Needle valve seat screen & carb tuning

[Guest]

I'm in the process of rebuilding the carbs on my '82 GS1100GL and tonight I'm going to take # 4 of 4 out of the dip and reassemble everything. I followed the directions on BikeCliff's website (thank you BikeCliff & to everyone who contributed to his site) but in the walk through, the needle valve seat doen't have a screen on the end like mine does. My needle valve seat has a half sphere metal screen on the end opposite to where the needle valve goes.

1. Should I clean and reinstall this screen? I assume yes.

2. The setting of the air screws on my carbs before work started was 2.75 turns out so I assume that I should start there. Does that air screw setting determine whether my bike is running lean or rich based on adding more or less air to ignite the given amount of fuel?

3. When I put the carbs back together, do I first set the throttle valve stop screw at just touching in a closed position and then prop that carb open with a paper clip and make the other three match it? Then when syncing the carbs with a gauge, I will be fine tuning those adjustments with the balance screws.... correct?

4. Are there any other adjustments to make other than the air screw and the throttle valve stop screw in conjunction with the balance screws?

5. Does anyone living around me have a carb sync gauge that I can use? I want to purchase one but it's not in the budget right now. If not I may try to build my own gauge to hold me over.

I apologize for the noob questions but I'm finding working on my cycle easier and easier with each passing project. I guess I was intimidated in the beginning because of a fear of the unknown... Thanks to everyone for their help so far.

-Sean

 

[Guest]

1. Should I clean and reinstall this screen? I assume yes.

That screen & plastic sleeve assy should just pop off the end of the needle valve seat - use a small screwwdriver blade, but take care not to lose it. It shouldn't go into the dip because of the plastic sleeve.

2. The setting of the air screws on my carbs before work started was 2.75 turns out so I assume that I should start there. Does that air screw setting determine whether my bike is running lean or rich based on adding more or less air to ignite the given amount of fuel?

Those are the idle mixture screws - it will only adjust the lean/rich mixture at idle. Yes, i would start them where you found them & then use the "highest RPM method" to set the idle (do a search & you'll find lots of info)

3. When I put the carbs back together, do I first set the throttle valve stop screw at just touching in a closed position and then prop that carb open with a paper clip and make the other three match it? Then when syncing the carbs with a gauge, I will be fine tuning those adjustments with the balance screws.... correct?

You are doing a bench sync, all that matters is that each butterfly is initially set to the same gap so the bike will run. An easy way to do this is to turn the throttle adjustment screw to open the butterfly on the carb that doesn't have a sync adjustment screw (#3?) so just a sliver a light can be seen when you hold the bank up to the light. Then simply match that visual light gap with the other butterflys. It pays to get this as close as possible, makes the bike start easier.

Yes, a carb sync with a gage after the bike is running will fine tune those adjustments based on vacuum, not gaps...

4. Are there any other adjustments to make other than the air screw and the throttle valve stop screw in conjunction with the balance screws?

Once the bench sync is done, use the throttle adjustment knob to close the butterflys completely, then open them up approx 1-2 turns from completely closed.

WARNING - be ready to hit the kill switch when you start the bike in the event the idle is set to high. Turn the knob back a bit if that happens & re-start.


Good luck,
Mike

 

[Guest]

Great, thanks for the response. Now I feel confident that I can tune a set of carbs for the first time... now only if I had a set of sync gauges....