Leaking petrol out of the airbox intermittently

[J.M.]

Essay Alert.

Thought I had fixed this problem.

On Sunday the 6th, me and my dad finished reassembling the bike at around 5pm. Started it and then stopped a few seconds later, petrol started pissing out of the airbox overflow pipe. Tapped the carbs (float bowl covers specifically) with the end of a screwdriver but the leak didn't stop.

Took the tank off, airbox off, carbs out. Had a look. Didn't know what we were looking at but had a general poke around. Reassembled the bike.

Started it, no leaking. Rode ~2 miles to the petrol station and stopped the bike. Checked for leaks, no leaks. Filled up and rode back to my dads. Checked for leaks again, no leaks. Rode over to my Grandma's, stopped, no leaks. Stayed there for around 40 minutes, went to start the bike and it just turned over endlessly and started pissing fuel out of the airbox again.

Called recovery, got taken back to Birmingham.

Last night I stripped the carbs. They were almost spotless inside. A few (and I mean one or two) specks of dirt in there but nothing worrying. The floats weren't sticking at all, neither were the slides. The slides were sliding perfectly no matter which angle I held the carbs at, and the floats would move effortlessly at any angle too.

Cleaned everything regardless and reassembled everything. The bike started a treat. Since then I have done:
- 25 mile ride out
- rode to uni (stayed for 3 hours)
- rode home from uni (stayed for <30 minutes)
- rode to ASDA (stayed for <20 minutes)
- rode home from ASDA (stayed for a few hours)
- rode back to Uni for a society event (stayed a few hours)

For all of the above the bike started a treat and didn't leak any fuel.

On the way to the society event I had become bored of riding it like a grandma, so twisted the throttle a bit more, only up to the 8-9k RPM range, redline being 11k. Sometimes this would feel okay and be fine, other times it would feel like I was hitting the rev limiter at 8-9k RPM. When this happened I would usually back off the throttle. However I just kept the throttle open on one occasion and then the bike kind of jerked a bit and then started running on just 1 cylinder (2 cylinder bike).

Got to Uni and stopped, no petrol leak.

Described the 1 cylinder problem to my mate and went out to show him. Bike started turning over endlessly and pissing fuel out of the airbox. I quickly turned off the petcock and removed the air filter. I put my hand inside the airbox and played around with the slides a bit, opening and closing them. They all moved smoothly. Tried to start the bike, started up alright with no petrol leak. Then I stopped the bike and went back inside for an hour or two.

Upon coming back out I find petrol leaking everywhere and the bike wouldn't start (wouldn't even turn over, it was like the engine was flooded). Took the air filter out again and played with the slides again. Then the bike started alright and it got me home just now. It also started running on 2 cylinders again rather than just one like earlier. Got home and turned the bike off and petrol starts leaking out of the airbox again (it might have been doing it for the entire ride home, I'm unsure). So I turned the petcock off on the tank.

I'm a bit stumped as to what the problem is. The carbs looked damn near spotless on the inside. The floats move freely, the slides move freely, the jets are all clear.

Any ideas anyone?
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2004 R1 & 2018 XSR900

[mospeed]

Sounds like the float is set at the wrong height or the fuel tap is not shutting off. If its only one carb most likely the float height.
other prob sounds like water in the fuel.
What bike is it?

[J.M.]

Suzuki GS500F, 2004 model.

Two cylinders so two carbs but as one unit.

I don't think it's the float heights because they have remained unchanged for the last 5k odd miles and the problem has only just occurred after the bike was stood for a month whilst repairing an engine problem.

How would water in the fuel cause fuel to leak like this? I would doubt there is any water in the fuel though because the petrol tank has been kept in a dry environment the entirety of the time since my last ride when it was working perfectly and now when it isn't.
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2004 R1 & 2018 XSR900

[GrumpyGuts]

Is the fuel tap vacuum operated or gravity operated? (i.e. a vacuum allows the fuel to flow when the engine is turned on or Sir Isaac Newton does)

If it's a vacuum tap...turn the switch to "ON" (with the fuel pipe removed) and see if any petrol begins to flow out.

