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Old 02-21-2014, 11:12 AM   #1
picinisco OP
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Mikuni Question

So taking the advice of people here who are more knowledgeable that me, I have decided (at least for now) not to pursue rebuilding my Bing that has resided at the bottom of the ocean for 40 years.



As such, I have purchased a couple of Mikunis in good condition. I like the fact that they are cheap, simple and easy to take apart. Now the question I have is what it this spigot sticking up here and what connects to it?





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Old 02-21-2014, 12:11 PM   #2
Kai Ju
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Almost looks like the inlet for a Power jet but a brief search nixes that. Maybe an inlet port for two stroke oil if the carbs came from a two stroke powered snowmobile.
Regardless, I would just plug it.
What size are the carbs if I may ask ?

BTW, get yourself some Pine-Sol and a tub and soak the Bings in a 50/50 water mix. Remove all the brass and and rubber, as well as the floats but throw the brass in with the carb. Check every couple of hours even though I've left carbs in a tub overnight with no ill effects, and that was with undiluted Pine-Sol.
Clean the floats separately and replace the rubber once it's all clean.

Kai Ju screwed with this post 02-21-2014 at 08:01 PM
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Old 02-21-2014, 01:08 PM   #3
picinisco OP
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Quote:
Originally Posted by Kai Ju View Post
Maybe an inlet port for two stroke oil if the carbs came from a two stroke powered snowmobil. Regardless, I would just plug it.
Good call. They came off a 440 Kohler

Quote:
What size are the carbs if I may ask ?
VM-32s

Quote:
BTW, get yourself some Pine-Sol and a tub and soak the Bings in a 50/50 water mix. Remove all the brass and and rubber, as well as the floats but throw the brass in with the carb. Check every couple of hours even though I've left carbs in a tub overnight with no ill effects, and that was with undiluted Pine-Sol. Clean the floats separately and replace the rubber once it's all clean.
Done all that 100% Pine Sol in an ultrasonic cleaner but the slide is badly corroded as is the slide bore and the bowl.

The other Bing if fuctioning. I suspect the bike was lying on its left side outside for many years.

My come back to that after the project is up and running.
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Bikes That have Moved On:
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Old 02-21-2014, 05:55 PM   #4
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It could also be a vacuum port for a vacuum operated petcock. On my RD350, the oil injection was on the side of the carb throat, not the top. Just block it off, I'd say.
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Old 02-21-2014, 08:05 PM   #5
Kai Ju
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Quote:
Originally Posted by JonnyCash View Post
It could also be a vacuum port for a vacuum operated petcock. On my RD350, the oil injection was on the side of the carb throat, not the top. Just block it off, I'd say.
No vacuum generated on that side of the slide I don't think, plenty of velocity though to atomize the two stroke oil as it's coming out the hole.
Pure speculation on my part though since I've never had a carb with a spigot there.
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Old 04-11-2014, 10:36 AM   #6
picinisco OP
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Where can I get this

Next question on the Mikuni Carb. This part (main jet) screws into the bottom of the needle jet and mates with the bottom of the bowl with an O ring. My heavy handedness resulted in the broken thread as shown. Cannot find a diagram anywhere showing this part. Where can I get a replacement that is extended like this. I believe the carb is a VM32 but cannot prove it.

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Old 04-11-2014, 03:21 PM   #7
685
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Looks like a variant. Doesn't look a lot like my VM38s, tho. You can get Mikuni parts here:


http://www.nichecycle.com/ncs/index....arts-list.html
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Old 04-13-2014, 05:31 PM   #8
685
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My VM38 doesn't have that long main jet--and no o-ring in the bottom of the float bowl. I wonder if you could replace the old needle jet with the modern one for the motorcycle application VM32 and use modern main jet? Need to do both and probably replace the needles too, which you would need to do anyway because you're repurposing a 2 stroke carb.

As I said in the other thread, I think you're gonna be S.O.L. trying to find a replacement for the part you broke. However if the carb body is the same as a motorcycle application, you can probably rebuild all the brass bits, main and pilot jet, needle jet, & needle, toss in a rebuild kit--gaskets and float valve, and maybe come out with a workable carb. Here's a pic of a stripped VM38, does yours look like this?


upload an image

I think that trying to adapt this carb for 4 stroke motorcycle use is probably a lost cause--the power profile for a 2 stroke snowmobile carb is way different from a BMW.


Your alternative is to find a replacement Bing to take the place of the knackered one.

685 screwed with this post 04-13-2014 at 05:41 PM
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Old 04-13-2014, 06:13 PM   #9
picinisco OP
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Absolutely. Plan B, C & D.

The knackered Bing is a 64/32/13. Looking for a replacement hasn't turned up a /13 yet but /11 or /201 etc. Do you think any of these will replace a /13?

That's plan D
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Old 04-14-2014, 08:18 AM   #10
picinisco OP
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Mystery Solved

I had sent out several enquiries to Mikuni parts companies and finally got an answer.

> That is not the main jet, that is the needle jet setter. You probably
> have a flange mount carburetor and the main jet comes out of the side of
> the bowl. I am currently out of the needle jet setter (Sudco part number
> 002-209), Mikuni says I will see them mid June. It sells for $3.00. The
> o-ring for it is also $3.00.

