Can't reach redline

[Guest]

Howdy folks. First off, let me double check that the gs650g redline is about 9500, and not the 6000-7000 I'm topping out around.
Also, let me mention that I have a small fuel filter in line to the carbs - like this http://lghttp.26404.nexcesscdn.net/8...7/2771_1ha.jpg

The carbs have been rebuilt (all new o-rings, no wear to the needle valves and no wear to anything else). Valves are in spec as of about 1250 miles ago (roughly, since the odo isn't working). Carb boots are new, and carbs are vacuum-synched.

What happens is the engine will rev freely up to 5000 no problem. between 5000 and 7000, the bike will suddenly bog like I've let off the throttle. I though this might be from a too-tight throttle cable, but I've adjusted it and that's not the case. I tried to get it to redline yesterday when I got to work and the bike was warmed up and I was about to park - wouldn't rev over 6500/7000.

I kind of don't know where to start, though maybe with eliminating that fuel filter. I have a new petcock with a very fine mesh screen and a clean tank, so it's unnecessary.
I'm wondering if a bad ignitor can cause this because it can't advance the timing far enough. I also can check the plug gap, but I'm pretty sure it was set right within the last 3000 miles, since the plugs are pretty darn new.

I'd appreciate some suggestions on where to look. This is my first carbureted engine, and I still have plenty to learn about them.

[kdo58]

i had a kink in the fuel line once when i was using a fuel filter.

[Nessism]

Is the bike stock?

If you remove the ignition cover you should be able to grab the rotor and rotate it against the advance spring pressure. You might want to make sure the rotor turns freely and springs back smoothly.

[tom203]

"...What happens is the engine will rev freely up to 5000 no problem. between 5000 and 7000, the bike will suddenly bog like I've let off the throttle. "

Does this happen in neutral too or just under load ? You don't need the extra fuel filter, but it would not cause sudden bogging. Yes, check timing advance, it's all done by 4000 rpm, but you never know.Stock air filter element,not over oiled?
remove tank and double check that throttle twist grip can pull throttle plates fully open (twist throttle grip to max and then see if you can pull connection at carbs up more by hand.)

[stetracer]

Need more info. Does it break up when it stops or just flatten out like you stopped adding throttle? Be careful about advancing the timing to much. To far advanced can cause damage

[Nessism]

To clarify, do not modify the ignition timing. Not sure you can do such anyway without slotting the holes in the signal generator plate. What you want to do is make sure the centrifugal advancer is working properly.

[Steve]

When it "flattens out" next time, hold it there for a few seconds, then hit the kill switch, pull the clutch and coast to a stop in a safe place, then look at your spark plugs. That will tell you if it is fuel-related.

.

[WilliamGLX81]

^ Plug chop for the win! I will seriously have to try that. Is it easier with new plugs?

So, the answer to does it do it in neutral and what happens if I hold it there is sometimes it goes higher, sometimes it doesn't. This morning I hit 8k in neutral with the bike warm (rode 12 miles, 8 of them highway) and the headlight off - that was just blipping the throttle though. Since turning the light off seemed to matter, kI thought maybe the coils aren't getting enough juice.
Tried it again tonight on the freeway w/headlight off in 3rd and It revved freely up to 5-6K, bogged at 6, made it up closer to 7 and almost 7.5 but was kind of oscillating between bogging and increasing speed.

The bike is bone stock other than handlebars, and the air filter is past due for a cleaning and oiling. ....... Maybe I should clean my air filter.

It just flattens out like I've let off the throttle, but the rpms don't drop ... they just stop accelerating. I wish I could take a video of it.

[WilliamGLX81]

I'm looking in the manual for a section on a mechanical ignition advance, but I don't see one. All I see is the electronic signal generator that feeds the igniter. The igniter, as I understand it, handles all ignition timing control. Is that not right?

[Steve]

The mechanical advance mechanism is behind the plate that holds the signal generator pickup coils on the right end of the crank.

.

[WilliamGLX81]

Thank you. I'll try to check it today.

[rudeman]

^ Plug chop for the win! I will seriously have to try that. Is it easier with new plugs?

So, the answer to does it do it in neutral and what happens if I hold it there is sometimes it goes higher, sometimes it doesn't. This morning I hit 8k in neutral with the bike warm (rode 12 miles, 8 of them highway) and the headlight off - that was just blipping the throttle though. Since turning the light off seemed to matter, kI thought maybe the coils aren't getting enough juice.
Tried it again tonight on the freeway w/headlight off in 3rd and It revved freely up to 5-6K, bogged at 6, made it up closer to 7 and almost 7.5 but was kind of oscillating between bogging and increasing speed.

The bike is bone stock other than handlebars, and the air filter is past due for a cleaning and oiling. ....... Maybe I should clean my air filter.

It just flattens out like I've let off the throttle, but the rpms don't drop ... they just stop accelerating. I wish I could take a video of it.

Clean your air filter.

Did you set the WOT properly when you rebuilt the carbs? Check that the throttle plates are set correctly for WOT.

Is the jetting stock or has it been changed? Compare them with the stock jetting specs in a service manual page 5-4.

Make sure your float levels are right as well.

Also need to ensure that all carb vents are clear.

Check that the slides are opening all the way; might want to dry lube to make sure they respond properly to throttle opening.

Doing a plug chop ( with good, serviceable plugs) will tell you if you're running the right main jets. You only need to run it at 5000-6000RPM. Run it for about 30 seconds in top gear, pull the clutch and kill the engine and bring the bike to a full stop without any engine braking. Cut the ignition and pull a plug and look at it. I look at plugs #1 and #2; they should look the same as long as the carbs are set and the ignition is working properly. They are on different ignition coils. This chart may help.

[WilliamGLX81]

Cleaned it last night, going to check the mechanical advance in a couple hours and ...hmmm. I actually don't know how you would set WOT. I assume there is an adjustable stop somewhere? I thought the stop was mechanical and not adjustable.

[Steve]

I actually don't know how you would set WOT. I assume there is an adjustable stop somewhere? I thought the stop was mechanical and not adjustable.

Rudy has been doing a lot of work with VM carbs ('79 and earlier GSes), and they DO have an adjustment for WOT. The BS-series carbs on your bike do not have such and adjustment.

.

[rudeman]

Look at your throttle plates when you have the throttle held against the stop and make sure that the plates are wide open. If they are not then you either have a mechanical defect or an error in reassembly.