I am finally getting around to doing some jet checking and tuning with the NGK AFX a/f monitor. I'll start with the 36mm that's on the bike, but also use the magic box to play with the CVK34 and the 40mm Mikuni waiting to go on.

After the carbs are dialed in and timed over a short sprint course, I'll do the cam mod and see how it's affected the mix on all the carbs at steady throttle positions before and after the cam mod. I see that I can replace the needle hold down plate's 3mm allen screw with longer ones to make an easy throttle stop and 1/2, and 3/4 - maybe even 1/4 if I can mate a couple screws together to give me something long enough.

That way the throttle will be in the exact same positions before and after the cam mod, and the readings will give an indication what's happening to the a/f ratio after the mod. Once I install the 331 kit sitting here, I'll also be able to see what the +80cc does to the a/f ratio.

This isn't going to be fully completed soon, but I'll post what I am seeing as I go along.


Yesterday I tried the TM36 with the jetting you see in my sig and saw surprisingly steady high 11 a/f ratios just about everywhere including WOT. A little rich but no burbling or anything; it runs fine. The bottom of the O2 sensor bung plug was sooty when I first took it out though, and I don't think I am leaving the choke on too long when I first start it-just 5 seconds or so.

So I thought I'd try the leaner P4 needle jet instead of the P6, mostly because I thought I could remove it out the bottom of the carb without taking the bike half apart, and because with luck it'd just lean everything out throughout the rev range. Also because the needle's taper seemed so darned perfect-just a little rich, that I didn't want to disturb that right away.

The needle jet had enough clearance to come out with an allen wrench in the backside of an 8mm socket, and it was an easy change.

I just got back from a test ride with the leaner P4 needle jet, and while the mid range leaned out to mid 13/14s with the smaller needle jet from previous high 11s , the a/f ratio at WOT is still hi 11s with a low 12 registering only now and then.

I may ride it around town wired up tomorrow a bit to watch the box some more, but generally speaking the leaner needle jet leaned out the mid range without disturbing WOT much at all. Todays' leaner test runs lofted the front wheel on the 1-2 shift what seemed to be a little longer in the air, and the bike accelerated great. It may take some timed video testing to actually know the difference.


This a/f monitor is the berries. No more mentally analyzing a mod via sotp and asking yourself over and over how it "felt". It's over so quickly too.

Almost effortless.







I am about 100' ASL, with a drilled air box and using gas with 10% ethanol of some sort. That's all they sell here.

 

Outstanding!

 

I just found a chart for ethanol mixes telling me that 12.2 is the best for max power at WOT..





A P5 needle jet would probably be just right, but they don't make one.

 

That 135 may get 12.2 and the P4 needle will keep the fuel economy up..?

 

Or ... leave the 137.5 alone and go back to the P6 while leaning the needle a half or whole notch..? The main jet is darn close to the 10% ethanol max power 12.2. It's obvious the P6/needle combo is rich as is, so though it's a bit more tedious to change the needle-at least the results can be read quickly.

I'd say I was closer to where I want to be with the P6 than with the P4. Not by much perhaps but worth fiddling with the needle next time and going back to the P6

Just to see what happens if nothing else

 

It appears the P6 is so aggressive that the bike pretty much runs off the main jet..? While the P4 is definitely metering...? If so perhaps the P6 with the 135..?

Seems like the needle - as usual - is not involved in WOT metering, just the normal regular range up to about 75%...?

 

I'd think the needle combo is doing its job with the P6; it's just a hair too rich.

I just remembered that this 9EBY1-51 needle I have here is a step leaner than the 9EBY1-50 that's in it. I'll put that in today with the clip in the same middle position and see what happens. It should have the same nice taper but be a little leaner after I put the P6 back in it at the same time.

I'd tried the 51 needle before and thought the 50 'felt better' but it's time to see what it's actually doing

 

Or maybe not?

Both the needles and needles jets are sized in .01mm increments. Going to the smaller P4 needle jet from the P6 leaned the mixture by way of its .01mm smaller hole.

So it seems then, if I reinstall the .01mm larger I.D. P6, and add the .01mm larger O.D. 51 needle at the same time, I don't think there'd be any a/f ratio change because the net clearance is going to be the same as where I am now.


But hey, the current P4/50 combo's 13.5 - 14.25 part throttle readings aren't such terrible a/f ratios; actually pretty good if you think about it. Close enough that changing it further will be as much to see what happens rather than expecting a hp gain


I may raise the current needle a notch or shim it half then test the a/f since I have to take the bike apart the bike to change carbs anyway; or just just leave the 36mm as is for now, and instead try a/f meter on the other carbs.

 

I noticed today that the 36's a/f numbers are lean for quite some ways as I roll it up past idle (idle a/f is good), yet too rich when it hits the AP. Next time this carb's apart I'll try swapping the #45 AP nozzle that comes in it for a 35 just to see what happens. Since the carb's sort of intended for much larger engines it wouldn't be a surprise if the #45 nozzle is larger than what's necessary for the KLX.

Then once that's done, I'll pull the carb top off and richen the needle a notch or 1/2.

Could be a sticky wicket to tune for gradual throttle roll on from idle, and try to get good a/f numbers while the AP is adding its booster shot at the same time.

 

Richard, isn't the AP going to create a short lived extreme rich every time?

I wonder what you tune the AP to produce?

I guess you could disconnect it for part throttle AFR testing...?