2009 GS500 at 6000 rpm bike losses power ?

[gsvaught]

hey so I have cleaned the carburetor, checked spark plugs, made sure the diaphragm is working properly, check the fuel lines and fuel filter, made sure I had the right octane fuel in it and it is still acting up around 6000 rpm. At low speed and high speed when it get to about 6000ish rpms the bike losses power and feel like it wasn't to go but it cant. the only thing I can think of is maybe something to do with the valves? does anybody have a clue to how to fix this.

[The Buddha]

6000 rpm valves hell no. Valves affect the idle and start up and warming up.

You sure its 6K if you're absolutely certain its 6K its electrical.

However if its 6L @ idle, 5k in first gear, 4 in 2nd (load dependent and dropping rpm with increasing load) then its carburetion.

Carburetion is dependent on throttle position, and not RPM.

Try the experiment and get back to this forum.

Cool.
Buddha.

[gsvaught]

I tried that and its still the same RPM 6000ish in all the gears. but when I pull in the clutch, the bike acts fine and I can go over 6000 RPM. I unplugged the throttle positon sensor and it did nothing. so maybe ignition? or something to do with the clutch mechanism

[qcbaker]

I tried that and its still the same RPM 6000ish in all the gears. but when I pull in the clutch, the bike acts fine and I can go over 6000 RPM. I unplugged the throttle positon sensor and it did nothing. so maybe ignition? or something to do with the clutch mechanism

My thought was ignition. Maybe the pulse signal generator or something?

[The Buddha]

Under no load it flys past 6k, under load its 6k in all gears ?

I've never seen that happen, but you can go crazy replacing every electrical part of the bike ... I'll however bet its in the carb.

For example signal generator - affected by heat, and hotter gets worse - so if you want to prove that 6K @ 6th gear its actually hotter than 6001 Standing with clutch in - LOL.

Advance chips are completed with their work by 4500 max, so they have done their part.

I dunno, I somehow think your observations are wrong - unlss you have a rev limiter set up.

Cool.
Buddha.

[hgodfrey]

Reading your opening statement I thought, "Great!", finally I found someone with the same problem I have and the same year model 2009 (actually mine is the F). But as I read other comments I realized I had never really tried the different gears (I will need to experiment with that). I just bought my bike a few months ago and have been learning to ride. As I finally made it to the higher speeds on the freeway I too also had this weird "wall" I hit at 6000rpm. The only twist in my perception was that I was memorizing my speed which was at 73mph. Of course I'm focusing on safety of the surrounding vehicles near me so I don't have the luxury of monitoring the speedometer. After several short trips over several weeks I noticed that it's not an exact speed or rpm, but rather "amount of power required". So if there is a 15mph wind at my back I can nurse it up to 75ish, and if I'm headed into the wind my wall appears to be about 69ish. If I try and twist the throttle for a few extra mph the engine starts dying, and as soon as a back off to were I was the engine is as happy as can be again. My current perception of the problem is that it's directly related to load and fuel flow. I'm sure that if I do some higher revs in lower gears it will work just fine, but I will run out and verify this hopefully this weekend. After reading my scenario do you think that changes your perception of what is happening to yours?

Bike has 22K on it. I don't have any history on the maintenance of the bike, so my current plan was to do a carb clean and carb sync. First I'll do the gear check, and maybe also try setting the valve to prime for a high speed run.

[Endopotential]

Carburetion is dependent on throttle position, and not RPM.

Cool.
Buddha.

Teach us more, Sensei!

I would imagine carburetion would be dependent on both?  Throttle position makes sense, to control the butterfly valve which controls airflow into the carbs.

But wouldn't higher RPM also demand more flow for both intake and exhaust, pulling more air into the carbs?

[Watcher]

Yes and no.

I'm sure mr72 will be along with a much more technical response and many corrections for me, but in layman's terms let me give it a shot.

In a nutshell the airflow through the carb determines the behavior of the carb and engine as a related pair, and the throttle itself is what controls this airflow.


The engine will always pull X ccs of air per stroke, at 100rpm, at 100,000rpm, so it really has a pretty constant effect on its end of the carbs.

Low velocity through the carb doesn't pick up so much fuel, and high velocity through the carb picks up a lot of fuel.
The velocity is restricted by the position of the butterfly valve.
If you didn't have a butterfly valve at all the engine would draw at its max velocity and pick up a ton of fuel each stroke and it would have no problem just racing up to the fastest RPM that the springs can close the valves.  Hold that throttle wide open, this is the effect.
But close the throttle, and this high velocity isn't there, the engine isn't picking up so much fuel, RPMs slow.
For a practical demonstration try breathing through a folded towel.  You can still breathe, and can still fill your lungs all the way, but the velocity of air is so slow it's not very effective at getting oxygen into your body, and it also serves to physically slow down your inhalation.

