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Carb adjustment screws-'77 GS750

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Anonymous

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I know the screw that is on the top of each carb which is at an angle is to adjust the air/fuel mixture, I don't know what the screw is for on the bottom of each carb which comes out threw a hole in the float bowl (The Chiltons repair manual doesn't say!) Can someone please post or notify me of what this is for and also how to adjust the 4 air/fuel mixture screws and also the 4 unknown screws on the bottom. Thanks, Richard
 
Re: Carb adjustment screws-'77 GS750

The screw on top of each carb which is at an angle is NOT for adjustment of fuel/air. It is an air screw needle for the idle/pilot circuit. Turning it OUT lets more air flow and leans the idle mixture, so turning it IN would richen the mixture. For your bike with stock airbox and exhaust, this screw should be 1 3/4 turns out.

The screw that is on the bottom of each carb is the fuel pilot screw. It adjusts the fuel flow for the idle/pilot circuit. Turning it out increases fuel flow and richens mixture. Turning it in decreases flow. For a stock airbox and exhaust and your bike, this screw should be 1 1/4 turns out.

Both of these screws are fragile. DO NOT turn them down/in tight. About as tight as you want to turn them in to seat them is how tight you could turn them in if holding a greased jeweler's screwdriver between two fingers coated with teflon. Dont break the needle tips/points off in the passageways, or you will be buying new carbs.

Earl



quote="medicinalmotorcycle"]I know the screw that is on the top of each carb which is at an angle is to adjust the air/fuel mixture, I don't know what the screw is for on the bottom of each carb which comes out threw a hole in the float bowl (The Chiltons repair manual doesn't say!) Can someone please post or notify me of what this is for and also how to adjust the 4 air/fuel mixture screws and also the 4 unknown screws on the bottom. Thanks, Richard[/quote]
 
Thanks for clearing that up Earl! My '77 GS750 has the stock airbox with a 4-1 Kerker exhaust. I do not think it has been re-jetted. So would the adjustment be different since I do not have the stock exhaust, or would the
adjustment you mentioned suffice? (1 3/4 turns out for the top screws and 1 1/4 turns out for the bottom ones)
 
Adjusting those screws is for idle mixture. I would set the fuel pilot screws (underneath the carb) to 1 1/2 turns out if using a 4 into 1 to get a smoother idle. A Vance and Hines 4 into 1 header requires increasing the main jet size from the stock 102.5 to 115. I expect the Kerker is the same. Replace the main jets 1st thing, you will be wasting your time trying to set things up right with too small main jets.

Earl


medicinalmotorcycle said:
Thanks for clearing that up Earl! My '77 GS750 has the stock airbox with a 4-1 Kerker exhaust. I do not think it has been re-jetted. So would the adjustment be different since I do not have the stock exhaust, or would the
adjustment you mentioned suffice? (1 3/4 turns out for the top screws and 1 1/4 turns out for the bottom ones)
Click to expand...
 
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