Power dying off

Hey, I've only used newer bikes until now, I picked up a 750 inline 4 ltd awhile ago, was running great until it wasn't - The bike still runs well and starts well, except at higher rpm it sputters and loses power. I make more power at 6k rpm than 8k rpm, and it'll no longer fill 4th gear, it just tapers off. Checked my petcock it flows well. Working a lot and just trying to make best use of my time. Should i leave the valves to last to check and my next step ripping apart carbs and looking for a rust block etc, new plugs, and cleaned wires. Couldn't order replacement caps. so just used di-electrode cleaner and sand paper to make sure i had no corrosion or rusty wires. Just wondering what the main thing i should be checking is.

It could be the battery. I do a high-beam test.

It could be the coils. Ride the bike at high speeds, then pull over & check them to see if they are getting hot to the touch - press hard w your fingers. Don't get burned by the valve cover. They should be warm but not hot.

A defective petcock can cause the bike to run bad. Try switching to PRI & cap off the vac line.

Battery or coils were my thoughts. Coils can be kind of a pain to diagnose when they're not completely failed. I'd check your bike's voltage across the RPM range and make sure it looks ok, and if it does, then I'd look into the coils a bit more.

I know you can measure the resistance across your coils and check if it's ok. If you're having more of an intermittent problem that may or may not show up, but it's easy enough to check. Grab an ohm-meter and check resistance between the leads on it. Not sre if yours uses the same coils as my 750, but mine come out to 3 ohm.

When was the last time you cleaned and lubed the timing advancer? If the answer is "I don't know" that could very well be the problem. If the timing advancer is sticking it can cause the symptoms you describe. Ed

Thanks for the ideas guys, battery is fine, and i'd assume carbs would still be fine as they were a very short time ago, coils or timing advancer seems a good next place to look. I'll check the coils on the weekend, and take a peek at that timing advancer, as it doesn't happen until the higher rpm range advancer seems likely to me.