WTF - Loss of Engine power at 5k RPM

So a couple weekends ago I finished taking care of the engine, Valve Clearances done, Vacuum checked, carbs synced, color tuned. Went out for a ride and she did beautiful. Rode her all day/Night on that Sunday. Finally took her on the Highway, rand perfect, Lots of power, lots of fun, lots of good times... It has been raining ever since then.
Finally today I had the opportunity to go back out and ride.
I went out and as soon as I hit 5k RPM she would lose pretty much all getup and go, she basically would bog, not down, but just lack of power. As soon as I put her into a higher gear the power would return and then again 5k and I would lose that power again.

Does anyone have any ideas?

Oh, btw I have followed Chacal's guide to cleaning the carbs, hell I did them 4 or 5 times because I made stupid mistakes. She was running perfect and after sitting for 1-2 weeks she is now acting up.
Help me please.

 

No ethanol in that gas, right?

 

Ethanol is NOT going to do that.

Haven't yet heard of this one... Perhaps something corrosive got on the rubber of the diaphragms, slowly eating them away, and now your cylinder isn't pulling the needle out of the emulsion tube, so the main jet fuel supply never gets to kick in?

Float levels super low, or petcock not allowing enough fuel to fill up the bowls in time? Is it *right* at 5k, same spot on the tach everytime? (If so, probably not this one).

 

Just a thought man lol

 

Just a thought man lol

 

Yup happening every time at exactly 5k, even when idling you can feel it

 

How many miles on this bike?

 

32k

 

Try taking it out with the petcock on prime

 

No change, Petcock was rebuilt too just about month ago

 

Could be a sticky slide in one of the carbs or electrical problem like coil or pickup coil or even CDI box

Good luck hunting it down

 

These bikes have TCI, and if he really did do his carbs as he said he did, then he did a 'clunk test'; besides, if it was perfect before, what over a week would cause it to get sticky inside?

(You did do a clunk test, right?)

It's an odd one.

5k... The main jet kicks in a bit before that. 5k everytime probably wouldn't be a straight up engine problem, though, I wouldn't think--what would cause it? Definitely sounds like fuel mixture/supply somehow, it has to be in carbs... Is it at all a gradient, or just a sudden cutoff of acceleration? Does it keep accelerating, just slowly, or is your top speed now effectively 55-60mph (5k in 5th, approx.)?

What do your spark plugs look like? How many turns out are your mixture screws? I know you colortuned it before, but it sounds like something changed, somewhere, and looking at your plugs could be useful to start making a diagnosis. If all is normal, try getting the engine warm (does it act differently when warm? Have you tried?), and then do a plug chop at 5k and see what they look like there.

 

Just a thought man lol

 

Konoc keeps thinking, that's good maybe...

Always at the same rpm's means it's somehow 'rpm' dependent. That eliminates a lot of things and helps narrow the field. At 5k you are entering the torque zone, but not yet to the HP peak. Hmmm.......I don't think your carbs are the issue unless it is your diaphragms.

All that rain worries me. Humidity is not your friend when it comes XJ's. It's possible your coils are failing but they manage to keep up until they are being asked for rapid fire voltage and it begins to fail-perhaps brought on by excess moisture. You should do the water spray in relative dark test and check the primary/secondary resistance. One idea....

Can the valves float on these bikes?? because that sounds more likely to me because of the rpms when it happens. What I mean is that when you get it revving they aren't snapping closed quickly enough to keep up and compression is dropping-springs are worn. This would create the symptoms you describe. I haven't heard of this with these bikes before but who knows.

Hope you get to the bottom of this because these bikes were made to LIVE above the point where your issue crops up-it must be solved.

 

Funny enough I was thinking coils too, sucky part is I am at work all day today. I will have to check the spark plugs, and also the coils, fortunately if it is the coils I have a newer pair from my parts bike that is only have about 5k miles on them.

 

Forget "valve float" the engine redlines at 9K+; you won't "float valves" at 5K.

Wet coils. Betcha. Unless your air filter somehow got soaked, or the problem is only coincidental to the rain.

 

throttle shaft seals, air jets in right places, emulsion tubes clean, intake/exhaust mods, intake manifolds condition, stock jetting ?
does it rev past 5k in lower gears?

 

Yes Clunk tests have been done too, I haven't done it since this problem happened, but yes before the bike was put back together all of that was done.

Oh and just so people have more info as well... Oil has been changed and there is enough drive shaft fluid.

 

Thanks for all the great idea to check, I am gonna check her again today *BigFitz for coils when I get a chance after work.

*Polock - All throttle shaft seals are in fantastic condition, no mods what so ever, all stock. Did have the issue months ago when I got her first to gether before shims were done with incorrect placement of air/main jets, but all corrected. plus again, Ran PERFECT about 1-2 weeks ago when I last took her out. No riding between then & now. So it doesn't make sense to be air/main jet mixup anyways.
It revs to max of 9k at this point, but it loses engine power/acceleration at 5k, all gears even in neutral.
Manifold/intake seals are all set no leaks, and yes a vacuum test has been done as well to make sure there were no leaks, as well as ether spray test.

 

what about the lower gears, 3rd 4th ?
you have a in-line filter right? try loosening the bowl drains and catch the gas in a glass jar, see if anything bad comes out. maybe some chunks rinsed through