I've been looking over AFR threads for about a week now, and I though I'd pick your brains a bit further.

So the bike runs GREAT at low-RPM's and mid-range and fuel economy is great (+350km per tank - still haven't hit reserve). Now that I'm beginning to get some more experience I've started to ride the bike harder. Harder riding means higher RPM's and I've started to notice a few things. First-off, the bike falls flat on it's face above 8k, sometimes it does, sometimes it doesn't. I find the higher the gear and the more load on the engine the worse the problem gets. All things are leaning towards lean (no pun intended). When I back off the throttle slightly, the engine picks up again. It sputters and pops under no-throttle deceleration, and the engine seems to be running quite hot and burns oil a little more than what's normal - about 1L for every 1200-1500km. Then I pulled the plugs and this is what I found.



So that sure looks like lean conditions to me. The previous owner said he rejetted for the exhaust, but he doesn't remember what jets are in it. Is there any easy to find out?

No easy way to tell jet numbers....removal & physical inspection only.
With new plugs see how it performs then.

That's what I figured. I guess this week is as good as any to do it with thundershowers every day.

Should I just sell the panel K&N filter and go with a lunchbox and go with the tried-and-true 20/65/145? I guess it all depends on what jets I find in the carbs when I pull them. I'm hoping the last guy didn't modify the slide or anything.

I do still have the stock air filter that the previous owner gave me, would putting that back in help at all or does the drop-in K&N not make a huge difference?

Quote from: Wagoneer on June 24, 2013, 07:08:38 PM
I do still have the stock air filter that the previous owner gave me, would putting that back in help at all or does the drop-in K&N not make a huge difference?

Sure would help....K & N's require re-jetting.

I don't know why I never thought of doing that before 

If that works out maybe I'll save the rejetting for a winter project so I don't have any down-time during peak riding season.

Sounds like I'm having the same exact problem as you.

Plugs and valves show lean (very lean), engine breaks up around 8k, running K&N in the air-box filter and a stock exhaust with a mufflerectomy.

Here's the problem I ran into, though.  Mine has been re-jetted by the previous owner to 135 mains.  I figured they'd be good, but with the leaned out plugs I went progressively bigger.  Each larger jet I installed (140, 145, then 150) made the problem WORSE!

No signs of the plugs fattening up, but the engine breaking up became more and more problematic and unavoidable.
Engine leaning out and larger jets not helping?  Fuel isn't being burned when you open it up and dump a lot in...

I'm in the middle of tracing back the ignition system, it's possible that under load the plugs aren't firing for some reason.  Could be bad wires, could be bad coils, could be wrong timing, could be a bad ignitor...  I already changed the plugs to no effect, next step is wires.

I'll be sure to let you know what I find out if you think it'll help you diagnose yours.

Not sure how quickly I'll figure this out, it is supposed to rain all week and I don't have a garage so I can't really try anything until the weather improves.

Damn, hopefully that's not my issue. Are ignition problems a main concern with these bikes?

That's a weird problem. You'd think with 150 main jets your plugs would be soaked if the plugs weren't firing properly under load. Does it run the same in reserve or prime? Maybe it's a fuel starve problem?

Quote from: Wagoneer on June 24, 2013, 09:02:56 PM
Damn, hopefully that's not my issue. Are ignition problems a main concern with these bikes?

That's a weird problem. You'd think with 150 main jets your plugs would be soaked if the plugs weren't firing properly under load. Does it run the same in reserve or prime? Maybe it's a fuel starve problem?

That's just it, I don't have the factory fuel valve.  I'm running direct fuel from tank to carb through an inline on/off and fuel filter.  No way its starving.

I thought the same thing with the plugs, but if it runs lean 75% of the time and only runs fat up top I'd have to hold it wide open for a bit then kill the bike for it to be evident.  As soon as you slow down to normal speeds the plugs would change back to the lean condition.  If the bike was just running fat the whole time, it'd be different...



One thing that did help me, check the routing of your fuel overflow/breather hose on the top of your carbs.  If it catches wind or doesnt exist it apparently makes the bike weird out at higher rpms.
Made my bike much more operable on the expressway...




How does yours behave when it "falls on its face"?
Does it pop and sputter, or does it just not give any more power?

Quote from: Watcher on June 25, 2013, 01:04:25 AM

Quote from: Wagoneer on June 24, 2013, 09:02:56 PM
How does yours behave when it "falls on its face"?
Does it pop and sputter, or does it just not give any more power?

Yes it pops a few times and hesitates and while that happens it has almost no power. But if I back off the throttle it goes back to normal, just slower obviously.

If I go WOT from a low rpm it actually starts happening as low as 7,000rpm.

Wagoneer, look closely at the screws on the float bowls - if they were rejetted, the screws will have small scratches at least from a screwdriver. Also look at the plugs over the mixture screws since they should have been drilled off for a proper rejet.

Either of you guys have an inline fuel filter? When they get a little clogged it can not flow enough fuel at WOT and appear like a lean main jet. Same goes with a clogged gas tank vent - it can also appear as a lean MJ.

Good ideas Big Rich, I'm going to start ripping things apart today and see what I find. I'd rather do all the easy things first just to get some troubleshooting out of the way.

The previous owner gave me the stock jets in a bag, so I hope that's proof enough that he rejetted.

Could this be a valve clearance problem? Luckily I ordered a valve tool last week since I was going to it as routine maintenance sometime this summer, but maybe I'll tackle that at the same time if that could be a contributor as well.

Wait, I thought GS500's didn't have a fuel filter, just a piece of mesh at the bottom of the tank? Is it regular practice to add an in-line filter? I guess I'll see once the tank is off.

Correct about the fuel filter: there is a stock one, but some people add an inline filter. And an inline filter is more prone to getting clogged.

Your plugs look 400 years old ... what you do, recover them from the titanic ?

BTW yes they are detonatingly lean ... looks like youve had a few of em "pings"

You may want to re  evaluvate your gas stattion, and/or grade - higher octane may help you ... atleast till you rejet and you start drowning in slow burning 93 ...

Cool.
Buddha.

Quote from: Wagoneer on June 24, 2013, 06:53:06 PM
That's what I figured. I guess this week is as good as any to do it with thundershowers every day.

Should I just sell the panel K&N filter and go with a lunchbox and go with the tried-and-true 20/65/145? I guess it all depends on what jets I find in the carbs when I pull them. I'm hoping the last guy didn't modify the slide or anything.

Well Iridium - the electrodes are skinnier and tapered. So ignore my comment about detonation. OK so you still leaner than Hilary Duff.
Your nice gas mileage etc etc while still being rideable in all weather/situations - your best bet is the stock filter and keep it clean and run the pipe and jet for it.
Pull them and get the numbers off it.
Cool.
Buddha.

Will do, bike isn't getting driven until the stock filter and new plugs go in.

I live in Canada, a first world country with fuel standards lower than third world countries. Not much I can do about fuel quality, maybe an in-line fuel filter isn't a bad idea if I don't already have one. And I'm already running 91 octane.

Previous owner said plugs were "new" last year. But I'm also thinking that's BS along with a lot of other "new" parts the bike had.

Is it safe to run some seafoam in the gas to clean out the fuel system?

I don't see why not. I run a can of seafoam through my car intake, oil, and gas every spring.
Haven't tried it in the bike, but I imagine it'll act kind of like an octane booster.

Is this line coming from the petcock supposed to be kinked like this? It almost looks like there should be a hard elbow there instead.