If petrol flows out, then the diaphragm of the tap is damaged and must be replaced as it will allow the fuel to flow, then overflow in your carbs then out into the airbox via the overflow tube

EDIT: Just googled your bike. It is certainly a vacuum tap, so try the above suggestion
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Theory test passed - 09/02/2012 >>>> Module 1 passed 24/07/2012 >>>> Module 2 passed 24/10/2012

[mospeed]

The float may have been wedged slightly by the small specks of dirt, as this model is known for rust forming in the tank. When you stripped the carb you may have inadvertenly moved the height slightly by bending the small metal tang. The floats push a small pin type valve which may be sticking. The floats are designed to stop more fuel entering the carb than is required. If this mechanism is working properly they would shut off the fuel and prevent the bowl from overflowing.
As it is intermittent I would suggest they are sticking sometimes. They may appear fine when the float bowl is removed, but sometimes they can rub on the float bowl when refitted causing this problem.
I wondered if there was water in the fuel as this might explain the running fault, not the sticking float.
Sometimes fuel from petrol stations is contaminated, there are many ways to get moisture in the tank, even condensation can form in the tank.
I would be sure that it is either the float sticking, incorrect height or the valve sticking. it could even be caused by a slightly bent pin that holds the float.
I would bend the small metal float tang slightly.
Failing that a sticking inlet valve would prevent fuel entering the cylinder, but is unlikely.
I'm sure you can appreciate it is difficult to dianose over the net without actually inspecting it.
Perhaps someone else will have another idea.

[hazza]

Have you measured the float height?

Should be 13mm +/- 1mm

Harry
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[Shinigami]

[J.M.]

I'm doubting it's dirt related. The carbs were practically spotless on the inside when I took a look on Monday night. Maybe one or two minuscule specks of dirt in there from 5k miles (when they were last cleaned out). They also all moved freely. This is a video I took before cleaning them: https://www.youtube.com/watch?v=6vDrj8Rcn3w

I haven't measured the float height, but doubt it would be float height related. The bike runs sometimes, sometimes leaks fuel. With incorrect float heights surely it would be a constant fault? Added to the fact that 1 month ago when removing the carbs they were working perfectly, then they have been sat in a box untouched before being reinstalled, so they haven't been touched since not being a problem.

I have discovered that after turning the fuel tap on I can start the bike and there will be no fuel leak. Upon stopping the bike there will be a fuel leak (takes a short while to show as it's very slow). So I have discovered that lifting the tank to turn the fuel tap off at the end of each journey and then again to turn it on before the start of each journey makes the bike usable. Annoying, but usable.

So with that new discovery, I would say that the diaphragm idea seems the most logical for my problem. No leak whilst there is demand for the fuel but a leak once there isn't a demand any more. I will check when I get home. Just to make sure, with a vacuum operated fuel supply, when I turn it ON there should be no fuel flowing?

Side thought: if the diaphragm in the petcock isn't functioning correctly... it would explain why my reserve doesn't work too.
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2004 R1 & 2018 XSR900

[P.]

I have a non vacuum petcock I can give you to try and see if it solves your issues.

You can leave yours on "PRI" and attach the 2nd petcock after it. It has on and off, admittedly, you'll need to keep an eye on your fuel level but to be honest, should only take 2 or 3 days to determine to issue

[J.M.]

Cheers buddy But how would a non-vacuum petcock sort the issue? Or do you mean simply so I can turn it off at the end of each ride?

I have found this which I'll read more in depth too: https://gstwins.com/gsboard/index.php?topic=37366.0
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2004 R1 & 2018 XSR900

[J.M.]

Okay, slight update, I haven't checked that trick that GrumpyGuts suggested yet, but I have noticed a new symptom which agrees with his theory.

