Jump to content
Sign in to follow this  

Help with high speed miss - jetting?

Recommended Posts

6 hours on new bike

Free mods done, snorkel out, promoto billet exhaust insert, drilled out baffle, gray wire snipped, JD jetting

Red needle on 3rd clip

175 main

42 pilot

JD leak jet

2 turns out on needle

Under hard accelleration at high rpm I get an intermittent miss, like water in the air filter or fuel cutting out, WOT throttle only. Otherwise runs like a clock. Any ideas?

I could drop a 180 main in there and see if that fixes it. It's almost like it's hitting the rev limiter but it's not.

Share this post


Link to post
Share on other sites

done the blue wire too ?

i woul dsay try the 180/185 that comes with jd kit... i had this issue but it was my gear selectors and gear dogs on 5th.. not gonna be that on your new bike... so try a slightly bigger jet or put needle on 5th clip as the kit suggests...possibly too rich or lean ? similar feeling to both ....

Share this post


Link to post
Share on other sites

Use the red needle if the air temp is in the 60's or 70's. Use the blue needle when cooler. Drop in a 180 main, sounds too lean.

Share this post


Link to post
Share on other sites

I had a similar problem - last 11 months since new. Found it was running too rich on the main jet, the bit that most affects fuel/air mix between 3/4 to WOT.

I dropped from stock 170 to 168 (came with the bike) and problem solved.

I went from flat/miss in WOT at high revs, to now having continuing acceleration and no flat spots/misses. Was just running too rich on the MJ.

Share this post


Link to post
Share on other sites

Dropped the 185 in there and raised the needle two notches and it's mostly gone but still there some. Will go back to a 170 and see if it goes away. Maybe it is too rich.

When I jetted the CRF230 they kept saying go big, bigger, was waaayyy too fat. Just a little richer than stock worked perfect.

Share this post


Link to post
Share on other sites

Starting with the recommended main, remove the airbox door and go for a ride (bike fully warmed up). Is it better or worse?

If it is better, you need a smaller main.

Go down one size, replace the airbox door, ride. Remove the airbox door and test again. Better or worse? If better, go down a size again. Keep repeating this till the test with the airbox door is worse.

If it was worse with the airbox door removed, tape over 1/3 of your airbox opening, test (airbox door on, of course).

If it is worse now with the tape and was worse with the airbox door off, your main is just right. You are done!

If it seems better, you need to go up a size in main jet. Then test it again (remove the tape). Replace the tape, test again. If with the tape on it is better, go up another size in main. Keep repeating this till having the tape on is worse than with it off.

To finish up and ensure you are set accurately, retest the bike with the tape off (airbox door on), ride it, then remove the airbox door (tape off, of course). Best performance should be with the airbox untapped, airbox door on.

Remember, the main only operates at WOT. Ideally, you want to be in 3rd or 4th gear doing the tests, hitting max revs (just shy of the limiter) for at least 10 seconds to get an accurate representation of the jet status.

Share this post


Link to post
Share on other sites

Okay, have installed all the way from a 170 to a 185 main and I still get this cutting out, surging, high speed miss at full throttle. Very frustrating. And we are getting ready to leave for 5 days and now I'm getting pissed.

Is there some other ignition related settings for these bikes? Is there something else I can check?

Share this post


Link to post
Share on other sites

From a 170 to a 185 is enough of a jump to of either made it better or much worse. Therefore, something else is amiss from a bad spark plug to a wiring issue that at high rpm, the vibrations are causing a mis-fire.

Share this post


Link to post
Share on other sites

Have you tried disconnecting the TPS?

Just grasping at straws here since that should be a midrange problem, but it can't hurt to check (and it's fast and free).

Share this post


Link to post
Share on other sites

Well I ran it down to my local expert, Steve at Motowest, he does a ton of race prep and works on all bikes. He put a new plug in it, it had a 9 and book calls for an 8, and we put the stock 170 main jet back in and it's 99% there. It's just too rich on the top end.

I had the needle at the 5th groove so moved it back to 3 and it was much worse, so went back to the 5th groove. I think the leak jet is probably too rich and it's over fueling the circuit on WOT. But at least it's ride-able and goes like slingshot, wheelies in 3 gears.

So we'll run it that way for this trip, back next week with an update.

Not impressed with JD jetting, it just doesn't work well on their settings. Oh well. Would have been far better off with a YZF needle and a couple of jets, and save about $70. So much for getting it right the first time - I am now an expert at getting jets changed out on this thing.

Share this post


Link to post
Share on other sites

try going lower than 170. My problem was identical and I dropped from 170 to 168 and that very small change (along with a little less oil in the air filter) and it was all fixed!

Share this post


Link to post
Share on other sites

I had the same final jetting on my '06 as out did. Just ran too rich everywhere after listening to all the posts on these boards saying to richen richen richen after free mods and AIS removal. Ended up almost back at stock for best results, using a YZ needle. I even marked my throttle grip to be sure where I was in the throttle opening. I've owned a lot of bikes, as most of us have, and never saw a need to go to JD for a "kit". Just my .02.

Share this post


Link to post
Share on other sites

Leak jet (AP) only comes into play when the throttle is moved. It does nothing when the throttle is held steady.

Try a 165 main, test, then move the clip back to the third position and test. Do not make the changs all at once. One at a time, test, make the next change.

Everyone thinks richer is better. Everyone thinks the bikers are all lean from the factory. All wives tales.

Share this post


Link to post
Share on other sites

Thanks guys. Yeah, I'm really pondering how the heck these guys are running the jets they say they are - 185 main?

I'm going to try a few more, I have a 168 and a 165.

It's almost like something is creating an extra boost of fuel after it's wide open for a couple of seconds. It's clean the first run, then subsequent it seems to do it again. What I really don't get is that dropping the needle made it worse, so maybe there's some kind of weird taper there that's causing a surge of fuel. I may try taking the o-ring off the acc pump and see if that helps. No off-idle bog, pulls strong all the way to the top (lots of pull) but then garbles. That sure seems like the main jet.

Off to the dez this morning...put some miles on 'er. Got the graphics on, they finally came; kid's bike, he loves it:

DSC02995.jpg

DSC02998.jpg

Share this post


Link to post
Share on other sites

Ditto on the main jet size - I run a 165 in my '07 WR and if anything it's a bit rich (3000-5000 ft). Running a '09 YZ needle on the 4th and it runs great.

Share this post


Link to post
Share on other sites

i second most of this. I am running a 168 main. i did drop my leak down to a 40 or 42, cant remember, and im running second clip position. it took me a while to realize i was waYYYYYYYY to rich after letting some knuckle head at a yamaha shop tell me he got the bike running like a dream. I start riding at 6000' and go up to about 8-10,000' and usually only need to adjust about a quarter turn out during the ride to stay a little consistent.

anyway, my realization is that these 06'ers need to go wayyyyyy more lean than most people think. and man it is a beautiful thing once you find their sweet. spot.

good luck.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×