81 GS1100E breaking up after 2800 RPM

[drewandkellie]

I am restoring an 81 GS1100E . I fixed the starter clutch with your help and am almost home. It is basically stock except for a Vance and Hines 4 into one(and of course the airbox was missing so the back of the carbs are open). The carbs looked suspicious so I swapped them with the good running ones (with stock jetting)off my other 1100E. The bike starts right up and idles smoothly. It pulls well at small throttle openings but breaks up at about 2800 RPM. If you twist the throttle open any more than about a 1/4 throttle it dies and bogs down to absolutely nothing. It is doing the same thing with both sets of carbs so I think I elimiated the chance of it being the carbs. (the good carbs run perfect on my other 1100E). All the exhaust pipes feel hot so I know all the cyclinders are operating. What could cause this midrange and upper end fall out? Seems fine under 2000rpm. Is it an airbox issue? Could it be electrical? I appreciate any ideas.

Thanks
Drew

[Joe Nardy]

Drew,

It is quite likely an airbox issue. These bikes flow way too much air without the airbox and will hardly run at all without one.

Joe

[drewandkellie]

Thanks Joe. I'll throw my airbox on it and post what happens

[drewandkellie]

Well it was the airbox! Put the old carbs (47.5 pilots[1 size over] 112.5 mains[2 sizes over])on and it runs pretty well. Pulls like a crazed animal above 3000 RPM. Only lingering problem is a roughness when riding at 3000 RPM.
Thanks for the help Joe.

Drew

[chef1366]

On my 1100 when I ran an airbox and 4-1 pipe I used 117.5 mains. 47.5 pilot jets. One up on the pilot air jet. I ran with the airbox lid off. Pull out those idle mixture screws and make sure the o-rings are good. With the 47.5 pilot jets you'll need to adjust them for a good idle. 3000 is too high. Have you tried adjusting your idle knob or do you have cracked intake pipes or serious airbox leaks at the rubber boots.