Mikuni VM34

FastFred · Sep 4, 2011

Well I have done a 1000 miles now on the above carb and my spark plugs are a perfect colour when on the needle cruising. The bike though is still a little tricky to start. It's kind of too warm for the choke and too cold without. I generally now kick it a couple of times on the choke then knock it off and start without. I then have to warm it up without the choke or sometimes I have then switched the choke lever on (down) and let it warm a a little but not too long as it will choke up. The pilot is the recommended 35 and the bike is a 850. It feels like the pilot is too small but then it feels woolly on the cutaway. DynoDave on here quotes the 3 cutaway is too rich... I'm a bit lost at the moment. Will a colortune show the state of affairs otrr are they not dsensitive enough. General running is perfect but it's just the starting.

1up3down · Sep 4, 2011

Hi Fred, I ran a Mikuni 34 on my 850 for 15 years.

Your 35 pilot sounds perfect to me, # 2.5 slide is optimum, air screw anywhere from one to one and half turns out.

Starting: With a cold motor, try putting the choke and ignition on and give a good full kick while also opening up the throttle about half way. I found that plenty of gas needs to be sucked in right away from the open throttle, and the choke really aids in holding an idle immediately from cold. After lighting up, I would right away turn the choke off and keep the idle around 1300 just by your throttle hand for about 30 seconds then ride off.

I think people assume that just putting the choke on, thereby reducing the air to the starting circuit, is sufficient.
Not so in my opinion with a cold motor, a nicely open throttle plus the enriched mixture with choke on always had mine lighting up on first kick.

slupdawg · Sep 4, 2011

1up3down said:
Hi Fred, I ran a Mikuni 34 on my 850 for 15 years.

Your 35 pilot sounds perfect to me, # 2.5 slide is optimum, air screw anywhere from one to one and half turns out.

Starting: With a cold motor, try putting the choke and ignition on and give a good full kick while also opening up the throttle about half way. I found that plenty of gas needs to be sucked in right away from the open throttle, and the choke really aids in holding an idle immediately from cold. After lighting up, I would right away turn the choke off and keep the idle around 1300 just by your throttle hand for about 30 seconds then ride off.

I think people assume that just putting the choke on, thereby reducing the air to the starting circuit, is sufficient.
Not so in my opinion with a cold motor, a nicely open throttle plus the enriched mixture with choke on always had mine lighting up on first kick.

I'll be interested in trying your procedure, but I thought that cracking the throttle bypassed the enricher circuit, thereby making it a vestigial feature? I have tried opening the throttle ever so slightly to see if it helps. I'm not sure that it does. Maybe even doing that cuts out the circuit and I don't get much , if any fuel? This would support opening the throttle wider if you do it at all.

bwolfie · Sep 4, 2011

I found a NOS mikuni accelerator pump. Made starting a breeze, two twists of the throttle=2 squirts. Plenty of fuel to get it going, plus a little extra juice when you whack the throttle open. I never used the choke with the pump.

pete.v · Sep 4, 2011

bwolfie said:
I found a NOS mikuni accelerator pump. Made starting a breeze, two twists of the throttle=2 squirts. Plenty of fuel to get it going, plus a little extra juice when you whack the throttle open. I never used the choke with the pump.

How are you running this? Single? 40mm? Whats the poop on the jetting? What bike are you running this on?

bwolfie · Sep 4, 2011

I had this on my 73 850. It was on a single 34mm mikuni. I would have to look back in the records on the jetting. I sold the setup a few months back.

pete.v · Sep 4, 2011

bwolfie said:
I had this on my 73 850. It was on a single 34mm mikuni. I would have to look back in the records on the jetting. I sold the setup a few months back.

No, im look into a 40mm pumper Harley kit to convert and i thought that you might have gone there.

Mikuni VM34

FastFred

1up3down

slupdawg

bwolfie

pete.v

bwolfie

pete.v

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