Hey, all. Have a freshly rebuilt '73 Jackpiner w/new electronic ignition and a fresh, 26mm Mikuni. With jetting as supplied with the carb, bike is a reluctant starter and tries to load up. Once in operation, it feels both lean and rich - if that makes any sense. Comes on decently if I "ease" into the throttle but will bog if throttle is opened abruptly. Plus, although I did not go flyin' down the road to test top end, bike does appear to break up some at higher revs.
Note, there is no intake restriction but I've not yet opened the exhaust to see if it is plugged up. Regardless, to save me digging through umpteen zillion pages of info on Mikuni tuning for everything from mopeds to TZ750's, does anyone have suggestions for what Pilot/Main Jets work will with this Jackpiner/26mm combo?
I've only used 30 and 32mm Mikuni's. The standard on a '73 was a 30mm Bing. You may find you might be running out of air at top end.
I would like to second the request for help on this topic. Is there anyone that has enough knowledge to help write some sort of guide?
My '73 has a 34mm Mikuni and it seems to run ok, but have not taken it out for a hard ride since installing it. When I was going searching this message board on the topic, it seemed most people were running 32mm versions. Doug may be on to something.
Ted,
I have run this on a couple of Jack Piners and it works fine.
Mikuni VM30 round slide
Main Jet 170
Pilot Jet 40
Needle Jet P-5
Jet Needle 6F5
Slide 2.5
Air Jet 2.0
Great thanks for responses, in particular Kevin's most in-depth specs. Please forgive my inquiry slip - carb on bike in question is indeed a 30mm, not a 26.
I will pull carb apart today and compare what's there to info provided.
A little bit different question, but related. How did you guys mount your Mikuni? My Bing is worn out so I ordered a Mikuni for my Berkshire 100, but the Mikuni is about 3/4" longer and I just can't seem to get it in there using the stock air intake boot.
The intake may have to be shorted for the actual fit. You also need to source a small section of filler neck hose from an automotive supply. Don't use a water hose as they are not fuel compatible. I'll get a pictur in the morning. You are only needing enough for 2 hose clamps such as the narrow ones that come on the Pentons. On the Harescramblers to fit a Mikuni you had to remove the rear spigot of the carb also to get the boot and carb fit.
My Jackpiner is set up with hose like Doug mentioned. Not the same bike but Will attach pictures below in case it helps. On the air filter side, I 3d printed a ring to fill the gap in order for the boot to fit tight. Not sure I love that solution long term, but it is working for now.
Thanks for the tips Doug & Rob!
Doug, when you say to remove the rear spigot of the carb, can you be a little more specific...ie: how do you remove it? Pics would be great!
All,
I'm in a similar predicament. I have a 1977 KTM 175 GS6 that I'm attempting to resurrect from the dead. It has an incorrect carb on it now and I'm considering swapping for a Mikuni VM32. Has anyone done this swap and be willing to post jetting and fitment information?
Thank you in advance for any help you may be able to provide.
Dan Morse
Prineville, Oregon
Quote from: motograndpa on October 29, 2024, 04:25:03 PMSpecial thanks to KJ Donovan and Al Buehner for their help with this. I ended up using a Mikuni VM32 sourced from Dennis Kirk, a Gunnar Gasser throttle assy., the offset intake from Al Buehner to match the carb to the GS6 aluminum airbox, and I jetted it according to KJ's recommendations above. It runs really well with the jetting as-is and doesn't run out of air up top.
Dan
All,
I'm in a similar predicament. I have a 1977 KTM 175 GS6 that I'm attempting to resurrect from the dead. It has an incorrect carb on it now and I'm considering swapping for a Mikuni VM32. Has anyone done this swap and be willing to post jetting and fitment information?
Thank you in advance for any help you may be able to provide.
Dan Morse
Prineville, Oregon