My new issue, awful running, no power

I will start by saying that I did do some work on my 82 XJ550 over the past winter, but I won't say what because I am looking for all possible answers to this...

So the new issue; Suddenly the bike feels like it has lost power. It struggles to get over 60 mph! I have to give about 3/4 of full throttle to get it there. At the same time this happened, my mile per gallon dropped from about 50-55 to around 20-25. This literally happened over night. It was running perfect for the past 1,200 mile or so and then just took a dive.

Any ideas?

 

are you firing on all cylinders?

 

Imagine going to your Doctor and telling him,,,"Doc I want you to diagnose what's wrong with me, but I'm not going to give you all of the details because I want you look at all the possibilities....

We have plenty of very knowledgeable people on this forum (of which I'm not one), but by telling them right off the bat that you're going to withhold information which might help diagnose the problem....most of them are going to tell you to "pound sand", or not answer at all.

I'm just saying

 

I'll just say if you want to do this the hard way then it's up to you.

-Do a compression test.
-If the valves aren't in spec, get them so and then re-check the compression.
-Float levels need to be accurately wet-set.
-Carbs need to be accurately bench-sync'ed.
-The running vacuum sync needs to be done with YICS blocked.

My first guess is that the float levels are not set correctly; or the vacuum sync wasn't done.

 

Who knows... It could be a brake thats dragging or not fully releasing.

 

Patmac, I am not withholding really. This is actually my first motor project, so my knowledge is very limited. I bought the repair manual to help me through and I am learning as a go. So I wanted to keep all options open to learn.

When we went through the bike in the spring, all cylinders were firing and the valves were all set to spec. I will start going through the rest of the list when I get a day or two off. Thanks guys

 

So all you did was check the valve clearances, and then the bike sat?

Then the answer is "all of the above except the valves."

Skyhawk might even be onto something. Are you sure the rear brake hasn't begun to delaminate and drag on you?

That repair manual has a "maintenance" section. Go through it, in order, and perform ALL of the recommended maintenance. Don't skip anything because it seems too complicated or intimidating; DO IT. All of it; and in order.