550 weird Power at 4000 RPM????

So I have been riding my new acqusition for a couple of weeks now. I have never ridden the XJ series before, so I'm not sure how they behave in relation to other bikes. So here is the question. When the bike is all warmed up I seem to have a weird vibration and it seems to have less power at 4000 RPMs and it only goes to 5000 RPMs and for the most part goes away. There is still plenty of power in the bike above 5000 rpms, and below 4000, but that is just a weird power band. I've recently done the carbs, and they all check out. It's seems to be a little better when the bike is cooler. Any thoughts???? Thanks!!!

 

Could be a missfire in that range, have you checked the plugs, plug caps, leads and coils to see if they are in spec.

Also possibly the mixture
A Lean condition gets better as the bike warms up
A Rich condition gets worse as the bike warms up

 

Lets read your Plugs.
Pull the Plugs
Line them up 1 -thru- 4
Take a close-up, in focus pic of the business ends.
Lets see what you got going on!

 

If all else checks out, reading plugs and making sure that the spark plug caps are in order. Check compression or do a leak down test to find out what is going on in the combustion chamber. What is the mileage? I have had 550's that were well in above 50,000 miles that still ran great.

The 550's were a bit of a pig down in the lower powerband but when you hit 5500 rpm they take off. Are the vibrations around 4500 when your doing 55 MPH?? if so than that is normal buzz but, you should check your engine mount bushings. They might have gotten hard and will no longer dampen some of the vibration.

 

The 550 definitely seems "happier" above 5K rpms; my '83 (7K miles) is noticeably smoother at 4000-6000rpm than my '81 (18K miles) so I will take a look the at aforementioned bushings. Are you referring to the front mounts? That being said, BOTH are a heck of a lot smoother above 5K rpms...nature of the beast?

 

I'll look into those bushings and see what's up. The bike runs super smooth at 5500 RPMs and up. It only has 7300 miles but was parked for 20 years too. I'll be sure to check into those plugs. Thing seem like it's getting a little worse too.

 

Any bike parked for 20 years usually requires some work to get it back up to snuff.
The Carbs ... for sure.

The Clutch; too.
Although it sat with the Frictions compressed up to the Drivers; there will be spotting on the Drivers where the Oil leeched off and allowed the plates to oxidize.
Sometimes it will wear off and get better just from being started and run.
But, it it remains harsh you might have to try refinishing the Drivers by sanding them down smooth or in severe cases replacing them if you can't put a smoothness back on them that good enough to let the clutches contact them without jerking and pulling.

You're way ahead on that deal, anyway.
Having to throw a whole new Clutch in there shouldn't be too much to ask.

 

Rick - I've definately been through those carbs. I think I've read about every post you've ever written on the matter so as to make sure I did it right. The clutch seems to be working pretty well on the bike. It operates smoothly, and has no wierd grabbing at all. I had to replace all the cables, but that wasn't too bad.