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Math

EJP/ EKP?....yz conversion

13 posts in this topic

I've been playing with my jetting. I've tried a 45 pilot and a 48 pilot but in the summer (80-90 degs) my bike needs the hot start almost all the time with a 42 pilot so guess what happened with the 45... well the plug turned all black and the bike would not start. I'm pretty sure it's lean on the pilot though since the bike does not come back to low idle as soon as I release the throttle. I've figured from other posts that the stock #75 paj can be switched to a #100 or even #120 with a 45 or 48 pilot jet respectively which I will try.

I also noticed that the stock paj in the yz426 is a #100 with a 42 pj. So since my wr is yz timed, I definitely have to go and try the #100...

Trying to cure the bog I have if I gun the throttle too fast, I've also been thinkin about replacing the Wr needle I have (DQR) by the YZ needle.

I don't know which one I should choose though. The stock YZ one is an EJP. I know of TTers that run the EKP.

Wr 426 01

No snokle on the air box

Yz timed

FMFpc4

#170mj

#42pj

#200maj

#75paj

#65 starter jet

DQR at third clip from the top

AP timing set properly / no BK

0'-2000'

35-85 degrees

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Math, with the EKP needle, I remember I ended up with 85 paj (adjustable one from sudco ) and a 180 MAJ. I believe the PJ is a 42 or 40 and the MJ a 168 or 170, but, I cannot really remember. You should not need the hot start all the time. That tells me it is rich on the PJ, not lean. If you need the hot start all the time with a 42 PJ, go to a 40 PJ. That should help.

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Here's mine for a similar elevation and early spring temps. (YZ converted)

EJP needle 4

162 main, 200 main air

42 pilot, 100 pilot air

The ap is at .5 secs

ACV diaphram is flipped (this allows the engine to backfire when lean on deceleration)

I have a Zipty mixture screw that I constantly have to reset as my base elevation or temperature changes significantly from riding areas. I adjust the mixture screw just open enough to stop any backfiring on deceleration. Over 2 turns out time to go up a pilot, under 1 turn from closed time to go down one. Once my temperatures reach over a 100°F I drop to a 40 on the pilot, a 160 main didn't seem to make an improvements to the upper end for this temp.

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Math DesertChris is right,

Between 160 to 164 sounds right for the MJ. What I told you for MJ is too rich.

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Thanks for your answers

I understand what you say about the pilot circuit being rich since the hot start is almost always needed once the bike has run during the day (on hot days). And keep in mind that i'm from Québec which means that hot = 90 degs. :D

Also it does not need the choke when it starts the first time of the day at those temps...

BUT. I've been reading how to adjust the pilot circuit. What I learned in the thumperfaq, and other sources provided by TT ers is that if the bike does not come back to idle when throttle is released but rather holds high rpms for a little while before going down to idle this means you are lean on the pilot. This occurs with the 42pj which should tell me I'm a little lean. :) I'm curious to know what will happen with the #100 paj.

There is another thing also, I don't know what the ACV is for. What does it do, what goes through it and when is it activated?

Still so much to learn :)

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Math, if it runs fine without the choke when it is ice cold, then the pilot is rich. When you first start the bike and it is ice cold, without the choke on, it should die, or almost die at idle. When you first start the bike and it is ice cold with the choke on, it should sound perfect for about 1/2 minute or so, then it should start sounding bad, then, you put in the choke in and it sounds perfect again.

For the sticking idle, check your linkage, throttle cable at the handle tight? Is the cable hanging up somewhere? Take the black rubber cover off the linkage on the carb and watch the linkage as you open and close the throttle.

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The throttle cable and such things is a good idea too check but it is clean, well lubricated and so on... definitely not what causes it.

Math, if it runs fine without the choke when it is ice cold, then the pilot is rich. When you first start the bike and it is ice cold, without the choke on, it should die, or almost die at idle. When you first start the bike and it is ice cold with the choke on, it should sound perfect for about 1/2 minute or so, then it should start sounding bad, then, you put in the choke in and it sounds perfect again.

For the sticking idle, check your linkage, throttle cable at the handle tight? Is the cable hanging up somewhere? Take the black rubber cover off the linkage on the carb and watch the linkage as you open and close the throttle.

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Well, I do not know, but, with a 42 pj and 75 paj, you should not be lean. I would say, take the rear intake boot off the carb and make sure the butterfly valve is completely closing in the throat of the carb.

Check also for some kind of air or vacuum leak. Vacuum leak always gives you a hanging idle. You could spray some starter fluid around the carb and intake area at idle, and if the rpms go up, you know the starter fluid is being sucked in somewhere and you have a vacuum leak. :)

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Well, I do not know, but, with a 42 pj and 75 paj, you should not be lean. I would say, take the rear intake boot off the carb and make sure the butterfly valve is completely closing in the throat of the carb.

When you talk about the butterfly valve, I assume you are talking about the " sliding door" that goes up and down in the carb as you twist the throttle... well is does not close the venturi completely. A space remains when I look from the air filtrer side. I don't have my carb in my hands at the moment but if I remember correctly this butterfly slide is double right?

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There is another thing also, I don't know what the ACV is for. What does it do, what goes through it and when is it activated?

I forget the exact process of what it does but it's function is to stop the bike for backfiring on deceleration. I think it cuts the fuel off from the pilot circuit when vacuum is very high (deceleration). The diaphragm has a little stud on the inside that is useless if the diaphragm is flipped but allows the chamber to remain sealed like it is in the functioning position as opposed to removing the diaphragm.

I believe that disabling the ACV stabilized pilot circuit fluctuations in the transition from deceleration to acceleration. In addition, I use the backfiring as a tool for tuning the mixture screw.

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Do you mean I should flip this diaphragm and inactivate the ACV?

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The YZFs of the same model don't have it, the casting is on the carb but not used. Being that it's accessable without messing with the carb I would say try it and if you don't like it put it back.

If I had to guess I would say it is on the WRs to run the pilot circuit leaner without backfire on deceleration.

I like it disabled. I can tell exactly what is going on in the pilot circuit and was surprised at the adjustment needed as temperature and/or altitude changed.

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Disactivating the ACV by reversing the diaphragm really helps stabilize the pilot circuit. My 2002 runs perfectly at 750' (40-90ºF) with 38 PFJ and drilled 83 PAJ. With airbox lid and screen removed, some porting, Power Now Valve, FMF Powerbomb SX header, uncorked WR muffler and YZ timing, I run an EKN @ position #2 and 170 MFJ. Judging by your mods, I think the EKP would be a good choice, probably @ position #3 with 165 MFJ.

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