Carb Drain Screw Leaking with new O-Rings??

[Guest]

I did a full carb rebuild and the bike runs pretty great with just a bench sync but I let it sit for a few days in the garage and I noticed the carbs are leaking gas from the drain screw.

Any suggestions as to what I should do? get new O-rings again? different O-rings?

[IanDMacDonald]

Does your full carb rebuild include new o-rings? Other members may not like me saying this, but, after you completely "re-build" your carbs, there is really no reason why you would have to disassemble them for some time (including removing the drain screw). In fact, there is really no reason why you should ever have to remove that drain screw after a re-build. So, if you wanna do it the lazy way and not investigate the reason for the leak, throw some "Seal-All" on the threads of the drain screw, and call it a day.

The proper way would be to ensure that you have the proper o-rings on the drain screw. If not, utilize the resources available to us to order the proper o-rings for those drain screws. It always feels better knowing it's fixed the right way, as it gives you a piece of mind.

[gmoore]

Thanks for the reply.

I actually did do the FULL carb rebuild including fully dismantling, soaking & cycleorings.com o-rings kit. That is the reason I'm little perturbed about them leaking as it is supposedly the "right" way.

That being said, I may have to throw some petroleum resistant sealer on the threads and call it a day, I was just hoping I wouldn't have to do that.

What is a good "seal-all"/gasket that is also petrol resistant? or are most of them petrol resistant? I'd imagine that most of that stuff is?

Thanks.

[Larry D]

Are you certain it's coming from the drain screws and not somewhere else and dripping down to the drain screw and falling off ?

I've never had mine leak, but, I would think an appropriately sized crush washer would do the trick.

[gmoore]

Yeah, I thought that having the drain screws leak was weird too. I have them off and have inspected the crap out of them and nothing else is wet. The other funny thing is that all of them are leaking but to different degrees.

Thanks for the crush washer idea! I think it will either be the crush washer or an appropriately sized washer gasket that I'm going to give a try.

[IanDMacDonald]

I literally meant "seal all". It comes in a yellow tube from Auto Zone for a couple of dollars. It's meant for gas cans, etc. Works great! But, Larry read my mind when I first typed my first reply, referring to the gas coming from somewhere else, and giving the illusion of it coming from the float bowl drain screws. I have a Yammie and a Suzuki both using these Mikuni carbs, and I never had a problem with them leaking, even using regular metric SS bolts from Ace Hardware. A little "Seal All" won't hurt anything!

[sedelen]

I had a carb drain screw leak also, before I'd ride it I'd wipe off the gas that seeped out of it and collected on the bottom of the bowl. Being that I had another set of carbs, I replaced the "O" ring, but it still leaked, that was many months ago. I had put together a order for some new parts, to include two brand spanking new "O" rings. As time went on, I never placed the order, but I still have it ready to go, in the meantime, the carb screw quit leaking, now I guess I can cancel those two "O" rings from my someday order .

[Coady]

I would be reluctant to put any kind of sealer on those threads as you will most likely find that you willl need to drain the carbs again in the future. Any kind of gunk on the threads will get worn off when you screw the srcrews back in and potentially end up in the bowls increasing the chance of blocking the carbs.

I've got the same issue on a couple of my carbs and think I'll get some OEM o-rings to see if that fixes it. I did a full rebuild with the cycle o-rings kit a couple of years ago but I think undoing that float bowl screw a few times may have damaged them slightly - even though they look fine.

[robertbarr]

When you stripped the carbs, were there O-rings on the drain screws? Some carbs don't use O-rings at all. They use a hard fiber washer. Putting an O-ring in its place will simply crush it, and of course it will leak.

[gmoore]

The carbs are VM 26's from a 79 GS 750. So, I bought the O-ring kit for the 79 GS 750. Also, yes, the drain plugs had O-rings on them when I unscrewed them.

Also, these are very slow leaks and I had the same thought that the leak must be dripping down from another spot but after some pretty thorough investigation I determined that it was indeed the drain screws BUT I will check again so I can be 110% sure before I try anything to remedy the issue.

Thanks guys.

[keman]

I have had issues with o-rings on screws before. Since you are twisting the screw into place, the o-ring sometimes gets in on the twisting action and deforms. I fix this by putting a drop of oil on the o-ring before I install the screw. It seems to work, since I have not had one leak since.

[OldVet66]

I have never had an O-ring leak unless I did something wrong. If you think about it, if both surfaces are perfectly clean and smooth and undamaged, the proper size and type O-ring used for sealing compression, slightly lubed and not damaged during installation, it can't leak. I would suspect the wrong size O-ring since they are all leaking, unless there are hard bits of the old O-rings stuck to the surfaces. I might add that the last set of carbs I rebuilt using Robert's O-rings were for a '79 750E, no leaks.

[robertbarr]

Well, if it were just one carb leaking, I'd say perhaps an improperly shaped O-ring or some problem with contaminated / corroded sealing surfaces. But since they all leak, I just don't know.

If these O-rings were the least bit problematic on these carbs, I'd have hundreds of complaints. Zero. (Until now...). They held fine on my own personal machine...

There's no way to know if they were installed improperly, but given that you assembled the rest of your bank together OK, odds are you didn't hamfist these.

If you want, PM me your address and I'll send a new set of drain O-rings, but I kind of doubt that'll make any difference.

RB

[Coady]

Well, if it were just one carb leaking, I'd say perhaps an improperly shaped O-ring or some problem with contaminated / corroded sealing surfaces. RB

I suspect this to be the problem with mine - corroded and slightly pitted carb bowl surface which has damaged the o-ring slightly.

By the way I wouldn't hesitate to buy the o-ring kit from cycle o-rings again and totally recommend it. It's a great service at very good price. I was just going to get a couple of OEM ones on my next parts order for convenience sake.