Fitting Mikuni to Hare Scrambler

[Mick Milakovic]

Hi all, I'm fitting a 34mm Mikuni to my 75 Harescrambler and having some trouble.  The puzzling part is I took this carb off Ambr's 75 Jackpiner and it went on and off very easily.

I used radiator hose over the stock intake manifold to mate the carb because the carb outlet OD is the same is the manifold OD.  The Bing slides over the manifold, but the Mikuni has to sit behind it, and therin lies the problem:  when assembled, the carb pushes the airbox boot back so far that the boot collapses and I can't fit the boot over the airbox.

Are the Jackpiner and Harescrambler intake manifolds different lengths?  Would that solve my problem, if the Jackpiner intake is shorter, thus allowing more room for the carb?  Another option is cutting the 250 manifold.  It looks like if 3/4" came off the manifold that the carb would fit, but I don't really want to cut it.

What have you guys done?  I don't have a lot of time before Mid-Ohio, and I have new engine I need to test.  Thanks ahead of time,

Mick

[Gary Roach]

Hi Mick,

Yes, the intakes are different. The bolt hole spacing on the cylinders are different so you can't use a 175 manifold on a 250. I've put Mikunis on a couple of 250s, but it's a pain. I tried cutting an intake off, but the hose would blow off when you revved the bike up. I ended up modifying the airbox so that the big end of the airbox boot goes inside of the airbox further. It works fine, but modifying the airbox is a really time consuming job.    

Gary

[sdm]

I just did the conversion on my 74 250 and cut about 1/2 inch off the intake manifold. I had an extra intake manifold to experiment with so it wasn't so traumatic. Matt Hildenberg from Speed & Sport had a carb joint that works well and it has been trouble free and holds the carb just fine.I used the narrow hose clamps and they are holding that joint. You are correct in that the airbox boot is a pain but I just scrunched it in for now until I can come up with a better solution. It really helps to use a heat gun to soften the boot so it will be more pliable then use the narrow clamps on those joints also. It is sealing just fine but not as clean an installation as I would like. I have one cross country race on my set-up and a few short trail rides and it is working well.
Hope this helps.
Sam

[Mick Milakovic]

Gary and Sam, thanks for the input.  What size Mikuni did you run on your bikes?  This 34mm was originally on our 175, but I thought it ran rich.  I put a 32mm on it and it's seems just right.  My thinking then followed that the 34 would be good on the 250, with a larger main and pilot.  Thanks,

Mick

[Mike Hufnagel]

I wound up making a flange for the air box (cut out the stock flange and riveting & sealing a plate and mounting a flange to the plate) and using a cut down tm 400 air boot for the air box. I am using a 36mm Mikuni on my 250. I would to get a better fitting boot though as the angle on it is pretty steep (from the carb to the airbox).     Also wound up milling my reed block at an angle to bring the angle down even more. I cut it a bit too much and wound up having to take some material off the drain plug of the carb. to keep it from hitting the cases.

I also am using narrow hose clamps that have the notches(?)(cut outs?) going all around the cirumference of the hose clamp to keep the clamps in place.  (I had a problem when using regular clamps as they kept slipping off)

74 Yamaha TY 250
75 Jackpiner w/ 250 eng.
80 Ktm Mc 400
82 KTM GS250II (import)
82 KTM 495
2) 84 Yam RZ350
98 KTM 300mxc
00 KTM Duke 2
06 KTM 950 Adv.
08 Suzuki DR70Z

[sdm]

Mick
I am using a 34 Mikuni as I wasn't sure the bigger body of the 36 would fit as well with all the angles etc. Sorry but I don't remember the jetting but I am at about 4800' elevation anyhow. I don't notice any difference in power but I am not that fast anyhow and it always has more power than I need.
Sam

quote:Originally posted by Mick Milakovic

Gary and Sam, thanks for the input.  What size Mikuni did you run on your bikes?  This 34mm was originally on our 175, but I thought it ran rich.  I put a 32mm on it and it's seems just right.  My thinking then followed that the 34 would be good on the 250, with a larger main and pilot.  Thanks,

Mick

[tomale]

I am using a bored out 34 on my 250. whick allows me more room in an already tight spot. I cut a 1/2 inch off intake manifold and then ground off the bump so that the rubber boot would slip farther onto the manifold. the other thing is that I use fuel tank filler hose that I got at the local Auto parts store. It comes in afew sizes including 1.75 inches.. My local independent VW dealer had the narrow hose clamps so I keep a small stock of them because I would rather replace them rather than worry about them possibly failing. One the MC5 the air box was not a problem but the air boot is much smaller than on a HS and I think I used a air boot off a 78 because part that mounts to the carb is off center to the part that mounts on the box. At least with the HS you can heat up the boot and move to where you need it..

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74'250 hare scrambler (project)
74' 1/2 440 maico
78' 440 maico
72' cr125 Husky (project)
74' TM125 suzuki
93' RMx 250 suzuki

[Mick Milakovic]

Thom, what does your bored out 34 equal?  Also, what part was bored, and did you have to replace other parts as well?

Mick

[tomale]

I bought the carb bored out. I think it came from Sudco but not sure. I was told that it has the same air flow as a 36 mm carb. I believe the size of the slide for both the 34 and the 36 are the same size so I would check that. All you really need to do is take the carb apart, remove the slide and the needle jet and such and then bore out the air passage..  I measured mine and it is bored to 35.15mm

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74'250 hare scrambler (project)
74' 1/2 440 maico
78' 440 maico
72' cr125 Husky (project)
74' TM125 suzuki
93' RMx 250 suzuki

[brian kirby]

I think a non-bored 34mm is too small for a 250, but the body is quite a bit smaller which makes is a LOT easier to mount. I've done a lot of 'glass work from my jet ski racing days, but I would probably go the direction Gary did and modify the airbox and mount the larger body 36mm.

Brian

[Mick Milakovic]

Got it running today.  34mm mikuni with a 210 main and 40 pilot. It smokes, but barely.  Starts pretty easy with no choke and one turn out on the air screw. I'm going to run it like it is for a while (not bore it out), and play around with jetting until it's broken in and I can find the best setting for power with no smoke.  The bike is very strong and pulls longer than I can hold onto it!  Gary Ellis built the motor, and I can't thank him enough!  The engine has actually sat on a shelf for three years, waiting for me to finally put it in.  Now I can rebuild the old one!  Thanks everybody for your advice, see you at Mid-Ohio!

Mick

[tomale]

That is great news, I have a friend that has a 380 CZ with a 34 mikuni on it, It pulls like nothing I ever rode before and there is no lack of power anywhere.. I would have thought it would not have been possible. So if the bike runs faster than you, you might find the carb may not need to be bored out.. just a thought.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74'250 hare scrambler (project)
74' 1/2 440 maico
78' 440 maico
72' cr125 Husky (project)
74' TM125 suzuki
93' RMx 250 suzuki