Give me an opinion on low RPM

[Jaynelson]

When sled was new, pulled 8,150 in deep snow no prob. Started this year having trouble getting any more than 7,800-7,900. The belt, clutch bushings, rollers, weights, all had some wear. Replaced everything whole clutch system...springs, belt, MTX weights, new washers, bushings, yada yada. Got RPM back in the pow and a bunch more bottom end from the new setup. Great!

Didn't last long tho (maybe 200 miles), as peak RPM went back down to only pulling 7,800 under load.

Now, I can pull steep hills with setup snow (i.e. on a track) at full RPM and the sled goes great....dive off into the pow and RPM drops. The more load, the more it drops. Would this indicate the power valves are operating properly? I cleaned them up maybe 300 miles ago and they looked great....and I imagine if they weren't opening, it wouldn't want to hit RPM in any condition?

No runability/driveability issues, sled idles great, has good throttle response and runs clean. Belt deflection and alignment bang on.

I hate to F with the clutching, as it was all bang on. The sled/motor has 1,800 miles on it....and all BS aside, it has seen PLENTY of WOT and deep snow in that time. Given the discussion on here, is it possible the motor has just gone soft? (pistons/rings). Have others experienced that? I can't think of much that would just kind of degrade the RPM over time, other than clutching (which is all up to date). Whadayathink?

 

[TRS]

"Do a leak down test". Not a compression test.

 

[m8matt]

From what you stated about changing everything and it worked for 200 miles then back to pulling down. I would blame the belt deflection. I find proper set up on stock sleds is very important for consistency.

 

[Jaynelson]

Don't think so, belt deflection is pretty dead on.

 

[Butta]

Is your secondary backshifting correctly? Sounds like it may be a little slow to respond to load on the track....

 

[die hard poo]

Well Jay, I would recommend a fresh top end. My 12' was have a hard time pulling the clutch weight it did before and then I ended up losing a pto crank bearing in the motor(2100 hard miles) and my dealer warrantied me a whole new updated short block. Now I am pulling 4 more grams weight than the beginning of the year and it still over revs on the trail. I have to run the ethanol mode on the trail to prevent det light and then when i get into the deep I put it to non-ethanol mode. So either try a new top end or it could be worn out clutch springs.
Hope that helps.

 

[AKSNOWRIDER]

Jay, hows the fuel economy? injectors start taking a dump and fuel economy goes south(along with rpm)..also, inspect pistons/cylinders....

 

[granto]

Im also having the exact same problem ive cleaned valves ,clutch, new spring, etc. Only pulls 7900 in deep and around 8100 on trail used to be 8150 all day. I have a 12 assault with 1700 miles. I too would like some answers to fix this problem. Ive heard new top end fixes it but really 1700 miles. Thanks in advance for any input.

 

[AdrenalineAddict]

Pull the Mag side exhaust valve (easy one) and give your piston a look, mine was scored pretty badly at 1,900 miles. My sled ran at reduced RPM up until 2,300 when it came apart. Another thing I noticed at around 1,200 miles was that my motor mounts were badly worn with enough slop that I could see the motor move almost 1/8" under load, this gave my sled long belt syndrome (reduced RPM's in all conditions). I changed the PTO side mounts and RPM came back to normal.

 

[AdrenalineAddict]

More thoughts, give your grafoil seal a look between the Y-pipe and pipe, mine was hammered at 1,600 and was replaced again one hour ago at 3,400 miles. My reeds were toast at 2,000 miles.

 

[mtncat1]

i fought the same thing on my 11,i would replace the pistons just because of the miles,and do the updated motor mounts if you havn,t done em yet. then inspect the reeds.good luck if any one can figure it you can, you sound like a real good tech.

 

[Jaynelson]

Jay, hows the fuel economy? injectors start taking a dump and fuel economy goes south(along with rpm)..also, inspect pistons/cylinders....

I would say fuel consumption same as ever within reason....given that I don't keep exact numbers. Do they give any other indication? Had a peak through exhaust valves maybe 300 miles ago and pistons looked good, but definitely time for another look. Leak down couldn't hurt if I can scare up a tester.

