adjust for carbon deposits?

[Guest]

So my #1 and #4 carbs are running a little carbon rich-I can wipe off a little soot from the spark plug ends, whereas the 2/3 plugs are pretty clean. The only adjustment I can think of is the air screw? And turning it out would help it run a little less rich?

I was gonna start by turning the #1/4 air screws out between 1/4 to 1/2 turns each. Maybe 3/8?

sorry, so damn busy with work, long weekend ride coming up, I could really use some help here.

-Emmet

[Nessism]

Can you turn the fuel screw in?

[1_v8_merc]

Had the same problem on my 78 gs750....

I had the fuel screws set 1 turn out(pretty lean), but it still didn't help.

I eventually set the Air screws out a little more, and it leaned the plugs out.

It will only affect the plugs at Idle though, at running speed your Jets are responsible for fuel/air mixture....(and other things are responsible too)

[midnightcafe]

Can you turn the fuel screw in?

i could

[AJ]

As others have said, you can lean out your idle on the affected cylinders using the mixture screws (the small ones on top of the main carb body at the engine side of the carb). Screw in or out for max idle - that should set the mixture right for idle.

If the plugs are still more sooty than you like after that adjustment, you'll likely want to do some plug chops to check the high-speed circuit. Search for "carb plug chops" and you'll find a good description.

Finally, check carb synchronization. All this stuff is balanced, so what you'd like to do is make small adjustments until you narrow in on the optimum setup.

All this carb stuff makes me really appreciate the fuel injection systems on some of my other bikes!

[Nessism]

As others have said, you can lean out your idle on the affected cylinders using the mixture screws (the small ones on top of the main carb body at the engine side of the carb). Screw in or out for max idle - that should set the mixture right for idle.

If the plugs are still more sooty than you like after that adjustment, you'll likely want to do some plug chops to check the high-speed circuit. Search for "carb plug chops" and you'll find a good description.

Finally, check carb synchronization. All this stuff is balanced, so what you'd like to do is make small adjustments until you narrow in on the optimum setup.

All this carb stuff makes me really appreciate the fuel injection systems on some of my other bikes!

You are thinking of CV carbs, the OP has VM carbs which are different.

I'd try setting the fuel screw to 3/4 of a turn open and then adjust the air screw from there to see if that helps.

[midnightcafe]

thanks again guys, appreciate the help. prepping my bike for a weekend ride through the Adirondacks with some guys from the local Brit bike shop.

went the see a Chiropractor today (chronic back pain SUCKS), another appointment Friday before the ride. bought new Hagon shocks, should be a comfortable ride