Quick blip on throttle, engine dies.

I installed a new header and pipe (powerbomb & SX1),I was given this new jetting:

pilot 50

needle OBDVR 4th

main 180

screw 2 turns out

main air jet 200

pilot air jet 100 (could not find, still using stock jet #75)

Bike feels a lot stronger from mid up,revs quicker but I feel that my low end was better before, (it could be my imagination).

At idle tried to adjust screw a little and anything less than 2 turns engine will stall, when I open the throttle quick to 1/8 - 1/4 same thing happens ,I could open screw more, (2-1/2) but did not notice any change at idle.

Bike starts only with hot button even if it's cold (weird).

How do I find out if I went to rich.

I usually ride @4000-5000 ft. my observations were made @400 ft. what changes can I expect when I get up there?

WR timig, throttle stop removed,air lid off.



2000 WR400 stock,(not for long), 2001 TT-R125L (son), 2001 breeze (son, wife)


It looks like a very rich idle and transitions to lean as you open the throttle. The hot start symptom confirms it.

Try a richer clip position #5 and turn the pilot screw in to reduce the idle richness. You may want to step back to a #48 pilot.


Thanks James I will try your suggestion.

Can I benefit from the "E" needle that I read so much about in this forum with my WR timing or should I stay with the OBDVR.

Also,is it necessary to remove the carb to get to the needle,is a pain.

Should I replace the stock pilot air jet to the #100?.

To change te needle pos you just have to remove the throttle cables on the carb.

Losen the carb fixations, and you will be able to rotate the carb to the left, remove the cap and get acces to the needle.

Follow JD or Taffy 's recomendations for the jetting and it will be fine.

Good luck. :)


'99 WR400 F, YZ exhaust, throttle stop trimmed, WR timing, airbox cover removed


Yes, the EKN(Yamaha) or EMN(Keihin/Sudco) are what I would suggest with WR timing and 0-5000ft elev. The #100 pilot is another good idea with your modified exhaust.

Search on "carb removal" & see 4/4/01 posting for a suggested method.


[This message has been edited by James Dean (edited 04-27-2001).]


I have the Powerbomb/Stroker set up on a '99

@ sea level and have been running PJ48, MJ178, DVP 4th,FS @ 2and1/8 out with great results. Starts first or second kick with choke and runs great t/o the throttle range. I had tried 50/180 and combos with mixed results. The 48/180 combo was o.k. but midrange hit was diminished. The 50pj seemed to rich @sea level, although a needle change and FS setting could accomodate. I race enduros and lugg the bike low in RPM range and like quick throttle response off low end. The 48/178 does this the best for me without compromising too much from the top end. No hiccups, bogs or pops. I also bought a chrome turn down for the end of stroker exhaust, makes a nice difference at idle and low RPM, but once you crack it open it's as loud as ever.

Good Luck, Keith.

Ditto everthing James has said to rich on the pilot dumping into too lean of a needle, also the stroke of the accel pump will further complicate things with this jetting combo. On my YZ cam timed 99 with the same exhaust I run the following jetting combinations:

Note my Accelerator Pump stroke was cut down from 3mm stock to 1.5mm today.

Good response top to bottom:

PJ = 48

fuel screw 1.5

PAJ = 100

Needle = DVP #5 or #4

MAJ = 200

Main Jet 178

A little snapper response:

PJ = 48

Fuel screw = 1.0

PAJ = 100

Needle = EKP #4

MAJ = 200

Main Jet 170

The best response (yet to be evaluated by me)

PJ = 48

fuel screw = 1.25

PAJ = drilled out to 1.32mm

Needle = EKP #4 or EKN #4 (EKP preferred above 3000 feet)

Main air jet = a 200 drilled out to 2.32mm

Main Jet 172

For your normal riding altitude of above 4000 feet if you go to the E** meedle taper I would not run a main jet bigger than a 170.

With the D taper needles still would not go larger than a 175/178 at that altitude.

The only time I ever run a DVR needle is when I am riding high altitude above 7000 feet. Its a little lean down lower in altitude, but if you raise DVR (ie clip #6 or #5 from the top) needle it will be better for you.

As a final note the first two jetting combos above have been extensively evaluated the last one was just installed base on the observations by Andrew, Taffy and James since I'm still recovering from hernia surgery I will not evalutate the last combo until a few weeks from now. I have every expectation that it will be very good based on e-mail conversations with James.

Good luck


[This message has been edited by Clark Mason (edited 04-27-2001).]

Thanks guys;

I changed the pilot to 48 today, the stalling problem is solved, I will try the #5 clip tomorrow with the same needle, I also have a 178 main. Tomorrow is my first ride with the new pipe and jetting.

Thanks again!


2000 WR400 stock,(not for long), 2001 TT-R125L (son), 2001 breeze (son, wife)

Nice posting Clark. :)

Read it carefully Alex, the summary is very good.

I can change the needle and the main jet by just loosing the two boots and remove the hot start button. I move the carb to the left and rotate it whenever I want to change the needle or the main. You should be able to do it without remove the throttle cables. You should just need around 5 minutes to access the needle or the main.

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