running rich

[OhioGS750]

My bike is running rich as i have black sooty plugs. not wet. Certain threads say the air fuel screw controls air others say fuel. Which is it? In to richen or out. Thanks

[don_gibb6512]

It controls fuel. Out is rich. If you have stock carbs, out no more than 3 turns max. A normal setup would have them out 1.5 - 2 turns out.

Check the voltage to your coils. Less than 12 volts will cause an otherwise normal running bike to foul plugs. While you're at it, check the resistance of your primary and secondary windings on the coils. 3-5 ohm for the primary and around 32K ohm for the secondary, if they're OEM stock coils.

[C.V.]

In or out depends on the carbs. Out richens for cv carbs, but leans VM carbs, if I'm not mistaken. What year is your bike?

[OhioGS750]

1979 gs750 l .

[ryonker]

I have the same bike.

You have a screw on the bottom of your VM carbs that adjusts the fuel mixture. I turn mine about 2 turns out. Turn them all the way in (gently, light hand till they stop), then turn 2 full turns out. Some turn them 2.5 turns out, but if your running rich, start with 2.

Then you have the screws on the side of your carbs; these adjust your air mixture. I would go 1 to 1.5 turns out. Again, lightly screw them in until they stop. Then back them out 1.5 turns. The more you turn them out, the leaner your burn will be.

Good Luck!

[Guest]

Before I start messing with the carb settings make sure the ignition is sound. Points, condensers and coils.

[don_gibb6512]

Before I start messing with the carb settings make sure the ignition is sound. Points, condensers and coils.

AMEN to that !! If you don't have a good, solid spark you can chase your tail forever trying to get it right with carb adjustments. My input on the fuel mixture screws was for a CV carb. Sorry. I didn't realize you had the old VM type.