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Mounting a Mikuni VM20 to a TB intake

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From reading TT forums and others I have learned that the Mikuni VM20 is a popular alternative to the sheng wey carbs that came with the TB 88cc kits. I've had fairly good results using the sheng wey, but I purchased a VM20 just to see if it offered any benefits in performance. I have the 88cc kit with the race head on my 93 ct70. I thought the vm20 would just bolt right on to the TB intake, which it will, but here is some mismatch in the ports. The flange on the VM20 is symmetrical, the center of the port hole being in line with the mounting holes but with the TB intake there is some offset. I remedied this issue by making an adapter using the heat stop. The heat stop matched the carb perfectly, just had to slot the mounting holes a little, and then I had to grind the intake to match the heat stop on the other end. So now the heat stop is between the intake and the carb where it really should be anyway. I think I read somewhere about someone doing something like this but I cant find where I read it.

Anyway, I"m not posing a question, just making an observation. No body seems to address this issue that I can find anyway.

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I wouldn't say its a popular alternative, lol. Hardly anyone is running this carb I found. I bought one used for cheap and ran into the same issues you did. I said heck with it and went back to the sheng way. What jets are you running in that VM20 Mine came jetted waaaaay to rich.

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It came with a 180 main (not sized the same as sheng wey), but I ordered some other jets because I read the 180 is too big. So I put a 150 in and basically it runs like crap lol. It takes off pretty good from idle, the pilot circuit is pretty good, but mid to full throttle its really sluggish, I think it's running to rich but I"m not sure yet. I havent had time to mess with it. Next weekend I'm gonna put in a 140 main and play with the needle adjustment. at least with this one I dont have to remove the carb to change the main jet. I had the sheng wey about 85% where I wanted it, just never could get it smooth at full throttle. I must have tried 30 different jet and needle position configurations. I"m so sick of ******* with this thing. I just want to ride it.

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PTECH.

I believe peddeler is referring to the real Mikuni VM20, which does come with a #180 main and a #22.5 pilot jet from the factory. The intake/flange is concentric, not offset like the cheap, cheesy 22mm Mikuni-clone that you're thinking of. That carb, as I recall, comes with a #90 main and a #15 pilot. The standard was to go to a #100 or #105 main and a #17.5 pilot to get that carb to work.

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Mine is a real mikuni, but I have a 22mm knock off too.

IMG_6357.jpgIMG_6358.jpg

I don't need the carb anymore since I upgraded my engine from 88 to a 106 so I gave up on trying to jet it.

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I found an inexpensive intake on ebay. Took a chance and bought it for $15 including the gaskets, insulator and shipping. I had to slot the mouinting holes on the head side just slightly, otherwise it matches the head and carb perfectly. Installed the 140 main jet and finally got this thing to run the way it should:banana:

this is the intake I bought http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=220886336963#ht_886wt_1247

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What size pilot are running?

I'm running the stock 22.5 that came with the carb. I have the air screw out about 1.5 to 2 turns and no bog issues at all. I did order the next size smaller when I ordered the main jets from DRATV, but I think the stock one will be just fine. What carb are you running on your 106? That mikuni you have would probably be a great carb to run with your 106 if it was properly jetted.

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