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I am just curious about a small issue that I am having with my '95 Storm.

The engine seems to be running quite well. The plugs seem to be a very good color it starts on the 2nd pull every time and seems to have lots of power.

It does seem to have a bit of a flat spot between 5000 and about 5800 rpm.  The problem is that this is the rpm the engine is at during normal trail riding. As soon as the machine hits 6000 rpm and gets on the pipe it runs great unfortunately 6000 rpm is a little too fast for most of the trails in my area.

The Clutch currently engages at about 4000 rpm and is fine until it hits 5000 then it falls flat until about 6000

Would it be possible to clutch the machine so the clutch engages at a higher rpm, or to go with a shorter gear and raise the operating rpm so the engine is on the pipe at lower speeds?

Thanks for the help!
 

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Had nearly exact problem you are describing with my 98 700 XCR I recently purchased. We increased the tension on the secondary, problem was considerably better. Tightening secondary made enough difference that the machine lost most of that twitchyness with the throttle trying to keep it off the pipe running down the trail when you only want to run 15 or 20mph, would suggest you start there.  Currently considering going with jetting recomendations for a little higher altitude to lean things out a bit. (currently running jets recommended for sea level-1000ft, will be installing jets for 1000 to 2000ft) Sled seems to run much better before it really warms up, indicating a rich condition. We're thinking that the rich condition isn't helping the problem a bit.
AL
 

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My 98 700 XCR (same as 97 Ultra) is running 82-8300rpm. Seems to be running pretty good for all stock.
AL
 

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What jets are you running and your elevation? I know when I owned that sled the power band started around 6000. Thats when the thing really started to move. I know it is just the nature of that beast. I was running 370,380,410 jets and they were good to -20F. This was at about 500' elevation. I could run WOT all day and not blow it up. If your jets are larger try going down a bit.
 

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Ninja-plumber,
I was refering to a flat spot between 5700 and 6000 in my 98 700XCR. The sled is trying to run this RPM going down the trail at some of the lower cruise speeds, say between 25 and 35mph. If you increase throttle to accelerate from the flat spot, even a tiny bit, the RPM's jump to 6100, and you are now a passenger on a rocket ship. At 6100 the machine comes on to the pipes, causing a lot more acceleration than you may have a need for in tighter sections of trail. If you back off the throttle, again even a teeny bit, you are back into your flat spot in the high 5000's. Effect is like a throttle with a hair trigger.  

WOT performance awesome, low end seems fine, lower part of midrange seems rich. Like I said in first note, before the machine really has a chance to warm up, it doesn't have that rich problem. We increased tension on the secondary which really helped, problem now nearly gone. Only notice it once in a while. Rich problem is still apparent though, therefore thinking of leaning ALL jets, pilot and main (which are now stock, as originaly supplied from factory),  down one step. Idle air bleed currently set at 2 turns, needle e-clip running in second ring from top. Gas milage in the low 9's, I'm sure it can do better, though that is not the purpose for the changes I have in mind .

Have an open mind for intelligent sugestions. Please note the machine is used on trails, not interested in developing it into a race sled. If I were, I'd just run it on the pipes full time.
AL
 

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hi ther michahicks: first off what are u running for clutching? is it stock? it sounds like its in the clutching to me.stiffining the secondary will cause u to upshift more quickly. and hold more (higher) rpm. how r  the clutchs? are they clean and in good shape. sometimes bushings will cause that very thing.
 

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Clutching is stock. Both springs new this year. Almond in primary, thinking secondary was blue, but have worked on a couple others, that may not be right. No wear apparent during inspection both sides. Machine is run in an area that is at approx. 1300ft above sea level. Polaris jets machines for sea level to 1000 ft. from factory.

Would have thought tightening secondary would delay upshift, not make it quicker as you say in your note? Were you thinking of backshifting?

AL
 

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I too would love to find the answer to this problem.

I run a 98 xcr 600. Complete rebuild from crank up. The engagement is 4800 rpm. I run flat and dull from 5000-5600.
After 5600 the engine runs like it's possesed - cranking up to 7500 rpm at same throttle opening. You really have to hang on.
It's a great machine for accelerating but difficult to wind down tight trails when your with a slower group.
I have narrowed the problem down to the fuel flow. Stiffening the secondary will only mask the problem. What will be ideal is for the machine to run like a rocket at all ranges and clean up the 5000-5600 rpm range.
This past week I rode around eastern Quebec on vacation and found that at 0'C - the boost in power hits at 5500 rpm.
This is odd because it would indicate that I am already lean at that throttle opening.
Trying v-force reeds makes it better but I would love to know what the best stock set-up is.

What makes it hard to troubleshoot is the problem is inconsistant with fuel system normal checks. because of the following facts:
1.  the engine noise is dull and flat - this indicates too rich
2.  the engine performs better in that range on start up or at warm ambiant temperatures - that indicates too lean
3.  At cold temperatures it is nearly impossible to hold a constant rpm because the engine wants to surge you right off the back of the sled - jumping from 5600-7500 rpm

If you need more info just let me know.
 

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madsledhead,
2 things in your note draw my attention, for whatever that's worth. Fuel flow problems would be more apparent at higher
RPM/loads than what we are looking at, so I have not considered that to be a part of this problem. Our sleds are all running fine at top end which is where we would see a fuel flow problem?

The other thing you say in your note is that you expect a sled running better when cold (engine temp, not OAT) than after it warms up to be running lean. That's not the case. It would be rich. The cold motor uses more fuel to run right, that's why we use a choke, to purposely cause a rich condition to keep it running till it can run on it's own. My sleds
all run much better when it's cold outside, say below 20F. They get all blubbery rich when the temps get to like 30F+.

Thanks for your input, It's nice to know others are having/working on the same problem.

AL
 

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One thing that may not have been well stated in my observations is the ambiant air temp - not the engine temp, affects the 5000-5600 flat spot.
The engine runs more crisp at low and high rpm with colder ambiant air - but the flat spot is increased.
At higher ambiant temp - the low end and top are boggy - but the flat spot is shortened  to 5000-5500 rpm.

I fully agree that there is no problems from 5600-8500 rpm.

One thing I am tempted to do is to advance the spark timming about 2' deg. Has anybody tried this?

good luck
 
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