won't rev over 3000 rpm

Okay tonight I went out for a ride on my 1978 tr7rv tiger it ran good for about 15 miles then I was decelerating down a small hill to a stop sign and at some point before I stopped I could feel a change. The bike started to pop out of the exhaust so I ran the stop sign and held open the throttle knowing I was only a few miles from home I kept the throttle open so it wouldn't stall, it wouldn't rev pass 3000 rpm and was popping bad out of the exhaust. I made it home pulled both plugs which are usually a perfect light brown but tonight they were both black. I checked the compression and both were within 10 psi of each other. Then I checked the spark holding the plug next to the stud on the motor and both sides had good spark. The tiger is all stock with original points it has around 9000 miles on it. I bought it with around 6000 miles and it has always run good starts easy idles great. ABout two weeks ago I replaced both rocker cover gaskets and re adjusted the valves and changed the oil. I rode the bike a few times and the bike ran great until tonight. still starts and idles good just won't rev over 3000 rpm. Any help would be appreciated thank you

When you get up the revs is it only running on one cylinder?

It sounded like fuel starvation to me, until I read about your black plugs!

It could be a tight tappet, holding a valve open too long perhaps.

But my money is on sparks, points gap closed? Timing out? Even a dud battery? They're what I'd check next.

I've had this exact same problem happen to me on my Norton.

It turned out that with vibration, my choke lever on the handlebars had decided to move to the on position making the mixture far too rich and not allowing the engine to rev.

Your problem maybe something else, but how simple a fix if it turns out to be only the choke lever?

Thanks for all the responses gents... It was a broken choke cable....Easy fix for sure