-13 pro rmk Wont pull RPM

[Melfjord]

Hi, my brother bought a used -13 couple years ago. Have not been used alot the last couple of years, But this season im forsced to use it.
I'm noticing it cant pull RPM past 7700-7800 on hard pack trial riding. It feels really sluggish, and not as crisp as i remember they used to be. I suspect there is some problem with the engine more so then with the clutches..

Dont know how many miles it got, because the display is bugged
Driving at sealevel

What i have Checked:
- primary clutch; weights was full of rust and was aftermarket adjustable 70g
cleaned it up and put in some 10-68 weight's
-Had stock spring
-Throttle wire is fine
- Checked one exhaust valve and it was clean and did not need to service it.
- new pluggs
-115 PSi compression test on each sylinder, one was slightly lower then other.
- belt deflection is good.
- belt looks good but dont know how old or used it is

I dont know if the exhaust valves works as intedned, how do i check the system?
I will try a new primary spring, and also check secondary, but my senses are that the engine is not operationg properly.
What can i check and tune before i by new pistons?

 

[Reg2view]

Don't know elevation. You should have picked up revs dropping from 70 to 68s - unless there's a head on it, max weights that motor pulls fresh is 68s at sea level. Obviously, elevation and weights matter. Assuming all pin, spider, and secondary bushings are good. Be good if the secondary helix/spring is stock, worth a look there, too. Got a hunch you know all this. I'd pull the VES and clean, but if they were sticking, you wouldn't be getting 7800.

Start with a new primary spring AND belt. Even if it the belt looks good. Owned two of the pro 800s, and at ~500 miles of mt riding, sleds always started to lose rpm, get worse with more miles - new belt, and wham, it's back. Just chalked it up to belts getting soft from heat and squeeze. I clean and maintain clutches myself, all the tools, JMPE. Chasing ghosts without belt and spring removed from the issue. Don't discount the belt. Good luck.

 

[MTsled3]

I've had this happen a couple of times on different sleds and all it took to recover rpms was a new secondary spring, they seem to wear out in 500-800 miles. I've started replacing them yearly.

When I've had primary springs wear out I don't notice it in the performance as much, but I do notice that the primary will start to "slam" on engagement.

Being a used sled I'd replace both clutch springs and the belt. Use heat on the helix bolts and buy some spare T27 bits, I like the Milwaukee torque bits.

 

[Melfjord]

I've had this happen a couple of times on different sleds and all it took to recover rpms was a new secondary spring, they seem to wear out in 500-800 miles. I've started replacing them yearly.

When I've had primary springs wear out I don't notice it in the performance as much, but I do notice that the primary will start to "slam" on engagement.

Being a used sled I'd replace both clutch springs and the belt. Use heat on the helix bolts and buy some spare T27 bits, I like the Milwaukee torque bits.

these helix bolts sit on tight

 

[05rmksteve]

Also check the motor mount bushings.