I recently aquired a HSR 42 carb and am trying to decide if I should install it or not. I've read some places that a properly tuned CV carb can make almost the same numbers as a HSR carb. I've read others that the Mikuni makes a huge difference.

I am running an SE aircleaner and will either go to slip-ons or a full exhaust. Also how hard is it to tune the Mikuni?

 

What is the bike and what other modes do you have besides seac and pipes in the future?

 

^^^ this is important for a good answer.

For me, I ride a dyna and when It was stock with SE mufflers and then VH short shots with AN big sucker air cleaner I added the Mikuni 42, the bike made NO extra power and had a overly FAT midrange even after some tuning.

Later on after the HQ big bore kit with cams and head work the Mikuni realy started to shine, I added one other thing to the carb, the HQ Mikuni tuning kit for like 20$, this kit made the overly rich off idle and mid range go away!

Now i can tune pretty much just with the main jet and the occational needle settings.

Doug at HQ runs the CV exclusively from what ive heard and has been using the BIG CVs
with great sucsess. This is with just jetting, no funky Dyno jet kits or other "gimmiks".

so, sometimes it boils down to $$$ and what your comfortable with working on or tunning with.

 

Big thing about the Mikuni is the much improved throttle response compared to the CV. The slide is connected directly to the throttle cable...no vacuum diaphram like the CV. The Mikuni is easy to work on, but there are a lot of things to tweak. Pilot jet, main jet, needle size, needle clip, accelerator pump nozzle, 2 accelerator pump adjustments, idle mixture. Mikuni has an excellent tuning manual on their website you can download, tells you how to dial it in fairly easy. A lot of folks end up with a 17.5 or 20 pilot jet, 98 needle with the clip in the middle, 165 main jet, 50 pump nozzle and the accelerator pump adjusted per the manual.
Downside is the slide rattles...a lot. Even more if you have cams with more overlap than stock.

 

Listen, i have a 1993 fat boy and just now got around to replacing the carb. I did absolutely nothing to the carb for settings and did not change the jets that come with the kit.
My bike has gusto for the very first time ever. I am now going to change my pipes to vance & hines longshots to get even more power.

In truth, i think the entire problem with the Mikuni is in the tuning of the jets and the #1 and #2 pump settings. It is rather confusing, but if you could only find someone that actually understands the Mikuni and knows how to adjust it, then you would be very pleased with the Mikuni.

 

I have also used mikuni's on engines with stage 1 type kit and also highly modified 100"+ engines. Performance and reliability is good and they are easy to tune if you take the time to read the tuning manual. As mentioned earlier, the throttle response is better in the low and mid range than the average CV, which is the most important feature to me.

That doesn't mean the CV's are not any good. I think the CV design is very sound. A factory CV on a factory or slight modified engine can work well with just changine the pilot and main jets and turning out the idle mixtrure screw a bit. I have tried multiple 3rd party jets kits on CV's, which did improved the performance, but also dropped 10+ mpg. I am also very intrigued with some of the new modified CV carbs that have been bored and jetted. However, they are more money than a mikuni, but would seriously consider one of them if I road all the time in the mountains where the atmospheric presure was always drastically chaning.

I think it comes down to budget and what you want your end result to be. I do prefer the mikuni due to their price point and that they perform well on a wide range of engines with minimal tuning. Both are good carbs, so don't loose sleep over it.

 

One think I have found on the mikuni 42 is that putting in a 60 accelerator pump nozzle instead of using the stock 70 will get rid of that richness some have talked about with no noticable performance hit. This will result in cleaner plugs and better mpg. Keep in mind that there will always be exceptions to this depending on the build.

Joe Minton use to sell a PAT (pass a truck) kit that included a mikuni carb with a 50 accelerator pump, mufflers and ignition module.

 

Have seen 111/112 from 95" T/C's, from OE CV's, modified, with razor-sharp throttle response, but have also seen about the same from 42 Mik, as well as S&S carbs as well.
The CV will deliver more torque coming to peak, sooner than a 42 Mik, as we have done back/back testing years ago.
No Holy Grail, or magic carb of those 3. All work very well in the hands of those that know.
Scott

 

Here's a good link to info on the modified 42mm cv carbs. http://www.dudeworld.com.au/ARTICVCARB.HTML
Has anyone out there done a straight bolt on conversion from a mikuni hsr42 to one of these 42mm cv's without changing anything else on the engine? If so, what were the results? thanks

 

I have a 95" w/ flat top pistons, andrews 26 cams and currently run a mikuni 42. Seems to work well but fuel millage suffers. I currently get around 32 mpg. I am thinking of going w/ a modified cv.