Idle and Synch Puzzle

[KEITH KRAUSE]

The air screw is often referred to as the Mixture screw" and the number of turns varies depending on the engine number.

The air screw IS often referred to as the mixture screw but it shouldn't be. That incorrect terminology just leads to misunderstanding.
The "air screw" is only used on the VM type carbs. It meters air only through a passage and feeds that to join the fuel going through the pilot jet. The same VM carb also uses a seperate pilot fuel screw that meters mixture. The pilot screws job is to ASSIST the pilot jet. Since there are differences in each cylinder, the pilot jet alone can't supply the exact mixture needed so the pilot fuel screw acts as the fine tuning to allow for those differences in each cylinder.
A mixture screw is used by the CV carbs and meters mixture.
The number of turns any screw is set at from the factory (air screw/pilot fuel/mixture) is determined by an emissions analyzer, not the engine number or engine type.

[KEITH KRAUSE]

After some more putting around, I did another plug check.

This beast is running richer than Daddy Warbucks. Plugs are black and sooty, and she was backfiring heartily. She also chugged gas like it was 1972.

Of course, the No. 3 cylinder is a complete mystery, oily and suspect. So I will have to tear into the top end.

As for the other mixture results, I am not that bummed out, because richness I can tackle.

So far, I pulled the carbs and reset the fuel screws to about 3/4 turn. Will try to fine tune that mix for one more ride before the weather craps out on me.

For those keeping score at home, the current specs are:

V&H 4-1 Pipes
K&N Pods
Main Jets 122.5
Pilot Jet 17.5
Fuel Screws 3/4 turn
Air Screws 1.5-1.7 turn (factory says 1.6)

Now I will put together a shopping and task list for the top end work. Time to wreak havoc in the 4-Cylinder Engine Forum with another "Noob" thread.

Not sure what throttle positions gave you the rich results. As for the pilot circuit, I suggested using the 17.5 pilot jets (if several tests showed the stock 15 wouldn't work with additional turns out on the pilot fuel screws) and at that time setting the pilot fuel screws to something close to factory which would be right around 3/4 turn out. If you tested the pilot circuit with 17.5 jets AND richer than factory pilot fuel screw settings then I can see the plugs being black.
As for your other jetting and if it's to blame for the very rich reads/performance, keep in mind that 122.5 mains are actually on the small side when compared to many members here with your model and same mods. They claim good results using up to 130 mains in some cases, 125/127.5 being the most chosen sizes.
Your jet needles being set two positions richer shouldn't be as rich as you describe but it is possible they could be rich and are PART of the rich problem. However, my experience shows that one position richer is NEVER enough for your mods and 1 1/2 positions sometimes works. 1 1/2 is the minimum needed. Hard to believe that you could be 1/2 position too rich and the results are very sooty/black plugs. Of course, you didn't say at what throttle position you were testing.
Sounds to me like something else is going on here. IF properly tuned and the motor in decent condition, experience shows your current jetting wouldn't result in black/sooty plugs. Electrical problems/weak spark will cause sooty plugs. Be sure all basic tuning is done first.
You have to test all 3 circuits at the correct throttle positions and tell us what the plugs/performance was at each test. Note any changes in color between tests and let us know.

[Guest]

The number of turns any screw is set at from the factory (air screw/pilot fuel/mixture) is determined by an emissions analyzer, not the engine number or engine type.

Right maybe I shouldn't have been so brief in my post. I was making reference, in this case, to the carb specs from which Mister Cinders may have interpreted the 1.6 as being the number of turns on the air screw as seen in the carb thread:

http://www.thegsresources.com/_forum/showthread.php?t=73723

And from which the mixture screw is actually referring to the air screw (misleading as you pointed out Keith).

I'm still wrestling with these VM carbs myself.

[KEITH KRAUSE]

Right maybe I shouldn't have been so brief in my post. I was making reference, in this case, to the carb specs from which Mister Cinders may have interpreted the 1.6 as being the number of turns on the air screw as seen in the carb thread:

http://www.thegsresources.com/_forum/showthread.php?t=73723

And from which the mixture screw is actually referring to the air screw (misleading as you pointed out Keith).

I'm still wrestling with these VM carbs myself.

Hey, no big deal.
Carbs are confusing enough so I don't want others to read something that's wrong and take it as fact.
I think some of the bad info out there such as how many turns out a particular screw is is the fault of Clymers and other manuals that often aren't worth their weight. And for anyone to think an engine number dictates screw positions is beyond me.

[Nessism]

In support of Keith's comments, electrical needs to be reviewed since a weak spark can mislead people to think the carbs are off. 11 volts or more at the coils is recommended and make sure the spark plug caps are in good shape and have a fresh attachment to the plug wires.

As far as baseline start point for the adjustment screws, 1.6 for the pilot air screw is about right, as is .75 for the pilot fuel screw. Of course, these are just starting points so you may have to tune from there.

And before fine tuning the carbs also make sure the fuel height is set correctly - using a gauge is recommended (they are easy to make). You can even check the fuel height with the carbs on the workbench (which makes it easier). To measure is to know.