I was riding home and the bike died from fuel starvation. I wasn't ragging it at all. I was barely touching the throttle in fact; about 5-6k RPM at 50mph ish.

I pulled over, turned the bike off, looked for fuel leaks. There were none yet. Tried to start the bike again after a checking there was fuel in the tank, it fired right up. Rode it gently home, not really exceeding 6k RPM (with an 11k redline).

A few hundred meters later down the road, the bike starts dying from fuel starvation again. I do all I can to keep it going but ended up coasting to a stop. Checked again, no fuel leak as of yet.

I tried to fire up the bike, it started and stopped again less than a second later. I then switched the fuel tap on to prime rather than on; prime being gravity fed and on being vacuum fed. It then fired right up and rode home a treat, also idled a lot better at low RPM.

Got home and shut off the engine and the petrol started leaking again. I was expecting that to happen though so already had a container to catch the fuel in and the tank lifted ready to turn off the fuel tap.

So it's definitely something vacuum related.
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2004 R1 & 2018 XSR900

[P.]

When it fucks up again and feels like fuel starvation, either open the petrol cap or switch to PRI.

Reckon you've pinched either the breather for tank (I just remove mine... pipe goes to nowhere anyway) or the diaphragm has done a typical GS fuck up and stopped working allowing fuel to piss off down south.

Also, what happens when you turn it to RES?

[Shinigami]

Just do as suggested, lift the tank a bit (won't need to get it right off) and take off the fuel hose (while tap is turned off)

Turn tap on, if petrol comes out then it's broked, if no petrol comes out try the starter with the hose still off and a container under the tap and see if it releases fuel correctly.
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"Once you realize what a joke everything is, being the Comedian is the only thing that makes sense.

[J.M.]

[P.]

Diaphragm is toasted like pop tarts.

They do a rebuild kit, easy for a man of your calibre.

What I would say is getting an additional shut off is what I'd do. Just an inline GTFO switch. Think mini moto fuel taps would be ideal.

[J.M.]

[P.]

I just jam car fuel pipe on them, jubilee clips, least amount of bodge ever.

Cheap as fuck

Cheaper than a rebuild kit

https://www.ebay.co.uk/itm/Mini-moto-minimoto-fuel-tap-switch-atv-dirt-bike-carb-tap-/290814443904?pt=UK_Sporting_Goods_Pocket_Bikes_LE&hash=item43b5e44180

[J.M.]

Nah, can't. The two nozzles underneath the tank are so close together that anything bigger than 8x13 doesn't actually fit on. I bought some 8x15 last time and on one end I made the pipe thinner on the outside and on the other I made it bigger on the inside.

Judging by the fuel coming from that though, I must have slipped with the knife by accident.
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2004 R1 & 2018 XSR900

[Tarmacsurfer]

Rebuilding a fuel tap is a simple job and fairly cheap, just don't try to make your own diaphragm/gasket kit out of hylomar and cardboard

For future reference, if you're trying to make a tube smaller in outer diameter then one of those large novelty pencil sharpeners is useful, along with some silicon lubricant so it doesn't catch as you twist it to shave it down
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I'm immortal. Well, so far.

[J.M.]

[GrumpyGuts]

[P.]

A replacement tap is just a time bomb. They all are on the GS.

If I had another, I would sort a secondary one and leave mine on PRI.

[J.M.]

[N cee thirty]

Bodging only works if you don't plan on keeping a bike for more than 2 months

so do it properly
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Jewlio Iglesias wrote: I actually did vote BNP once

[Blau Zedong]

Jesus christ, will either of you ever learn to fix a problem properly??

Judging from previous posts this GS is your only method of transport, yet you subject to a level of maintainance even Smiler would find laughable.

Buy fuel tap repair kit, rebuild tap so it works as Suzuki intended.

Don't JB weld rubber hoses, it's retarded.

Sorry, to be a bit cunty but it seems to me all the issues with this bike are sefl inflicted due to poor spannering skills.
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