For those of you that have the mikuni 42 mm carb can you tell me how you like and if it has made any differanc in your performance
Thanks

I don't have the 42, but I have jetted and ridden several Road Stars that did.

The 42 doesn't add any appreciable numbers to either Torque or HP. The reason people like it is primarily improved throttle response and faster acceleration. It takes the CV portion of the carb out of the equation, so eliminates the throttle lag while the slide catches up to the air valve (stock carb throttle plate control the air valve). The 42 throttle plates are hooked to the slide itself which functions as/for both air valve and needle adjustment.

The bikes I rode had really good, and slightly more predictable throttle response. It feels like your more in control.

The downside is that the 42 can be more sensitive to altitude changes.

Its on my list for the project bike.

Thanks Gram for the feed back

Like Gram said....
I have a flat slide and love it. however, the hsr has no accomodations for the tps unless you mod it somehow..I use a voes instead...but I've heard thru the grapevine that a member is currently writing up a tech article that will address this...I'm anxiously waiting..

Just put one on my 06 Roady. You really need to have the whole package such as pipes, BAK, etc. You will feel the difference in power at the top of the low end and mid range. The big difference from what I understand is when you go to a bigger displacement and worked heads.

I held one last week at the mikuni display in Daytona it was a nice piece, seemed much cleaner and simplier then the cv40. I've heard a big reason to install one is to get rid of your fuel pump? If so does it come with a 2.5mm float valve?

If you get it from yamaha, the speedstar version is set up for the fuel pump, (smaller float valve) if you want to do away with the pump then you need the regular version that is sold for HD's......

eblack wrote:
I held one last week at the mikuni display in Daytona it was a nice piece, seemed much cleaner and simplier then the cv40. I've heard a big reason to install one is to get rid of your fuel pump? If so does it come with a 2.5mm float valve?

As Flash said, the Yamaha version is setup for use with a fuel pump. As are most that are sold for Road Stars even from other vendors. The advantage they have is that they are designed to be used with the Road Star cable ends. The HD versions require cable replacements.

Unlike our BSR40s, the 42mm has a ton of parts available from Mikuni distributors that you can use for rejetting, including replacement float valves for a variety of requirements. So its real easy to get a replacement needle/seat for the float bowl.

There are also a few options on the main needle depending on usage and requirements, so aftermarket jet kits are just not needed for this carb. All the parts you need are available directly from Mikuni through their distributors.

The 42mm belongs to Mikuni and they own all rights to distribution. So they make the stuff we need available to us. The BSR40 is made by Mikuni, but distribution rights belong to Yamaha so Mikuni can't sell it (or any parts for it) through their normal distribution.

If I get one for the project bike, I am planning to buy a Yamaha version (Speedstar. Barons etc..) and replace the float bowl valve. Its cheaper than buying new cables and there will be less to mess with. Only saying if because I am also looking into S&S and Weber options too. I really like the Weber but it is going to require a lot of mods to work with the Road Star, and the S&S needs manifold adaption. So the 42mm is going to be the easiest route.

42MM Parts diagram, Needle Valve (float bowl valve) is #69:
42/45/48 mm Parts Diagram

42MM Parts list, including various options. Look at the Needle Valve options at the bottom:
42/45/48 mm Parts list

Gram, I'm sure you have looked into the genesis carb, have you had a chance to see one in action?

Flashback wrote:
Gram, I'm sure you have looked into the genesis carb, have you had a chance to see one in action?

I had never heard of the Genesis carb until now. So googled it and found some stuff on it. Wow...

That looks incredible. Its a fine tuners dream come true.

Thanks Flash!! I will dig into that and see what I can find out.

Gram