Dear rotary heads,

Just installed a mikuni 44phh on my 12A.
Completely stripped, cleaned, rebuild by myself with new gaskets/rubbers. Re-jetted: 39mm venturies, 240 air, 200 main, 62,5 pilot, 90 acc. Fuelpressure set at 0.3bar.

As i had the butterflies removed and re-installed, i wonder if there is a special way to mount them so they are sitting equal. I'm asking because the lowest i can make it idle is 1000rpm. Guess the butterflies are sitting a bit off. How to correct mount butterflies?

I have the vacuum advance disconnected. But i wonder if i can make a connection on the carb for vacuum advance. Acting the same as a nikki: no advance at idle, advance when opening the throttle. I was thinking to drill a tiny hole just behind one butterly. So no vacuum at idle, but when the butterfly opens, and passes the hole: vacuum!
How does this sound?

Greetings from Bart from Holland.

 

My Mikuni has a brass tube on the rear throat near the throttle shaft that is a fitting for vacuum. Not knowing what it was I ran the carb for a little while thinking it was some kind of vent, then I figured out what it was and plugged it. Fixing this vacuum leak increased the idle quality alot and also helped cure my off idle stumble. Look to see if your carb has one. If it does then your lucky and can use it to hook up the vacuum advance, (this is something that I have been meaning to experiment with). Mine is a streetported 13b and it will not idle well below about 900. Other issues like ignition timing, sparkplugs and compression are important, so I would recommend checking them as well.

As far as the butterflies go, first make sure they are facing the correct direction. They are bevelled to seal up to the carb throat, if they are backwards they will not seal properly. Next, back the idle speed screw out, loosen the butterfly mounting screws and make sure the throttle shafts are completely closed and then carefully retighten the butterfly mounting screws. They should be fitting tight against the carb throat.

Hope this helps.

 

no need for vacuum connection. it will run without it.