rough running when cruising

I have just started to have a problem when driving at a constant speed. What I get is the engine runs a little rough with a bucking sensation. It idles ok and during acceleration there doesn’t seem to be any problem. First I suspected a vacuum leak but have not been able to locate any. I’ve tried adjusting the timing without any success. One thing I noticed is that if I apply a little choke things smooth out some. Fuel delivery is my next suspect. I replaced my entire fuel system with new pickup, electric fuel pump, and fuel lines.

I’m running triple Webbers with a DUI distributor.

Any ideas?

Gene

this just happened to me and it turned out to be my air filter was clogged. so try driving it without the filter then adjust the air fuel mixture if that doesn't work, just make sure not to drive it when its wet outside without the filter. Also make sure the choke is functioning properly

I’ve run it without the air filters and it seems to run better with the filters than without. I think it may just be some crap from the old tank plugging up some jets. I think I’m going to try cleaning out the carbs and install another filter.

Could be some dirt on the fuel intake screen in the tank. Did you clean the tank?

Yes, I took the tank out to do some body work. I rinsed out the tank but I may have made it worse. I'll have to check it out to.

Might check the float levels on the carbs while you are at it. I am assuming that you have some sort of progressive linkage on the 3 carbs such that the middle carb is the only one running under light throttle cruise conditions. Maybe you need to increase the jetting on the "primary" carb since it sounds like it wants more fuel.

Another possibility is that maybe the secondary carb throttle plates are partially open and they do not need to be at that point. If their plates are open too early, then there may not be enough air flow thru each of the carbs to generate a sufficient vacuum signal to pull the fuel into the circuit. You might need to adjust the outer carb linkages.
Just some ideas.
Doug

Another question I have is what kind of transmission, rear axle ratio and wheel size do you have?
What kind of cam do you have and what are your engine rpm's and engine vac when you are getting the bucking? Could it partially be a cam / gearing problem? (just drawing on my own mistakes for this one)
Doug