Mikuni carb conversion questions for 73 125

[Ron]

Hi Ernie,
If you look close at the pics of my bike you can see a aluminum block that is welded to the cylinder and then bored out to 30mm.
It uses a Mikuni rubber manifold. It was that way when I bought the bike, but its a neat set up.
The rubber manifold is #VM-34-200.
Unless your going to bore the intake on your cylinder, I'd stay with the 28mm. The 28mm probably works better on a stock cylinder.
The stock boot fits the back of the carb, but I had to cut a ring off the large end and then use a hair dryer to stretch it back on the airbox.
RonW

[Ernie Phillips]

I searched the POG on Mikuni jetting and results can be seen at link  below.

http://pictures.aol.com/ap/singleImage.do?pid=c060XSuUTqrrxPgwkZuYlTOlDXjmtGxpl*y5v4xQp5Fd3Ig%3D

On Christopher's 6B with 28mm Mikuni, we went down to 165 main from 180 and we are now good to go.

Ernie P.
Chattanooga, TN

[chuck]

170 to 270 on the main jet. How is that possible?

Chuck,


72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore

[Ernie Phillips]

Chuck,

I just tabulated the results of the "search."  It is intended to be an aid for someone jetting their carb to get in the "ballpark."  There does seem to be a very wide spread of main jets on the 30mm.  Donnie S and RonW use 170/180 in the 30mm, so that is what I would use as a starting point.  There are just so many variables; state of engine tune, altitude, compression ratio, pipe ... use it as a guide.

Ernie P.
Chattanooga, TN