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Old 11-19-2012, 02:42 PM   #12
TheRadBaron OP
Gnarly Adventurer
Joined: Jul 2010
Location: Central Illinois
Oddometer: 476

I got the carbs on. They're Mikuni VM28s from a '72 Yamaha R5 (350cc 2-stroke twin). I originally had VM32s on it and they were way too big for the motor. Most people seem to use VM30s when they switch to Mikunis on their Honda 350s, but these are still too big for a stock motor. I just put a set of VM30s on a CB350 for a friend and they'll run pretty good, but I believe that a stock motor will run best with VM26s or 28s. I was planning to put 26s on, but I had this extra set of 28s that are in really good shape so I'm just using them.
I think one of the big reasons that people like the VM30s is that they'll fit into the stock carb flanges on the head and can be made to work with the factory battery box and air filters. The VM28s require a different (smaller) flange. Since the readily available aftermarket flanges don't have the angle built into them like the stock Honda ones do, I don't think the setup I'm using would work with the factory battery box and/or air filters.
For my purposes, though, it works great. The flanges are made by Mikuni and they're part# M-VM28-200K. They bolt right up to the Honda head without any modifications and the inner diameter is almost an exact match for the diameter of the intake runners in the head. Some very slight port matching would smooth things out, but I didn't worry about it since I won't be competing on this bike.
I'm using a mix of jets and brass that I had on hand that I think will put me in the ballpark. I'm using a 1750-8 needle jet, 5DP7 needle (clip in #3 position), 160 main, 32.5 pilot, with the screw 1.5 turns out. The needle jets that I'm using are the "bleed type" that are accepted to be better for 4-stroke applications than the more common primary type. Hopefully this will be close enough that I can work on fine tuning it once the bike's up and running.
The desire for safety stands against every great and noble enterprise. -Tacitus
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