Background info:

• My 2006 GS500 is leaking fuel from the airbox drain hose
• I've checked everywhere else to confirm there are no other leaks and it's just from the hose
• It's a slow drip (once every few minutes or less), but consistent
• There is much less leakage (sometimes none), once the tank is down to 1/3 - 1/2 full
• The bike has been sat for over a week in a garage but still leaks
• The petcock is set to 'on'
• Setting it to 'prime' doesn't have any noticeable effect

I'm thinking this may be both a petcock seal and also carb float issue. The logic being that fuel in the airbox is likely overflowing carbs, hence a float issue. And also having sat for a week any overflowed fuel should have exited by now, so the continued leak suggests a constant supply of fuel caused by a faulty petcock.

Can anyone verify my logic before I order a carb gasket & float valve kit (opinions on the wemoto one? http://www.wemoto.com/bikes/suzuki/gs_500_k6_k7/06-07/picture/carburettor_gasket_and_float_valve_kit/ ), and a petcock repair kit (such as http://www.ebay.co.uk/itm/MS-Fuel-Tap-Petcock-Repair-Kit-SUZUKI-GS-500-E-550-750-D-E-850-G-GSX-400-L-/151450889123?_trksid=p2385738.m4383.l4275.c10 ).

What about installing an inline fuel filter too?

Yea can be faulty petcock followed by bad float. Try cleaning the float and "blow" testing it.
You could also have a bit of blow by and that can end up in the airbox but then it will be a bit contaminated, with water, combustion by products and oil etc etc. Some if it in normal, and can get worse when cold, but not in the several cup ful category, more like a drop or 2 in a few rides.
Cool.
Buddha.

The Buddha is wise  lol, i agree with what he said to a T. ^
Aaron

Thanks for the responses, I'm going to check the float heights using clear tube once the right size pipe arrives as an initial check, then will be sure to clean the floats and blow test them as suggested.

Is there a preferred method to check if the petcock is faulty? I can't find any rebuild kits explicitly stated for the 2004+ carbs and would prefer to avoid £50 for a new one if I can avoid it.

I'm thinking that by opening the carb drain screw with a working petcock set to 'on', fuel should stop flowing, whereas a faulty petcock will keep on feeding the carbs and let a constant supply of fuel through to drain out?

Would this work? Any other suggestions are appreciated.

Quote from: max on January 13, 2018, 03:11:40 PM
Thanks for the responses, I'm going to check the float heights using clear tube once the right size pipe arrives as an initial check, then will be sure to clean the floats and blow test them as suggested.

Is there a preferred method to check if the petcock is faulty? I can't find any rebuild kits explicitly stated for the 2004+ carbs and would prefer to avoid £50 for a new one if I can avoid it.

I'm thinking that by opening the carb drain screw with a working petcock set to 'on', fuel should stop flowing, whereas a faulty petcock will keep on feeding the carbs and let a constant supply of fuel through to drain out?

Would this work? Any other suggestions are appreciated.

Yeah that would work.

Some people have put non-vacuum petcocks on their GS500s. I believe that they come on some Honda trail bikes. You can check out this site index. I was going to do so, but I got my vacuum petcock to work properly by cleaning it out and running a separate vacuum line to it.

Finally got some time to do some testing so here's an update.



Floats:

Left-hand side


Right-hand side


I did the float height testing on the centre stand in prime. The LHS level seems pretty close to the gasket level, but the RHS level is noticeably higher. I was expecting a float failure would cause the levels to rise to the gas tank's level - was that therefore an incorrect assumption?


Petcock:

Checking on the bike the past few days there actually hadn't been any leakage.

After testing the float heights in prime, I let this begin draining into a jar at a steady flow, then switched the petcock to 'on' and after some further drainage the fuel flow would then stop. I tested this both sides switching from prime to 'res' and this also stopped each time.

Could this indicate the petcock may actually be functioning and the previous leaking was simply a buildup in the airbox?

A few hours after all this testing I went back and found some leakage, but I'm not sure if this was petrol that spilled when I accidentally pulled my clear tube off early, or from the airbox/elsewhere.


Fuel:

When draining the fuel I noticed a buildup of milky immiscible liquid at the bottom of the jar.


An oily substance caught in the U-bend


Rust/Dirt particles


So I'll be completely draining the tank and cleaning the float bowls.



What are some opinions based on this initial testing? I will still be cleaning the float bowls and will be purchasing 2 new needle kits ready to be expecting the worst (www.wemoto.com/bikes/suzuki/gs_500_k6_k7/06-07/picture/carburettor_gasket_and_float_valve_kit/).

Water+oil turns the water milky. You got milky residue from the carbs ? Or airbox ?
Cool.
Buddha.

Quote from: The Buddha on January 17, 2018, 01:12:09 PM
Water+oil turns the water milky. You got milky residue from the carbs ? Or airbox ?
Cool.
Buddha.

The milky liquid in the jar was from draining ~0.5 L of fuel via the carbs.

Although when watching fuel leak from the airbox drain hose I've also noticed that being milky before too.

