mikuni jetting for six-day

[Rick/calif]

does anyone have some jetting specs and mounting advice for converting the bing on a 72 six-day 125 to a mikuni, say 30mm? thanks, rick

[tomale]

Hi rick,
I did some research on the strenghts and weakness of such a change for my 250, what I found was although the Mikuni is a very good carb, dyno tests showed that the Bing actually netted more horsepower on the top end. that I would think would be important I would think. If I remember right, at low speeds the makuni did a little better job. the difference was not that much considering all the work it will take to make the change. Getting that carb to meter right is a lot of work. Something else to think about, hopefully if you do get some spec. They will be at best only a starting place because they may not work for your local. It is not just elevation but humidity as well that can effect the jetting.
I hope this is helpful to you, good luck

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[Dwight Rudder]

I don't have the specs but from what I have seen on the 125s the Mikuni conversion is a must. You may lose a bit on top as the Bing is a better high rpm carb. But the increases in the low / middle rpm range far out weighs the losses on top.

Dwight Rudder
7 time ISDT / E medalist
7 time National Enduro Class Champion.

[LINDEMAN]

Rick,I have used the stk. bing 27.5mm and a 30mm bing on a stock 125.I also tested 28mm and 30mm mikunis.I preferred the 28mm mikuni.It was from a yamaha DT-175 I think.The bigger carbs may make a little bit more power on top but not worth the mid-range loss which is significant.I ride sportsman 125 Expert and have learned that you cannot beat the CR,s with top end power.You have to pick smooth lines and keep very high corner speeds.Which is possible thanks the the superior handling of the Pentons.The 28 makes great mid-range power and enhances this riding style.We all know smooth is fast!It also works much better for Hare Scrambles type riding.Anyway here is what works on my stk.125 with 28mm mikuni. Sea Level-165 main,60 Pilot,2.5 Slide,5EI4 Needle 2nd from top,Air screw 2 out.B8HS plug.In Denver area where I live 5500ft.I run a 155 Main,50 Pilot,Needle top.Good Luck!Dave