77 MC250 QUESTIONS

[penton117]

Hi Guys,

a MC250 just found me (isn't that the way it always is?) and I have a couple questions. Does anyone know the original jet sizes for the Bing type 54? Also, any suggestions on where to find an air filter element? Thanks as always, and happy holidays to all!

[tmc3c]

Hi 117, My Bing also has #54 on the side but if you look I belive it will have a part#2/36/102 and if it does it is a 36mm.With a stock cyl. the jeting that Kent Knudson uses is as follow's 160 main,#283 neddle jet and a #35 pilot with a #1 {281} jet needle with the clip in the middle position. All of my info came from summer 2002,STILL....KEEPING TRACK ,A great issue,I am also in the same boat as you,I have a 74 mc5 motor that Kip Kern is rebuilding for me and I am going through my carb as we speak, do you need the reeds # if so use the 250/400 kit from Boysen @ {800}441-1177 part # bult01. Hope this help's .

Thomas Carmichael

[penton117]

Hi Thomas,
thanks for the help. Don't need any reeds, in fact mine didn't have a reed valve on it. Is that the correct set-up for a 1977? And of course I am still in need of an air filter element. Thanks again

[Rocket]

Penton117
Check the parts suppliers on this site, Al or Larry will help you out.
Rocket

[Big Mac]

I don't have a manual for a '77, but do have a DB mag with test on the 77 MC5 and it lists the carb as 38MM, 165 main, 35 pilot, 2.83 needle jet. That's the same jetting showing in my manual for a '74 250, so there's a chance DB screwed it up and the carb was actually a 36MM. If yours is a 36MM, those settings should work great, they do for my '73 and '76 250s...if it's a 38MM, then DB mag says it should be stock anyway.

By the way, I've found the old Bings, especially the slides, tend to wear and cause jetting grief. Make sure the lower air box side of the slide doesn't have a "half moon" worn into it (one look, you'll see what I mean)..if so toss it for a better or new one. Replacing the needle (not sure the needle #, but should be a single groove below the clip slot--think that's called a #1) and needle jet does a lot to clean things up too. The Bing Agency has all parts needed, just bring lots of cash.

[Bob]

quote:Also, any suggestions on where to find an air filter element?

I think Unifilter has one to fit. You can order it through your local cycle shop. Check with Uni to make sure what they have will fit.

http://www.unifilter.com/vintage.htm

Bob in Va

[tomale]

Big Mac is right if that Bing is worn, plan on spending lots of money, There is another way to go if you are not dead set on using a Bing. I put a mikuni on my 76 250 and I love it. It is the best thing I have done to my bike. It starts easyier has better bottom end, it revs faster and generally just runs better. And the cost to make the change is not too bad. I think that I have about a hundred and fifty bucks into my conversion and that is with buying a used intake that I could modify. They other thing too is that the jet are availble locally.
If I have any regets at all it is in that I am thinking that I should have gone with a 38 instead of a 36. The reason is that It does lack a little bit on the top end. I think that going to a 38 could fix that. but I am not sure that I could make it fit. I had actually gotten a 34 that was bored out to a 35.5? I was told that it is a smaller carb but it flows like a 36  either way it is a tight fit.
let me know if i can help


Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[imported_n/a]

Tom,

I'm going through the same dilemma now with a 38mm Bing for my '74 400.  The motor is a '74, but was in an MC-5 configuration, with the rubber mount between the angled intake manifold and an aluminum tube pressed into the Bing.  I have measured the space available for the manifold/carb unit and I don't think it will be a good fit with the airboot.  I was going to remove the tube from the carb and clamp it on a stock manifold, until the discussion here about spending lots of money on the Bing.  Then I measured the room if I were to put a Mikuni 38mm on instead, mounted with the rubber manifold, but the Mikuni is longer than the Bing and so creates a space concern.

What has been successful out there for mounting a 36/38 Mikuni, both space-wise and performance, on a '74/'75 Penton 250 or 400?

Glenn

[rdrnr]

Glenn, I have a 74 400 that I bought from Donny, it came with a Mikuni.  It runs great, if you give about half throttle in any gear and the next thing you know the front tire is sky word:).  I can tell you what it looks like or I can email pictures to you of it and what was done. Anything I can help with just let me know.  James

[imported_n/a]

Thanks, James.

An e-mail is headed your way.

Glenn

[imported_n/a]

James,

Thanks for the pictures.  They are a big help.

With the location of the bell of the carb with respect to the airbox opening, do you find the motor running out of air on the top end?  

Also, does the airboot seal well on the carb bell?  It's kind of hard to tell.  

Thanks again.

Glenn

[rdrnr]

Glenn,

  Yes it does seal well, because of the two rubber donut; they are a tight seal.  One on either side, they push and fit very tight squezzing on the boot.  No air can go thru that tight fit.  It took about ten minutes to put them back on after I took the carb off to clean.  
   
  As for top end, in the dirt no problem that I can tell.  I will take it out on the highway this weekend and try it there and let you know then.

 James

[rdrnr]

Glenn,
  Tried it on Saturday felt great.  I will let Teddy try it on Saturday and he can give his two cents worth.  
  James

[imported_n/a]

Thank so much, James.

You have been really helpful.

Glenn