Vibration when accelerating while cruising

[valk2128]

When I am cruising around 45 mph in 5th gear, and I give it a lot of gas there seems to be  a good amount of vibration as the Valkyrie accelerates.

If I wind the gears there is no problem and it acclerates real well, without the vibration mentioned above. 

Is this normal??   

[Zorba]

Have to feel where it's coming from , engine , wheels driveshaft etc?
At 45 in 5th you're almost lugging the engine , so when you gas it it might be a Normal engine strain vibration , gas from 55 and see if it vibrates ?
You're probably under 2500 on the take at 45 mph?

[MITCH]

I think Zorba is on to something there with the lugging down theory. I have an I/S and in 5th gear at 45mph I’m running about 21K and if I goose it up there is a vibration up to 55mph then it will smooth out. However if I downshift it performs normally.

[Grandpot]

I had the exact same conditions.  I synchronized the carbs and it got much better.  However, you will always have some vibration when you lug the engine.