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Mikuni conversion for Honda XR500

Turning ponies into horses

There is nothing wrong with the Keihin 36mm carburetor. It does its job very well for a very long time. It just needs a new air cut-off valve every 30 years or so...

However, if you want more oomph out of your XR500, fitting a Mikuni carburetor is how you get will the most bang for your bank!

Once you have started playing with less restrictive exhausts, then you really have to fit a Mikuni anyway to see the bike's behavior get transformed.

Do not get into hot cams, high comp pistons and head porting before you have fitted a Mikuni carb, this would be putting the cart before the horse.

I like to tweak my XRs with period parts, so I stay away from the more performant and modern set-ups such as flat sides and accelerator pumps. A good Mikuni VM 36 or 38mm round slide keeps it all the way it would have been back in the day.

Now the best source for a Mikuni VM is one that come from a 2 strokes bike. BUT, the settings of a 2 strokes are VERY different from what a 4 strokes needs.

Genuises and magicians have spent years testing and refining the settings to make a XR500 roar. I took a simple route to get my settings right.


I bought a XR500 tuned by Don Vesco that runs like a bullet train, took the carb apart, documented all the references, bought all new Mikuni innards from SUDCO and fitted them all to the other Mikuni VM carbs I had lying around (38 and 36mm).

So, here are, for your delight (and for free) the Mikuni VM38 settings that I KNOW work very well on my XR500's.


Now, do yourself a favor and use a carb body that has the idle screw on the left...

Check out what happens when you fit the Mikuni in a XR500 engine... :)