Night before 1st Enduro, and I change my jetting!?!?

Ok boys, we got issues on our hands......

This is my progression:

DTM 5th clip position

172 main

200 maj

45 pilot

74 paj

Went to:

EMM 4th clip position

*160 MAIN*

200 MAJ

40 Pilot

55 PAJ (adjustable screw)

At first ride, the bike idled fine, but would sometimes hang up about 200 rpm's high. When riding, throttle response was slow, and the engine would bog if I hit the throttle hard.

Second run:

EMM in 3rd clip position

*160 MAIN*

200 MAJ

40 Pilot

45 on adjustable screw

Engine did not idle high, and the throttle response was much better, but still seems as though I can find a stumble or a bog.

Also, (and Darrin, this will kill you) I have effectivly screwed up my throttle shaft adjustment.

As it stands, to get my bike to idle, I have to turn my idle adjustment screw 100% clockwise. I cannot turn it up any higher, and the bike is idling no higher than about 1,200 rpms. It runs, but barely.

So, on the second run of ajustments, I use the "Throttle Shaft Adjustment" specs that Darrin posted yesterday, all to no avail.

I cannot seem to raise the height of the slide by making this adjustment. I started by turning the idle adjust screw counterclockwise until it was not touching the boss on the carb pulley. Then I backed the locking nut off of the slotted screw, then tighten the slotted screw until it bottoms out, then back it out 1-1.5 turns, then lock with the locking nut. The slide is still at the bottom of the carb, and I have to use the idle adjust screw (the one on the outside of the carb) to raise the level of the slide, and I can only raise it high enough to get the bike to barely idle, not to the 1800 (+/- 100) that I want.


Hopefully I will have this all back together for the ENDURO tomorrow!!!!!


[ August 23, 2002, 03:16 PM: Message edited by: BrandonW ]


Couple of things here...

First, if you were running the DTM in clip #5...then try the EMM in #5 as well (due to the differences in needle tapers, the taper start will be in approx the same position as your old setup with a difference in 6 letters...M - N - P - Q - R - S - T). I was running a stock DRR needle in #3...and now have an EKP in #3 (K - R = 6 letters).

Second, Taffy did some tests regarding appropriate pilot air jet settings for each pilot jet. I believe you're way too lean on your pilot circuit using that 40PJ with a 55PAJ. I run a 38PJ with a try a 70PAJ with the 40PJ. FYI...the bike comes stock with a 42PJ and a 75PAJ.

Good luck...hope this helps. Try searching for those Taffy posts on pilot air jet settings...but if memory serves me correctly, a 40PJ/70PAJ works well.


I went home during lunch, and all that I was basically able to accomplish was moving the needle to the fifth clip.

I have the carb removed from the bike.

How do I set the slide height? Here is one of my problems; the excellent "Keihin FCR tuning page, by Partick Burns"

Click Here for document

states that to sync the carb, you tighten the idle speed screw as tight as you can, as you might even have to remove the locking spring to tighten it as tight as you may need to tighten it.

Then you make your slide adjustments at the top of the carb. BUT,......

On the "TECH EXCHANGE" that Darrin posted yesterday, it says that you "Turn the idle speed adjustment screw counterclockwise until it no longer contacts the boss on the pulley..""

Then it directs you to make the throttle adjustments at the top of the carb.

So, that is where I am stuck. Darrin, you might have to bail me out here!!!! I cannot seem to "adjust" my slide (other than the idle adjuste screw on the outside of the carb) off the bottom so that the bike will idle?!



You only sync carbs if you have more than one on a bike.

Yeah, I should not have used that word. It was the Throttle Shaft Adjustment that I was after, and both documents where describing kind of the same process, and it has me confused.

I took the carb back to the guys in the mechanic shop (those guys have also been a great resource!) and I think maybe I was looking to adjust it like the carbs on my V-Max4 snowmobile. They said that I was adjusting it, but the increments of adjustment are just very small.

I have the needle in the 5th postion (like my stock needle) and I will open up my adjustable pilot jet just under 5/8th's, which should get me very close to the 70 that has been stated.

If this does not work, I will probably have to pull it all out and put the stock stuff back in.

Hate to loose the ground that I have gained in this, so I really hoping that it comes together tonight.


*After reading all posts in this thread, it should also state that that my main jet has been changed to a 160 from the 172*

[ August 23, 2002, 03:16 PM: Message edited by: BrandonW ]

Just my 2 cents, I never do a mod before a race with out testing it out first. Primarily for safety reasons, but not being able to run or run competitively are secondary.

I learned my lesson this year after doing a GP with brand new Race tech suspension, and beat myself to a bloody pulp.

I think the difference between the Burns article and darrin's is that Burns used a drill bit to support the slide as the adj is made. It sounds (I haven't read it yet) that darrin's method is having the slide supported by the bottom of the carb.

The difference being that Mr. Burns must get the idle screw in the ballpark for a slightly opened slide. While the other way you must back it out beyond normal settings to accomodate a closed slide.

Clear as mud?

You may be better off running with familiar jetting on your first enduro though.

I get best results with PAS opened relatively more, with a smaller PJ. Very closely matching with Taffy's results from the jettingQ's thread.

I don't remember reading results with Taff jetting and the 200 MAJ, not sure how that will balance out with everything else.

When I got home last night, I put it back in (5th clip, 70 pas, 1 turn out) and it was mostly good, but not acceptable.

The idle was adjustable to 1,800, it dropped to idle well, but hammering the throttle created a bog. I would guess that it has something to do with the 200 maj. I did not have a 160 (I almost thought about trying the adjustable air screw over in the main side, but ...) so, I ended up placing the stock jetting back in the bike. It is running well, so I think I need to redo that some other time.

This was a silly time to attempt this.....


i think that going to a 40PJ with the 45PAJ makes it very rich at the bottom and therefore introducing more air via the PAS is the way to go so turn that screw out to 60 or 70 PAS.

to set the slide i would turn the slide screw all the way out and then when it picks up the slide it should be turned in 5 turns which is about 5mm i think (could be wrong there).

point is that you need a tickover just to get tuning!!!! so you may need to whack it right in and then start from there. you'll know when you've gone in the right direction because you get a crazily high idle and you'll need to reverse everything.



Youre right.

The adjustments to the carb slide adjuster are made in very small incraments. So if you go 1 turn from where youre at clockwise or counter it is going to make a big difference in the idle.

In my case, there was no idle, so I had to go counter clockwise as you suggested and that cured my problem.

I wish I could give you more advice but Im not real steeped in carb knowledge sice I have not fiddled with mine that much.

Good luck and I hope one of these jetting guru's on here can get you to where you want to be.


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