GS850GL plea for help - bike won't pull past 5000 rpm

[Isetta]

based on my experience with 2 GS550 (about 1982) bikes which had similar problems, i believe it needs larger main jets than the original old ones. petrol (gasoline) is not as potent as it was decades ago. keep the original airbox in place. Put larger main jets in. I can't be exact on what size you need. maybe 2 sizes bigger and see how it goes. I tried so many things on mine trying to get it right, wasted hours and hours, just needed some larger main jets.

[Isetta]

Actually what I wrote above must be wrong. If it runs better with no air filter then it can’t be because the main jets are too small. If they were too small it would get worse with no air filter. Still sounds like a main jet problem due to the problem being at higher revs under load.

[Reckhard]

Okay, got new main jets. The bike is almost 100% now. It runs great at higher rpms but doesn't pull as well as before up to 4K rpm. I'm going to tweak the air screws to see if that makes a difference. Also the vacuum valve in the petcock seems to be functioning as it should now. My theory is that I was a bit too aggressive in cleaning out 32years of varnish in the mains and made them bigger. Too rich a fuel mixture caused the stumble when the bike hit around 5K, which created all the issues.

[pdqford]

I've nearly convinced myself that the issue is with the main jets. I may have messed them up when I cleaned the carbs.

There you go! Good call!

Are the new jets the same size as the old jets?

[Reckhard]

There you go! Good call!

Are the new jets the same size as the old jets?

I went with the factory spec'd 115 mains.
I've also now ordered a new set of pilot jets just so I can get the carbs back to original. Once I get those I'll need to rebalance and everything should be perfect just in time to park the bike for winter

[luftkoph]

Is it possible that when you oiled the uni filter you used motor oil? or did you use filter oil? maybe the motor oil causes restriction in the foam media that filter oil does not, just wondering, hope you sort it out.