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Carb rebuild question 1977 gs750

  • Thread starter Thread starter Veez_strom
  • Start date Start date
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Veez_strom

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I read the sticky on carb setting and I am even more confused.
I bought 4 Keyster rebuild kits. The kits provides the jet needle, main jet and both the pilot fuel and air screws.

I am not sure what setting to put the Pilot fuel screw to. I checked the turns from "seated" as defined in the rebuild instructions. But the carbs are old and who knows who else has adjusted these. Is there a safe average initial setting?

The Jet needle from the kit seems "pointier" than the original with a longer finer taper. If I use the kit needle, what is the stock clip setting? (there are 4 possible slots):confused:

I intend to use stock mufflers and airbox. I have no idea what mufflers or airbox was used on the parts bike that these came from.

Thanks in advance.
 
Why are you replacing these parts? If the Mikuni parts are damaged or incorrect size I can understand but the brass main jet, pilot fuel screw and air screws generally don't need replacing. Many aftermarket kits don't match the precision of Mikuni when sizing their jets. If rebuilding the carbs, I do recommend the o-ring kit from a member here, Robert Barr.
Unless you have a good reason, I'd re-install the factory jets.
It varies a little from bike to bike, but if stock, I'd start the pilot fuel screws (underneath) at 3/4 to 1 turn out from LIGHTLY seated. The side air screws can be initially set at 1 3/4 turns out and then final adjustment using the highest rpm method.
The '78 carbs had the jet needle e-clip in the 3rd position from the top but I'm not sure if the '77 was the same or if it was the 2nd from the top. There's a carb spec' thread around here that may tell you since the jet needle position is critical. If not, ask for help from a '77 owner.
You will then need to bench synch the carbs and then follow that with a vacuum tool synch. The VM carbs require a re-synch whenever the jet needles are disturbed.
 
After reading your post again, identify what size jets are in them now. Re-use if stock. Do not use the Keyster jet needles that are shaped differently. On a stock bike they'll give you problems. Be sure to study a carb diagram so you know if your model uses plastic spacer(s) with the jet needle/e-clip assembly.
Factory pilot jets are #15.
Main jet I believe is #105, but again, check the carb spec' thread as some 750's ran 102.5 mains? I'm pretty sure the '77 needle position was #3 but check on that.
 
Last edited:
KEITH KRAUSE said:
After reading your post again, identify what size jets are in them now. Re-use if stock. Do not use the Keyster jet needles that are shaped differently. On a stock bike they'll give you problems. Be sure to study a carb diagram so you know if your model uses plastic spacer(s) with the jet needle/e-clip assembly.
Factory pilot jets are #15.
Main jet I believe is #105, but again, check the carb spec' thread as some 750's ran 102.5 mains? I'm pretty sure the '77 needle position was #3 but check on that.
Click to expand...

I read the specs page and see alot of numbers. Are these diameters, lengths, or actual numbers stamped on the parts?

Is #3 position counted third down from the top?

The original parts looked fine, but I was confused why the Keyster jet needle was a different style.

Thanks for the help and patience. this is a first time rebuild for me.

T-
 
Veez_strom said:
I read the specs page and see alot of numbers. Are these diameters, lengths, or actual numbers stamped on the parts?

Is #3 position counted third down from the top?

The original parts looked fine, but I was confused why the Keyster jet needle was a different style.

Thanks for the help and patience. this is a first time rebuild for me.

T-
Click to expand...
Yes, 3rd position from the top.
Main and pilot jets will be stamped with a number and if genuine Mikuni, there will be a symbol next to it that looks like a small box inside a larger box.
There's a a lot of info here so you can do a first rate rebuild if you take your time. Sorry, I'm not sure where the VM rebuild link is. Do a search or maybe someone can supply the link.
 
hi,

yeah, the keyster kits are CRAP, well known here and on other bike forums. reuse the original jets. i think you can find the vm rebuild notes on cliff's site. i just did mine for the first time last winter, just take your time, it took me a while to digest all the carb info here.
 
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