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'79 "S" carb adjustments

  • Thread starter Thread starter robinjo
  • Start date Start date
R

robinjo

Guest
Hi guys, got the "S" up and running now and am fiddling with the carbs and it's running a bit rich (black plugs) in the midrange.
When I first got the bike it was running without an airfilter and running bigger main jets, #110 wich I replaced with #96, stock is #95 but they didn't have them.

Can you adjust this with the airjets on the side of the carbs near the intake or do you have to adjust the needles for this :?: And what are the stock settings for the air and fuel screws and the needles :?: , my manual doesn't cover all the stock settings.

btw it's a '79 with the VM28SS carbs with stock airbox and exhausts.
 
Needle clip should be on middle groove.
Screw on side of carb should be 1 to 1 1/2 turns out.
Screw on bottom is factory set, but is usually about 5/8 turn out.

BUT... make sure there isn't an air corrector fitted to main air jet. Look down carb from airbox end and see if any of the drillings in the end are threaded. If they are, unscrew the brass air jet fitted and discard it; the stock air jet is a press fit.

Also check the float heights, the bike will run rich if they are set too low, i.e. more fuel in float bowls.

The will also run rich if needle valves are worn and leaking and if any of your air drillings are partially blocked....blowing everything through with compressed air is essential.
 
Already cleaned and inspected the carbs and everything looks like it's in good condition, set the float heights at 24mm (level should be 23 to 25mm) and static synched the carbs per manual. I will check the air jet.

So what affects the midrange mixture, the air jets or the needle?
 
Mostly the needle, although there may be a bit of overlap depending on where you consider 'midrange' to be.
 
lhanscom said:
Mostly the needle, although there may be a bit of overlap depending on where you consider 'midrange' to be.
Click to expand...

By midrange I ment from idle up to 5000 rpm, with the old settings there was a real change in power at that point.
I put the clip on the middle groove of the needle, it previously was 1 position below that so the needle was higher and set the air jet at 1 turn out and went for a testride. Much better throttle respons, before you could only give it a bit of thottle a medium revs and beyond that it would hesitate to rev higher untill you got more revs and you could open it more an more, now it takes gas much better and the switchpoint at 5000 rpm is less pronounced. Checked the plugs and they burn a dark grey, so I opened the air jets a quarter turn more out and will test it again tomorrow but it's pretty close :D :D :D
 
Robinjo,
This motor does have some differences compared to the other GS 1000 motors. Mine at 5K is not a light switch BUT does have a pronounced step in power at that RPM. 3/rd gear 5K rpm and crack the throttle WOOOHOOO :!: Best be in a straight line.
I did not do the rebuild of my carbs.........I paid my mechanic. He also owns a S model. Since then it runs great.
Mine was bored 20 thousands,stock carb abd air box with a K&N filter in the box. Also a Kerker 4>1 That's it and I still love it after 15 years.




Keith
 
KGB said:
Robinjo,
This motor does have some differences compared to the other GS 1000 motors. Mine at 5K is not a light switch BUT does have a pronounced step in power at that RPM. 3/rd gear 5K rpm and crack the throttle WOOOHOOO :!: Best be in a straight line.

Keith
Click to expand...

Yeah I know what you mean, after getting it running right I went for a ride on some back roads to see what it could do. Coming out of a corner in 3rd gear at about 6000 rpm opened the throttle and the rear tire slid out for what felt like a foot wide 8O 8O 8O.

Guess it's time for that set of Dunlop GT501's that you suggested :!:
 
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