KDX unusual jetting question

[M0T0MAN]

Hi guys I've been looking aroiund different forums and sites to find the jetting recommendations for my 1991 kdx200 but everywhere says you should run the bike with 155 main 48 pilot 1173n needle in middle clip.

My bike ive been running like it is for over a year now (since I bought it) and the jetting is quite different to what people recommend. I have an FMF fatty pipe with the airbox lid modified. And I run a 158 main jet, 52 pilot and a 1172n stock needle in second from top clip position. It runs fine and has plenty of go but the pilot does seem somewhat odd in comparison to what people recommend.

I ride sand that can become quite thick in some places, And im using a premix of 40:1 with fully synthetic motul oil.

Anyone have any ideas on what I should be running or if it is fine as it is.
Also any settings that could be modified like the jet needle without replacing it.

All input appreciated, thanks

 

[76GMC1500]

Sounds like KX jetting. Did someone put a PWK carb from an older KX250 on there?

 

[M0T0MAN]

Im not sure

im not sure maybe ill check thanks that info

 

[2 strokes for life]

If it aint broke dont fix it. But, if it is meaning to you then i would mabe go down one or so down on the Pilot. But, if it has a KX250 carb the better.

 

[adam728]

All bikes will be different, jetting recommendations are only a base to get you started. If it works, use it!

Have you fiddled with the air screw? The setting of it will tell you whether the pilot is rich, lean, or right on the money.

As for "KX jetting", well, I don't know about that. If a larger KX250 carb was put on the bike you would have to go much richer on the jetting. Smaller engine pulls less vacuum through the big carb, which means less signal at the jets, which means larger jets must be used to get the same amount of fuel. For the same reason a bike will often end up with smaller jets with a big bore engine. If you went from a 35mm to a 38mm carb you would have jetting no where near where people recommend for your bike. I would bet the main would be at least a 165 to get it to run out on the top end.

My carb went from a 33mm to a 36mm. My main jet went from a 145 to a 158.

 

[M0T0MAN]

Sorry about the length...

One more question, I bought a 45 pilot from the kawasaki dealer today and put it in my bike. My jetting is now a 45 pilot with a 158 main and the needle set 2 clips from top. I started my bike up with the new pilot in it and turned the air screw out, I counted how many turns till its fastest idle and it was 2. Considering I went from a 52 to a 45 the air screw still seems to far out. After starting it and running it I took my plug out and had a look at it (I dont know if this is remotely useful as it was not a plug chop) the plug indicated me running rich it was black. Do you think I should go even leaner in the jetting, that would be going against what fredette recommends. Do you think I should ride it first to make sure it is at normal operating temperature or maybe I should raise the needle clip (lower the needle). Im not an expert in jetting would appreciate some suggestions thanks.

 

[CaptainObvious]

Jetting is more art than science. If you have a set-up that works for you and your bike, it doesn't matter what others are running for jets.

Do you suspect that there is a problem with your jetting?

 

[M0T0MAN]

yeah because my pilot was a super rich 52 also my throttle response does not have the snap I would like to lift my front wheel over objects

 

[KDXLance]

I am in NZ also and changed the stock jetting to 155 main, 45 pilot and 2nd clip from top on stock needle. This gave me the snappy throttle response that you are looking for . You will hear people say that jetting is specific to each bike but you will not be far away with 155/45 jets. You will not seize an engine by being too lean on the pilot any how. The main jet was the most dramatic power increase $7.95 can buy.

 

[DWreck]

I can't help with the specifics for your bike but typically you will need to jet a little richer for sand because of the extra load on the engine. When you figure in the different combinations of pilot/main/needle with 5 clip positions it can get confusing. Make sure to write down what you have in there and the air screw position, temperature and what you like don't like about it. That way as you make changes you can compare different combos to each other and not get confused.

 

[paab]

I think the 91 needs leaner jetting than what you've got. I just got mine sorted pretty well after lots of testriding and plug chops. I ended up with a baseline set-up of:

40 pilot
CGK needle on the second clip
air screw 1-7/8 out
148 main

The bike has improved by leaps and bounds. It's worth the time to get in the neighborhood of good jetting.