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Carbs - unusual problem (or not)

  • Thread starter Thread starter ChicagoBob
  • Start date Start date
C

ChicagoBob

Guest
Well, after rebuilding my '78 GS550 carbs (VM22S type), I have an unusual situation (or maybe not), and that is that the bike runs perfectly. Idles fine, revs freely, returns to idle promptly and all the exhaust header pipes are equally hot. Plugs look good also. So, my question is, should I bother to undertake any of the adjustments set forth in all carb rebuild manuals?

This bike is stock, except for a 4-into-1 pipe. I bought it with 23K miles on it. I have adjusted the valves and ignition timing. I pulled the carbs because the plugs were loading at midrange and the #3 pipe was cool. I discovered no problems other than that the #3 choke plunger wasn't screwed in tight. I cleaned the carbs (they were already pretty clean) and replaced all the carb o-rings and the intake pipe o-rings, set the idle fuel and air screws 1 turn out, bench-synced the slides, and reinstalled everything (stock airbox).

What do you guys think?
 
I think you need to tweak your mixture screws just a bit.

With a pipe and stock airbox, 1 full turn on the fuel screws might be a bit much.
I might suggest trying 3/4 turn.

As a starting point, the air screw usually goes to about double what the fuel screw is, then tweak for maximum idle speed.
Did you do that and end up at 1 turn or did you just set it at 1 turn and leave it?

With the fuel screw at 1 turn and the air screw at 1 turn, your pilot mixture is going to be running rather rich.

.
 
The only thing I would do is a vacuum synch. There is no way a bench synch is accurate and although the bike apparently runs fine now, it will run better with a proper carb synch. The purpose of a bench synch is to get the carb slides close enough that the engine will run, which allows you to synch them correctly. After the synch, I would install new plugs and in about 50 miles, pull them and check for color on the center ceramics of each plug to be sure they are all running the same.

Earl
 
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