Lack of power at 5000 RPM

Hello, I am new to the forum and on top of everything I am in Costa Rica where these bikes are not so popular.
I have a 1992 Yamaha XJ600 that started burning oil and lacking power. Rings looked fine and we couldn’t find what the problem was so I decided to have the head sanded, the valve seals replaced, new piston rings installed and all other seals and gaskets replaced with new. Now the bike starts right up, is not using any oil or smoking, but it has not power.
If you accelerate the bike in neutral you can easily go up the RPMs let’s say to 10000 with no problems, but if you get on the bike and try to ride it – it will have no power and it will kind of reset and go down on the RPMs at around 5000.
The problem here is that this is considered a big bike and most of the mechanics if not all only deal with bikes that are under 300CC and nobody has experience with my bike.
Some guy here is telling me that it is the CDI box, but we cannot even open it to see if something is damaged and I cannot find another one to test it.
I was reading the Haynes repair manual and it talks about the pickup coil and I am going for that next, but I was wondering if someone had any ideas or has seem similar problems. Any info will be greatly appreciated. Esteban

 

Esteban, welcome to the site, lots of info here & knowledgable folks to help. A few questions we all will have: 1. how many miles on your bike?
2. How long has it sat without running? 3. have you pulled & cleaned the carbs? 4. are you running stock air filter & exhaust? 5. Have you removed the tamper plugs for the idle mixture screws?
Your problem may be as wimple as a tuning issue.
All of these will help in narrowing down your problem.
I wouldn't be reving it to 10k in neutral, your asking for problems doing that, IMHO.
Post this info & someone will have a better idea of where you are at & where you need to go.
Good luck,
Gregg

 

Thanks for the guidance and welcoming Gregg. I really appreciate it any help.
I am posting the answers below as you suggested.

1. how many miles on your bike?
The board said fewer than 20K, but I don’t think that is true. I have only had the bike for a year, it was not using oil when I got, but it was not performing very well.

2. How long has it sat without running?
It sat for about 4 months. Parts where not available locally and I had to ordered them from the US and it took me a long time to get them delivered here.

3. have you pulled & cleaned the carbs?
Not totally out, we used the non disassembly required carb cleaner spray, but I could disassemble them and do a deeper cleaning if you suggest it may help.

4. are you running stock air filter & exhaust?
The exhaust is stock, but I replaced the air filter before the problem occurred with a lifetime K&N for this model.

5. Have you removed the tamper plugs for the idle mixture screws?
I guess this can be done when deep cleaning the carbs, however for the record the bike is idling fine.

Your problem may be as wimple as a tuning issue.
I hope it is tuning.

All of these will help in narrowing down your problem.
I agree.

I wouldn't be reving it to 10k in neutral, your asking for problems doing that, IMHO.
Well, I usually don’t do this; I guess we were just testing…

Thanks for the help.

 

secacr:

I would suggest taking the carbs off and getting them spotless, synchronized, etc. before trying anything else.

If that doesn't cure it, check the resistance on your pickup coils. I've had a couple go bad on my 400 and it causes a serious lack of midrange power.

Good luck!
Herb

 

Thanks, I am proceeding with these instructions.

 

It may be your K&N air filter - Some guys have used them with no problems, and others have lost power with them because of the higher air flow through the carbs.

 

+1 this could be an issue - more air flow in the K&Ns . Worth a try, also cleaning the carbs is always a good idea if you don't know their condition.