re jetting sequence

[yarrowkevin]

I want to clarify this before I start to try to jet me bike,
the first jet to adjust is the MAIN
second is the clip position on the jet needle
third is the pilot
and to top it off is the air screw

I have read all the info but dont want to start bass ackwards if possible
:worship:

 

[Rhodester]

There's a few who jet from the bottom up, but most probably jet from the top (main jet) on down. Your top down method will get you pretty close so you can fine tune with different combos. After 8 main jets, 5 pilots, and 9 needles, I just bought 4 more needles to continue the logging and learning process. My last session brought me to 42 pilot, air screw 1 1/4, DEJ/5, 155 main @ 75 degrees and 2600'. My main is just barely rich to bring out a smooth bottom end and soften the hit tendencies of the 'D' needles.

 

[canyncarvr]

You're down to 2.685mm? That's skinny.

What's the cut on your throttle valve?

re: 8 mains, 5 pilots, 13 needles......

Yeah. Isn't this fun?

I agree!! ;)

 

[Rhodester]

CC, you may remember that I have a low end hesitation problem that I've been fighting for the last year. I've made headway on it in several small ways (base machining, head mod, timing, pipes, silencers, etc.), but have only been able to change the hesitation (when wicking it) to a moderately pulling flat spot by running too rich of a main jet with my needles (xEx) in position 5. The trade off is that I've been too rich not only on the main, but also where I just start into the taper section of the needle. That's not too good of a trade off in my book. Up until recently I've had a hard time believing that I could run so much richer of a straight section without more richness in that area of operation of running as well. BTW, I ground my slide progressively and eventually down to a 7 or just barely shy of it.

It seems that to kick that main jet in effectively when wicking it I need to get that needle farther out of the main jet as soon as possible. The drawback is that when not wicking it I'm blubbery rich when first getting onto the taper. I've gone from several B needles to several C needles to extend the straight section lower onto the needle and yet have more of the main exposed as soon as possible on the end of the taper as well. I've made progress, but not enough.

I've been reading about how you've been experimenting with richer straight sections and 'D' needles with good results so I took the plunge and left that CEL/5 behind and reluctantly started the whole testing process once again with D needles. So far I'm again making progress and going in the right direction.

With the D needle I'm getting less spooge when running on the straight section and upper part of the taper section. I now can be a leaner on the main without too big of a penalty in the area of a flat spot when wicking it. My power has also increased significantly. It likes to be ridden more like a 125 mx even with a -35 pipe. The drawback is that it's developed a hit a little before the KIPS opens. With 1 step richer on the main I can broaden the hit and slightly decrease the flat spot tendency some more. That seems to help bring back some of the woods characteristics of the power that I like. The DEK seemed to have a little more flat spot tendencies than the DEJ so that's what I'm running with now. Who knows, I may end up even trying some E needles before I'm done with this!

...and yes, I'm having a really good time playing and learning. I guess for me half the fun is making the thing run better and better. I think I'm hooked. :-)

 

[shr]

Call me crazy......., BUT! a EEK needle is a good starting place to try out. I have only been able to convince one person to try this needle idea and he thought I was nuts, but guess what he loves it!

Note this was on a 38 mm PWK and runs in the sand most of the time.

Thank you for your time.

 

[canyncarvr]

I'll bite! EEEeek!! Here we come! ;) Thanks for the hint SHR!

Rhodester: Thanks for the input. I always appreciate reading what you have to say.

You say 'head mod.' What did that consist of? I doubt you would consider taking some metal off the mating surface to be a 'head mod,' but I'm asking anyway. If Ron did it, fine. The point is to be sure (like it matters if I'm sure about anything on your bike) it was done right. Ron has said that kdx heads vary a whole lot volume-wise. If yours hasn't been redone right with attention to squish angles/depths and such I'd be wondering about it.

What are you running pilot/main-wise?

There are other kdxr's that find their bikes to be 'off' from what is 'normal.' Just goes to show you the variance between this-that-and the other bikes. Probably a lot to do with individual tweaking styles, too.

The important thing is that it works to suit you. Yup... sounds like you're headed in the right direction for sure.

I went back to a (sorta) baseline 'B' needle (R1174K) last weekend to sort out some new jetting problems of my own, those 'problems' a result of cylinder porting. Once I get back to known territory I'll be back in the 'D's again. Probably try an EEK myself. Looking at JD's plot of an EEK it is exactly what you would expect..leaner longer (throttle advance-wise) due to the sharper taper angle, and for the same reason richer on the top end of the throttle, both of which I'm looking for myself.

BTW..the above needle description not for your benefit (Rhodester) cuz you know it already....but for the casual otherwise-unknowing reader.

