GS550 with modified baffles jet sizing and type

[Guest]

Hey everyone!

Ive modified my stock exhaust on my '79 GS550 and now need to re-jet. Here's a link where I describe the details of the baffles. I've since cut a couple half moon shaped pieces into the baffle to create a serpentine for the exhaust gasses to travel around. It's added a bit of back pressure and tamed down the sound at idle a bit. http://www.dotheton.com/forum/index.php?topic=73326.0

Running stock airbox and filter. Valve shims have been done, o rings have been changed, intake boots are good, so I'm pretty sure everything upstream of the carbs has been taken care of. The bike is running lean as evidenced by the plug colour, and the fact that it idles a little high once the engine is warm. Looking for advice as to a start point for rejetting. I'm also somewhat confused as to which type (small round, or large round) main jets to order... I can't seem to find a definitive answer on how to tell the difference. The diameter of the head of the jets currently in the bike are 8mm. The entire jet is 9mm in height. I'd rather jet the bike a little on the rich side, and if I have to, I can cut one of the half moons that I welded into the baffle out. I'm also guessing that the pilot jets need to be changed as well, as the idle runs high after warm up so advice on how much bigger to go there would be helpful as well. Jetting is currently factory spec as referenced below.

Thanks everyone!


GS550L (77-79) the specs are for the VM's

idle r/min 1100-1200
carb mik vm22ss
id no 47110
bore size 22 (0.87)
float height 24.+/-1.0 (0.95 +/-0.04)
fuel level 4.0+/-1.0 (0.16 +/-0.04)
air screw 2.0 turns back
cut away 1.5
jet needle 5dl35-3 (the -3 3rd notch??)
pilot screw 1.0
pilot jet #15
pilot outlet 0.6
needle jet 0-6
by pass 1.0
main jet # 80

[Steve]

Saw the baffle build, but did not bother watching the video. (The sound on my work laptop sucks.)

Nice work on the baffle. If it sounds as good as it looks, great job.

If you plan on keeping the stock airbox and filter, you may not have to re-jet the carbs, but only testing and reading the plugs will tell you for sure. From the looks of it, if you have to change anything, it might be to add one (possibly two) sizes to the main jet, taking it to an 82.5 or 85.

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