Having an RPM problem...need trouble shooting.

[Scott]

It's always great to hear from more than one idea-man.

PSI 1155cc twin in a GenII chassis. RMI gear drive, 159 finger track.
10t drivers. 2.08 gearing.

Last year when I put my sled away, it was only getting about 7500 Rs. Had fresh clutching in it. New springs and helix. 165/310 primary with 60g weights and 52/48 secondary with Tison red/white in 3rd hole.

Decent bottom-end and mid range power. Still snappy and quick. When I wack it, it bends my handle bars back even when I have them resnugged up tight. Good stuff under 7000 R's.
Top end.....ran like crap.

Had some work done on it last summer.
New crank to be safe. New pistons. Cleaned up porting.
No problems there. That's got nothing to do with this, I suspect.
New engine, right....

I've had my sled out twice this year...it ran like crap both times.
I thought it was snow injestion, because my prefilters were junk and I had no hood screens.

Got my hood screens all in and no snow gets in. I used alum screen mesh for screen doors. It looks very nice. Got new air filters and prefilters. Put rubber automotive coolant hose elbows on it to stand my filters up. IT looks good, I hope it works fine. It seemed to be just fine this weekend. No snow injestion. It ran great.

IT's a little fat on the bottom end, but it's pretty crisp and strong when it comes out of it at about 5500 to 6k. Bent the handlebars on many occasion on the grooomed road. I guess I need to clamp them down even tighter. LOL

MAJOR bluebird day here on Sunday. Spring riding down low, set-up powder up top. Beautiful.

BUT, I can't get it to run right on the top end. It's still doing the same crap it did last year when I put it away. Runs GREAT in the midrange up to about 7000, but won't open up and release on the top end. She doesn't even sound like she's singing. It sounds held back somehow. It might hit 8100 for a sec, but really quickly the r's snap right back down around 7500. And it never sounded like it was singing when it blinked up there at 8100.

NOTHING we did last year should be causing this...so it's gotta be in clutching, carbs or electronics, RIGHT?

CAN'T be in pipes or inside the engine because that was all cleaned up and it didn't fix the problem.

I haven't pulled the plugs yet nor have done any real testing. I had my 4 year old out for a kid's ride on Sunday so it wasn't a day I could spend working on it. But when I got on it, it ran like dog crap on the top.
It doesn't surge or burble on the top end, it just won't release and go.

Things I've thought about......

---The stock Polaris head sensor could be the problem. I have that blocked off with some sort of an electric diode that the guy sent with it when I bought the engine from him. He said to do it this way. It ran fine for 3 seasons that way. Could that be going out? Maybe I need to get a head sensor and put it into the dial-a-dome coolant rail on the back of the head somehow.

---Clutches binding up? Primary was totally rebuilt and balanced this summer. The ONLY thing that's old are the weights, but they only have about 500 miles on them.

---Carbs plugged? Main jets? Because it's just from about 7000 rpms and up? Varnish or some debris?

---CDI and ignition system? I am NOT an eltronics guy at all. I'll need help on that one.

---What would stator symptoms be?


WTF else could it be?

 

[snowmanx]

Scott,

I've been having the pretty much exact same issue as you describe on my 1150 Cutler. New crank, stator, flywheel, pistons with only about 80 miles on them, and it just won't hold at 8000 RPM. Went through the clutching, actually bought a brand new secondary, new K&N filters ( I thought maybe it was being starved for air),.

I check my PTO runout after about 300 miles and my rnout is .006"!!! I haven't blown any belts, I can't figure it out.

Could the cases be wore out and not holding the crank the way they should be???? Would that rob RPM/power??? That's my last bet/ guess at this point. So I've got her all apart and am sending in the crank and cases to Northern Crankshaft to have everything checked out..I actually hope that is what it is as if it's not....I'm stumped!

Just a thought, hope you find out what is wrong.

 

[Hardass]

Run out?

Though i do not know what is causing your problem , i beleive that .006 on the run out is exessive.

 

[snowmanx]

Yes it is.

Though i do not know what is causing your problem , i beleive that .006 on the run out is exessive.

Yep..that's why it's not longer in my sled.

Didn't mean to highjackl your thread Scott.

