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GS 750 Air screw adjustment

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

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I have a 1977 GS 750 and my two outer head pipes are running quite a bit hotter then my two inside pipes. The bike itself is running well. But I can grab ahold of the inside pipes with my bare hand and can feel the heat from the outside ones just by putting my hand near them. I think it may have to do with the air mixture screw in the outside rear of the carbs but I'm not quite sure.
 
Re: GS 750 Air screw adjustment

77Zuk750 said:
I have a 1977 GS 750 and my two outer head pipes are running quite a bit hotter then my two inside pipes. The bike itself is running well. But I can grab ahold of the inside pipes with my bare hand and can feel the heat from the outside ones just by putting my hand near them. I think it may have to do with the air mixture screw in the outside rear of the carbs but I'm not quite sure.
Click to expand...

Hi:

Have you seen the spark plugs?
They looks the same appearence?
Black is rich mixture wiht gas or and oil.
White poor mixture, too much air.

Eliseo.
 
The outer 2 spark plugs are a very light tan almost white and the middle 2 are black but it is not oil as far as I can tell. So the outer are running lean and the inner are running rich. If it is the air mixture adjustment screw which way do I turn it to lean it out or enrichen the mixture?
 
You are saying you can hold the #2 and #3 header and not burn your hand. How long was the bike running when you did this test? My pipe is too hot to touch in about 10-15 seconds. You also say it's running good. I can't believe good combustion is taking place. Two cylinders firing that poorly should make the bike barely run. It's possible you have an over-rich mixture, but I think you have a bad coil. One coil feeds #2/3, and the other feeds #1/4. But if you want to try the screws, the pilot screws (underneath/engine side), turn in (clockwise) to decrease fuel, out to increase. The side air screws, turn in to decrease air, out to increase.
Never tighten these screws down hard, seat them lightly if you are counting their turns out. And be careful about turning them, they can strip easily.
 
Its probably not your carbs and their adjustments. Try replacing the right pointset and timing the 2-3 cyclinders.

Earl


77Zuk750 said:
The outer 2 spark plugs are a very light tan almost white and the middle 2 are black but it is not oil as far as I can tell. So the outer are running lean and the inner are running rich. If it is the air mixture adjustment screw which way do I turn it to lean it out or enrichen the mixture?
Click to expand...
 
Both sets of points are brand new and don't have any burnt spots on them. And I just re-did the ignition timing. A friend of mine messed with my air adj. screws though. Thats why I thought it might be the settings on those. I can let the bike run for about 45 seconds or so and still grab the 2 & 3 pipes. It is running smoothly and not sputtering or anything else. All the plugs are getting spark too.
 
77Zuk750 said:
Both sets of points are brand new and don't have any burnt spots on them. And I just re-did the ignition timing. A friend of mine messed with my air adj. screws though. Thats why I thought it might be the settings on those. I can let the bike run for about 45 seconds or so and still grab the 2 & 3 pipes. It is running smoothly and not sputtering or anything else. All the plugs are getting spark too.
Click to expand...

So did the bike have this problem BEFORE your friend played with the screws? If the bike is running fine, I'm surprised. You cannot be getting good combustion and still hold the pipes. Your 2/3 plugs are running black, which is proof. You either have a weak spark at 2/3, or a very rich mixture. Did you try adjusting the pilots or side air screws yet? Did I explain how to adjust them OK? Are the plugs all the same heat range and are they gapped correctly?
 
Actually the bike was not running well before due to improper points gap but i fixed that. While I was doing that though my friend messed with the carbs. I had the bike running a few days ago and now it will not start. I'm getting gas and spark but I think the ignition timing is off again but I'm not sure. All the plugs are in good shape and the correct ones and they are gapped right. and I know gas is getting to the cylinders but it is not igniting properly now. Oh well back to tinkering :roll:
 
77Zuk750 said:
Actually the bike was not running well before due to improper points gap but i fixed that. While I was doing that though my friend messed with the carbs. I had the bike running a few days ago and now it will not start. I'm getting gas and spark but I think the ignition timing is off again but I'm not sure. All the plugs are in good shape and the correct ones and they are gapped right. and I know gas is getting to the cylinders but it is not igniting properly now. Oh well back to tinkering :roll:
Click to expand...

Since you probably have no idea where the screws were set, I can give you a "ballpark" estimate of how to set them.
The PILOT screws (underneath) are set at the factory and cannot be re-set exactly. They are commonly set differently from each other because of differences in each cylinder. My experience has been they are about 1-1 1/2 turns out from lightly seated. This should be close enough to help you get started again (if your problem IS incorrectly set screws).
The AIR screws, on the side, should be adjusted for the highest idle.
Turn them about 2 turns out and then start the bike. Once warmed up and on the centerstand, turn 2 screws at a time in 1/2 turn increments and listen for the highest idle you can achieve. Do the same to the other 2 air screws and then adjust your idle by the idle knob/screw or throttle stopper screw.
If your bike still does'nt run right, I would check the battery voltage, also the coil/sparkplug leads/caps for poor/corroded connections.
Did the problem start suddenly? Are the carbs clean inside? Air filter clean?
There are several things that can make 2 cylinders run rich, but going on your info, if adjusting the screws does'nt help, or the above checks, I would look at the coil to #2/3.
 
Everything is now adjusted right but I finally figured out why the bike will not start both of the coils have died. It must have been a sudden death because they are getting power in but no power is coming out of them. No spark and no juice to my test light either. Oh well I'll just have to see about getting some new ones. Thank you everybody who has posted any tips or advice to this topic.
 
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