 8000 RPM's. Go for 8250 at your riding elevation (not the trail head or lower elevation).

12 RMK 800 won't pull more then 7200 RPMs

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