[hgodfrey]

I rode the bike today. Much colder weather today at 55F, whereas my usual outings are 70-80. Being a newbie bike rider I really have never attempted the higher revs. So today I did just that and like gsvought I could get above 6000rpm in any gear. Actaully it was more like 5600rpm (maybe because of the colder weather). Hoping on the freeway I topped out around 64mph. I also switched the petcock to prime and did the same attempts with the same results.

[The Buddha]

Carburetion is dependent on throttle position, and not RPM.

Cool.
Buddha.

Teach us more, Sensei!

I would imagine carburetion would be dependent on both?  Throttle position makes sense, to control the butterfly valve which controls airflow into the carbs.

But wouldn't higher RPM also demand more flow for both intake and exhaust, pulling more air into the carbs?

Correct sansui. And I prefer Marantz over most any others. Carburetion is dependent on throttle position once it reaches steady state rpm. As its accelerating it has slide rise rate and float level play a part.

As to the OP and the new one that's tossed in his hat in the ring - you guys got me. Maybe you are rich as hell with floats being the biggest culprit. Followed by the jet needles.
Cool.
Buddha.

[hgodfrey]

So obviously, as rpm's increase, so does fuel flow and so does air flow. Could there be a cracked tube/hose somewhere that is bleeding air or fuel such that it creates an imbalance? For example if the fuel flow increased, possibly a cracked fuel line would allow some air bubbles into the fuel feed causing a lean mixture. Maybe at the higher rpms the float bowl finally gets overwhelmed with bubbles that it's almost a foam and now the feed into the carbs is way out of balance (lean). I guess what I'm asking is what things can I inspect or do externally before tearing apart the carb. Like can I do lean/rich mixture adjustment externally?

I'm planning on tearing down the carb for a cleaning, but at this point it's really an inspection to solve this particular problem. Cleaning is just a side maintenance task. Am I correct in saying all the jets are fixed pieces of metal and can be adjusted, just cleaned or inspected for obstructions? I'm really hoping this will be so obvious, like an "ah ha!" moment...lots of build-up on this jet or similar.

Also, in my mind there is no way this can be ignition related. Anyone have theories that this could be ignition related?!?

[mr72]

If it won't rev beyond 6K rpm in any gear but will accelerate fine even at WOT below 6K then I would suspect airflow. Perhaps the slide is not coming up due to a very bad vacuum leak or both diaphragms damaged/torn. This would mean both the airflow is blocked and also the main jet never opens, so you are revving to 6K on the mid jet and can't rev beyond that because the slide's in the way of the carb throat and also the main jet is closed.

Easy enough to watch with the airbox off just looking in the throat of the carbs while opening the throttle at idle, see if the slides move all the way up.

[The Buddha]

If it won't rev beyond 6K rpm in any gear but will accelerate fine even at WOT below 6K then I would suspect airflow. Perhaps the slide is not coming up due to a very bad vacuum leak or both diaphragms damaged/torn. This would mean both the airflow is blocked and also the main jet never opens, so you are revving to 6K on the mid jet and can't rev beyond that because the slide's in the way of the carb throat and also the main jet is closed.

Easy enough to watch with the airbox off just looking in the throat of the carbs while opening the throttle at idle, see if the slides move all the way up.

Slide with leak will be load dependent. Not 6k always.
Cool.
Buddha.

[mr72]

The engine will always pull X ccs of air per stroke, at 100rpm, at 100,000rpm, so it really has a pretty constant effect on its end of the carbs.

right.

Low velocity through the carb doesn't pick up so much fuel, and high velocity through the carb picks up a lot of fuel.
The velocity is restricted by the position of the butterfly valve.

Actually, the velocity is relatively constant, which is why this is a "CV" or "constant velocity" carburetor.

What is affected by throttle position is vacuum, and vacuum affects the position of the slide, which controls the volume of air per unit time.

If you didn't have a butterfly valve at all the engine would draw at its max velocity and pick up a ton of fuel each stroke and it would have no problem just racing up to the fastest RPM that the springs can close the valves.  Hold that throttle wide open, this is the effect.

Yes but it's not because of velocity, but volume.

You open the throttle, vacuum increases (the difference in air pressure between the engine side of the slide and the intake side of the slide), and this causes the slide to come up opening the carburetor throat to allow [more] air through, which also pulls the needle from the main jet progressively so more fuel can flow to match the increased air. The slide comes up because of the vacuum across the diaphragm in the top of the carb.

But close the throttle, and this high velocity

it's vacuum.

isn't there, the engine isn't picking up so much fuel, RPMs slow.

The engine isn't picking up much fuel because the slide is closed and the main needle is in the main jet.

For a practical demonstration try breathing through a folded towel.  You can still breathe, and can still fill your lungs all the way, but the velocity of air is so slow it's not very effective at getting oxygen into your body, and it also serves to physically slow down your inhalation.

