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Fuel/Air screws on 79 GS750 carbs

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Gentlemen (and Ladies)
I know this has been covered before, but I can't find it for my bike specifically so I'll ask humbly for assistance.
On my '79 GS750E (N) carbs there are two adjustment screws. One is underneath the float bowl, more or less surrounded by it and on the engine side of the throttle slide. The other is on the airfilter side of the throttle slide and above the bore (much more easily accessible). I did a carb rebuild and tried to put the new screws back exactly as the old ones were (I replaced both screws on each carb), but I must have gotten the number of turns wrong. Can one of you more experienced people please tell me which screw does what and how many turns are required for the adjustment? Does one turn equal a full 360 degrees? Is there ever going to be a carb rebuild series for the non-CV type carb?
Any help will be much appreciated.
Thank you,
Harrison
 
On my 79 750EN with stock airbox, stock original pipes/mufflers and carb jet sizes, I have my fuel pilots set to 1 1/2 turns out (that would be 540 deg of rotation) :-) and I have my airscrews two turns out (720 deg rotation)

Earl
 
Earl says:

I have my fuel pilots set to 1 1/2 turns out (that would be 540 deg of rotation) and I have my airscrews two turns out (720 deg rotation)
Click to expand...

I'm not too familiar with this "degree" stuff, Earl. Do you think you could give it to me in "mils" instead? :lol: :lol: :lol:
 
Wouldn't that depend on the pitch of the screw as it's entering the orifice??
 
Oh, I'm gonna give it to you all right Ron. :-) :-)

Earl



frosty5011 said:
I'm not too familiar with this "degree" stuff, Earl. Do you think you could give it to me in "mils" instead? :lol: :lol: :lol:
Click to expand...
 
Thank you both, Earl and Terry.
However I am not sure which screw is which. I believe the fuel/pilot screw is the one underneath and on the engine side of the carbs. I've got 110 main jets and a stock airbox and filter but a 4-into-1 V&H exhaust.

Harrison
 
I reviewed the source that Terry gave me and what Earl wrote there differs with what he wrote just today. Maybe I oughta spend the $833 that Mikuni wants for a set of RS carbs jetted to my bike or send the carbs out to Motorcyclecarbs.com for a rebuild at a little over half the cost of new ones. It's just that I'm losing riding time and it hurts.

Harrison
 
My carb settings have been an ongoing process. I've been using the settings I gave for the last 10,000 miles or so. They are for a completely stock setup.
I would be surprised if they were correct for the way your bike is configured.

Earl


Harrison Clement said:
I reviewed the source that Terry gave me and what Earl wrote there differs with what he wrote just today. Maybe I oughta spend the $833 that Mikuni wants for a set of RS carbs jetted to my bike or send the carbs out to Motorcyclecarbs.com for a rebuild at a little over half the cost of new ones. It's just that I'm losing riding time and it hurts.

Harrison
Click to expand...
 
Re: Fuel/Air screws on 79 GS750 carbs

Harrison Clement said:
Gentlemen (and Ladies)
I know this has been covered before, but I can't find it for my bike specifically so I'll ask humbly for assistance.
On my '79 GS750E (N) carbs there are two adjustment screws. One is underneath the float bowl, more or less surrounded by it and on the engine side of the throttle slide. The other is on the airfilter side of the throttle slide and above the bore (much more easily accessible). I did a carb rebuild and tried to put the new screws back exactly as the old ones were (I replaced both screws on each carb), but I must have gotten the number of turns wrong. Can one of you more experienced people please tell me which screw does what and how many turns are required for the adjustment? Does one turn equal a full 360 degrees? Is there ever going to be a carb rebuild series for the non-CV type carb?
Any help will be much appreciated.
Thank you,
Harrison
Click to expand...
The pilot screw is the one underneath and engine side of the floatbowl. To richen this screw you turn it OUT(counter-clockwise). Make sure you never seat these tightly, the tips can break off. The factory sets these with an emissions analyzer, you cannot re-set them exactly. They will come from the factory set differently from each other. There is no single factory setting. These are for fine tuning to allow for the differences in cylinders. They are generally out between 3/4-1 1/2, but that is just generally. You have to adjust and test.
The side air screws. To allow less air(richen) you turn these IN(clockwise). These are also set at the factory but are not quite as sensitive as the pilots. To set these, run the engine at normal operating temp and adjust all 4 to achieve the highest idle possible. Adjusting 2 at a time in 1/2 turn increments is easiest to hear the rpm's. After achieving highest idle, re-set the idle with the idle knob/screw. These are also intended to temporarily fine tune if you are riding in different elevations or large temperature changes. And yes, 1 turn is 360 degrees.
You may not have to re-jet just for the pipe. You have to test and do what the plugs say.
 
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