XP 860 Surging 7-8000 RPM

allrevsrule · Dec 5, 2009

I have a 860 XP when pulling on a hill it surges between 7-8000 rpm. The EGT's are around 1120 tried jetting down from 430/420/410 to 400 no change. Changed out DPM off another sled that was running fine no change. The inside of the air box is soaked with fuel, indicating too much fuel , checked V-Force reeds and they are fine. I had this problem last year, thought was TPS had it set in spring but never rode it since.Raves slide fine.
Any suggestions.............................................

shortstop20 · Dec 5, 2009

Bad needle/seat in one of the carbs maybe?

fredw · Dec 5, 2009

might want to take a look at your raves, sticky, or maybe a diapram leak, also could be issues with primary clutch, binding bushing...ect

it could also be that your engine has too narrow powerband for the clutching, causing it to not be able to stay with in its rpm, or maybe a combination of all above

i would think if others are not having the same issue with similar setup, it will be soomething easy, but could be hard to find

how does it compare to spitseconds BB

good luck

portgrinder · Dec 5, 2009

cyls cutting out like a rev limiter almost? or is the engine firing fine, just cant hold rpm?

allrevsrule · Dec 5, 2009

The raves function fine as far as pushing them in and out by hand. I could pull them and check them. This problem was there last year but more evident this year. I added a bit more compression and changed over to the 07 DPEM. And the problem followed me. I changed jugs, heads, domes kept carbs.raves,pipes.
Primary is cleaned after every weekend and is in good shape.
The engine is not missing or rev limiter cutting in and out.

I suspect fuel issues because of the air box very very wet with fuel.
Wonder if the knock sensor does not like the extra compression 14.8:1 ? ?

winter brew · Dec 5, 2009

Add pin weight or click down and see if that helps or eliminates the surging.

LRD · Dec 5, 2009

I would be more suspect of lean and ignore the EGT and just try jetting up or raising the needle half a clip.

Also have had this happen with a customers sled many years ago when Cat came out with the 800 triple off of the 900 ThunderCat. Did my normal Cat porting and Aaen assured me his ThunderCat triple pipes worked fine on the 800's.

It surged so bad while dynoing it with my Land & Sea Dyno it broke the torque arm off the dyno. Very embarrassing. Sometimes you can end up with a very bad combo of porting, crankcase volumes and pipes and maybe pipe back pressures that flat won't work. Ignition timing also might be tied to it.

Good Luck

portgrinder · Dec 5, 2009

Airbox being wet is normal. they kick back quite a bit.

check the bushings in your primary?

ledoo · Dec 6, 2009

allrevsrule said:
I have a 860 XP when pulling on a hill it surges between 7-8000 rpm. The EGT's are around 1120 tried jetting down from 430/420/410 to 400 no change. Changed out DPM off another sled that was running fine no change. The inside of the air box is soaked with fuel, indicating too much fuel , checked V-Force reeds and they are fine. I had this problem last year, thought was TPS had it set in spring but never rode it since.Raves slide fine.
Any suggestions.............................................

did u change your gearing too?
last season i put a 2.5" track on and figured with the xtra load i would gear down to compensate. 20/51 did exactly what you're saying.i guess with the lower gearing it was shifting into high gear too fast and not allowing the rpm's up, the clutches would try to pull down and it would spike again.
I put the 21tooth top back in and it was perfect.

I don't know if that applies to your situation or not , good luck

madmax · Dec 6, 2009

winter brew said:
Add pin weight or click down and see if that helps or eliminates the surging.

If youre over reving and banging the rev limiter that is the most common thing. Do what winterbrew suggests. Have you had the box modified to increase the rev limiter? Got the new Doo update to help with the knock sensor? Do you have a check engine light on?

allrevsrule · Dec 6, 2009

Yes the box has been modified by Doo to increase the limiter. I have just put the 174 x 3 track on and put 49/20 with 8 tooth Avids. This 08 XP now has 07 box not sure if it has a knock sensor up date........

Idaho Slim · Dec 6, 2009

allrevsrule said:
I have a 860 XP when pulling on a hill it surges between 7-8000 rpm. The EGT's are around 1120 tried jetting down from 430/420/410 to 400 no change. Changed out DPM off another sled that was running fine no change. The inside of the air box is soaked with fuel, indicating too much fuel , checked V-Force reeds and they are fine. I had this problem last year, thought was TPS had it set in spring but never rode it since.Raves slide fine.
Any suggestions.............................................

So is it surging back down when you hit 8000, or are you hitting more, like 8500+ rpm? makes a difference, if it is 8000 on ths nose, I don't think it is the rev limiter, more likely a fuel delivery issue, like a piece of silicone or similar stuck in the main jet (Happened to me on a mod motor

)

allrevsrule · Dec 6, 2009

About 7-8000 rpm not always dead on. I pulled the float seats out still the same. The engine seems lazy at that rpm crisper at 2-6000 rpm. Lots of wet fuel in air box.

live2beel · Dec 6, 2009

I had the same problem. Never found it, just went away

whitefish · Dec 6, 2009

Sounds like an electrical issue. Not getting full spark all the time.

allrevsrule · Dec 6, 2009

Is there a procedure for checking raves correctly? I may replace or check them........?

winter brew · Dec 6, 2009

DPM solenoid? Rave's not opening?

allrevsrule · Dec 6, 2009

Took the DPM off another sled that was working no change looking into to how to check rave solenoids

winter brew · Dec 6, 2009

Just take the rave caps off, they should move in/out smoothly by hand. Start the sled and give it some throttle on the stand and you should be able to see them open/close.

07xrs · Dec 6, 2009

try and swap your box and teather cord from another sled.
i sent my ecm out to ski doo race department and had my rev limit moved
to 8900.
took my sled out for a test ride and found they programed my ecm
wrong. would not rev past 8100 and was loading up bad.removed a ecm
from my other sled and sled ran fine
also the rav valves were not open and closing correctly with the ecm i had reprogramed

XP 860 Surging 7-8000 RPM

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