M8 Not reaching full RPM's and It's not the clutching!

Well at least I'm pretty sure it's not. I'll explain why I think that after I give you a quick run down of what I have. This is the second M8 that I've had with the same problem and I don't think I'm alone on this one. The first sled was a 2007 M8 and this one is a 11 M8 both started having the same problem around 750-1000 miles.

The problem is the 2007 wouldn't rev above 7850 and the 2011 won't rev above 8050. The 2011 has a SLP stage 3 which is designed to be happy around 8200. But before anybody gets excited I was having the problem before I installed the kit on the 2011 and the 2007 was bone stock.

I don't think its in the clutching because on a recent trip to Idaho where the elevation is significantly lower then home here in Colorado. I tried every combination of weights from 65-75 and multiple different spring rates from 305-360. I also tried MTX, CPC Racing, and even OEM weights as well as Speedwerx, SLP, and OEM springs. I've tried loading the heel and the toe new belts and even a different helix. This thing wouldn't get above 8050 and most combinations left me around 7800. It didn't matter if it was hard pack or pow, downhill or uphill. I even held it to the bar on the trailer with the belt off and it still wouldn't climb above 8050.

The last sled I tried droping as much as 5 grams in the clutch. And even bought a new primary for it. I also tried gearing it way down and differnt springs in it as well. I have inlaws that own several M8's 4 in the old chassis and 2 in the new. They also had the same problem (The Older Chassis) around the same amount of miles.

So what can it be? What keeps this thing from over reving?

1.So far I've checked the Power valve cable adjustment they are fine at 34.8MM.
2. Verified the TPS Sensor voltage is within spec at idle and WOT.
3. Verified the Throttle cable is hitting stop to stop.

It just seems like its something simple. Like a stretched cable or a switch just out of adjustment. But I can't find anything like it. Any thoughts?????


Update 3/15/12
Installed Fuel Regulator. Helped out a ton. But still didn't get me there. Solved a bunch of other problems
Sent Primary in to have it reshimmed to run the SLP MTX weights. Also installed billet spider, and had it bead blasted and balanced.
Sent Secondary in and had it rebuilt. Got maybe 50 RPM from the clutch work but I'm now using all of both clutches.
Checked clutch alignment and parallelism. Shimmed secondary out .030.

Rode with a 09 M8 running the exact same setup. Guy killed me all day long. Way above me on hills and won ever drag race.

m8magicandmystery said:

your tach peaks out and won;t go over 8050..???..lol..you said something simple..

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I wish it was something that simple. But I used to see 8200 all day everyday no matter the conditions or elevation. But before 750 miles.

redigar09 said:

motor mounts

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I checked them and they seem to be in order. I do have the little rubber snubber that mounts between the big engine plate on the left and the DD on order. It looked fine but I heard from a couple of the guys in Idaho that they can wear out over time.

m7 said:

did you look to see if your getting full throttle. cable my need adj.

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Yep even pulled some of the slack out of it even though it was hitting the hard stop at WOT.

CATSLEDMAN1 said:

you say nothing about the secondary ?? so if it had rpm and now you don't something is WEARING OUT most likely changing due to use ?

So simple like dirty clutch's and YOU WILL NEVER HAVE RPM.

bad secondary rollers, cracked or broken primary spyder, wrong belt/dirty clutch's/bad belt deflection , flopping pin deficient primary weight, you may not find one item that all of a sudden gets the freeely reving 8200 engine back.

the 800 is not a 440 opr 500 or layingdown 700 meaning it has a wide power band, torque e er motors respond differently to clutch problems, things that worked on your ?? other sleds , it's different territory with an 800 or 1000 cat engine

also possible a vindictive japanese electrical engineer using computer modeling added a 7725 rpm limiter on two sleds, projecting that you were going to buy them in non consecutive model years knowing it would drive you crazy. OR start checking out possible drive train conditions. just a thought

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I've definitely dove in to several of these possibilities. We checked the rollers, Tried different belts with the proper belt deflection set each time. Looked over the primary for a cracked spider or a flat spotted roller. I do a pretty good job of blowing the clutches clean with compressed air after each ride and scrubbing down the faces of both clutches with some scotchbrite and alcohol followed by a clean rag.

On the last sled I changed the rollers in the secondary and tried a new spring but never with any luck.

I do agree that some of the problem might be a couple different things playing in but I still think there is something bigger.

Love the feedback keep it coming!

summ8rmk said:

2007 m8 should max at 7,600-7,700 so 7850 was actually over reving. Ur 2011 has to be clutching. Unless its the angry Japanese engineer ;-)

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You are correct I can't remember what the max was but I know I was well short of it no matter what combination of clutching I threw at it.

Rixster said:

Secondary clutch bushing ? They fade slowly you don't really notice tell it is toast. I didn't think mine was bad until I tried a new secondary.

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Although it may be a problem It still should over rev on the trailer without a belt on it. Granted I was terrified to hold to the bar for to long. It still jumped to 8050 and no more.

TINKER said:

Look at your helix for a crack.Mine had a small crack at about 900 miles and I lost a couple hundred RPM.

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I've tried two different helix the stock one and the 44/36 the SLP sent with the kit.

hd4rob said:

Try to find another 11 ecu to try, maybe there is something wrong in yours. You could also check that you are getting full output in your stator coils or timing sensor. Did this also happen on this sled before addition of the power commander?

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Will look into these. Not sure how I can check for power but I should be able to check resistance. I don't think its in the ECU but I do think that it might be something the ECU sees like the TPS sensor. I had a problem of it last spring before the addition of the PCV but just figured it was my clutching and the spring snow. But now that I've got some time on this thing I starting to think its deeper.