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Old 06-09-2012, 12:06 PM   #1
Velocipede OP
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Changing to Mikunis

Bike Bandit has Mikuni Carbs for what seems like reasonable prices.They range from round slide 36/38mm spigot mount VM series to 38mm TM series.To my uneducated eye the 38mm VM series looks to be the easiest to fit to an airhead.My GSPD is the Canada model with 40mm carbs.

The original carbs on my bike have over 90,000 miles on them and need a rebuild so I'm wondering how the Mikunis might work.I would be interested to hear from any inmates have done this swap and what were the results.


John
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Old 06-09-2012, 12:23 PM   #2
disston
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Could you supply a link to where these are advertised or sold.

Sorry can't answer your question because I haven't done the Mikunis although I have considered it. Other that the cost the main problems seem to be adapters to fit the plumbing and cables that fit. If these don't come in some kit form then they will have to be fabricated.

In general riders report good things from Mikunis on Airheads.
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Old 06-09-2012, 12:34 PM   #3
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I put Mikunis on a '71 R60/5 years ago and it was the best upgrade, ever. Had to trim the choke lever on one of them to prevent my pants from snagging it, but that's all. Rocky Point Cycle set them up, a phone call describing your altitude and whatnot was all they needed to jet them to your bike's personality. Put them on and go.
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Old 06-09-2012, 02:09 PM   #4
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90,000 Miles? Your Bing's are most likely damn near perfect. Rebuild? Chances are the only thing they need are new needle jets and jet needles, enricher gaskets and a few O-rings.

Mikuni's? The downside is mostly the airbox snorkels. The best setups I have seen still are not that great. I have seen a lot of them letting dirt in big time. Then the flat slides have independent floats that very often do not work right just like Bing's "alcohol proof" independent floats which I believe they have since stop selling? They at least now offer an alternative regular "alcohol proof" float. Independent floats flood the carbs a LOT! I see it ALL the time. Both in Bing's and Mikuni's. Excepting the independent floats, they are better carbs. Better performance and mileage. But then chances are some real good jetting skills will come in handy to get there or at least get close to as good as they can be.

The BMW 40mm carb spigots to the small port heads have a very abrupt taper. They look like they would cause flow issues but I know from experience that looks can be deceiving when it comes to what flows better. But still . . . .

I run Dellorto's mainly for the better snorkel fit. With the later square airbox setup you can file about a third of the Dellorto's velocity stack threads off and the original snorkels will slide on as if they were Bing's for a super clean looking setup that works!

supershaft screwed with this post 06-09-2012 at 02:15 PM
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Old 06-09-2012, 04:04 PM   #5
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http://www.bikebandit.com/mikuni-sta...carbs?m=143994


are these the ones? That seems like a good price. almost cheaper than rebuilding the bings.
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Old 06-09-2012, 05:05 PM   #6
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I suspect they will come jetted far from what you need. The Rocky Point kits look expensive at first, but start to make sense quickly when you consider cost of jets, cables, etc. 34mm Mik's are the biggest that come R&L.
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Old 06-09-2012, 07:33 PM   #7
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I suspect they will come jetted far from what you need. The Rocky Point kits look expensive at first, but start to make sense quickly when you consider cost of jets, cables, etc. 34mm Mik's are the biggest that come R&L.
+1 Besides, you very rarely need to spend even close top $120 per carb to fix your Bing's. Plus, not only do you have to spend money on jets, you need to know which ones to use. I hate to say it but most people don't have a clue. Most people never get past the fact the jetting requires a lot of jets.

