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Monday, April 1, 2013


Pre-blow up, my chopper was a 650cc machine with twin 30mm Amal carburetors. Post-blow up, she is a 750cc machine, sporting a single 34mm Mikuni round slide. Not knowing a bunch about Mikuni carburetors, I consulted the lads over at the Brit Bike Forum. After a brief description of the motor, I was given a good starting point to set up my new Mikuni.
Now it's just a matter of tearing into the Mikuni a little bit, and finding out what jetting I have. Then it's off to see my new friend at the dealership for jets. I hope she can get them, because searching for the exact one's on my barely-faster-than-dial-up internet is a real pain.

My new 34mm Mikuni, with the top and slide removed. See the three small holes at the bottom of the main bore? The one to the left houses the air correction jet, it's a tiny little bugger.

The slide and top. The jet needle is captured in the slide, and can be moved up and down by moving an e-clip into different grooves for fine tuning.  It was recommended that I start with a number 3 slide, that's a 2.5.

The tiny little air correction jet.

With the bowl removed. Dead center is the main jet, just to the right of that is the pilot jet.

When you remove the main jet, you can push the needle jet out of the body. The needle and needle jet work together to control your fuel mixture from about 1/4 throttle to near full throttle. It's important to get them right.

This is one of my Amal carburetors. I had these modified a while back to use Mikuni slides. The advantage of which is that the Mikuni slide is chrome plated brass, and therefore much heavier and less prone to sticking.

Then a thought struck me. 30mm-34mm Mikuni carburetors use the same size slide! Well, my 30mm Amal has a number 3 Mikuni slide, why not use that? Well, I forgot that the slide was modified to fit the Amal body. There is a guide brazed into the top of the groove. I would have to remove that in order to fit it back into a Mikuni carburetor. But then...I wouldn't be able to use it in my Amal if I was ever to put it back onto an engine. Damn. Oh well, slides are only $25.

Consult the book for part numbers! Lots of tuning and part number charts in that book.
And remember, kids...don't use your motorcycle carburetors on your airplanes!

Now it's just a matter of ordering a few jets and a slide. I have to pick up a part for my Aprilia today, so I'm going to consult with the parts clerk at the dealership and see if she can get me what I need. If she can, she'll be my new best friend (I'm sure that's honor she's looking forward too).

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