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Well I've been all through the old posts and I haven't found much on this topic other than a few people fighting with vm36 carbs being to rich for their bikes. Here goes...
I've got a 1980 Suzuki GN400 all stock. The factory CV carb is a BS36SS and it's completely shot. All diaphragms and rubbers are dried and cracked thanks to being in Arizona all these years. I am not a fan of CV carbs whatsoever and I'm in need of a new unit anyways so I'd like to go with a round slide VM carb. I've been reading a lot of mixed reviews on sizing... Some people say I need a 36mm and others say when you switch from CV to VM you have to drop in size. Any help getting me into the right size carb will be greatly appreciated. Thanks in advance!
Basic rule of thumb is that a CV carbs has a big fat shaft across the outlet that disrupts flow and has to sized larger than the equivalent 'slide carb" by a factor of around 15% or so. Assume that you will want a carb around 85% of the CV size and that works out to 30.6mm.
So for a smooth bottom end and midrange, go with 30mm and for a littler more top end at cost of bottom end, try a 32mm. So much for the theory. Does anyone have any experience they can share of putting VM Mikunis on a GN400 for this poster? (corrected)
I'm thinking i'll go with the 32 since i'll be gearing the bike to run 30 min commutes to work on the highway. I'm not too concerned with bottom end but I don't want her to get winded real easy. Will the vm32 support modifications down the road? I know I'm going Pod filter and open exhaust right off the wing with possible high compression piston and valve work a season or two down the road.
I gave the place I ordered the carb from a ring and they don't do rejets. Looks like I'm going to have to order all the jets separately. I understood most of your previous post about carb setup except 2 parts...
what were you referring to when you said "slide 2.5"?
And also what did you mean by "needle 6dh3-1 [i1is the needle slot]"?
Thanks I can change jets and whatnot but i'm not too keen on the carb lingo
in a mikuni vm carb the throttle (valve) slide comes in different cutaways the cutaway you need is a 2.5 that is wat should be in the carb when you get it so no issue
the needle 6dh3-1
has groove in the top a circlip fits in
i would order a 32.5 pilot and a 300 main to give your self a bit f range
in this case the needle is in the top groove or at the leanest position to start
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