surging - vaccuum, fuel filter, or something more fun?

[mixelpix]

I just rode the 101 north from LA to SF and noticed some strange behaviour with acceleration.

I was stopping about every 50 miles to refill and go. For the first 4 miles of each ride the accelleration is really smooth, and I was generally cruising above 65 - the bike responding very neatly to the throttling. After four miles from topping off with the throttle held constant somwhere between 1/4-1/2-ish (depending on incline and headwind) I would feel the engine lose power - slightly. keeping the throttle held in position, the engine would surge and lose power, never quite bucking, but definitely some uncomfortable loss of control when hitting a stiff crosswind while trying to pass a big-rig...

Maybe the float level? time to triple clean the carbs (needles, jets, etc.)? Time to refit new rubbers for the vaccuum pressure lines/diaphragms? A crimped fuel line? Any trouble shooting advice would be greatly apreciated. Thanks!

[mixelpix]

one more detail

this surging continues for the next proverbial 46 miles, though it seems to go away when I drop down to 50mph, or if I decellerate to a lower gear. Maybe the fuel cap seal?

Thanks Again!

[skids]

You might first check a couple of things. Try running the bike with the gas cap ajar to let it breathe. This is to check the breather oriface.

Next, try switching the petcock over to prime. One of my three standards, one petcock will act up and turning the petcock to prime immediately fixes the problem. I swear the hose has no leaks.

The filter towers in the tank may be clogged.

If the bike is a model prior to '81 it might have something to do with either the pick-up coil wires. The centrifugal advance thing behind the pick-up plate might also need some attention. Mine has been rusty looking before, but the weights and sprinds were working.