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Vm34 jetting help

Discussion in 'The Garage' started by 82xs400dude, Feb 26, 2021.

  1. xschris

    xschris XS400 Guru Top Contributor

    cv carbs are perfect for street use. They make for smooth and even operation with best overall performance. A very well setup VM or direct lift carb will make more power at top end over the cv but are not great for every day 4-stoke street bikes. Members with sohc xs400 bikes that have used both complained about hard engine braking and lots of "jerking" throttle/operation. If your going to race one of these on a track where full on and off throttle happens at every turn, a VM carb setup would be a must. The stock cv carbs are the best setup for stock every day bikes. Yamaha xs400
  2. 82xs400dude

    82xs400dude XS400 Member

    I haven't been online in a while but I'm encountering some issues already. It idled perfectly for a while but about 20 minutes ago it started spewing raw fuel out of cylinder 2 exhaust. I've got spark. But the plug is pure black. I replaced the plugs but cylinder 2 is still spewing raw fuel
  3. amc49

    amc49 XS400 Junkie

    Exactly and why they use them so much now. Modern street bikes are the equivalent of hard core race bikes just a short time ago and the complaint is commonly of direct lift carbs opened too quick at too low an rpm to often get a big fat bog when the engine rejects too much carb down low. The opposite can be even worse, if you've ever driven say Kaw 1000 with well set up engine and still using the direct lift Mikunis the bike will nearly wrench your arms out of sockets if you suddenly gas it up too much at a takeoff, it can kill inexperienced riders easy as spit. That bike wants to GO! and you better be ready for it!

    CV carbs get rid of all that. The key words above in post #41 are 'best overall'.
  4. amc49

    amc49 XS400 Junkie

    Post #42 most likely you have begun flooding. Check float height, inlet needle and seat. Trash in fuel.

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