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Half throttle studder

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So i have an 08 drz400sm

Just did a 3x3 JD kit with the pilot jet, the blue needle clip 4 (then switched to clip 2 more on this in a sec) 2.5 turns out on stock fuel screw and a 155 main.

I am at 0-2000 ft average riding is done under a thousand feet.

I did those two mods at the same time as my brand new full yoshi rs2 system without the spark arrest screen.

Heres the problem, when i started with the blue needle at clip 4 (as per most of the threads i found respected members post in) the bike ran like shit through 75% of the throttle range I found this quite weird, I took the carb apart and finding nothing plugged or out of place put the needle on clip 2. It runs Much better however it still runs rough at about 1/2-3/4 throttle.

Me being somewhat car savvy, i figured put the petcock on prime while riding, for testing and pull that vacuum line off to see if the additional air will lean it out (thinking maybe its running rich and should move to clip 3 or 4 again). To my suprise it appears to get worse.

Why is it i think my bike is running lean? if i keep on the throttle at wot it gets better then PULLS up top, the thing moves way better than stock, but that dead spot is terrible. And for th record its not a lack of power, i can physically feel the engine struggle, wack it to wot hold it there and it quickly regains its power and winds up nice.

Hopefully someone can fill me in. Im hoping its just a stupid mistake i made setting it up, or that my settings are wrong. I don't want to have to pull that carb again without actually fixing anything, thats like doing power steering on a volkswagen :) .

Thanks in advance.

edit; sorry if this should be in the jetting forum mods please move, figured its drz related?

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did you reuse all the stock needle spacers? correct order? vacuum line connected to the petcock? intake hole exactly 3x3?

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Yes sir, checked double checked and now tripple checked.

It feals and sounds lean, and its most definitely not running rich, even during warm up no black smoke, no residue on anything that would indicate running rich.

Could there possibly be another problem in the carb thats interrelated to the jetting? maybe when i took it out or put it in i shook something out of spec? I have to admit i was not all that nice to it getting it out, took me bout half an hour :)

Going to pull the plug today and see what i see. also going to do an oil change, tho i know thats not going to fix anything, just want to be 100% positive nothing is getting washed out or something super silly like that.

Maybe when i tour down to the states this winter i'll swing by your place for a couple days and let you massage this bike into a monster. (you've got a pm)

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Tape off 1/3 of the airbox and give it a run. If it is better, put your needle back to where it was and go up a size on your main jet.

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Tape off 1/3 of the airbox and give it a run. If it is better, put your needle back to where it was and go up a size on your main jet.

Will try that this afternoon and report back.:)

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Are you 100% sure you replaced the main jet, and didn't put the 155 main in the starter jet position?

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140% sure, i removed a 145 main jet and tossed in a 155. Just got off work about to go tape and ride to see how it is.

Its very very noticeable 1/2-3/4 throttle then works well.. better at wot. this would make me assume that a 160 with the needle at clip 4 should suffice. Jet kit was shipped up from my house should be here round 8 pm tonight so i can fiddle.

till then let the testing commence.

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I thought stock was 142.5, and those are the same symptoms I had when I replaced the stater jet instead of the main. :) Has the starting ritual changed any since the rejet? On my '07 SM w/ RS2 (uncorked) & 3x3, I ran the blue needle in the 4th clip, 160 main, 25 pilot, and 2.75 turns out on the Kientech screw. It ran flawlessly at very similar elevation.

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Right now i am at 715 feet. Bike runs better with the box covered 1/3rd with tape. However it seams to have moved the studder down to 1/4-1/2 throttle and its less noticeable.

Im going to switch to a 160 jet tonight clip 4 on the needle, hoping that does it.

Is there many people that run a 160 with these mods? most of what i read stated clip 4 155mj, 2.5-2.25 turns out with the jd pilot jet and stock screw.

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155 w/ stock pipe, 160 w/ an uncorked aftermarket exhaust. I'm @ 600', your settings should be the same as what I ran. Are you running the 22.5 or 25 pilot jet, and did you confirm your pilot circuit?

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Ah i must have miss read some info on the jetting specs.

I did confirm the pilot circuit, i had it die on me a couple of times, however once or twice it did remain running (tho not sounding 100%) i believe i had the idle up too high, or maybe even the choke out cant recall.

I will rejet with the 160 going to pick it up now and check the pilot circuit again, then go for a test run.

Thanks a bunch you guys have been quite helpfull. :)

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Sorry for the late response, took for ever to get this package, and as im working nights it took forever to work on my bike in the parking lot.

While waiting i taped off the airbox, it made it better, Then i dropped the needle back to notch 4. Bike ran way smoother than stock nice improvement.

Couple days back i got the jet kit in, tossed in the 160 main, cleaned out the 25, tho it did not look dirty just good house keeping and untaped the air box. Needless to say they call me mr korean hands because i did all of that with the carb on the bike, just pulled off the bottom cover had it done in 5 min or so. EASY.

Bike runs Awesome, wheelies are soo easy with me only weighing like 130 ish.

Biggest problem is keeping the front wheel on the ground.

Thanks for the advice guys, i figured i'd post up the results incase anyone else has this trouble again.

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did the 3x3 about two weeks ago when it was cold and snowy.

Bike started fine in basement and sounded great.

setup

stock carb

stock exhaust

3x3 mod

JD jet kit

45 pilot

155 main

2.5 screws out (and everywhere inbetween 2.5 and 3.75 after the following problems)

950ft above sea level

took it out for first ride yesterday

rode about 5 miles seemed fine, no real noticable increase.

then lost power under load. bike shut off

sat for a bit cursing

started up

idled fine

rode up through 2nd gear and bike shut off

(repeat for an hour)

trucked it home

just realized that the stock exhaust has been cut down about 6 inches and tip welded back on. (not my doing)

any suggestions

increase to a 160 main?

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jetting does cuase the bike to run fine then suddenly lose power and not run.

you have fuel flow issue. vacuum line connected to the petcock?

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jetting does cuase the bike to run fine then suddenly lose power and not run.

you have fuel flow issue. vacuum line connected to the petcock?

Yeah, there are two hoses total to the petcock. Both are connected. I made sure.

It seemed strange to me that the bike was fine then cut out.

extra info

Blue needle third clip from flat side

It did Backfire shortly before the bike quit. But only the one time.

It started several times after and just would not keep running under load.

Idles great!

I'm about to go dive into this problem, cause i'm pi$$ed and it's going to be 58degrees today.

I have no idea what could be wrong if it's not the jetting.

I have mechanical ability, but no patience.

thanks for the help.

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