Really Annoying Intermittent Gas Leak

[speedfreak]

So, I've been dealing with a gas leak from the left carb ever since I tried to fix my petcock diaphragm. I've now repalced the diaphragm and the float in the carb (original was slightly dented) and it's still happenning. I'm getting very frustrated. Sometimes I lose a couple of tablespoons out of the left carb overflow then it stops. Other times I lose a liter or more. And it will sit for 20 minutes with no leak, then dribble a teaspoon out the overflow. It's by no means a consistent fault.

I bought a used petcock and stole the diaphragm for my petcock (which has been totally cleaned and rebuilt and was working with original diaphragm (excpet cracks were letting fuel out the vent hole). Now, the petcock isn't completely sealing - sometimes. Any time I pull the gas lines off, then most I get is a drip every 20-30seconds - or sometimes none at all. Though if I'm losing a liter of gas, clearly it's going through the petcock.

I also went ahead and set the float height in the left carb up 3/4mm to ensure I'm actuating the needle. I know if the needle was sealing perfectly it wouldn't be overflowing - or is that normal behaviour with a leaking petcock? I would guess not considering the right carb isn't overflowing.

At this point I would just like to understand if I have a petcock issue, carb issue, or both... I hate chasing multiple issues at once.

[Suzukidave]

The vacuum petcocks have a o ring attached to the diaphragm plunger , if the o ring isnt sealing for what ever reason the petcock will leak . Look at the o ring to make sure its still soft and check the seat the o ring seals angst inside the petcock body .

[Coyote]

Hmmmmm. I bought a rebuild kit for the petcock on my GS1000. It's the same as the GT petcocks - just a different shape. New diaphragm, new o-ring (the seal), new V-seal and new 4 hole gasket. It still leaks horribly. All new parts and it's like I just picked out of a junk pile. Had it apart about 20 times. I can't even make it seal by pushing the o-ring on the seat with my finger. No way the whimpy spring is going to make it seat.
I started to purchase a manual petcock to get rid of the misery. I didn't want to shell out the money for a really good one. So I went to an ACE hardware store that handled lawn mower partsn and bought an inline fuel shutoff. Mounted between the petcock and the carbs. Just like a manual, you must remember to turn it on and off. About an $8 part and the problem is solved,
Yes, your float needles SHOULD prevent the bowls from over flowing. Have you checked out that needle under a magnifier? If you can see a small step / ridge, the needle is shot. You would need to replace both the needle and seat. The problem there is the slightest tiny fleck of dirt will keep the needle from seating correctly and it will leak anyway. It really sounds to me like that needle is shot That's why it seats differently at different times. Or, you can just go with something positive like this.

[speedfreak]

Thanks gents. I'll pull off the petcock and check the o-ring - hopefully that'll do it. If not, I guess it's time for a needle and seat. Have you found a source for less than $60? I can't seem to find it for less and it seems like a lot for a Mikuni part - they are usually pretty inexpensive in my experience.

I've considered the inline shutoff option. Two issues - 1, I would have to adapt the fuel lines to go to a single output on the petcock (currently dual output) which just sounds like more work and more chance to break something; 2, I hate to give up and just add a part that doesn't need to be there (makes me feel defeated). Last resort

That particular inline shutoff is what I put on the oil feed line! I got sick of clamping the line when I was dealing with pump issues, plus the ebay check valves I got were not stopping flow when I first installed them, so I put in the shutoff to fix both problems. I'll probably take it out once I get the chance to test those check valves again.

[Suzukidave]

I have read on the list here guys rebuilding the petcocks having to smooth and polish the O ring seat in the petcock to get the O ring to seal as it should . With todays fuels it would be a great idea to make that O ring a Viton type material .

[tricky1962]

I gave up chasing my tail and plugged the prime line in the tap with a bit of rubber. Now I have an "Off" position and two "Run" positions.

If the carbs are drained for some reason, it makes it tiresome to get it to fire up, but providing I remember to switch the fuel off after each ride (so far so good - old school) then I have no problems with flooding.

