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Is there much difference between carbs set up for 2-stroke vs. 4-stroke engines? Will one work on the other?
 

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some of the 1970s two stroke bikes have an oil feed (1974-75 kawi h2s for example) that adds 2 stroke oil into the float bowl but other than that with appropriate jetting and adjustments they should work fine. Kawasaki and suzuki used mukuni VM carbs on both their 2 and 4 strokes in the 1970s.
 

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The carbs use the same bodies and floats and such but the slide cutaway is sometimes different and the needles and needle jet tube are different series. Sudco can tell you about what needle, needle jet and slide cut away you need for most applications. In fact I am going to need to do the same thing myself in the near future.

Ken
 

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I know in some cases it can be as simple as a jet changes...like Keihin PE series carbs that seem to work will for either. Other carbs like Mukinis like to have the different slides, emulsion tubes all kinds of crap. Some time check out the difference in the emulsion tubes, the two stroke tubes are shorter and four stroke longer (or vice versa) something about a two stroke providing more "signal" to the carb.
Personally I've found the Keihins far easier to tune for a four stroke than the Mukunis. The Keihins respond in very predictable, repeatable fashion to jet changes, needle height etc.
JohnnyB
 

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I agree with JB - the Keihins are pretty much a bolt on solution. For our 175 racers it's raise the needle, change the main, race.

Most of the VM Mikunis come with a bleed type needle jet. That's typically used on 2 strokes. It has a lot to do with the way the motor wants to get fuel off idle and when going from closed to open throttle rapidly. I haven't checked but the Mikuni tuning manual may have something to say about that.

The primary type needle jet includes an emulsion tube and works differently. The Sudco paper catalog has good pictures of the two different styles, not sure if the online catalog does. They do have primary type emulsion tubes available for most of the VMs they sell. They might even be able to help with jetting specs, needle choices etc if they've sold enough of the carbs for the application.

There are a lot of adjustments available on a carb - main jet, needle jet, needle jet style, needle diameter, needle taper, needle taper length, throttle valve cutaway, idle jet, and air mixture screw at least for most carbs. For FCR's they have even more adjustments and also include a accel pump. They're a bit like Webers on a vw/porsche - infinitely adjustable which for most folks means infinitely f$^kupable.

It's pretty nice when the carbs are very close to correct from the get go and need only minor adjustments to get them right.

Michael
 
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