• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

750 '77 carb main and pilot jet size question

  • Thread starter Thread starter tmaenner
  • Start date Start date
T

tmaenner

Guest
Hi everybody,

I've got a '77 GS750, Mikuni carbs and need to re-jet the carbs.
The former owner took off the airbox w/o rejetting the carbs and of course with after-market cone air filters performance sucks... :cry:

Currently, the jets are 22.5 for pilot and 117.5 for the mains.
Based on some peoples' advice I was targetting two sizes bigger on the mains and one size bigger on the pilots.

What would you recommend?

Thanks a lot! Appreciate your help!
 
I believe stock jet was 105 so they have done some work. Have you taken a plug reading??
 
Thanks for your reply.
The plugs were pretty black.
I was also told that the carbs are a non-CA edition; maybe they have different stock sizes?!?

Thanks again
 
MY 79 GS 750 CAME WITH 102.5 MAIN STOCK. I PUT UNI PODS ON WITH STOCK EXHAUST. WENT TO 115 MAIN JET AND RAISED NEEDLE TO 4TH POSITION. SO IT DEFINATELY SEEMS LIKE YOURS HAS BEEN REJETTED. DO YOU HAVE THE STOCK EXHAUST? TRY GETTING SOME SMALLER JETS. THERE CHEAP.
 
Just the "cone" filters, but stock exhaust?
Depends on filter brand. K&N...Emgo?
Good chance the stock #15 pilot jets will work fine with just richening the pilot fuel screws some (from where the factory would have set them). Try 1 to 1 1/2 turns out for starters. Then adjust the side air screws by the highest rpm method. The air screws effect all three jetting circuits.
If Emgo pods, try the jet needle e-clip in the 4th position (2nd from bottom). If K&N, try the clip in the bottom position with a .022" (or close to) thick jetting spacer on top the e-clip. Look at a diagram for your specific model/year carbs and make sure any plastic spacers that go above or under the e-clip are in place and installed in correct order.
Just as a guess I'd say 115 mains, but 117.5 is certainly ballpark.
REMOVE the two floatbowl vent lines and leave the ports open to breath.
A vacuum synch is a must to get good performance and plug reads.
Test each jetting circuit at the correct throttle position and go from there.
Wide open throttle for the main jets, 1/3 throttle for the jet needles and minimal throttle (4th gear at about 35 mph steady) for the pilot circuit.
Be certain the ignition is timed correctly and the spark is good before testing.
 
Really appreciate all your help!!!

Ouch, I haven't thought of the exhaust; it's 4in1 rather than stock, brand unknown.
How much would that change the optimum jet size?

Thanks again
 
tmaenner said:
Really appreciate all your help!!!

Ouch, I haven't thought of the exhaust; it's 4in1 rather than stock, brand unknown.
How much would that change the optimum jet size?

Thanks again
Click to expand...
With the 4-1 pipe, if it's good quality, I'd probably try 120 or 122.5 main jets.
I'd also try the jet needles with the e-clips in the bottom position, no jetting spacer. Best to start on the rich side. Test the needles at 1/3 and see what the performance/plugs say.
If the plugs are rich, lower the needles by raising the e clips. If the 1/3 test shows lean reads, you'll have to install a jet kit to make the bike run correctly. This would mean the stock needles aren't capable of being richened correctly.
All other jetting info in my first reply still stands, though I'll add clean carbs are necessary too. Good luck.
 
You must log in or register to reply here.
Back
Top