Air Screws - what counts as "lightly seated"?

[Fenixgoon]

82 GS650G with the mikuni CV carbs. I know the factory setting is supposed to be 1.5 turns out from lightly seated.

However, I don't know what lightly seated is supposed to mean. I have both a small, jeweler's screwdriver and a much larger (normal sized) one. With the small screwdriver, I encounter resistance much earlier on, due to the limited ability to apply torque. This would leave me with a much richer fuel mixture, compared to using the normal sized screwdriver.

So, what do I do to get the "lightly seated" position? I guess it's better to run rich than lean? Not that it's difficult to adjust (especially if I do the highest idle method), but I'd like to get as close as possible the first time around


edit: I'd like to apologize in advance for beating a dead horse

[BassCliff]

Hi Mr. Fenixgoon,

If you screw them in too tightly you'll break the tips. That would not be good.


Thank you for your indulgence,

BassCliff

[Fenixgoon]

Hi Mr. Fenixgoon,

If you screw them in too tightly you'll break the tips. That would not be good.


Thank you for your indulgence,

BassCliff

so use the small screwdriver and be too rich, rather than overscrew and be too lean?

[lurch12_2000]

So, what do I do to get the "lightly seated" position? ...

Try using a regular screwdriver that fits exactly to the screw head and just use your thumb and forefinger when turning clockwise until it stops to lightly seat it. Then back off(counterclockwise) 2 turns to start. Usually I count four 180 degree turns so as not to lose my orientation.

[Nessism]

The important thing is to set the screws to somewhere in the 2 - 2.5 turn range, and then tweak the settings to archive the highest idle speed. Setting to some arbitrary point like 1.5 turns since Suzuki set them there due to emissions reasons is not a good approach. Also, a vacuum sync is important so do that before fine tuning the carbs too much.

[Fenixgoon]

The important thing is to set the screws to somewhere in the 2 - 2.5 turn range, and then tweak the settings to archive the highest idle speed. Setting to some arbitrary point like 1.5 turns since Suzuki set them there due to emissions reasons is not a good approach. Also, a vacuum sync is important so do that before fine tuning the carbs too much.

yeah i fashioned myself a home-made manometer. do i do the carb synch before or after the air screw adjustment?

[49er]

yeah i fashioned myself a home-made manometer. do i do the carb synch before or after the air screw adjustment?

You should set your fuel screws first, synch the carbs, then fine tune their mixtures to their highest idle positions. Because they are fuel, not air screws, increasing the number of turns off their seats will richen the idle mixtures.

[Steve]

edit: I'd like to apologize in advance for beating a dead horse

Poor horsey.

Try using a regular screwdriver that fits exactly to the screw head and just use your thumb and forefinger when turning clockwise until it stops to lightly seat it. Then back off(counterclockwise) 2 turns to start. Usually I count four 180 degree turns so as not to lose my orientation.

That's exactly how I do it, too. I will even scratch a line in the perimeter around the mixture screw to show where the slot was when it was lightly seated.

yeah i fashioned myself a home-made manometer. do i do the carb synch before or after the air screw adjustment?

Care to share some details about your manometer? Many have tried, some have succeeded. Might be able to save you some grief if yours has some blatant errors.

You should set your fuel screws first, synch the carbs, then fine tune their mixtures to their highest idle positions. Because they are fuel, not air screws, increasing the number of turns off their seats will richen the idle mixtures.

And, ... before you do your carbs, you should have adjusted your valves.

Yes, you will need to set your mixture screws out far enough for the bike to run decently, then warm up the bike enough that you are not using the 'choke', and sync the carbs. When the carbs are synchronized, you can fine-tune the mixtures. I like to leave the gauges connected when I do the fine-tuning, just to be sure that the sync is still good. If the mixture was way off, it could conceivably affect how that cylinder was running enough to affect the sync. Have not had to re-sync a set of carbs yet, but it makes me feel better.

The screws you are adjusting are not strictly fuel screws. Neither are they strictly air screws. They actually adjust a mixture that is pre-determined by the pilot air jet in the carb intake and the pilot fuel jet in the float bowl, next to the main jet. That just might be why their proper name in the manuals is "idle mixture adjustment screw".

.

[49er]

The screws you are adjusting are not strictly fuel screws. Neither are they strictly air screws. They actually adjust a mixture that is pre-determined by the pilot air jet in the carb intake and the pilot fuel jet in the float bowl, next to the main jet. That just might be why their proper name in the manuals is "idle mixture adjustment screw".

.[/QUOTE]

Touche They're a lot less likely to be mis-identified than on the VM carbs though!!!

[Fenixgoon]

steve, i did adjust my valves according to the suzuki method. they are on the tight side of things - 0.04-0.05mm clearance for all 8 valves.

got the idle screws out, put new o-rings on, put them back in... now i am fighting to get the bike running. it has a strong crank, but it hasn't actually started. arg

any marylanders want to help a brother out?

[twr1776]

IMHO you are better off going "looser" on the valve clearances. The valves will "tighten" up between adjustments. As Nessism mentioned 2 1/2 turns is a better starting point. On my 850 with CV's I am running at 3 turns out.

[Fenixgoon]

IMHO you are better off going "looser" on the valve clearances. The valves will "tighten" up between adjustments. As Nessism mentioned 2 1/2 turns is a better starting point. On my 850 with CV's I am running at 3 turns out.

well whatever they're at right now, they seem to work pretty well (idle screws, that is)! before, i was able to have a steady idle only when i had the choke on. now, i started up with the choke, but took it off and it held just fine. took the bike out for a short ride (a few miles) after that to warm it up, but rain/thunder/lightning just started, so the bike's back in the garage in front of a fan cooling off. tomorrow i will carb sync and do highest idle for sure!