Won't Rev While Riding

I recently purchased a 77 Bonneville that had been sitting for 8 years. Had the carbs rebuilt and now starts and revs freely on center stand. while riding, bogs down at 4,000 rpm then revs freely after that. Gas or electrical?

 

I rode at a stready 4K to see if it would free up, but really started to break up at lower rpm's also...that's why I'm thinking may be electrical...like a coil. Barely made it home. Thanks for your thoughts

 

If the jet was clogged (which is what I think is the problem), any idea why it would it still rev up freely on the center stand? tks.

 

I just had the carbs rebuilt and new fuel lines put in...but we didn't clean the tank. Probably a mistake. First ride was problematic. I'll check the coils (2 6V). Interesting while riding, it will get past 4K then rev up with no problem. Is there a jet that handles the 4K range and then another jet takes over? Tks for your help.

 

this cap was leaking, even with a new gasket, so I just ordered a new one. that's a new one on me. I'll also try pulling in the clutch and see what happens like someone suggested. thanks so much.