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Mikuni carb tuning

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63panhead
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Mikuni carb tuning

#1

Post by 63panhead » Thu Jul 28, 2005 7:45 am

It looks like only a couple of guys here are running the Mikuni from the poll. I'm one of them. I 'm looking for some advice. I have a brand new Mikuni VM38 installed. It has a 30 pilot jet and 350 (maybe 360) main jet. The motor is a stock 63 pan with 40" shotgun drag pipes. The bike starts and runs but after a few seconds starts to pop, and miss. The air screw needs to be almost all the way which I believe tells me that I need a larger pilot jet. I haven't gotten far enough to evaluate the main jet. I am interested to know what jets anybody with a similar set up is running so I can use that as a starting point.
I am still pretty new to this bike and panheads. I had it at a shop for some other work. They "tuned it up" for me. Big mistake. I'll start another thread aout the electrical. Anyway, they did the tuning with the choke on. So I'm starting over from scratch.

Thamks for any and all replies.



DanM
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Re: Mikuni carb tuning

#2

Post by DanM » Thu Jul 28, 2005 11:05 pm

Check out Victorylibrary.com- he has a booklet on tuning the Mikuni. I had one when I ran one on my 45 and it was very good. Here's the add from his site:
Mikuni Tuning for Harley-Davidsons for the Mikuni round-slide VM type carburetor. Want more performance from your Harley-Davidson Knucklehead, Panhead, 45, or U-Series? Already have a Mikuni carburetor, but don't know how to adjust it? Doesn't run "right" and won't respond to the changes you've made? Can't make any sense of the original Japanese "instructions"? Looking for an affordable alternative to replacing or rebuilding your tired Linkert? This booklet will help you! Click the cover for a complete list of contents.

Dan

mbskeam
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Re: Mikuni carb tuning

#3

Post by mbskeam » Thu Jul 28, 2005 11:58 pm

hello

on my carb a VM 38 stock was:
main jet #330 now #280
pilot #30 now #22.5
needle #166 Q2 left this alone
jet needle 6DP1 left this alone
air jet 2.0 now 0.5
throttle valve 2.5
this is on a 74" pan with drag pipes.As you can see there is a diff. from there set up to mine, hope this helps.
this set up will give you that med. tan on your plugs
mbskeam

The only thing that I feel.......will be the RECOIL

oh....
air screw in will richen idle mixture
out it will give more air= lean
mbskeam

63panhead
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Re: Mikuni carb tuning

#4

Post by 63panhead » Fri Jul 29, 2005 4:37 am

Thanks for the replies. I thought that I would be lean with the jets I have. Doesn't look that way, thanks mbskeam. I must have a fundamental problem that needs to be fixed before tuning. Have an adapter for checking intake leaks with Mikuni?

Installed 25 pilot jet and 330 main jet. Tightened manifold fittings. Started second kick. Ran fine with choke on. No more missing. Turned off choke. Still ran OK for a minute then started to pop through the carb. Made adjustments to air bleed screw and idle speed. Still pops through the carb. Died, wouldn't restart. Will try again cold. Any ideas?

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Re: Mikuni carb tuning

#5

Post by mbskeam » Fri Aug 05, 2005 2:11 am

hello,
thats good to hear,
what jets are you runnin?
now dont forget to turn off your gas when you park it.
dont want you to have the good morning I had today,
forgot to turn off the gas last night and when I get out into the garage I smell gas ......
as I was pushing it out the door, gas is coming out the breather port....oh this is not a good sign
well, filled the front cyl full (hydro lock) pulled plugs and out came the fuel. then took off the oil return line, and ran it into a container, pulled the gas filed air cleaner and kicked some more.
finally got it runnin and it spit a buttload more out the breather, ran it untill the oil started to come out and not gas from the return line.
I get to change the oil now,
I wonder if this is the pans way of getting back at me for ridding another bike, just lick a women scorned I tell ya.
mbskeam

oh....
after this weekend I can take a pic. of my hanger bracket for ya
mbskeam

63panhead
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Re: Mikuni carb tuning

#6

Post by 63panhead » Fri Aug 05, 2005 6:24 am

mbskeam-
Sorry to hear about your gas problem. I have a new Mikuni now, the old one did the same thing as yours. I think the needle valve seat was worn. I haven't left the gas on since changing carbs but gas does not run out of my air vent tubes now when I stand the bike up. It always did with the older carb. I am running a 25 pilot and 330 main jet; 166 Q2 needle, 6DP1 jet needle.

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