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Boyesens Jetting


dannyb
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Just installed some power (dual-stage) boyesen reeds in 14 evo 300. Followed instructions it said the jetting will need one bigger pilot, one smaller main.

I put one bigger pilot in but left main (a 50 and 125 in there now) but bike still feels lean. Everything else standard (needle on 4th clip, air screw 1.75 out)

Anyone else put a richer needle in or bigger mains?

Also just repacked silencer - don't know if that would affect it

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The instructions I got with Boyesen dual stage reeds that I fitted to Evo 125 and then 2012 Evo 200 (PWK 28mm Keihin carb)was that the "Boyesen reeds tend to make engines run rich, with the main jet being most affected". I ended up with a slightly different needle (jjj) and with the needle in the third position (middle), one step down on both main (122) and pilot (45). But to achieve that I followed a logical process and also used a spreadsheet from JDJetting that modelled the fuel flow. The process I used worked for me (search the forum and you should find previous posts) and then confirmed and adjusted with riding - note we ride basically at sea-level (no more than 400m alt). For example, on the stand the ideal was 2-sizes down on the main, but wanted to be sure that on long runs between sections that the main was slightly richer so went up one more size (up to 122). May be different with the 300 of course and all bikes may be different as well.

Also, if not genuine Keihin jets there may be differences in quality control of the size of the jet - so I am told.

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Those are definitely signs of a lean pilot circuit. When i rode my stock 09 290 EVO at sea level it ran a noticeably lean. Im sure the dealer here installed a fifty before i took delivery. He also lowered the floats a few millimeters. At very high altitude I installed the Boyeson reeds and went one up on the pilot from the dealers delivery setting. Im pretty sure i am using a #52 pilot. I left the needle and main alone. High altitude jetting is different than low altitude jetting. My air screw is 2 1/2 turns out. Try one more larger size pilot to see if you can get the air screw out to 2 1/2 turns out. Some may disagree with this, but i have found that my 290 is smoother and noticeably easyer to ride and the plug looks fine no fouling.

Edited by liviob
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So after an afternoon of tweaking and testing I ended up with the following 50 pilot, jjg needle on third (middle), 128 main and air screw just past 1 1/4 out. I tried same jets but with a standard needle (jjh) which felt smooth but just a touch too lean still. I'm awaiting some larger pilots/mains and when I get these I might experiment with standard or leaner needles on 3rd or 4th clip.

128 and 50 were largest I had in my box

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