RPM loss

[srx70024]

I have noticed that my belt sits lower in the secondary after only 700 miles and I have lost rpms, about 500. It used to turn 10,500 all day long and all I get now is 10k. Could this be reason? I run the track very loose and this was in good snow conditions, so I don't think the slides were heating up. I also installed the CR10EK plugs. Could I have a plug fouled? It still runs pretty good and has plenty of power.
I will be installing the washers to raise the belt. Any other ideas to get back to 10,500?

The clutching is stock.

Thanks.

 

[srx70024]

I changed my plugs back to the stock plugs and it now revs to 10,500 like it used to. All of the CR10EK's looked good. Could one of them be bad? Should I try another set of these plugs? It's getting a bit pricey for 2~3 hp. lol.

 

[KnappAttack]

I doubt its the plugs unless they are fouled. When they foul you'll know it. These sled are very condition and weather dependent when using stock clutching especially. I don't think you can get a cheaper couple of easy HP as the plugs. Its your sled. Stock clutching only rpms with some speed as you know.

 

[Yamzilla]

I have noticed that my belt sits lower in the secondary after only 700 miles and I have lost rpms, about 500. It used to turn 10,500 all day long and all I get now is 10k. Could this be reason? I run the track very loose and this was in good snow conditions, so I don't think the slides were heating up. I also installed the CR10EK plugs. Could I have a plug fouled? It still runs pretty good and has plenty of power.
I will be installing the washers to raise the belt. Any other ideas to get back to 10,500?

The clutching is stock.

Thanks.

Before you go changing too many things try getting your belt back where it belongs in the sheaves. Check to make sure it's not over-worn too. Greater than 1/16" generally means you need a new belt. Then go check your rpm. With the belt sitting in the secondary as you described is like taking off in 3rd gear...not good. Other thoughts: What you're describing sounds like excessive belt wear to me. Verify your clutch alignment. If that's ok then you may want to consider one of the following. 1. Go faster so your belt is slipping less and spending more time deeper in the clutch. 2. Gear down to at least a 1.73 gear ratio and clutch accordingly. What that will do is force the belt deeper into to the clutch and less time slipping. Your belt will love you for it because it will run cooler, last longer, which spells improved efficiency all around i.e. longer clutch life, less belt wear, more power to the track, better acceleration. And if you setup your clutching proper you'll be surprised at how little top-end is lost. In some snow conditions you will gain top-end. Please understand, this advice is not for everyone. However, I perceive you to be a trail rider and it should help your hot belt. Zilla.

 

[Yummy]

I changed my plugs back to the stock plugs and it now revs to 10,500 like it used to. All of the CR10EK's looked good. Could one of them be bad? Should I try another set of these plugs? It's getting a bit pricey for 2~3 hp. lol.

WOW, I have the SAME problem.

Last year I had 11,200 RPM. In March I installed the CR10EK plugs and Ulmer Air box. Lost 400-500 RPM. Just didn't make any sense.

I then, suspect clutches...Had them check No problems. Then I changed back to the original air box. Same problem! Checked all bearings..Nope!

Early this season the Yamaha mechanic told me that sometime spark plug could affect RPM. I had doubt about what he was saying, because I figured other people on the TY site would have noticed this problem!

Now, I'm reading that someone else is having the same RPM loss. Well I'm due for the OIL filter change I will certainly go back and try the stock plugs and see if I will gain back those RPM.

Maybe my mechanic is not that half bad.

Can anyone explain this?

 

[srx70024]

I should have mentioned that the only thing I did above was change the plugs. I didn't do anything with the secondary belt height. The belt still sits a little below the top of the sheeve, yet I got my rpms back to where they used to be by going back to the stock plugs.

dunno....

 

[**sj**]

your belt is most likely the culprit....and you would want to check your slider pucks, bushings etc...they need to be cleaned every once in a while also..
I have found with these machines if them temps get warmer and you have ski pressure..the drag can load the motor enough to run fewer rpms..

 

[Yummy]

I will know soon enough. I changed the oil filter last nite and tonite will changed the plugs for the stocker. Will let you know if my RPM are back.

 

[**sj**]

what were the temps you experienced this in

 

[srx70024]

The temp was low 20's before and after I changed the plugs. I run my track a bit on the loose side, no studs. There was 2" of powder on top of hard pack, plenty of lube for the slides.

I think I'm gonna try the 23t top gear and the white secondary spring for the heck of it too.

 

[**sj**]

when sudden drop of rpms given all the same conditions...two things come to mind..

spring bind or sag!

 

[KnappAttack]

CR10EK Plugs WILL NOT HURT RPMS OR PERFORMANCE. Unless of course they are fouled. Something else is going on. These things change so much due to conditions and weather. Don't try and compare one day to the next, or one season to the next. You should always try to change only one thing at a time to determine a problem. I suppose its possible that putting the caps on the plugs they could have been twisted and broke internally. I have seen plugs that won't fire right out of the box for the two-strokes but never run across it yet for these four-strokes. Thats not to say its not possible. That is why I used to run Autolites in my racing two-strokes. Never had one that wouldn't fire. NGK's however seemed to have a higher failure rate right out of the box, (10-15% maybe. I used to check the NGK's with an ohm meter before I even used them. They were all over the board. The Autolites were always perfect everytime. I wonder if we should be checking these cr10ek's like that? I never have checked these plugs now that I think of it.

 

[srx70024]

All,
Thanks for all this good info.

Mike - If I test them with an ohm meter I should have 0 ohms from cap to electrode, correct? Maybe one of them is a bit funky. Just kinda weird how the only change was the plugs. We'll see.

 

[Yummy]

Last nite, just came back from a 300 miles run. Sorry to annonce; I did not gain back my RPM using back the stock plugs. the highest RPM I saw was 10,800. Had to do the last 100 miles with a broken runner/carbite, not fun! Tomorrow, I'm bringing her to the dealder so they can install the updated chaincase cover. Also, will ask them to check/change all bearings inside the chaincase.

Still in the quest for finding my loss RPM.