From Bing to Mikuni

[Mike Hufnagel]

While searching the board for Bing to Mikuni setups It seemed to me that boring out a 34 mm to 35 is the trick. (it is going on a 74 jackpiner with a 250 motor in it with gem reeds) I did a little research and it seems that Pro Flo is out of business, could not find a web site. And on other forums, people were very irate with Pro Flo. Considering the set up I have, were could I get a carb bored out or should I go with a 36mm?

[brian kirby]

Typically to get the same flow you have to go up a size when going to a Mikuni. Since the 250 came with a 36 Bing you would want at least a 36 Mikuni, but a 38 would be best.

Brian

'72 Berkshire

[Mike Hufnagel]

Thanks. I think I have both a 36 & a 38. Now I just have to rip em off my RZ.

[VICTOR MONZ]

Only my opinion....stay with the Bing and just dial it in....it will be a better performer...just my opinion and experience.

victor

Bing Supporter....obviously.

[brian kirby]

I used to be pretty negative on Bings, and I still am in some ways, but they can work very well and make lots of power if they are in good condition. The tickler also makes is much easier to start big bore bikes. The problem with Bings are the parts are hideously expensive, I can buy a brand new Mikuni for the price of a slide for a Bing. Also, the Bing gets horrible fuel range, which was an issue at the ISDT ride last weekend.

My rule of thumb is, if a bike comes to me with a Bing and it is in good condition I keep it fresh and leave it on, but if the bike comes with a worn out Bing or no carb at all I replace it with a Mikuni or  even better a Lectron.

Brian

'72 Berkshire

[Charles Gresham]

The Bing will run better IMO due to the angle which it mounts on the engine.. the carb is tilted downward and normally slightly off vertical when mounted to a Penton. Bings are used as aircraft carbs due to the variety of mounting angles and attitudes it can run without affecting carb performance, and I guess thats why KTM used them as OE. The Mikuini's like to run straight up and down / side to side and can be the devil to get dialed in. MY 250 HS came with a Mikuni, and I never could get it to tune out correctly, so I put the Bing back on..

1974 Penton 250 Hare Scrambler
1973 Honda CL 100
1978 Suzuki RM 125
1983 Honda XL 185
1993 Yamaha RT 180

[brian kirby]

I have to disagree Charles, the Mikuni is far superior at odd angles. The Mikuni split float system has much better fuel level control, and is far less likely to flood and load up if the bike falls over while riding. European bikes came with Bings because, well, its a European carb. Rotax is the engine used in all those ultralights and its an Austrian company, but just as many of those aircraft have Mikunis as Bings.

Bings definitely make more power, I can feel the difference when I swap the Bing and Mikuni on my Maico 440. But I also know I can fall over with the Mikuni and it will restart immediately, if I fall over with the Bing it will take 45 kicks to get it restarted.

Brian

'72 Berkshire

[Big Mac]

Search posts for Mikuni conversion by Thom Greene. Thom had good results with a 250 motor using a bored out 34mm, which works well since the body size is smaller and fits in the tight space available.

Charlie Brown at Superior Sleeve should be able to bore the carb for you if you go this route. He's very experienced and reasonable. //www.superiorsleeve.com

[brian kirby]

Mac is right, the 34mm Mikuni is a much smaller body than the 36/38 and will make fitting it in the tight space in the Penton much easier.

Brian

'72 Berkshire

[skiracer]

I put a 36mm Mikuni on my 250 MC5, and yes, it was tight.  I modified the airbox by cutting down the carb end, installing a flat plate over it, and then I made a rubber boot to fit the new Mikuni; net gain of an inch and a half.  Now I can take the carb out and still keep all my fingers!  I think the bike runs better now than with the original Bing.  Hey Jerry, could I get your jetting specs?  Mine bike is still running a bit lean.  Thanks, James

[tomale]

Yes I still have a Mikuni on my 250 and it really works great, I use to think that no matter what a mikuni is the way to go but I am not so sure anymore. When I built my 74 440 maico I put a mikuni on it thinking it would work best, but my buddy Rick who also has the same year 440 pulls alot better and longer with a Bing on it than my bike with the Mikuni....It maybe a matter of not quite having the right jetting but I have been fiddling with it for over a year and it still does not work like my buddies bike... So a Bing is going back on that bike. for the 250 the Mikuni is staying put.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)74'
250 hare scrambler (project bike)