Cant get WOT rpms up!

[Sno-Xr]

From what Im seeing, wot rpms should be up around 8900-9000 on the Vipers? I picked up a 16 RTX that had Bikeman perf clutch weights already installed, and supposedly stock otherwise. When I grab a handful of the flipper, it will spike to about 8250(after Ive unloaded several tip and center magnets), but will steadily drop to the low 7's as speed increases.
Decided to pull both the primary and secondary(and belt) from my 15 STX DX with the Big Venom clutching and install them on the RTX, as it hits 8900+ right from the git go and stays there on the 15. But I'll be damned if it doesnt run approximately the same as it did with the Bikeman weights in the stock clutches. It will barely get into the 8's, and drops back to the low 7's.
Any thoughts? Motor seems to be running fine otherwise, just wont keep the R's up during hard pulls.

Thanks

 

[mbarryracing]

It's absolutely making less power for some reason. It's not the clutching.
Possibly the fuel pump is not supplying enough fuel for adequate AFR at WOT?

 

[Sno-Xr]

Hmmm, thats what I was afraid of. Now to figure out exactly what the issue is

 

[2015ViperMTX]

How many miles on the sled? Does it have fresh fuel? I’d change plugs and fuel filter.

 

[Sno-Xr]

Ive run about 700 miles on it this year, had 3000 when I bought it. Plugs will definitely be on the list, but seems to start and idle fine. May end up swapping fuel pumps since the 15 is waiting for a new chain case, jackshaft and related parts! Lol

 

[super1c]

When I couldn’t get proper RPMs after exhausting clutching, plugs ect it ended up needing a valve job. Got all my power back and RPMs after.

 

[Sno-Xr]

When I couldn’t get proper RPMs after exhausting clutching, plugs ect it ended up needing a valve job. Got all my power back and RPMs after.

What was involved? Pulling top end and replacing the valves? Or lashing/shimming?
Also, was compression low?

 

[super1c]

I was fortunate enough to be under warranty. The valves were too tight. Shimmed best I know and he followed cannondales post here as he had not done one yet. Sorry not more help on that but there are some great posts here about it. Was like a new sled after.

 

[Sno-Xr]

I was fortunate enough to be under warranty. The valves were too tight. Shimmed best I know and he followed cannondales post here as he had not done one yet. Sorry not more help on that but there are some great posts here about it. Was like a new sled after.

Thanks for the info, I will look into whats all involved.

 

[Sno-Xr]

It seems most are having issues with idling and start-ups when the valves are too tight. Is that what your issue was? Or did you lack top end rpms?

 

[super1c]

Starting issues and top rpm. No idle problems. And starting issues were hot start issues.

 

[cannondale27]

Valve cover removal is easy so yes check the valve clearance. But pull the plugs first. Look at them. If fuel they will be white and would think it would missfire.

 

[Sno-Xr]

Sounds good. Thanks Steve

 

[Thunder Products]

From what Im seeing, wot rpms should be up around 8900-9000 on the Vipers? I picked up a 16 RTX that had Bikeman perf clutch weights already installed, and supposedly stock otherwise. When I grab a handful of the flipper, it will spike to about 8250(after Ive unloaded several tip and center magnets), but will steadily drop to the low 7's as speed increases.
Decided to pull both the primary and secondary(and belt) from my 15 STX DX with the Big Venom clutching and install them on the RTX, as it hits 8900+ right from the git go and stays there on the 15. But I'll be damned if it doesnt run approximately the same as it did with the Bikeman weights in the stock clutches. It will barely get into the 8's, and drops back to the low 7's.
Any thoughts? Motor seems to be running fine otherwise, just wont keep the R's up during hard pulls.

Thanks

Hey bud, hope you get your sled figured out.

 

[Sno-Xr]

Hey bud, hope you get your sled figured out.

Thanks Terry, you and me both!! Been a crazy sled year for me. Still havent figured out my elec gremlin haunting my Nytro. Picked this sled up so Id have 2 good running sleds and find this issue, and then jackshaft bearing went out in the Viper I bought from Krissy, and it took out the chain case. "I love Snowmobiling, I love Snowmobiling I love Snowmobiling I love Snowmobiling"!!!! Hahaha