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1978 gs750 jetting

  • Thread starter Thread starter gsbuggie
  • Start date Start date
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gsbuggie

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i recently picked up a gs 750 with straight pipes and k&n pods.she wouldnt run right so i tore into the carbs...inside i found the main jet to be 100 and the pilots are 27.5....havnt got to the needle yet....ive been trying my homework on this site and have found good usfull information..i guess stock jetting on my rig is 105 mains and 22.5 pilots.....if thats the case,then a good start would be 3 mains up and tweak the pilot setting or just go one up on the pilot.....shes a hard starter so any help from the pros would be awsome...thanks for your time,mike........:?
 
Those are your stock jets...

Those are your stock jets...

either 102.5 or 100 main is stock, they changed during the year.
You will probably need a 120something main, a size or two up on the pilots, maybe a lower needle clip position or a washer or two under the needle clip.
Do a search, start with Keith, take lots of notes and post your results when you are done.
 
102.5 main and 15 pilot is stock, I went to 115 main and 20 pilot with pods and different exhaust.
 
guess they were off quit a bit on the pilots,huh?wonder why these carbs possibly have stock mains and huge pilots?im suprised i even got the motor to run,seems like it would be extremely lean...plugs looked good though...almost too fresh...
 
P.O.s do the damnedest things....

P.O.s do the damnedest things....

If the plugs look too fresh, they might be too lean?
How exactly does it run?
Not much top end I would guess?
Should be way lean at full throttle.
 
hard to start...need to check choke pasages i would guess....barely idles..sometimes dies unless throttle is applied some...revs fast(lean guess)pop on one carb(not sure wich one)it just blows my mind how my jet #s are off so much.why would i have a smaller main and huge pilot??
 
Where is everybody getting pilot jets? I have found a source for my 78 750 mains on ebay and it comes with four different sizes for all 4 carbs, but nothing for the pilots.
 
gsbuggie said:
i recently picked up a gs 750 with straight pipes and k&n pods.she wouldnt run right so i tore into the carbs...inside i found the main jet to be 100 and the pilots are 27.5....havnt got to the needle yet....ive been trying my homework on this site and have found good usfull information..i guess stock jetting on my rig is 105 mains and 22.5 pilots.....if thats the case,then a good start would be 3 mains up and tweak the pilot setting or just go one up on the pilot.....shes a hard starter so any help from the pros would be awsome...thanks for your time,mike........:?
Click to expand...
Ballpark guess....127.5 mains, stock jet needle w/e-clip in bottom position, 17.5 pilot jets and pilot fuel screws about 1 1/4 turns out to start. Set side air screws at 1 3/4 and fine tune using the highest rpm method. Carbs MUST be vacuum synched. REMOVE the two floatbowl vent lines at carbs 1 and 4 and leave the ports open to breath to avoid fuel starvation when running pods.
If the 1/3 throttle tests show lean, you'll need richer needle jets or richer jet needles. No more jet kits available for your model.
The 22.5 pilot jet info is wrong. Stock is 15. I suggest a good carb clean and all inner o-rings replaced with Robert Barrs VM o-ring kit. Be SURE to replace the manifold o-rings too. Coat them with some bearing grease to help them last. Replace the stupid Phillips screws at the intake manifolds with Allens and torque the manifolds to 6 ft/lb to avoid squeezing the new-rings too much. Of course, be sure the manifolds are in good shape too. Adjust valve clearances, set ignition timing, etc, before re-jetting. Basics must be done before re-jetting.
 
I just went with Keith's advice on my 78 750. I went with a 4-1 and pods, cleaned carbs and replaced all o-rings. 17.5's and 127.5's, needle clips on highest setting.

Started getting late tonight, so wasn't able to do the full timing/clearances/syching, but I took it out for about 5 miles and it pulls strong with no real hesitation. It really screams in the higher RPMs. It's supposed to be rainy the next few days, but I look forward to doing the rest of the tuning and plug chopping over the weekend.

Great advice, thanks.
 
beergood said:
I just went with Keith's advice on my 78 750. I went with a 4-1 and pods, cleaned carbs and replaced all o-rings. 17.5's and 127.5's, needle clips on highest setting.

Started getting late tonight, so wasn't able to do the full timing/clearances/syching, but I took it out for about 5 miles and it pulls strong with no real hesitation. It really screams in the higher RPMs. It's supposed to be rainy the next few days, but I look forward to doing the rest of the tuning and plug chopping over the weekend.

Great advice, thanks.
Click to expand...
Glad to help!:)
 
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