Yeah just substitute "volume" for "velocity" and this is correct.

BTW if it absolutely won't rev above 6K rpm in any gear including neutral regardless of load then it's most likely electrical as Buddha pointed out.

[The Buddha]

If you were stopped with the clutch in and you put it in 6th gear and rev past 6k
If you can, find out exactly what rpm in each gear and post back. It clearly isn't 6k in all gears.
Cool.
Buddha.

[hgodfrey]

Gave that experiment a try. Zips right on up to 9K+ in neutral and all gears.

[mr72]

Gave that experiment a try. Zips right on up to 9K+ in neutral and all gears.

Then it's not electrical. It's fuel or air related. The problem is somewhere between the air box and cylinder head.

[hgodfrey]

Finally got time to mess with the problem 9 months later. Did a carb clean and before I even opened the bowls I discovered a broken part. It is a rubber T-fitting. Is has partially worn or should I say disintegrated on one side and still attached on the other side. This rubber T-fitting is located in the middle of the carbs just above the carb air intake (whereas the fuel supply is on the lower side with a plastic T-fitting). The left and right side of the T are connected to brass tubes which enters each carb and looks like it has something to do with the air sliders vacuum valve (not sure of the correct name). I'll order this part #50 from the online parts diagram which shows it to be #13683-01DB0.

I have many Q's. First, the bottom part of this T is supposed to have a hose connected to it, but there is none right now as I found it. I'm also ordering this missing hose as well (Part #51 Hose #13683-01DN0. The online diagram does not show where the hose is connected to on the other end. Coincidentally I found one of the connectors at the bottom of the Air Box was missing a hose. Will this hose go from this T fitting to the air box? What exactly is this function? My logic conclusion at this point is that as speed increases, the negative pressure in the air handler box increases, which increases the vacuum to this #51 hose and increases the vacuum to the slider valves. Or is this whole thing designed to spew out occasional fluids to the pavement below?!?

By the way, I did check all hoses were still supple and checked all 4 boots for carb connection to the air box and carb connection to the intake manifold. All hoses are in excellent shape. I even sqeezed and severely bent the boots to make sure there were no possible signs of cracks. All was good.

My next Q'n is about the vacuum lines. The vacuum line starts in the right carb venturi then T's off into two paths, the first goes to various components, the 2nd goes to a solenoid before it T's into the left and right sliders vacuum valves. What is the logic of how the solenoid works? At rest with the bike off, I tested the lines going thru the solenoid and it was closed. So I'm wondering what triggers the opening of the valve?...is it when the motor becomes hot? is it when rpm's are above idle? or above a certain rpm?

Also, there is a potentiometer attached to the throttle butterflies. I'm guessing this is to sense position and wondering what it does with that info? It's part #59 (13550-13D60). Wondering if it is somewhat related to getting the solenoid to open up.

[The Buddha]

That upper T fitting is the carb vent and the fuel exit if you drop the bike. So It being ripped isn't a problem, if it was plugged - it will be a problem, it wont let fuel into the carb. The T fitting hose goes nowhere - to the back of airbox into nowhere.
The drain hose @ bottom of airbox - here you need to have it fitted with a hose and route it right and cap it. Its an inlet for unfiltered air. Can lean it out because of loss in back pressure.
You should study the vacuum hose routing for your year bike, I am likely to confuse you.
Potentiometer attached to butterflies - yea some bogus garbage. Look up for your model, it doesn't do crap.
Cool.
Buddha.

[hgodfrey]

1) The upper T fitting is the Carb Vent: so I'm assuming my recently cleaned and emptied carb will vent here as fuel fills up the float bowls, correct? So even if I were to completely remove the T-fitting, this should not hinder normal bike operation, just that an occasional drip of fuel might splash.

2) Drain hose: you mentioned to cap it, looking at the online diagram I can't see any specific part at the bottom of the drain hose, yet the drawing definitely shows something there. It makes sense that you would want to guarantee backpressure because the opposite could push contaminants into the airbox post filter. Wondering if another year/bike model might have reference to the part I might use for the cap?!? Now for an unusual interesting item: On the airbox is not just one connection point for the drain hose, but two. The 2nd one is about 1" above the lowest. What is that for and why is it not showing in my online diagram?!? There was no hose attached to it when I disassembled it.

3) I studied the vacuum line routing intensely. I verified that the bike matches the diagram. I really just want to understand the function of the solenoid. What triggers it? Can I apply voltage to it to statically test it? How should I test it's proper functioning with the bike running?

I completely forgot to mention my actual problem has a new twist. Originally, 9 months ago, I couldn't get the bike to go over 70mph. Bike sat in garage for 4 months, then could not get it above about 50mph. No other rides since then and now I'm taking it apart.