Not running right?

My bike starts right up like always, but it is acting like it is running on less than 4 cylinders. It has no power when you rev it. Actually i noticed the rpm gauge goes to zero when you rev it up? Then it will go back to 1100 rpm when just idling. I can not ride the bike this way. This started up 2 weeks ago and i thought ignition problem. The coils have about 2000 mi. on them. There the Dyna's from Chacol. Same time i replaced the wires with new solid core. So what i did 2 weeks ago is put new ngk resistor boots on the ends. This fixed it! I rode it a few times around town and once out of town for a total of about 80 miles and im back to were i started as i speak. Help. Have no clue what to check next. The fact that the rpm gauge drops when rev'd bothers me.

 

After searching i found someone with a similar problem. In that post they mentioned the TCI. They said the rpm gets its input from the TCI. Is there a way to check this? And were is it located? 83 xj750

 

The tach dropping does indicate some sort of electrical problem.

I have a question though. The bike has 21,000 miles on it. Did you check the valve clearances yet? Have you run a compression test?

The tach problem is likely electric, but your lack of power could be due to a whole pack of tight valves.

 

The tach does indeed get its input directly from the coil drive for the right-side coil. It could be a coincidence, but, since lack of good ignition on one coil would certainly cause a loss of power, I would start there.

I would pull the boot from one of the plugs that's driven by the right-side coil, put a spare plug in it, and then watch to see what's happening with spark from that plug when the engine is revved and the tach drops. If you get intermittent, or no, spark from that plug, the next things to check will be the wiring to the coil, the primary of the new coil, and then down to the TCI itself. Maybe you just have a bad connection at the coil....

 

Have not checked valve clearances. Just got off work and started bike up. Now it runs fine again. Its intermitent. The compression test at warm is 149,150,150,160 sitting on bike left to right. This was taken at 21,200. Bike is at 22,900 right now. This was using a new higher end tester. I have a spark tester for checking that end, but wont get around to it till this weekend. I did a complete tear down of carbs 4 years ago and maintain the bike very well all season long. It has been a great running bike for me. I would put money on it that one or more of the cylinders are loosing spark when this issue happens.
Thanks for the help

 

OK, so when WAS the last time the valves were checked?

Or do you just plan to ignore the need until you burn one?

Those are good numbers, but at that mileage if the valves haven't been checked you're flirting with disaster with each additional mile.

Wanna bet me $5 for every too-tight valve you find?

I just love how everybody pretends valve clearances don't matter until it's too late OR they finally break down and check and then discover how close they were to disaster.

Yes, your problem is likely electrical. But check your clearances before it's too late. And you're getting close.

 

Since you seem to have an intermittent problem with drive to the right cylinder, I'd recommend (for this problem) that you start the bike, and then take a dowel and poke around the harness up behind that right coil, and also wiggle the connectors on the TCI, and tap on it. See if you can aggravate the problem so you can narrow down where the bad connection is.