I wonder why Rocky Point only has 34mm Mikuni's?? Too small for most models IMO. I think they would maybe be right for a R65? If RP carbs are jetted good I would bet that is a good place to start with any size round slide. The expensive part is if you need richer slides and you often do with bigger carbs.
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Old 06-09-2012, 11:19 PM   #8
Kai Ju
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Mikunis installed

VM 38 Mikunis on a 1977 R100/7

I just finished my VM38 Mikuni installation and probably did it the hard way.
I bought a pair of bodies on E-bay only to find out that one of the float pivot needle towers was broken off. I got another one at the Long Beach swap meet and then bought the jets to suit from Sudco. Total investment is less than $200.
Modified the stock throttle cables to work with the Mikunis and used some bicycle cables for the choke using the Mikuni cable choke plungers and the stock lever set up on the stock air cleaner case.
The stock throttle cam off an R100/7 won't open the slides all the way, I added an extension to the throttle cam to do so, made from Delrin. I didn't want to spend the money on an R90S throttle cam which I assume will work as is since it has to open straight slide carbs as well.
The stock elbows are slightly smaller in OD than the ID of the bellmouth and I used silicon tape to make up the difference. It's two layers thick and is a squeaky tight fit.
Since they are both right hand carbs, i.e. the idle and air screws are on the right side of the body, I added and extension to the air screw for the left carb which allows me to adjust the screw with my fingers, the idle screw is already long enough and grooved to be able to adjust it.

The engine runs awesome, starts and idles like it should and I went from getting 34 mpg to 40mpg.

Here are the jetting specs for anybody interested:

Description Spec
Main Jet 210
Pilot Jet 25
Needle Jet 166 P-8
Jet Needle 6DH3 middle groove
Slide Cut Away 2
Main Air Jet 0.5
Needle Valve Ass'y 3.3
Idle air screw 1 turn from seated

Here are a couple of pics of the installation:






Kai Ju screwed with this post 06-09-2012 at 11:28 PM Reason: to add info.
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Old 06-09-2012, 11:34 PM   #9
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I run the VM34s purchased new on ebay a few years ago, fitting the air cleaner pipes to the carbs is a hassle and mine is a bit crude looking[supershaft is correct there]but functional, i think they respond better than the 32mm bings they replaced with a lot lighter wrist/throttle action, also very easy to tune[i use a colortune and take it from there]
Overall i would definately reccomend but if somebody offered me a pair of 38/40mm dellortos i would love to give that a try
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Old 06-10-2012, 01:31 AM   #10
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Quote:
Originally Posted by Kai Ju View Post
VM 38 Mikunis on a 1977 R100/7

The engine runs awesome, starts and idles like it should and I went from getting 34 mpg to 40mpg.

Here are the jetting specs for anybody interested:

Description Spec
Main Jet 210
Pilot Jet 25
Needle Jet 166 P-8
Jet Needle 6DH3 middle groove
Slide Cut Away 2
Main Air Jet 0.5
Needle Valve Ass'y 3.3
Idle air screw 1 turn from seated
my 900 is getting 41 on original bings and a 100k motor. Not sure I see a bonus to going with them. Seems like if you were getting 34 something else was wrong that needed fixing with your carbs.
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Old 06-10-2012, 04:09 AM   #11
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Installed these for a friend who got the carbs as part of a deal, I ordered the cables from Rocky. The bike seemed to run quite well after.



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Old 06-10-2012, 05:03 AM   #12
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I will gladly sell my 64/32/3&4 Bings to any Bing lover here to finance a new set of Mikunis. There, I said it! This model of Bings is lame, lame, lame...

oldroadie screwed with this post 06-10-2012 at 10:43 AM Reason: I can't spell...
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Old 06-10-2012, 08:18 AM   #13
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Thanks for all the replies,I think I'm going to give the 38mm VM carbs a try.I'm going to wait until the short Canadian riding season is over as it looks like it will take a while to get them set up.

Thanks John
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Old 06-10-2012, 12:51 PM   #14
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How did you get to those jets Kai Ju?
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Old 06-10-2012, 02:03 PM   #15
Kai Ju
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Quote:
Originally Posted by mfp4073 View Post
my 900 is getting 41 on original bings and a 100k motor. Not sure I see a bonus to going with them. Seems like if you were getting 34 something else was wrong that needed fixing with your carbs.
You're missing the point. I'm getting stronger performance and 10% better mileage with the Mikunis.
There was nothing wrong with the Bings, I'm just a bit heavy handed with the throttle and you're also comparing an R90 with an R100.
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