Back in business. Although I may still shelve the Mikuni idea and go back to Bings.

Plan D
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Bikes That have Moved On:
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Old 04-14-2014, 08:59 AM   #11
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Looking in the Bing manual I think the 201 carb is a bad substitute for you. It is an R45N carb. That sounds like an R45 bike European model to me. It uses a different slide in addition to other not commonly substituted parts.

The Carb you need is a left side R75/6 carb, 64/32/13. The one you may consider, 64/32/11, is a left side R90/6 carb. The only difference is a couple of jets and needle settings.

Tell me what bike, what year this is for, and I will tell you which jets should be in the carbs you use. Either set may work but I do think you want a matched set. The difference between an 11 and 13 is the main jets, needle jets and idle jets.

You could take your good carb apart and just read the numbers on the jets.
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Old 04-14-2014, 08:10 PM   #12
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Quote:
Originally Posted by picinisco View Post
I had sent out several enquiries to Mikuni parts companies and finally got an answer.

> That is not the main jet, that is the needle jet setter. You probably
> have a flange mount carburetor and the main jet comes out of the side of
> the bowl.
That is not a flange mount carburetor, and your main jet definitely doesn't come out of the side of the bowl that I can tell. The long center stud casting that goes through to the needle jet and then needle/slide in the center is where your main jet would mount. Just update to the hex head jets and screw them right into the bottom of the needle jet. You'll need a washer there.




That is a spigot mount carburetor, and I am running Arctic Cat carbs on my r75 and plugged the oil inlets (that's what those are). The benefit of the older Mik's like you have is the smaller throat (inlet) which just so happens to fit the stock intake elbows perfectly unlike the new casting Mik's that have the larger bellmouth.

Your Mikunis will work well with the proper jetting, etc. If it is an R75 I can tell you what I run in mine and it will run just fine. You'll need the cable kit from Rocky Point cycle for a seamless install.

http://www.rockypointcycle.com/p-bmw...kits-2910.html
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Old 04-14-2014, 08:51 PM   #13
picinisco OP
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Quote:
Originally Posted by Kanticoy View Post
That is not a flange mount carburetor,
Correct it is not a flange mount carb.

Quote:
and your main jet definitely doesn't come out of the side of the bowl that I can tell
Incorrect. main jet does come out the side.

It has been correctly identified as a needle jet setter.

Quote:
The long center stud casting that goes through to the needle jet and then needle/slide in the center is where your main jet would mount. Just update to the hex head jets and screw them right into the bottom of the needle jet. You'll need a washer there.
The thread is different so a main jet will not screw in here although maybe with a different needle jet.

Quote:
That is a spigot mount carburetor, and I am running Arctic Cat carbs on my r75 and plugged the oil inlets (that's what those are). The benefit of the older Mik's like you have is the smaller throat (inlet) which just so happens to fit the stock intake elbows perfectly unlike the new casting Mik's that have the larger bellmouth.
Your Mikunis will work well with the proper jetting, etc. If it is an R75 I can tell you what I run in mine and it will run just fine. You'll need the cable kit from Rocky Point cycle for a seamless install..
I have gone back to plan D (Bings) however I will keep your offer and may take you up on it if things change.

Thanks
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Bikes That have Moved On:
1978 Suzuki GS550E, 1978 Kawasaki KZ1000P, 1982 Honda XL500R, 1995 BMW R1100RSL
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Old 04-14-2014, 08:55 PM   #14
Kanticoy
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You would need to change the needle jet anyway. Two stroke stuff would be entirely too rich. I ended up with a 159PO needle jet in mine and it works well. I couldn't see the threaded portion in the bowl. I'm not a fan of that. Sounds like you got an oddball set of carburetors, though the bowl seating surface looks like the non jet bowls would fit just fine.

I've got two airheads, one with Mikunis and one with Bings. They both run fine. To me it is just a "coffee vs. tea" argument.
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Old 04-15-2014, 06:13 AM   #15
MotorcycleWriter
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Rebuild the Bing!!!

That carb may look bad but it is amazing how well it could clean up. You never know until you try, and it might well be cheaper and easier than retrofitting with crap of unknown origin. While the aluminum body may be corroded, most (yes, most, so don't tell me about the tiny idle ports behind the throttle plate) of the metering parts are replaceable brass.

Contact Bing and get a rebuild DVD from them. It'll take you step by step through the process of cleaning out tiny passages you didn't know existed and are too small to see. Soak in a good solution for a couple of days before attacking it. Once you've got it as clean as you can get it, take it to someone for an ultrasonic bath. Once the body is spick-and-span, replace everything that can be replaced. A carefully rebuilt set of Bings will run like new and can be rebuilt again and again.

The truly amazing thing I'm discovering about these airheads is the depth of knowledge and the maintenance support. While you may not be able to get any information out of Mikuni, Bing will be happy to help you as much as you need. And MaxBMW proved earlier this year that you can build a brand new BMW R90S from readily available parts from BMW. (Almost.)
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