83 GS550L rejet

[Robyle3]

Hoping to get some suggestions/information on jetting my ‘83 GS550L. Have ruled out air leaks on engine side of carbs and tightened all spark plugs/exhaust bolts. Even installed a brand new exhaust clamp to rule out a pesky leak between the header and exhaust joint. And when I pulled my carbs they were clean enough to eat out of, and o-rings were supple and undamaged.

Despite all these factors, I have a hanging idle, and even with the idle adjustment screw set perfectly at 1100 rpm, just a quick jaunt down the road and the idle jumps up to 2-3000rpm.

PO installed a 4-1 exhaust and to my knowledge hasn’t rejetted, so I’m fairly sure most of my problems could be fixed with a rejet. I’ll list my stock setup below:

GS 550 L
1983
Mikuni BSW30SS Model

Carb (2 separate carbs, twin bore)
bore size 30mm (1.2in)
id no 43510
idle r/min 1100 +/- 100r/min
fuel level 6.5mm +/- 0.5 (0.26 +/- 0.02)
float height 20.5mm +/- 1.0 (0.81 +/- 0.04)
Main jet: cyl 1 and 4 #95 cyl 2 and 3 #105
Main Air jet 1.0mm (0.04in)
jet needle SC64-1
Needle Jet P-3
Throttle valve # 120
Pilot Jet #35
By-pass 0.8/0.7/0.8/0.8mm (0.03/0.02/0.03/0.03in)
Pilot Outlet 0.7mm(0.02in)
Valve seat 2.5mm(0.10in)
Starter jet #55
Pilot Screw............. pre-set
pilot air jet # 150
throttle cable play 0.5-1.0mm(0.02-0.04in)
choke cable play 0.5-1.0mm(0.02-0.04in)​

My biggest question I guess is if I go up one size on just the pilot and main (pilot because I have issues starting in cold weather, have to keep the petcock on prime), or if I should back the needle up one more position as well? Or should I rejet the needle too?

 

[Cipher]

Petcock on prime? It would appear an issue with the petcock or Choke mechanism is at play.
I ran mine for years in sub zero and all manner of temps but never had to do such a thing.

There's not many parts for these carbs dyno jet makes a stage 1 and stage 3 kit. You cant get jet needles anymore from suzuki nor were there any alternatives that I have seen. Jet needle has one clip groove so raising is not doable.

You can check the petcock by affixing a suitable hose to the vacuum spigot and sucking on it gently.
With the main fuel pipe to carbs disconnected from the petcock you should see flow.

 

[tom203]

Poor cold starting…not enough extra fuel.
wandering idle as it warms up…maybe leaking “choke” plunger letting in air instead of shutting off.

 

[Robyle3]

I never thought to check the choke plungers actually. I turn the petcock to prime because it feels as though I’m not getting enough fuel in the cylinder to start, esp cold, and that is simpler in a pinch to taking the seat off and holding my hand over the intake.
I’m assuming loosening the chicken cable so the springs activate more is the way to go here? Or is it a “pull them out, clean them up, and then readjust” situation?

 

[Cipher]

I never thought to check the choke plungers actually. I turn the petcock to prime because it feels as though I’m not getting enough fuel in the cylinder to start, esp cold, and that is simpler in a pinch to taking the seat off and holding my hand over the intake.
I’m assuming loosening the chicken cable so the springs activate more is the way to go here? Or is it a “pull them out, clean them up, and then readjust” situation?

The cable from the lever on the bar routes to a point above the engine. It is split in a box with a separate cable leading to each plunger.
Over time road dust and slurry from wet dust pack into the plunger and makes movement impossible or just very hard. Add that each side can be impacted by this action to differing degrees you have a recipe for dysfunction.

Id remove the cable end to and and clean it all. iirc I replace fibre washers at the carb side of the plunger with rubber o-rings in a vain attempt to keep dust out.
The plungers appear to be teflon coated from factory so any nice brass shining through is from abrasion due to dust or from the plunger being cocked in the bore due to the high forced dneeded to move it when things are dirty.

Please do a petock flow test as well. Not also that the vacuum line can collapse with age so a new bit may be in order.
If you open the petcock take care of springs and the odd metal bits. You can polish the conical cavity with a suitably modified dremel felt bob.
expect corrosion. the spring may have crumbled to dust by now.