Need help: air screw adjustment CV carb...

[jlvdo]

How do you actually adjust the air screw once the assembly is replaced on a 1980 GS750ET??? I've searched the threads long, far and wide and cannot find any ready solution.

HELP!!!

[doctorgonzo]

Sure I will be corrected if I'm wrong, but CV carbs don't have an air screw. The one screw on the engine side of the carb is a fuel screw. It's a bugger to get to, but with tank off can be done with an extra short screwdriver.

[jlvdo]

http://www.thegsresources.com/gs_carb_03.htm

Pics 26-29... air screw. I probably shouldn't have replaced it, but, too late now, at least for carb #1.... And on further reflection, probably have to replace all of 'em to get uniform...performance? Unless there's a "stock" setting I can get this one back to.

[doctorgonzo]

You're probably right. I always thought it controlled fuel. Tighter is leaner (on my 81 with CV carbs) and open is richer. You can get back to stock, BassCliff has online manuals and they list the setting. A good start would be tighten til they seat and then turn out 2 turns.

[SqDancerLynn1]

Generally 2-2.5 turns out from lightly seated. Before you start messing with the carbs, order a set of carb O rings if you haven't done so,

[jlvdo]

o-rings... check. I've complete rebuild kits.

Anyone have the definitive (if they exist) factory setting for this air screw???

[Nessism]

Set as Lynn stated, warm up the engine, then tweak the screws until you achieve the highest idle setting. All carbs should be pretty close to each other when it's all said and done.

[renobruce]

And the pics are wrong in calling them air screws. Those are pilot fuel screws. In leans the mixture, out richens it. If you haven't already removed the others, just count the turns out on them and set the one you removed the same. They should all be about the same within a 1/4 turn or so. Do the highest rpm on them at idle, then once the bike is back together, do a synch and do some chop tests at minimum throttle openings, and adjust accordingly.

[duaneage]

You're going to have to synchronize the carbs with a 4 way device, and you won't believe the difference. I checked mine tonight because I had a little off idle stumble and an erratic idle. # 4 was lagging behind a bit. After a little tweaking and it runs like an electric motor. But it takes a mercury tube kit or similar apparatus to get 'er done.

On a technical level, the idle screw allows fine tuning of air for the engine's operation at idle while the throttle is closed. You need a richer mixture to idle an engine, about 8.5 to 1 versus 14-1 at cruise. It also smooths the transition from idle to slow speed when you take the grip up a little. Everything has to be balanced in the carb and all 4 have to do the same thing at once. Robert Barr ( a member here) offers the o ring that fits under the needle and without good ones you can't get the thing to behave.

[doctorgonzo]

Well, I feel better that I'm not retarded and they are fuel screws. Made sense with out being richer.