Lousy Mileage - Rich Mixture?

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Bonwit

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My 850 with a single Mikuni conversion is getting lousy milage (27 to 30 MPG!). Other indications, like sooty plugs, point to too rich a mixture. Today I pulled the needle and found the e-clip set to the middle position. Is this a reasonable default? In changing it, should I only move it a notch at a time?

Any other ideas what may be causing this bad mileage. The bike runs okay, but this fuel flow is killing me!
 
Needle height affects 1/8 to mid openning of the slide. If you have the needle in the wrong position you will notice while slowly accelerating the power is not smooth. You didn't mention what venturi size Mikuni.
 
I got a VM 34 on my 850 Mk2. Make sure the air filter is OK. Also fit the biggest you can. Try dropping the needle a notch at a time. Also check the float level. There is a circle mark on the main jet body that the arms of the floats should align with. Also the main jet should be 240 to 260, not more than that. It may be possible the needle and or needle jet is the wrong type. See if you can verify these settings -

Main Jet 240 - 260

Needle Jet P2 or P4

Needle 6DH3 or 6DH4

Pilot Jet 35 - 40

Air Jet 1.0

Slide 3
 
I run Keihin FCRs, but I had a similar experience. Carbs came "prejetted for [my] application." Bike ran fine, but lousy mileage and black plugs. I ended up going from 155 to 140 mains and raising the needle clips several positions, as well as tinkering with the slow fuel and air screws.

I started with about 35 MPG and now get above 50. On extended cruises, I have topped 60 MPG.

Best I can say is one step at a time, lean it out a bit and see what happens. Keep an eye on your plugs.
 
ML said:
I got a VM 34 on my 850 Mk2. Make sure the air filter is OK. Also fit the biggest you can. Try dropping the needle a notch at a time. Also check the float level. There is a circle mark on the main jet body that the arms of the floats should align with. Also the main jet should be 240 to 260, not more than that. It may be possible the needle and or needle jet is the wrong type. See if you can verify these settings -

Main Jet 240 - 260

Needle Jet P2 or P4

Needle 6DH3 or 6DH4

Pilot Jet 35 - 40

Air Jet 1.0

Slide 3
Click to expand...

I pulled it apart today and found a 260 Main, 35 Pilot, 2.5 Slide and 6DH3 needle. Not sure how to get to the Air Jet or the Needle Jet, but given the other numbers, I suspect they're in the ballpark. I raised the e-clip a notch and will give that a try. I think BrianK's advise is sound. . . One step at a time.

Thanks
 
Make sure your timing is correct for what ever type you are running ,undo the main jet and the needle jet should just push out through the top.
 
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