surging at hiway speeds

[obgrayone]

one of my projects is almost done i got it running today so i took it out for a small ride. it ran really strong so i took it out on the freeway it pulled strong got it up to speed [70mph] and held it there and it felt like it was surging. droped down to [60mph] still felt it surging droped down to [50mph] seamed to run ok . ran it home changed the plugs checked the chain even checked the tires, ran it out on the freeway still acted the same. it feels like its starven for fuel it has no tach so i cant tell if the rpms are jumping up and down any ideas guys

[Big T]

Could you give us less information on which to base an opinion and advise?

[cowboyup3371]

Yea things like bike type, maintenance, pods or stock air filter, etc are kinda necessary to know what's going on.

[chef1366]

Bad petcock is my guess.

[obgrayone]

its a stock bike with stock everything no modes and everything is hooked up its a 83 GS750E i sprayed carb cleaner all over boots and manifolds and no change in rpms at idle

[dr_fosg8]

Sometimes it is hard to find air leaks in the intake by spraying stuff around the outside. Are the carb boots in good shape and have new o rings? Carbs been disassembled and cleaned with new o rings? What did the old plugs look like?

[Dogma]

Usually when this comes up it's the carb vent lines not properly routed. I don't know where they're supposed to go on that bike, but it'll somewhere behind the airbox, or under the seat, or some other place out of the wind.

[MisterCinders]

Fuel tank not venting. Starving it for fuel when you pulling a lot of it thru system at 70. Check your gas cap or try a freeway run with the cap loose.

[bubby]

you said it was doin it at 60-70 try cruiseing at a lower speed with a high rpm does it still do it or only in 5th gear? (wondering if its a high rpm clutch slip) my bike did this only in 4th and 5th gear i adjusted the clutch at the push rod and it took car of the problem just a thought

[obgrayone]

stupid question here where are the vents located ? and it seems to be a certan rpm range

[btbarb]

from most to least

A link to your manual on BikeCliff's site Your service manual

also in the carb rebuild tutorial on the site CV carb rebuild tutorial

or the specific answer to your question on the site Where do these hoses go?

[obgrayone]

The vent tubes are behind the airbox and in frnt of the battery,I took it out this morning and its not as bad in 4th as it is in 5th but its in a different rpm range for doing 60mph .I did let a freind ride it he thinks its the chain and or sprockets

[obgrayone]

Fuel tank not venting. Starving it for fuel when you pulling a lot of it thru system at 70. Check your gas cap or try a freeway run with the cap loose.

pulled the cap off and it works great no surging from the eng, i do feel a little something not right so i put it on the center stand and slowly rotated the rear wheel and i have a link that binds so i need a new chain and sprockets thanx for all the advice