You don't say exactly which 'D' needle, but do say xEx. Using DEK as an example, the needle profiles of the EEK/DEK match a hair past 3/8's throttle which is real close to JD's hint of matching diameters in the 1/4-3/8s area when changing needles.

Forgive my not recalling...but do you have Ron's modification on your carb? I don't recall and won't go looking to see if you've said. You will find that his (Ron's) modification to the pilot circuit is a big help in tuning the area you're dealing with because the airscrew comes so much more into play.

And, if you already have it, DO look for the #2 sweet spot in the pilot circuit. It's around 2+ turns on the airscrew. Spend the time it takes to find it 'cuz it's worth the effort. That will lean out the

...when not wicking it I'm blubbery rich when first getting onto the taper

and get you a real strong mid-throttle pull that will

...help bring back some of the woods characteristics of the power that I like.

Another BTW..

I need to get that needle farther out of the main jet as soon as possible.

You are getting the needle out LATER with a 'Dxx' and later still with an 'Exx'. Once it starts it progresses faster (compared to a 'Cxx).

That is one point of what you say that I don't unnerstan.

 

[Rhodester]

CC, I had the base trimmed to lower the overall port height (albeit minutely) as suggested by E.G. and also relieved the head for piston clearance and a compression raise. E.G. did the work. It only raised my compression 8lbs. though because I specified 91 octane pump gas as the fuel I'd be running.

I'm using a 42 pilot, AS at 1 1/4, and a 152 or 155 main depending on temp.

I haven't yet popped for the RB mod yet. I'll probably go for his complete Air Striker carb if I decide to go that route. Even with my stock carb I see that the air screw seems to come more into play as I get closer to that sweet spot on jetting that I'm looking for. I know it's no where near as sensitive to the AS as Ron's carbs are.

What I meant by getting the "needle farther out of the main jet as soon as possible" is that I'm running them in position 5 as opposed to a leaner clip position. I can get almost as good of a result (with the flat spot) by putting the clip in #4 and running 1 main size richer, but not quite. I've found that the bike seems to run leaner below 1/8 throttle with a longer straight section (L1) which is one of the things I'm shooting for. The D needle provides me with just that and still has a fast taper angle to provide lots of vacuum signal to the main jet as it 'gets out of the way' quicker with that skinny tip...if that inadequate description makes any sense. It seems that a long straight section tends to compensate for the rich diameter of the straight section in my experience. The longer the L1 the narrower it can be without blubbery rich results at and below 1/8 throttle. That rich diameter seems to be helping with the flat spot problem and is the most effective solution I've tried so far. The #7 slide is easily the best fix for richness from 1/8 to 1/4 or 1/2 throttle. It was a very noticeable effect.

In an E length L1 (meaning BEx, CEx, or DEx) it seems that I get a hesitation at position 3 or sometimes 4, a pronounced flat spot (usually) at position 4, and a reduced flat spot or moderately decent pull at position 5. Diameter changes (Q though around M) made only a small differences until I got below about an L diameter. Then things started to change enough to see the differences more clearly. I tried a CCN and CCJ, but raising them up beyond position 3 (same position as 5 on a CEx needle, for the uninformed) just created too much richness in lower throttle positions to make it worth considering. A DCJ or especially an ECJ may be worth trying, however.

As you can see there's allot of 'seat of the pants' trial and error here. I think that jetting just may be some art and not all science, if ya know what I mean. It's hard trying to describe sounds and sensations in these little nuances of jetting changes. Hope I made some sense.

 

[Porter]

Sweet spot

CC,it's interesting you mentioned the #2 sweet spot.I've realized in the last month that my bike is always running good with my jets set for temp and two(+/-) turns out.After having the head done by ron for pump gas I had trouble with needles,so I went back to the 1174.My current set-up is 45/1174#2/152@75*.The carb is stock35 w/#5 slide.-35 pipe.Now it seems like once I find the needle and clip position I want for delivery of power then I change my jets for temp,like it being 68* and running a 155.Or it being 82* and running a 42.Isn't that jeting from the needle out? :laugh:

 

[canyncarvr]

Rhodester said:

The longer the L1 the narrower it can be without blubbery rich results at and below 1/8 throttle.

Yup!

You made perfect sense. It's good to read of someone's decent attitude and work toward jetting.

You'll really enjoy one of Ron's airstrykers.

Porter:
Sorry..I don't understand the question. Maybe it's only rhetorical......

The -35 takes a considerably leaner jet set than the -30 does. Pilot jets aren't going to make much difference in overall air/fuel requirement changes that come about by temperature changes. That's not to say you won't benefit from changing them for such...