BTW it's probably not just float level problem, it may be float needle valves leaking too. Those are cheap to replace and well worth it once you get the carbs off.

Along with all of the o-rings IMHO.

Quote from: mr72 on January 17, 2018, 02:14:37 PM
BTW it's probably not just float level problem, it may be float needle valves leaking too. Those are cheap to replace and well worth it once you get the carbs off.

Along with all of the o-rings IMHO.

I expect that it's the needles rather than level too. If I'm going through the effort of taking the carbs off I thought I might as well replace the parts too which is why I'm ordering the kit quoted.

Quote from: max on January 17, 2018, 12:47:03 PM
...

What are some opinions based on this initial testing? I will still be cleaning the float bowls and will be purchasing 2 new needle kits ready to be expecting the worst (www.wemoto.com/bikes/suzuki/gs_500_k6_k7/06-07/picture/carburettor_gasket_and_float_valve_kit/).

These are the parts in the kit, no jets just the float needles and O-rings that I'm hoping will do the job.

I'd also replace those intake boot o-rings which are not included in that kit. Dunno if that kit includes the pilot needle o-ring or not (many don't), but if it doesn't, I'd order a couple of those too.

BTW you can find a lot of this info including where to buy o-rings on my blog: https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Quote from: mr72 on January 17, 2018, 02:36:49 PM
I'd also replace those intake boot o-rings which are not included in that kit. Dunno if that kit includes the pilot needle o-ring or not (many don't), but if it doesn't, I'd order a couple of those too.

BTW you can find a lot of this info including where to buy o-rings on my blog: https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

Thanks that looks like a useful read!

By intake boot o-rings are you referring to the ones that sit against the cylinder head (part 21)? Why do you suggest replacing those if so?

Quote from: max on January 17, 2018, 03:43:46 PM
By intake boot o-rings are you referring to the ones that sit against the cylinder head (part 21)? Why do you suggest replacing those if so?

Yes, exactly.

They are a common cause of vacuum leaks that send a lot of well-meaning home mechanics on a wild goose chase. Once the carbs are off of the bike it's trivial to get to that part and replace it, so if it hasn't been done on a 10+ year old motorcycle, I'd swap them, no question. They seem expensive for o-rings (like $4 each or something) but so worth it.

These are rubber o-rings that sit against the head and are exposed to a lot of heat all the time. That really does warrant a different solution, but there it is. So they are likely (imho) to go bad rather quickly.

And replace the retarded JIS phillips head screws with real bolts (allen or hex - in fact hex - same as the engine case bolts would be my choice).
Cool.
Buddha.

Quote from: The Buddha on January 18, 2018, 11:23:27 AM
And replace the retarded JIS phillips head screws with real bolts (allen or hex - in fact hex - same as the engine case bolts would be my choice).
Cool.
Buddha.

I can't find any info online about the length or thread size and pitch for these screws - any idea? I'd rather have all my parts ready to go when I come to do this. I also don't have a JIS driver so if you happen to know the driver size that'd be great too.

Just a note on the needle and seat ( floats).
Suzukis are noted for leaking at the N+S, but it isn't the needle or a worn seat.
The seat pushes in to the carb body and is sealed by an Oring. The leak often occurs between the O ring and the carb body. This is the cause of the dreaded DRZ400 crankcase full of fuel problem. Often changing the Oring with a suitable fuel resistant replacement will cure the problem. The problem is made worse by Alchohol fuels so a modern alchy resistant ring is the best way to go.
I put a light smear of fuel resistant gasket liquid on the O ring when I put them in ( both sides), which seems to help it last longer.

Quote from: gregjet on January 21, 2018, 01:00:36 PM

I put a light smear of fuel resistant gasket liquid on the O ring when I put them in ( both sides), which seems to help it last longer.

LOL, I have received many a complaint about carbs getting sent back with a purple goop on the side, including "hey man, its dirtier after you clean it than when I send it" ...
The gasket maker is purple, and it stays flexible and pliant for decades, I get carbs back that people that bought bikes from other people who have sent me carbs ... and I can usually tell cos they have purple smear on them.
Sometimes they may have a thumb print on em too.
Cool.
Buddha.

" Sometimes they may have a thumb print on em too."
Possibly taking creative pride a touch far?

Hi all, update time.

Since my last post I got everything ordered, but the conditions in my garage were unworkable so I took the carbs and seal kit to a mechanic to do the job instead. Of the kit of 5 o-rings, they didn't install the carb-body to top cover o-ring, and the jet needle holder o-ring because "they didn't need doing".

I self-checked the float heights which came out at around 14mm (at the high end of the spec, 13+- 1.0mm).

Although one of the floats appeared to be slightly sticking, it became smoother after some persuasion.

However, I went to bench test them before putting them back on the bike and fuel began leaking immediately.

I was sure to not create excess pressure by keeping the fuel bottle's level only slightly higher than the carbs, but it still steadily leaked from main body.

Any advice would be appreciated at this point because the bike has been out of action for long enough at this point.