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Kmorris

WR 450 Jetting Question - YZ Pipe

13 posts in this topic

Greetings

Environment - 75-80 degrees

600 feet above sea level

JD Jet kit

170 main

45 Pilot

blue #3

Adjustable fuel screw - about 1 1/2 turns

Free mods - fuel screw - air pump, etc.

At that point the WR just screamed all the way up top.

I installed a YZ pipe and lost my top end completely. Nice low power band and very clean and powerful surge up through the middle but once I'm at the upper RPM range the power goes south and the engine stumbles - seems like lean stumble.

Could that YZ pipe make that much of a difference? I'm thinking I'm going to need to start experimenting with the needle position. What is the difference between the red and blue needle - I thought the red needle was for warmer climates.

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Your main seems rich for the temps, but I like the 45 pilot. Some people like the 48, but you're on the edge. You should probably be using the red needle at anything over 60 degrees, try clip 5, or 4 if it gets any hotter.

Check Indy's Jetting Chart.

FYI, I found a huge difference at WOT with the YZ pipe versus the WR without the baffle. Definitely needed a re-jet.

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Hi BG,

Your comment:

FYI, I found a huge difference at WOT with the YZ pipe versus the WR without the baffle. Definitely needed a re-jet.

... is exactly my issue - exactly. What was the difference (same symptoms I've described?) and what jetting changes did you come up with?

Thanks!

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I'm using a 168 main with an opened up airbox, backfire screen removed, 1-2000 feet and the thing screems on top. Better than with a 170. I have a YZ pipe with a Dr.D sparky. Using the needle that came with the AIS kit, cant remember what notch.

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Yes, it sounds exactly like my problem. I read your post in the jetting forum and the only difference was that I was running the stock WR pipe without the baffle, where you had the PMB insert. Anyway, I had a slight WOT bog/miss when I removed the baffle and then it was huge when I switched to the YZ pipe. Not sure what year you've got; jetting specs will vary, but I'm at a similar elevation (< 2000') and I ended up with Red #4, 165 MJ, 45 PJ, 52 LJ for my "heat of summer" jetting (it's almost 100 degrees here today :ride: ). For slightly cooler weather I run Red #5, 168 MJ, 45 PJ and 40 LJ. :thumbsup:

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Thanks BG, Sound like you solved your WOT bog - which would suggest it's a jetting issue and not rev limiter related. But, I do wonder about the rev limiter - could I actually have been high enough to have hit it? I'm going to have to work that one out.

From your earlier jetting BEFORE the YZ pipe would you say you were solving a lean WOT or a rich WOT condition as you were working the issue AFTER you installed the YZ pipe. I'm finding it hard to imagine that YZ pipe causing the mixture to get so lean at WOT where I'd notice.

I'm planning on experimenting with the red needle and different main jets after a little more research.

Thanks again.

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Vancouver island BC so pretty much the same temps and elevation as you. JD blue #3- 168 main- 48 pilot- YZ pipe- balance of free mods. Runs really well from idle to top. (it does pop pretty bad on decel but I live with it) You may be hitting the rev limiter.

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From your earlier jetting BEFORE the YZ pipe would you say you were solving a lean WOT or a rich WOT condition as you were working the issue AFTER you installed the YZ pipe. I'm finding it hard to imagine that YZ pipe causing the mixture to get so lean at WOT where I'd notice.
I bought my bike supposedly jetted, but with only the throttle stop and the grey wire mods. I removed the intake and exhaust restrictors and had the slight WOT bog. I then put on the YZ pipe and the WOT bog got huge. I re-jetted and found a 145 MJ, but it looked to be drilled (looked bigger than a 165), so I disregarded it and started over. Now here I am, happy with my 3 season jetting solution. I usually only require a pilot screw tweak to get right on.

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I'm using a 168 main with an opened up airbox, backfire screen removed, 1-2000 feet and the thing screems on top. Better than with a 170. I have a YZ pipe with a Dr.D sparky. Using the needle that came with the AIS kit, cant remember what notch.

Hi XRYoda:

Sorry for my ingnorance. :ride:

What is the backfire screen that you removed ???

Does it improve the intake flow ??

Thanks :thumbsup:

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Thanks Old Man Dan,

What I'm gathering is that most of the problems associated with a WOT bog seem main jet related - or - at least the majority of those who switched pipes to a YZ unit have found their WOT bog going away with a LEANER main.

I'm running a 170 with a blue #3. I think I'll try a 168 - Blue #3, then a 168 and Red #4. If these fail I'll start again!

:thumbsup:

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Turns out I was hitting the rev limiter. Up to about 9/10 throttle (this time on the road) the engine screams and build RPM's immediately. Then about a 1/2 second or so after going to full throttle the engine starts to cut out.

Seems too much like a rev limiter.

Thanks for the idea Eddie.

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Yes, the backfire screen made a noticable difference (some will probably argue). It is the screen in the airfilter frame. It is a pain to remove, be warned!!. A heat gun might be the trick. I used a razor blade and it took me about an hour. I used to do it on road race bikes and it always made a difference on the dyno. Make sure that your airbox is opened up, too.

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