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I think you might have wandered into the wrong forum. Should be in the repair forum. You're sort of there, but not quite. You might get more views thus more help.

I don't know specifically where this bike should start out, but generally the screw should be set around 1 1/2 turns out, maybe 2. I'm assuming this is a fuel mixture screw, but it could be an air mixture screw. Bike carbs have one or the other, not both. They have similar functions in that they're important for air/fuel mix at idle. If it is on the side of the carb near the engine, fuel mix, if it is on the side of the carb to the air box, air mix. These only affect the fuel/air mix at and just above idle. More open throttle settings involve a gradual handing over of duty from the pilot jet to the main jet. So you're only influencing fuel mix at lower throttle settings. An important task, but not the only one in need of consideration.

I'm of the mind it shouldn't be the only adjustment made for the installation of an aftermarket pipe. I'm assuming that is why you're asking. If you are also making other mods, like a free flowing air filter, pod filters, etc., they'll affect the breathing of the bike and require some carb fiddling too. You'll be wanting to look at the jet sizes for both the pilot circuit and the main circuit. The jet needle may also need adjusting to accommodate the changes in aspiration (it can be raised or lowered to change the way fuel is metered through the main jet). Google plug chop testing to get an idea of what you're going to need to do to get the job done correctly unless you've got access to a dyno and an exhaust gas analyzer. Someone mentioned acolortune elsewhere in here (I think). Handy tool to have in hand for this task.

The bottom line is that putting a new pipe on, unless it is an OEM replacement, is going to involve more work than just installing the pipe and making a simple screw adjustment to the carburetors. It will require you to obtain a few extra jets in different, usually larger, sizes. I recommend getting sets that are close to stock, but 1 and 2 sizes up for starters as this might be all you need. You'll need a pocket full of brand new spark plugs to do the chop testing as you want virgin plugs for each run.
 

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Tuning

There are tuning guides for this sort of thing.
They tell you to start with the main jet and work your way down.
After all, going down the highway at 70, is more important than how it idles.
Same thing with pulling away from a light.

It is also possible to have two identical bikes, with the same pipes and filters, and require different size jets.
Elevation is also a factor. The compression may drop 10 pounds of pressure from San Diego to Reno.

Time of year is another factor. The air is more dense in the cooler winter months.

Unkle Crusty*
 

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All good responses you have received. I have also ready 1 1/2 to 2 turns out, for a Stock setup.

Somewhat related.......I had a 1984 Honda Shadow 500cc that was sluggish entering highways, on entrance ramps. It seemed to lag a bit.

I took the Carbs totally apart and made sure everthing in those was up to snuff, and checked the fuel line and filter. Still did not solve the problem.

Seeking some advice, I was offered the option of getting some igition washers and putting one or two on the Main Jet, to allow more fuel in. It worked.

May be totally unrelated to what your trying to solve, but perhaps not.

More on track with your question, changing the pipes can potentially have an effect (affect?) on your combustion ratio. Thus the reason Ignition kits are often recommended with pipe conversions.

If it were "me," I'd make an adjustment; try the bike out..........if it was bluing the pipes, I'd assume I'm running lean, and give it a half turn.......try it out........see what it does.
Trial and error can help you find the right fuel setting. Your not likely to ruin the bike by a few short rides to see how the bike reacts to various conditions (such as highway entrances; accelerations at lights, idling,etc..)

-Soupy
 

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Seeking some advice, I was offered the option of getting some igition washers and putting one or two on the Main Jet, to allow more fuel in. It worked.
Would you expand on this? Are you talking about raising the het needle in the slide a bit so it is opening the main sooner as the slide rises to open the carb? On some carbs the jet needle has several slots so all you do is move the circlip up (lower the needle) or down (raise the needle) to make adjustments.

What do you mean by ignition washers? I was thinking those were index washers used to position the spark plug's side electrode in the combustion chamber so the gap faces the intake valve(s).
 

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Bwana: At the time I did the modification, it was back when I didn't know much about Carbs on a bike, and I can't say I'm any expert on the subject.

Basically, I went out to my local Bike shop, after being advised to put Ignition Washers on my Main Jet (they were just silver washers that slid on to to Main Jet when I disassembled the Carbs and bottomed out on the head of the Main Jet) told the guy I wanted a set of ignition washers for my two Carbs on my bike. He handed me a bag of four, and I put two on each.

I re-assembled the Carbs, and re-installed them, and whala!! The Main Jet was now restricted from bottoming out, since it sat higher because of the washers, allowing more fuel to flow.

Gas mileage could suffer a bit but I didn't care. Gas is "cheap" with a bike, and I wanted the performance to improve.

Hope that helps.......

-Soupy
 

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Actually 1 1/2 turns of air screw or 1 1/4 turns are for bikes when new.assuming ur old motorcycle. Best way is to start the bike let it attains normal working temperature. Then tighten the idle screw for 1 /2 rounds to raise the rpm.then tighten / loosen the air screw and see where at point I get maximum rpm . This point is the ideal air screw settings. Then loosen the idle screw as per ur requirements

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