Stuttering at speed, R75/5

Hey folks,
I have a R75/5 that is in good tune, starts and runs great, except for a stutter at around 70mph. In 4th gear as I'm gradually accelerating as the bike gets to about 4200 rmp and 70ish mph it stutters a bit, then gets past it and keeps on accelerating. Same thing will happen at slower speeds if I wack the throttle open suddenly.
Where should I look next? Carbs have been cleaned, valves set, points and timing set, new plugs, and new plug wires.


Thanks for some help.

It sounds to me like a carburetor problem. If it were my bike, I would be focusing on the needles, jets, and carefully examining the diaphragms - and probably clean the carbs (again). Good luck!

You didn't mention if the bike was doing this before you changed plugs, etc. (I'm assuming it did not)

If it was, did you check the diaphragms when you did the carburetors?

If not, are you running inline fuel filters? Replace them, with the thought that perhaps they aren't passing sufficient fuel at the given rpm.

It would not be the first time a bad spark plug made it passed QC. I fought a "stutter" in my Karmann Ghia (also an airhead) for about two weeks before I identified the problem as a defective plug. On the flat it would run like a champ, but up any of a grade it would start to miss... a minute crack in the insulator.