I am running a mikuni hsr 42 mm carb. jetted it down as lean as I dare and I get a whopping 30 mpg with a bassani pro street pipe. Dyna adj. ignition, S&S 510 gear cam . I would be interested in anyone elses experiences with this carb. Has great performance . TERRIBLE gas mileage.

 

I don't have the complete answer but I remember hearing of this 30 m.p.g. problem and it had to do with the choke linkage. I know two guys who had the same problem and gave up. They went to S&S carbs and say they lost performance. I run a 45 Mikuni on my Fatboy with a pretty hot motor and get well over 40 m.p.g. I use the stock harley choke cable but it's been over 5 years since the install so I can't remember every detail.

 

I put the same exact carb. on my '97 Fatboy, ran really good, but terrible gas milage.

 

Mikuni carbs aren't really for gas mileage they are to give you maximum throttle responce and HP. I haven't heard about a problem with the choke cable but that could be a possability. What do your plugs look like after 2000 miles? They should be a medium light brownish color if they are dark then you could be running rich and if you jetted it lean then the choke problem might be something to investigate.

 

I have an HSR42 on my '94 Evo. With "stock" jetting, I got between 38 and 42 MPG (compared to 50+ MPG with the CV carb.

I rejetted the carb by installing the Joe Minton designed "Mikuni mileage kit". this consists of a #98 (leaner) needle, a #17.5 pilot jet (instead of the #25), and a #50 accelerator pump nozzle (down from #80), then set the accelerator pump rod to zero clearance, so the pump comes in sooner.

After these mods, I get a pretty consistent 45 MPG, and the bike runs great in warm weather, but the bike is noticeably cold blooded in cool weather, so I may go back to a #20 pilot jet.

 

I run a Mikuni and could care less about mileage, I'm more concerned what the feel is like when I twist the throttle

 

Opps double post...

 

I would have to agree with that ^

 

Hahahaahahahaa yea bro high performance = shitty milage, but remember running lean is bad for the engine

 

It has been a while but I ran a 93" Evo with a Rev Tech 40 cam, 10.5 compression, Thunder header and a Mikuni flat slide for years and it was 40 mpg bike on the highway. Never touched the jetting, just slapped it on and ran it for years.