Machining Project: Boring VM26 Carbs To 29mm

A while back I wrote a small piece on boring carb bodies. With the current price of 29 Smoothbore carbs lately I figured I would try boring out a set of 26mm to 29mm and see what happens. Some of you wanted pictures (as always) so here are a few shots of the carbs getting machined. Just so you understand what your looking at . The first pic is in my CNC Lathe getting bored to the 29mm diameter. The next is in the mill getting the recess in the bottom cut deeper. This is a critical step , if you don't do this the slide won't drop far enough and the bike won't idle under 2500 rpm. I have a set of these on two of my bikes and it make seems to make quite a difference.

After machining you have to raise the needle to the bottom clip . Since now the slide sets lower in the bore, otherwise it will be way too rich. So what do you guys think?

Does the slide clear the top of the carb?

I think its cool but I want moar pics!!

Yes, the slide only sits aproximately .07 lower in the bore. There is plenty of range of motion to get slide all the way open.

More pics? OK here is 1 more showing the difference in bore size. 26mm on the left 29mm on the right .

Looking good. Have you used them yet? Results?

Yep, put them on my 77 kz1000 1015cc with 10.25 wisecos. Pulls great! runs better than ever.

Excellent! Always nice to have something work out that well!

nice mill work.bj

Excellent info Dshelly. I'm glad to see that I'm not the only person on here who's not afraid to do a little Mikuni machining.

Did you chuck directly on the casting where the carb boot would normally clamp, or is that a jig that the carb bolts to for the lathe work? Do you find that the carb bore is fairly concentric to the outside of the casting for the boot?

it looks as though you did not offset the bore at all,is this true?

was the clip change and the machine work the only things that changed?

i am glad that you have done this and posted the pics,
thanks for answering the questions as well.

leon