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Back again GS750

  • Thread starter Thread starter Scudder
  • Start date Start date
S

Scudder

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Got one more little (hopefully) issue with the 1978 GS750. So far this is what I have done.

1. 4 to 1 exhaust
2. Pods
3. Main Jet 127.5
4. Slow jet 17.5
5. Needle clip on 3rd groove
4. Fuel mixture 1 1/4 turns out
5. Air Screw 1 1/2 turns out

Bike Idles great. Plugs are looking fine. But... it's still not catching hold and really showing the power that I know it has. It is jumpy in the lower gears, and when I get to 60-65 mph it is working way to hard and won't go beyond that point. I tweeked it some the other day, and it got to 75 mph, but that was it.
Shall I have a professional look at it?

Is there anything or adjustments that I can do to help remedy this situation?

Should I go one larger on the Slow jets?

I've read that I need to go up one size in slow jets for every 4 sizes in the main jets.

I appreciate any suggestions.

Scudder
 
Scudder said:
Got one more little (hopefully) issue with the 1978 GS750. So far this is what I have done.

1. 4 to 1 exhaust
2. Pods
3. Main Jet 127.5
4. Slow jet 17.5
5. Needle clip on 3rd groove
4. Fuel mixture 1 1/4 turns out
5. Air Screw 1 1/2 turns out

Bike Idles great. Plugs are looking fine. But... it's still not catching hold and really showing the power that I know it has. It is jumpy in the lower gears, and when I get to 60-65 mph it is working way to hard and won't go beyond that point. I tweeked it some the other day, and it got to 75 mph, but that was it.
Shall I have a professional look at it? NNOOOOO!!!!!

Is there anything or adjustments that I can do to help remedy this situation?

Should I go one larger on the Slow jets?

I've read that I need to go up one size in slow jets for every 4 sizes in the main jets.

I appreciate any suggestions.

Scudder
Click to expand...

So it idles well, how about throttle response when you just barely crack the throttle? It seems to run good when you open the throttle about 1/4 or so? If so the screws and clip position is probably close enough for now.
Have you done proper plug chops where you kill it and coast to a stop while running at half throttle and again at wide open throttle? Is it half throttle or full throttle where it won't go any faster? Both? I would guess that main jet is too big, it could also be too small, but it would only be a guess without looking at the plug. I don't know for sure, I haven't messed with a 750 in a while and everything is different here at high elevation. Plug chops will tell you the story.
 
Another test drive

Another test drive

I suspected it was running lean, and the plugs suggested as much. Turned the air screws all the way in an took it for a drive. Although it was running rich, it didn't cut out when I accelerated, and the ride was fine. However, I know I don't want to have the air screws all the way in. So...

What is my next move? Will richening the fuel mixture help? I'm at 1 1/4 turns out on fuel mixture. Will 1 1/2, allow me to open up the air screws a bit and still get the same noncutting out performance? Thanks for your patience.

I am starting to understand some things, but clearly, I have a ways to go. Are the plug chops that many guys talk about, just looking at the plugs and seeing if it's running rich or lean by the plugs appearance?

thanks

scudder
 
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