Recently had an issue with my carbs after fitting new fuel pipes where some rubber contaminent had stopped the float needle from closing fully, causing my bike to leak fuel when stopped/idling for too long.

This also lead me on to discovering that the vacuum operated petcock wasn't functioning properly. Essentially ON was free flowing fuel with the engine off, like you would expect prime to do. I wasn't able to find a petcock rebuild kit online so I carefully dismantled the petcock and found the issue; the spring had compressed too much. I stretched the string out a bit and reassembled and now it's working fine.

However getting caught out riding with a petrol leak and no tools is horrible, especially being as you can't even turn the fuel off because you need tools to reach the petcock underneath the tank.

So what I am thinking about doing is adding a simple ON/OFF tap on the petrol line between the vacuum petcock and the carbs so that if this problem comes back (which it shouldn't), I'm able to shut the bike off with ease whilst out. A fuel filter wouldn't go a miss either.

So does anyone know the size of the hose running between the vacuum petcock and the carbs?

It's the GS500F 2004 model, UK, if that makes any difference.

Thanks for your help

Not a direct answer, but I know 5/16 works best for the fuel line, however the size is probably different for the line you're talking about.

Have you thought about an aftermarket petcock? A few people here have them. They can turn the fuel off from the outside.

I've thought about it yes, but with my ones functioning and not suffering from fuel starvation at all, I find it very hard to justify such a cost when I don't have much money. The ON/OFF fuel taps seem to be around £5 on eBay so if the petcock does break again, I can just run the bike on prime and go old school, shutting the fuel off at the end of the journey.  

I have some 5/16 (8mm) pipes just fitted although Suzuki have a really silly (in my opinion) system for the pipe sizes! 8mm on the tank petcock and 10mm on the vacuum petcock! (Sorry, I don't know the imperial measuring system!)

I guess the pipes are really only going to be 8mm or 10mm, so I couldn't go far wrong by purchasing an 8mm fuel tap and using some hose clamps

Fuel lines stock are 7mm.  Hard to find.

Most use 5/16 (a little bigger) or 1/4 (a little smaller).

Quote from: J.M. on January 12, 2013, 07:06:55 AM
Recently had an issue with my carbs after fitting new fuel pipes where some rubber contaminent had stopped the float needle from closing fully, causing my bike to leak fuel when stopped/idling for too long.

This also lead me on to discovering that the vacuum operated petcock wasn't functioning properly. Essentially ON was free flowing fuel with the engine off, like you would expect prime to do. I wasn't able to find a petcock rebuild kit online so I carefully dismantled the petcock and found the issue; the spring had compressed too much. I stretched the string out a bit and reassembled and now it's working fine.

However getting caught out riding with a petrol leak and no tools is horrible, especially being as you can't even turn the fuel off because you need tools to reach the petcock underneath the tank.

So what I am thinking about doing is adding a simple ON/OFF tap on the petrol line between the vacuum petcock and the carbs so that if this problem comes back (which it shouldn't), I'm able to shut the bike off with ease whilst out. A fuel filter wouldn't go a miss either.

So does anyone know the size of the hose running between the vacuum petcock and the carbs?

It's the GS500F 2004 model, UK, if that makes any difference.

Thanks for your help

if you are going that far i would recomend removing the stock petcock entirely, there is a thread on here called pingle my petcock where it is replaced with a pingle petcock, i would recommend this route over making a more complicated system that could potentially effect the flow of fuel to the carbs.


if you bring in a section of your fuel line to any auto-zone you should be able to buy it buy the foot.

Quote from: J.M. on January 12, 2013, 07:06:55 AM
This also lead me on to discovering that the vacuum operated petcock wasn't functioning properly. Essentially ON was free flowing fuel with the engine off, like you would expect prime to do. I wasn't able to find a petcock rebuild kit online so I carefully dismantled the petcock and found the issue; the spring had compressed too much. I stretched the string out a bit and reassembled and now it's working fine.

It is very rare for the vacuum petcock to go bad. They're used in all kinds of bikes.
If you replace it with a new one or a used one from a low mileage fairly new bike you'll be fine.

I know - there are a few people that stand high on the pedestal proclaiming vacuum petcocks are the work of the devil. In reality, no, they are not. Your fork seals will go bad more often than a fuel petcock will ever go bad. Those who declare you should remove the petcock and go to manual of off valves should weld their forks when the seals go bad. They should JB weld the engine head on when there is a leak in a gasket. I challenge them to cobble up something when some other part goes bad - but they won't. They fix it - they will fix everything except the vacuum petcock. It makes me wonder.....

Any part can go bad. Don't cobble up some hack when it happens. Just fix the real problem. If the spring is bad, then replace the unit or take the spring out of one with a torn diaphragm.

Also remember that if fuel is coming out of the carbs - your carbs have stuck floats or the needles aren't shutting off the fuel. When the bike is ON, fuel is free flowing (no matter what fuel valve you use - stock of a cobbled up thing). The floats and needles in the carbs stop the flow of fuel when the float bowls are full. When they overfill it is a problem of the carbs.

Keeping  that in mind: you CAN leave the bike in prime all the time because it is the same as ON or RESERVE when the bike is on: fuel is free flowing. The carbs stop the flow.

Fix your carbs. If the carbs were working right, you'd never know the vacuum petcock was not stopping the flow of gas when the bike is off.

The vacuum on the petcock wasn't bad, it was simply the spring. It had compressed a little bit too much so that the piston inside wasn't shutting off the petcock. I have no idea how long it had been like this for, I didn't notice it until the carbs started playing up.

The carbs have been cleaned out and I have checked the petcock since the repair and it's working a treat now too. The bike is working properly now. I know you can leave it in prime because I accidentally did this the other night (forgot I had left it in prime during the reassembly).

In this case it was the needles. A little bit of rubber had gotten in to the barrel that the needle sits in, meaning the needle couldn't shut off the fuel supply. All cleared out now.

The shut off tap isn't a hack in my opinion, it's a precautionary measure that will be left in the ON position forever hopefully. I'm just thinking that if my floats ever do get gummed up in the future, I can switch the tap OFF to stop any leakage whilst I wait on an opportunity to open up the bike. Much less of a hack than a Pingel in my opinion!

Definitely not going down the pingel route anyway. If the GS was one of the older models that suffered from fuel starvation at higher speeds then I could understand it, but it seems a little pointless to replace a working system with a more expensive system when you don't have much money.