Adren & mtncat - Good call on motor mounts. Broke one earlier this season, maybe others getting pounded out. Blown reeds should run crappy on the bottom tho, eh?

Mtncat - I'm a good test rider/driver and I know some theory, but a really 1/2 assed mechanic if I'm honest lol. That's why I like asking all the snowest guys way over my head!

 

[AKSNOWRIDER]

Jay, only other noticeable trait of injectors I have noticed is they will backfire out the exhaust as they go bad, every time you chop the throttle..reeds would cause idle/lowend issues, most likely...flaking rings/ring seal issues.....but that is just a guess on my part..easy clutch check is swap clutches with a buddy and see if it cures it....

 

[800poodragon]

I had that problem last December...ended up being motor mounts. Started with the rubber mount in the factory torque arm tearing then wore the rest. Changed them all and put in an SLP torque arm as well.

 

[TRS]

You eliminated clutch maintenance/drive train issues so where to next.
A dealer had me look at an 800 yesterday with just over 400 miles on it. Rings were junk, flaked on the intake side to the transfer ports.
Flaking generally starts on the intake side. Pulling your ex. valves to check your rings will give you a false reading. This old guy needs a good light to check them.
I stopped in numerous shops on my way to Denver a couple weeks ago. Their comment when asked about the flaking,"Haven't seen it". So we would head to the shop to look at down motors, guess what, all had major flaking. They are now watching for the ring issue. I stressed a leak down test for customers having running issues. It does't take long to eliminate or confirm this known problem early. IMO ring flaking starts the process that ends in cylinder skirt failure.

 

[tdbaugha]

Does anyone have any data on how their rings were holding up if mixing a bit of oil in the gas?

I turned my oiler up quite a bit and still slowly lost compression throughout the year. I have over 2000 miles on this year and my sled is nowhere near what it was at the beginning of the year. Just hoping it holds together for these last few rides!

 

[AKSNOWRIDER]

TD, Most ring flaking I have seen on the pro is from moisture getting thru the intake(snow)..hence why it shows up on the intake side..while it wont help now if you do have flaked rings..when you re piston it I would spend some time insuring the intake tract is tight and sealed...

 

[assault11]

Does anyone have any data on how their rings were holding up if mixing a bit of oil in the gas?

I turned my oiler up quite a bit and still slowly lost compression throughout the year. I have over 2000 miles on this year and my sled is nowhere near what it was at the beginning of the year. Just hoping it holds together for these last few rides!

We mix about a cup of oil per tank and my motor still looked awesome after 3100 miles when I pulled it out and put my BB in. No scuffing or flaking at all. Also a big part about making these motors last is letting them warm up good, even if you stop for 15 minutes let it warm up to 120 before you hold it wide open up a hill. We had good Luck with the dragons and now good luck with the pros. If you take care of them they will last.

 

[Jaynelson]

We mix about a cup of oil per tank and my motor still looked awesome after 3100 miles when I pulled it out and put my BB in. No scuffing or flaking at all. Also a big part about making these motors last is letting them warm up good, even if you stop for 15 minutes let it warm up to 120 before you hold it wide open up a hill. We had good Luck with the dragons and now good luck with the pros. If you take care of them they will last.

I have always added oil to the fuel as well and am anal about warmups. I would guess ring flaking (if present) would be due to either poor ring construction, and/or snow/water ingestion as AK mentioned. Don't think oil would hurt....but doubt it would make a huge difference if it's eating a bit of snow. If that's happening, it's probably more due to what type of snow you ride in and/or how well sealed your intake is.

 

[assault11]

I have always added oil to the fuel as well and am anal about warmups. I would guess ring flaking (if present) would be due to either poor ring construction, and/or snow/water ingestion as AK mentioned. Don't think oil would hurt....but doubt it would make a huge difference if it's eating a bit of snow. If that's happening, it's probably more due to what type of snow you ride in and/or how well sealed your intake is.

We ride in deep dry snow all year and never had that problem between 5 pros