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Purchased a 2008 crf 150r and installed a yoshimira silencer spark arrestor "slip on" . Due to the bike being new and not broke in my son took it easy after third ride I took it out and noticed that at the top of every gear the bike sputter's out. Yoshimira says that you do not need to rejet I have not made any other mods to bike. !! Please Help !! I am not even sure if the bike always had the problum before installing slip on due to it being new.

yoshimura means after you jet it first with the stock pipe on so look into what other people are jetting thier 150s at. and i am looking for a pipe too, how does the yoshimura pipe work on a scale of 1 to 10

bigdog1 wrote:Purchased a 2008 crf 150r and installed a yoshimira silencer spark arrestor "slip on" . Due to the bike being new and not broke in my son took it easy after third ride I took it out and noticed that at the top of every gear the bike sputter's out. Yoshimira says that you do not need to rejet I have not made any other mods to bike. !! Please Help !! I am not even sure if the bike always had the problum before installing slip on due to it being new.

I'd be certain it's not the rev limiter. Just sayin.
With a pipe, you typically increase air flow. Which in turn increases fuel demand. You may need to increase a main jet size and/or raise the float level. Both of which may cause your symptoms. I would also check what others are running for jetting. I would imagine that a pipe is the most common upgrade to the 150R...

Good luck.

I'd be certain it's not the rev limiter. Just sayin

And I am certain it is the rev limiter !
It is.
We get around a post a month describing what you're describing and you are hitting the rev limiter.It's always the rev limiter.
If you shift up and it goes away... you're hitting the rev limiter.
Glad to have you here on the site too, let us know how we can help you.
This guy arrives at needle taper and jetting sizes by tuning the bikes on a dyno with exhaust gas temp and content analysis. It takes the guess work out of setting up your jetting, and there are a ton of very happy owners running his set-ups :
http://www.crfsonly.com/catalog/product ... ts_id/2253
This will make your life a lot easier too, just remember to use the spring, o-ring and washer from your OEM fuel screw on this one :
http://www.crfsonly.com/catalog/product ... ts_id/1333
Even with the jetting really dialed there'll be days where it's lots cooler,hotter and /or humidity changes. You'll need to tweak the fuel screw an 8th of a turn either way or so when that happens and this fuel screw replaces the very hard to access OEM fuel screw.
Note also the heavier you are compared to the bikes "target" rider the faster you'll get to the rev limiter. Doug

Describe the sputtering. The rev limiter is a very obvious thing, and I think he would know if he were hitting it. To see if it is the rev limiter, put it in neutral and rev it till it cant go any higher. If you get the same cut out, it's the rev limiter.

The rev limiter is a very obvious thing, and I think he would know if he were hitting it

.
Nope.
It's not at all an obvious thing when people aren't familiar with these bikes and their high rpm operation.
What is obvious is for the vast majority of cases when someone writes in with a high rpm "bog" or what he's describing that it turns out to be the rev limiter.
Simply revving the engine without it being under load tells him nothing.
If the sputtering ceases after up-shifting it's the rev limiter.
Find a post where the mysterious high rpm "bog" goes away magically after installing a larger main jet when what we're talking about a motocross bike,changing the needle clip, or some mysterious latent electrical problem is found.
You'll look a long time.
Then look at the posts where the poster finally says 'it was the rev limiter". There are dozens.
Our job is to first provide the person with the problem with the most common, obvious and easiest solution, not to get into some intellectualizing that has them chasing their tail. Doug

JD jeting makes a great kit that i used on my 150r it gives it more low end power and easier to control, it puts in a fatter jet then what its stock with and u have to put in fatter needles too. it makes it a lot better to handle in the trail.