In fact, if I've drained the carbs, I can leave the tap in the "On" position for a few minutes and it fill itself up!! Win all round in my opinion posting.php?mode=reply&f=2&t=11547#" onclick="window.open(this.href);return false;

[yeadon_m]

In-line on/off taps on all my GTs, but easy as they're the later, one fuel hose type.
They don't leak much even left permanently on, but it removes one failure mode and has been a blessing for a number of years now.
Mine are in brass.
Mike

[joolstacho]

I haven't needed to work on my GT500 petcock, but I've recently fixed a similar fault on my RZ250. Fuel was leaking through petcock, flooding carbs, seeping past reed-valves and into crankcase.
Problem was with the very fine return spring that holds the diaphragm valve/o-ring back into it's hole when the vacuum stops (engine not running).
It had lost spring tension, so I just stretched it out a bit, reassembled, and so far so good.
(Like these (rare) easy fixes!)

[speedfreak]

Thanks for the advice gents! I drained the tank and carbs last night - going to pull it all apart (again) tonight. Interesting note that before I drained the tank the petcock had the worst drip rate I've seen yet - just about constant.

Plan is to swap the o-ring, probably stretch the spring just a little, and clean/polish the sealing surface. Hopefully that does it. If not, I like the rubber in the prime line - at this point an "off" option sounds really nice.

I'm also going to pull off the carb and give the needle and seat a polish. I figure it's not going to get (much) worse and perhaps the better sealing surface combined with the fractional change in the sealing diameter will help it to get a decent seal. Enough that with a fully closing petcock it won't drain...

I'll report back.

[Coyote]

I am interested in learning more about plugging the prime line and making it an off. There is no separate prime line so I assume you mean one of the petcock holes. Can someone give me a step by step instruction on this? It's the later type with the single outlet. Over the years I have rebuilt about a half dozen of these, including the one on my current GT550.. The one I am having fits with is on my GS1000. The petcock internals are identical to the later GT type. It just has a different shape and outlet location.. My current plan is to use an inline valve, but I'm really strapped for room.
Converting it sounds like a better plan. Just not sure how to do it. Odd, the petcock worked perfectly for close to 20 years. It has a new diaphragm, a new o-ring and all other rubber parts. The sealing surface is perfect, but it just won't seal. I even tried a double length spring in it. Looking at it from the open lever end and working the diaphragm plunger with a toothpick, it appears that the sealing o-ring is slightly off center when it seats. I sum this up to inaccuracy in the rebuild kit. The plunger must not be dead center in the diaphragm as it is not hitting the seat square. I'm not looking at shelling out another $25 and getting another kit with the same problem. How do I give it an 'off' position? Note that the plunger and it's o-ring are off center in the third pic.

[tricky1962]

Here is my post about plugging the line

viewtopic.php?f=2&t=7024&start=15" onclick="window.open(this.href);return false;

The link in that post takes you to a guy who replaces his diaphragm with a thick bit of rubber, this removes the need for vacuum as well turning the tap into a standard gravity feed tap. I ignored that bit, but it does mean that if the engine is not running, I am relying on the leaks to fill the float bowls or the vacuum created when I kick it over to fill the bowls.

If my float bowls are empty, it takes seven or eight kicks (from a first kick starter normally) to get it going, but my tap leaks badly enough that if I switch the fuel on and give it five minutes, my float bowls are full or full enough to start it easily anyway.

Coyote, you will have to work out which hole is the one you need to plug, but I'm going to make a stab and suggest the right hand one from the bottom picture - don't sue me if I'm wrong though, I'm broke

[Suzukidave]

If most of the GS1000 petcock is in good shape why not try to center up the plunger O ring so it seats correctly and try it again .

[Coyote]

The diaphragm is located by the 4 screws that hold the back on and the plastic block. I suppose I could enlarge the holes in diaphragm, but probably still wouldn't be able to tell where I'm at when assembling. I have a feeling that the o-ring in the rebuild kit is not correct. As I stated, I can hold it down with my finger, (about 100 times the spring pressure) and it still leaks lung air.
Possibly the o-ring groove is out of round, making the o-ring oval shaped? The kit was by K & L -- Japan.

[speedfreak]

So I polished the float needle & seat and the petcock port last night. The needle and seat seem to seal much better - at least to air. Don't have the petcock back on yet, but I'm sure it will be better - the amount of buildup on the sealing surface was rediculous - not sure how I missed that in previous inspections... Hopefully that'll do it.

[speedfreak]

That did it! Three seperate rides and about 20miles, not a drop overflowed. Thanks for the advice gents - you saved me a serious headache and some $.