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motaman38
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VBMWMO #9318
Joined: 08/31/2017
Posts: 7

On a recent motorcycle ride, as I was upshifting gears to 4th, I was cruising at about 50 mph and 4,000 RPM, then
noticed a drop in power, (drop in both engine speed and wheel mph speed). Then it climbed back up, then shifted
to 5th gear and again, and as I increased the throttle, the same drop in power, both engine speed and wheel speed occurred.

I pulled over on the shoulder to check and looked at the fuel supply lines, from both sides of the tank. I tapped on the
in line filters (transparent), and noticed air bubbles in the fuel? Could this be an issue? Or other fuel delivery
issue?

I switched the fuel supply valve from the standard fuel supply position to the reserve position to see if drawing fuel from a different area of the tank would help and the problem seemed to go away. Therefore, I switched the fuel valve position back to the standard supply position and after about 1/2 an hour of driving in the standard fuel supply position, the problem cropped up again.

Any advice/or assistance is appreciated, thank you!

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Motaman

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6480
Check the float

Check the float levels...could be running lean on high demand situations. First, crack the gas cap to see if they also helps...could be the tank is not venting. Next, when you're having this problem, as quickly and safely as you can, chop the throttle, turn off the engine, and coast to a safe work area. Drop the bowls and see where the fuel level is. Not sure what it should be on the slide carbs but for CV carbs, the height of fuel in the center of the bowl should be about 22-24mm deep.

If the float setup is the same as the CV Bings, the fuel should stop flowing when the float is lifted up by a finger and the mold line on the float is parallel to the body of the carb.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

motaman38
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VBMWMO #9318
Joined: 08/31/2017
Posts: 7
fuel starved engine at high speeds 4th/5th gears

Thanks for the advice Kurt.

I checked the vent and the tank appears to be venting well.

I actually tried disconnecting the fuel lines from the carb and running them. the fuel valve screen had gunk
in them on both sides. I cleaned them and reconnected. The fuel starvation appears to have gone away. If it occurs
again, I will check the floats, as you suggested for correct levels in the bowls.

Steve

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Motaman

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6480
What was the gunk? Was it

What was the gunk? Was it red in color? BMW lined their tanks with a red coating...it works well, but over time it will probably begin to flake off. If it becomes a frequent deal, then the tank will have to be relined with a newer technique...there are a few options out there.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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