Fuel level in float bowls too high...even though floats are set properly

[Darkstar]

To troubleshoot my rich idle circuit, I measured the float height both with the carbs attached to engine, and unattached.

Attached, the levels are about 12mm higher than the float bowl gasket line--------> http://imgur.com/a/NawFL
Unattached, the levels are almost level to the float bowl gasket line---------> http://imgur.com/a/38rXL
This is my setup for unattached, pics were taken though with a bubble level on the gasket line--------> http://imgur.com/a/r7tdK

A few things to note: There's fuel in the airbox drain which makes sense. When I remove the vacuum hose from the canister/chamber, there's seems to be a lot of pressure, and I don't ever recall seeing this before. A water spray test doesn't turn up any vacuum leaks. The needle slides move freely. The needles on the float bowls look to be seating right when I bounce them. Something's preventing the fuel level from dropping back down, pressure from the top of the diaghrams, any ideas??

[Watcher]

You measure fuel level in the bowls with the carbs on the bike.

Setting aside how you aren't getting anywhere near the same fuel pressure to the carbs, you likely aren't holding them at the same angle the engine does, either.


According to your first test, the float is set too low.  You need to bend the needle tab up (towards the carb) so the float closes the valve sooner.



As for the carbs holding pressure when the bike is off, that I'm not sure of.  But that may indicate a clog in a vacuum path, which may be affecting the action of the slides.

Nothing in the lower half of the carbs is affected by vacuum, not in the sense of being from a hose that draws from the engine.
The bowl is essentially exposed to open air, through the jets.

[Darkstar]

To clarify, the close-up pic showing fuel height with carbs off was taken with a level. I dont show that level in the pic of the setup. The bubble was at the same spot as when the carbs were on. When you tilt the carbs, the fuel level changes, but not by 12mm. Are you sure there isn't back-pressure coming from the diaphragm? There's a pocket above those with vacuum tubes attached. 

[Watcher]

To clarify, the close-up pic showing fuel height with carbs off was taken with a level. I dont show that level in the pic of the setup. The bubble was at the same spot as when the carbs were on. When you tilt the carbs, the fuel level changes, but not by 12mm. Are you sure there isn't back-pressure coming from the diaphragm? There's a pocket above those with vacuum tubes attached.

There are 4 or 5 active holes in each of the GS500 carb bowls.

1) The needle valve which opens to let fuel in.
2) The breather/overflow line which leads to the top of the carbs and comes out of the "rail" with a hose you can route.
3-4/5) The jets, which lead to the air chamber of the carb.  At one end of this air chamber is the engine, at some point in the middle is the throttle butterfly, and near the rear are the jets.  This end is where the air filter is attached.

Fuel cannot be forced down 1 unless the float is out of spec or the needle/seat is worn or leaking.

Fuel often flows out of 2 if 1 is severely malfunctioning and just hemorrhaging fuel.

Fuel comes out of the jets one of two ways. 
Either 1 is malfunctioning and the fuel flow isn't severe enough to come out of 2 (or 2 is clogged), so fuel flows up through the jets and leaks into the air-box and potentially into the engine.
Or it is drawn as a vapor into the air chamber of the carb via the direct vacuum of the engine.  So air from the world is pulled through the filter, into the carb, across the jets, then into the engine.

If the diaphragm could cause enough pressure in the carbs to actually lift fuel out of the jets, you wouldn't be able to breathe since all of the air in the room would have been sucked into the carbs as well.

[Darkstar]

OK, I see now. I hadn't quite thought of it this way. I'll give it another shot

[Darkstar]

I just finished another round of adjustments. Using the tube method I managed to get the fuel levels quite close to the float bowl gaskets. Left cylinder is spot on, and right is 2-3mm too high. I had to bend the tang quite far to get the right there so I suspect something needs work. The plunger/needle is moving but not as much as the left. The metal clasp attaches the needle to the tang seems a bit stretched. That could be it, or maybe there's an o-ring problem inside? I was thinking of swapping the needles and floats to troubleshoot. That would help me decide whether I need replacement parts. Choke has improved slightly, but stalls if I open it more than a little.

Either way and went for a long ride and the results were much better. At 1 3/4 turns out I get more power than stock. It's still a bit chubby on the bottom, like between 3000-5000 rpms, but not too bad. Much better pull from there to WOT though. 2.0 turns gave me better pull on WOT, but bogged down a bit on the bottom. 1.5 turns was much more linear, with fewer flat spots, but slightly less power. I'm getting 54mpg on a cruise which is pretty good for me. At this point, rejetting has yielded noticeable improvements, With this and the cam shim job, the bike has run better than it ever has and is no longer lean. These were my original goals. I could mess around with the needle height but I'm not sure if I should keep screwing around, if the return will be worth it.

[The Buddha]

The float needle spring plunger can get stuck, you can try to ease it and lube it with wd40. Sometimes it would work normally after a few of those push in and let it spring out. You want to not make it plunge in and get stuck. Make sure you lube it well and work it.
Cool.
Buddha.

[Darkstar]

The float needle spring plunger can get stuck

Thanks. I noticed some wear on the metal side of the plunger, like the finish got worn, so maybe it's sticking. Wouldn't WD40 be washed away by the fuel after i reassemble?

[The Buddha]

The float needle spring plunger can get stuck

Thanks. I noticed some wear on the metal side of the plunger, like the finish got worn, so maybe it's sticking. Wouldn't WD40 be washed away by the fuel after i reassemble?

Yes, so will anything this side of concrete, but you've re worked and cleaned the spring that causes it to plunge.
Cool.
Buddha.

[Darkstar]

Well, whatever it was seemed to have worked itself out. I took it for a 150 mile ride yesterday and about 20 minutes in it surged a bit, and then opened up. It's as if something was clogged or stuck, and then got cleared up. The bottom end is now stronger and I have no complaints. It's still a bit rich with the choke bogging it down, but without that on it starts right up with a bit of throttle. It's never run this good, so I won't mess with it until I find another reason to open it up again. Thanks for the parts and the advice buddha!

[mr72]

It still should require choke to start.

I think there is still stuff wrong with your carbs. As Hans and Franz used to say, "hear me now and believe me later," you're going to wish you had just replaced all of the stuff that is worn and old in those carbs while you had them apart.

[RideShield]

This method was posted somewhere on the forum before. Anyway, it involves resting the floats on the needles without depressing the center pin. You can leave the carbs on and cables attached and just rotate them to take the measurements. The hardest part for me was waiting until the digital calipers went on sale for under $10 USD at Harbor Freight

Here's the link http://www.motorcycleforums.net/forum/mechanics-corner/52158-suzuki-gs500f-float-height-adjustment.html 

My float needles and seats needing to be replaced gave me problems even though the float heights were spot on.

[mr72]

My float needles and seats needing to be replaced gave me problems even though the float heights were spot on.

+1 that. And don't forget the o-rings on the float needle seats and the float itself. If those leak, all bets are off.

[Darkstar]

Yes, and I suspect that's what I'm up against. The o-rings I've replaced so far on this bike were dry, flattened, and lined with some white crud. I bet this is the same case. The needle assembly is $50 and I'm out of work right now so cash is tight. As soon as I land a job, I'll buy these and replace. Until then I have to ride on what I have. I suppose worst case scenario is that the performance will slowly drop. I hope o anyway, I have a couple 500 mile rides coming up soon.