 

[02RMKer159]

Double check that your jetted correctly. One jet size down can make a huge difference. Then if your jetted correct you can take you weights down a gram or two to get high rpms. More horsepower means lighter weights same for altitude you go lighter.
Hope that helps a little.

 

[Spaarky]

I'm no mech. genius, but I am gonna try and hit a few things you possibly missed???

- Stingers, you went through the pipes, but did you go through the stingers? Some sort of blockage???

- Watertemp? are your boards circulating water properly?? This one caused me fits on my last edge. Would your sled partially retard if it wasnt cooling properly.

- Carbs? Did they get gone through?? Maybe something is a miss there? Obviously all things the same your jetting should be on. I know you, and your prolly havent been running around with a sloppy sled for a long time.

- Fuel Supply? Are you getting a full dose of fuel? I think that would affect top end and not bottom...

- Clutching? Did you get a bad spring right out of the box?

Other than that... IMO, its gotta be in the electronics... could be wrong, hopefully a great mech. chimes in..

 

[Scott]

crank runout: Brand new crank.

B]Stingers and Pipes:[/B]
I am running different pipes, but the stingers are the same. I have not checked them for blockages.
But diff pipes shouldn't matter, cause it ran this way with the old pipes too before I changed them.

Watertemps:
Usually about 120° to 135° on the roads, and about 110° off trail, in the powder.

Carbs: were gone through, I think. Not personally by me.
My jets are 450/440, and I run 4500' to 8500'.
Compression is about 150 at 3500'. I run 2 gals of 110 race gas in 5 gals of fuel. (4 gallons per 10, of course). Have not inspected any jets, or the needle yet though.

I do need to get in and check the floats. Maybe the engine vibration is keeping the float from moving up and down properly, although she vibrates way less than it used to. She kinda purrs pretty nicely now.

Fuel Supply:
turbotater told me how to check the fuel pressure. I'm going to have to mess with that.

clutching:
Bad spring out of the box...ya know.....I thought of that too. I don't have a spring tester. That's a good idea. Might have a bum primary spring. If it does engage about 3800 to 4000, right where it should...could the top end be sacked out???????

 

[SAWYER]

Scott I think this is your problem You were a cheerleader in high school

 

[snowmanx]

crank runout: Brand new crank.

QUOTE]


So was mine. LOL

 

[h2otoyz]

the rubber elbows...

did you add the rubber elbows on the prefilters to get them up higher this year over last year scott?

toss them to the side and just run the prefilters... see if it makes a difference. the vacuum your motor creates can actually pinch/pull the rubber hoses almost closed (depends on the rubber hose you used). i ran into this on one of my mods and got rid of them along with a few other changes and found that after i did it it ran fine. Not sure if it was my problem or not as i changed a few other things also, but not long after i was bs'n with another guy who had the same problem, rubber elbows... tossed em away and problem was gone.

same thing though, good bottom and midrange... top-end with the suction and no problems. some guys run em and have no probs... harder rubber or the pvc pipe they use to join up isnt sticking in the filter? hard to say but something thats easy to try.

 

[jim]

I doubt it's the weights...you get higher rpms if those were binding. From the sounds of it, with it coming on hard and signing off on high rpms it sounds like a flow resriction...elbows may be causing that. I trouble shoot the intake by not running an intake at all for a pull or two...no filters, etc. The new set-up might be more resrictive than you think. I assume powervalves are OK (not sure if you have them though) and opening up. I'm still thinking elbows though...a bend can cause a big restriction on airflow. Also, are the stingers packed fresh? That can cause change the backpressure if they aren't fresh...could be enough to throw it out of balance. If it was progressive, I'd focus on things that go away slowly, like packing. If it just happened one day, could be more in the timing department. TPS OK? If you have that? Just throwing lobs out there...

 

[CSV]

Man this is going to sound stupid as sh!t but here it goes. My sled is no huge twin but it started to run like azz pull real hard then fall on its face. I tried one thing after another nothing would fix it. Then I started think about when I cut the ring around stingers so that it would be flush. It only hung down bast the belly pan like a 1/2". So last ride I tip it on its side a see that me deflector has bent towards the bellypan the half inch I cut off the stingers. So put my foot on it and bend it back plus about 1" past the factory postion. After that it ran like a top. Pretty stupid frickin small of a thing but it help me. Good luck

 

[Scott]

This poorly running condition wasn't progressive. It was sudden. Ran fine when I parked it the year before....ran like crap on the maiden voyage the next season. The only thing I did to it on that off season was freshen the clutching. I WILL check my primary spring to make sure it's not a lemon.

