Can't rev over ~6000rpm. Ignition or fuel to blame?

[Guest]

Hey folks. I believe I've posted about this before, but right now, I'm trying to narrow down the cause so I can troubleshoot it.
This is on my 81 gs650GL.

The carbs are rebuilt with all new o-rings and clean, the petcock is new, the vacuum feed works, there is no fuel filter in line. I synched the carbs and could re-check it pretty easily.

The plug wires are new, the plugs have about 2-3000 miles on them. I've cleaned the connections on the harness under the seat for the wiring to the coil and igniter.

I feel like it should rev higher, and standing still, I can get it to overshoot 6000. The redline marked on the tach is 9000, but I've never broken 7000.

I was having issues with my charging system that cleared up when I cleaned the connections to the coil, igniter, and R/R unit. I get up to 13-14V no problem now.

How do I tell if it's a fuel or spark problem? Plug chop? Dirty = spark, clean = fuel? The change is so abrupt, I feel like it must be electrical in nature. It'll be running great, pulling hard and then I hit 6000 and it's bog city.
I appreciate your advice in advance.

[tom203]

Since you say this is "abrupt" and you've have discovered dirty connections (and done some cleaning)... I'd suspect electrical too, so let's try to rule it out. Do the quick test charging stuff- the stator is really working hard at these speeds and maybe your charging voltage is dropping/erratic giving the ignitor fits

http://www.thegsresources.com/_forum/showthread.php?164993-Charging-System-QUICK-TEST/page2&p=1272192#post1272192

you are running stock airbox stuff with lightly oiled filter element ? Feel sure about float height settings?

[ShadowFocus603]

I'd definitely double check the airbox and carb to airbox boots. I see new carb boots in your sig which i assume are the carb to head boots so we can rule them out, assuming you installed new o-rings under them (not sure if this is a model with the o-rings but I think it is). Also, when you say cleaned the carbs did you uncap the mixture screws and remove them so the passages could be cleaned as well? Then reset them to factory settings as described in your applicable manual? A plug chop will tell you if she is rich or lean at the time in question but it won't necessarily indicate electrical vs fuel.

[Good Times]

What process did you use to clean the carbs?

[WilliamGLX81]

I did a full disassembly, cleaned all the passages with carb cleaner, checked all the orifices, removed, checked, and cleaned the mixture screw passages and put some antiseize on the mixture screws. Then I went back through 6 months later and replaced all the o-rings.

I still need to tune the mixture screws, which I forgot about until now.

[mrbill5491]

I did a full disassembly, cleaned all the passages with carb cleaner, checked all the orifices, removed, checked, and cleaned the mixture screw passages and put some antiseize on the mixture screws. Then I went back through 6 months later and replaced all the o-rings.

I still need to tune the mixture screws, which I forgot about until now.

Aaah no dip and soak for 24 hrs in Berryman's. Antiseize on the mixture screws? that could be a problem there. I sense several steps were missed here. Shall we start over...yes. Start here http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

[WilliamGLX81]

I followed that guide when I did them. That's what recommended the anti-seize on the mixture screws. There was no need for dipping them. Every passageway was sprayed out and flowed the same way - freely. The carbs are not dirty.
So, no. Let's not start over.

[tom203]

Ok, your carbs are clean enough, besides at 6000 rpm the pilot circuit is out of its element. But you said this...

"I was having issues with my charging system that cleared up when I cleaned the connections to the coil, igniter, and R/R unit. I get up to 13-14V no problem now. "
That's sorta low
At this speed ,the stators windings are maxed out and could be deceiving you- charging voltage might be unstable and affecting ignitor. Can you temporarily rig up your multimeter to bike and go for ride to rule this out?
I'd also do posplayr 's quick test if you haven't already.

[WilliamGLX81]

Not trying to Necromance this old thread of mine, but I did find the cause - the mechanical advance (for the digital ignition) was seized up and stuck at 0. It was rather rusty, and some WD-40 freed it up.