Wind speed, air box and lean condition at higher speeds

[Guest]

I’m having this problem with my all stock 1981 GS850 (CV carbs) just off idle cruising at higher speeds. It hesitates after coasting and when rolling on the throttle easy at higher speeds. Opening the throttle more and the problem goes away. It acts likes it running lean at partial throttle and it seems to be worse going against the wind and also when I remove the fairing. Seems to be related to how fast air is passing over and around the air box. I’ve replaced the air box to carb boots and sides seals are in good shape. Is there anything else needed to make sure the air box is sealed well or do I just need to change the pilot jets?

[tkent02]

Where do you have your mixture screws adjusted?

[Dave8338]

What have you done to the bike so far?

[Steve]

How are the carburetor vent lines routed?

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[Dave8338]

How are the carburetor vent lines routed?

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VERY good point !

[dcs]

Bike was in storage for many years. Rebuilt carbs with all stock jet sizes. Replaced all 0-rings, carb intake holders & o-rings and carb to air box boots. Tried richer mixture screw settings but lean hesitation still there. Bike also has new plugs and runs fantastic in all conditions except as mentioned, the lean condition just off idle and only at higher speeds after coasting with the throttle closed.

[Steve]

Bike was in storage for many years. Rebuilt carbs with all stock jet sizes. ...

Carbs may have been "rebuilt", but were they CLEANED?

And I don't mean "spritzed with some carb spray", I mean DIPPED for 24 hours each, then all o-rings replaced.

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[NickNoo]

Before tearing down the carbs etc, check the easy stuff first.
I had a similar problem on an 850, which turned out to be a small gap in the air filter seal (only about 1cm). The original seal was marginal at best and after 30+ years it probably leaks like a sieve. I replaced it with a generous bead of polyurethane sealant and the problem was solved.

[dcs]

Carburetors are clean. Vent hoses are routed over top of air box. I'll check air filter for seal gaps.

[dcs]

Thanks Steve, it was the routing of the vent hoses. Vent hoses were routed more towards the outside and in the wind stream, routed them inwards towards the center and the hesitation off idle at speed is gone. Thanks again, the GS was running near perfect before and now I don't know how it could run any better.

[gearheadE30]

I actually had the same issue and ended up running longer vent lines all the way to the battery tray to get some really nice, stable air.