Hmmm.
I'm open minded, Jim and Bwock, but it ran like crap before I put the elbows on the filters. It's running just the same as it did last season when I put it away. I doubt it's the elbows, but I'll pull them and see. It's a thick hard rubber for radiator hoses. It was hard to cut with a carpet knife.

I have a CMX throttle block and the RMK cdi. and it ran fine until all of a sudden. So the TPS shouldn't be bad as a result of that. Maybe something else, but not that.

Also, are the stingers packed fresh?

No. Haven't been touched.

So last ride I tip it on its side a see that me deflector has bent towards the bellypan the half inch I cut off the stingers. So put my foot on it and bend it back plus about 1" past the factory postion.

I'd be silly not to look at that. My sled does sound a little different with this problem.

 

[snowmanx]

Don't shoot me for suggesting this, as I'm sure it's one of the first things you changed, but how many miles on your belt? Have you tried dropping a new belt in there? I know I loose RPM when the belt starts getting old, and it can still look good.

 

[Scott]

I have about 200 or 300 miles on this belt.

But, I'll put that on the list.

 

[kfa670]

Scott I have been having the same problem with an 1100 hooper motor I have. I live at about 5000' and ride around 8-10. If I slam on the throttle behind my house I can grab about 8300rpm and stand it on its tail. I went to cooke city this weekend and lost about 1000 rpm, from 8300 to about 7200. I rejetted and took weight out of the primary and was able to hit 8000 BRIEFLY when I took a whack at a hill but it always falls on its face if I keep it mashed. I'm running 400 mains with the needles dropped in so I'm really lean down low.
I've bought all kinds of different things to try including a different CDI, primary clutch, etc. Throttle position sensor is brand new. Im going crazy because if I could just hold 8000rpm the damn thing would work awesome. I've thought about maybe different pipes? Possibly they don't create enough back pressure when you climb in altitude? I don't mean to high-jack your thread either but it seems there are a few of us with this problem.

 

[HardKor]

me too... here's my list...

I've been battling a similar problem this season. I changed a million and a half things, but here's what I've tried to rectify my low rpm problem.

I put a set of 48 lectrons on a 1010. I had to go with a cable controlled TPS. The PSI one was a piece of junk... someone flunked 8th grade geometry and then designed the PSI block. So I tried a Cutler. A little better but not the full adjustment... so I set the WOT and left the idle setting a little high.
Next I tried leaning the lectrons down with different metering rods. Still not there.
I dropped 8g of weight off each arm, only to go from 7400 to 7600.
Power valves and servo seem to be working correctly.
Swapped belts around.
I talked to a buddy and thought maybe the cryogenic treatment that I did screwed up the electronics. (He actually had a king cat that wouldn't spin over 7000 and changing out the stator, pick-up and flywheel fixed it) So I tried that today... no luck for me. I'm ready to throw my stock carbs back on to see if she'll come up with those.

I can't even get it to spin in the trailer without a belt on. If I punch the throttle quickly, multiple times, I can see just over 8000 on the max recall, but don't really hear the motor coming on the pipe.
Thanks for all the ideas... keep them coming!

 

[bmanke]

How about exhaust valves? If they are stuck shut that could cause the top end to fall off. Good Luck.

 

[go high fast]

I would lose the prefilters for a ride and see how she runs. I have never been able to run the prefilters and maintain good airflow. If your new hood screens get plugged then your sucking nice warm air which is also no good for proper air/fuel ratio and no good for HP.

stator/flywheel problem i had one time on the PSI motor would create problems once the motor warmed up to full operating temp. motor would then run like a machine gun cutting in and out when on the gas.......doesnt sound like your problem though.

do you run a water temp gauge. Its not getting hot is it.

anyway before you get this thing figured out......lets race.

 

[go high fast]

kfa670,

next time your in Cooke try gearing down a bit and dropping 2 to 4 degrees on your helix. motor wont fall down then on the hill.