Penton Jackpiner bing jetting / Mikuni conversion

[Dwight Rudder]

I'm having issues with my stock Bing on my 1973 Jackpiner. It tends to run lean on current jetting unless you have choke slide about 1/3 of the way on. Needle has been in the next to richest position.  I raised the needle all the way and now it loads up badly. Cost me a class win this weekend at barbers when Chicago Jerry beat me as I cleared a loaded up engine. I figure I need a richer main for sure so I can drop the needle.
Also who has had good luck putting a 32 VM Mikuni on one ?  What needs to be changed and what jetting. I need to get something going for the ISDTR.
Thanks.

[Doug Bridges]

Dwight                                                                           I got these jetting specs for the 30mm Bing from a very good tech article by Jack Penton that was posted by one of the members and they worked very well on my 73 Jackpiner. #1 Slide, #1 needle, 150 Main, 2.80 needle jet,35 Pilot and a #40-404 atomizer. Mine was running a lot like you are describing.Mine did not have the 40-404 atomizer so I got one on ebay. I also replaced the needle and needle jet with new parts from Bing international as I also read that as these wear they can contribute to the problem. My slide was a #2 and I could not find a #1 but the #2 worked just fine. after making these changes the bike ran fantastic. If you don't have the 40-404 atomizer these specs will not be correct.

Doug Bridges
73 Jackpiner
74 Rickman Zundapp
78 Suzuki PE175
82 XR200R

[Mick Milakovic]

Dwight, I replaced the Bing with a 32mm Mikuni on my daughter's JP, not sure what year the motor is but I'll check tonight; it's in a '75 frame.  Bought the carb new off eBay and didn't change a thing jetting wise, started right up and runs great.  I'll check some numbers on it tonight and get back to you.

Mick

[Dwight Rudder]

Thanks Mick !

quote:Originally posted by Mick Milakovic

Dwight, I replaced the Bing with a 32mm Mikuni on my daughter's JP, not sure what year the motor is but I'll check tonight; it's in a '75 frame.  Bought the carb new off eBay and didn't change a thing jetting wise, started right up and runs great.  I'll check some numbers on it tonight and get back to you.

Mick

[Dwight Rudder]

quote:Originally posted by Mick Milakovic

Dwight, I replaced the Bing with a 32mm Mikuni on my daughter's JP, not sure what year the motor is but I'll check tonight; it's in a '75 frame.  Bought the carb new off eBay and didn't change a thing jetting wise, started right up and runs great.  I'll check some numbers on it tonight and get back to you.

Mick

Mick, what mods did you have to make to install the Mikuni ?  Did the air boot fit ? Was it a problem to streatch over the bell ?  Did you have to shorten the spigot mount ?

[KJDonovan]

Dwight,

This past spring I replaced the Bing on my 72 Jackpiner with a new Mikuni VM32 spigot I got from Sudco.   I used the following jetting; 165 Main, 45 Pilot, 5F21 Jet Needle.  I used a short piece of rubber pipe connector from Lowes to connect the carb spigot to the spigot intake. I did not make any mods to the carb or intake spigots.  After a lot of warming up with a heat gun I was able to get the original air boot over the big bell on the Mikuni then attached to the airbox.  The boot has a couple of wrinkles in it, but I did not need to cut it.  Bike starts easier, idles nicely and runs great and this changed a chronic rich issue with I could never resolve to my satisfaction with the Bing.  Only tweak I needed to make was to replace the straight cable guide on the top of the new carb with a slightly longer one with a 45 degree bend, which I also got from Sudco.  This eliminated some slop I had in the throttle cable.

Thanks,

Kevin



Kevin J. Donovan
Foster, Rhode Island
72 Jack Piner (My Ride)
72 Six Day (Wifes Ride)
71 Suzuki TS125
73 Yamaha AT3
72 Montesa Cota 123
88 KTM GS250

[Mick Milakovic]

Dwight, sorry but got home late last night and couldn't check jetting, but I'll ge to it.  Just like Kevin, I did not have to cut the intake manifold (I had to on my Harescrambler).  I bought my radiator hose from Auto Zone and used regular hose clamps to mount the carb to intake, and also used a hair dryer to soften the airbox boot to stretch it over the intake bell on the carb.  Also did not cut the air box boot.  Like I said earlier, the bike starts right up and runs smooth.  I suppose I could get it smoother with fine jetting, but it's not an issue since the only time the bike gets ridden is when Ambr is home from the Navy.  I'll try to get to it tonight for those specs.

Mick

[Mick Milakovic]

Main jet 200, pilot 35, needle jet 159 Q-6, needle 616DP17.  These are the numbers (as near as my old eyes can see using a magnifying glass) on the stock Mikuni ordered off eBay for $95.  As a matter of fact, the carb has been sitting on a shelf for over a year.  I pulled it off the bike and cleaned it after the last ride because I knew it would be a while before it ran again.  I put it on the bike today and it fired after only 3 kicks.  Ran smooth and strong.  Good luck with your project Dwight, I think you'll be pleased.

Mick