Need some brainstorming

[kungpaodog]

I've had the carbs on my '81 gs650gl all apart and tweaked and tuned and synced and adjusted and plug chopped and cleaned and leak checked and rebuilt and sealed and anything else that I can do to make them run as well as possible. No leaks, no worn parts, good compression, good air filter, good spark, good idle, good running, etc.

BUT after riding the bike hard, it's like a switch comes on and in an instant it runs a lot better. Usually it's at high rpms that this change happens, but it can come and go. It's not a gradual change, it is very quick. When it is not running well, it won't pull past 65 mph, but when it is running well, it runs up to 90mph no problem. I suspect it may be something electrical, but I really have no idea what is going on. Please ask me any questions you can think of, and please throw out any crazy ideas that I can apply towards making this bike work well all the time. I really don't want to give a local shops hundreds to tear the whole bike apart, and I know I can beat this in my garage. Coils? Wires? Exhaust? HELP!

[chiphead]

So when you pound the snot out of it, consistent red line activity, bang-all of a sudden it runs well? Then if you just putt around town at low RPMs it eventually starts to run poor?

[MissFabulous]

I wonder if Uncle Mike will chime in here about valve clearances... you might want to read this thread from a while back!

[kungpaodog]

So when you pound the snot out of it, consistent red line activity, bang-all of a sudden it runs well? Then if you just putt around town at low RPMs it eventually starts to run poor?

Yes, pretty much. It is always a SUDDEN change when it does switch over, and it has changed over at lower rpms, but it seems the best way to get it running well is to pound the snot out of it. One time it popped over to good running when I downshifted to first and dropped the clutch hard enough to make the rear wheel chirp. Generally unpredictable, not like I know I can flog it at redline for 20 minutes and it will run well.

[chiphead]

I'm thinking maybe electrical. Get anal on all the grounds. Also throw a fresh known good battery in it.
Check the mechanical advance unit on the igniter plate. Take it apart and clean it.

[mark]

You could be dropping a cylinder once in a while. Bad connection at the plug or coil, or poor grounding. Check the wires that run to your coil and make sure your grounds are good. Checking your battery as above post says is a good idea as well.

At start up, check your exhaust pipes to see if they are warming up evenly.

[prxbadger]

mine does something similar and its the transition between pilot and main jet

[kungpaodog]

You could be dropping a cylinder once in a while. Bad connection at the plug or coil, or poor grounding. Check the wires that run to your coil and make sure your grounds are good. Checking your battery as above post says is a good idea as well.

At start up, check your exhaust pipes to see if they are warming up evenly.

The pipes seem to warm evenly.
I don't mind trying a new battery, but it is pretty recent.
I also know that the mechanical advance is well lubed and working well.
What's the best way to check the coils? And if it is new coils that I need, where could I get new ones? Any good online sources?
By the way, all the parts on the bike are stock, and it only has 11,000 miles on it.

Thanks guys! Anyone else got ideas for what I can go over tonight?

[nabrams]

Sounds like an intermittent electrical issue to me.
Something I've learned after restoring five non-running bikes: I originally thought that electrical components (igniter, coils, R/R, etc.) either work 100% or don't work at all. Now I know that is not true. All of the electrics can fail gradually and show up as intermittent problems until they finally fail totally.
I've had R/R (on two Suzukis), coil and electrical rotor (on a 1980 Honda CB750) that failed gradually. I spent tons of time messing with carbs when the problem was electrics all along (which I found out when the component finally died totally).

There are many posts on this forum detailing how each of the above components can be tested.

[kungpaodog]

Thanks for the ideas to all that responded!
I had time to do a few tests with a multimeter tonight. The no load alternator test was fine, but the battery test was a little low.
The ohms off of the pickup sensor were right where they were supposed to be at 330 ohms.
The manual said that the voltage coming off of the battery was supposed to be between 14 and 15.5 volts, but I read it at between 13.2 and 13.5 volts.
Is this too low, or is it likely that this slightly low reading is just due to the contacts being a little dirty, or even a small discrepancy in my multimeter? Or is this unacceptably low? Does this mean the rectifier needs to be replaced, or that it's on it's way out? Or does it mean that the battery is shot?
(I know that's a lot of questions, thanks to anyone who answers them.)
I plan on testing the coils after work tomorrow, and maybe checking the timing while I'm playing with my electric testers. Anything else I should check while I'm at it?
Thanks again to all the help all the GSRers give me!!

[chef1366]

What's the gap on your spark plugs. This may sound silly but if your plugs aren't gapped or your running rich you can "clean" your plugs while beating the snot out of your bike and it will fire all right until they foul again. Same applies to oil burning.

[Mike McNaney]

I vote cracked coil casing. or fine rust in the gas tank hanging and plugging carb intermitant.

Ive had the same experience on two seperate bikes. Rust in my 1100e and cracked coil casing on my Kaw 550. They both acted the same yet unpredictable.

[kungpaodog]

I just put in new plugs as part of plug chopping, and it hasn't run well when cold with brand new plugs ever. I have them gapped to about .027", within the reccommended .024" to .028" (I think, that's from memory).
The coil casing doesn't look cracked, but I haven't had a chance to pull them off and inspect or test them.
I haven't done any treatment to the gas tank, but it is possible that it needs some help. I can't remember if the discoloration in the bottom of my float bowls was always the same shade, or if it's gotten any worse since the last time I cleaned them. How hard is it to clean and do the anti-rust treatment on a tank?

Thanks again for the tips, all!

[KEITH KRAUSE]

Sounds like electrical to me too.
Check all connections first. Check the plug caps. Could be the ignitor if all the connections are clean/tight.
Sounds like it's running off and on on 3 cylinders. By your description, I doubt you could be losing 2 cylinders but that's possible too. If 2 cylinders, I'd suspect a coil or sensor behind the ignition cover.

[kungpaodog]

Thanks, Keith. My understanding is that the way the plug caps are connected to the coils, it is easier to replace the whole coil than to try and splice new wires into the old. Is this true?