Bad valve needle seat o-rings, some insight needed

[Tighthead]

I have an '81 GS450L that I can get started but as soon as I open the throttle , gas pours into the airbox and out of the outlet hose.

So I learned that the problem behind this was (at least partially) because of bad valve needle seat o-rings. I think my petcock is OK.

So I pull the carbs off and sure enough the o-rings are brittle and just sad looking. The needles and everything else look really good--the needles came out smoothly, and everything else looks clean. What I can't understand is how these tiny little o-rings can be responsible for the volume of gas that's coming into (and out of) the airbox.

Can anyone explain this to me?

Edit: One other thing: there is definitely gas in my crank case--can this happen if just the o-rings are bad and petcock good, or does this mean that the petcock is definitely bad? The reason I think my petcock is good is because when I removed the gas tank with gas in it, none came out of the petcock in the ON position--can my petcock still be bad?

[Anonymous]

Because as they get brittle and shrink they act as a bypass around the needles. Don't forget that you have a certain amount of gravitational pressure trying to force that juice past the needle valve. Give it any way through and it will do it. If you want to query the volume of gas they'll let by then just look at how small the hole that the needle valve controls is yet it'll allow enough fuel to flow through it to feed a cylinder.

[Giblet]

Did you fix it yet or would you like me to find the web site where you can get partial kits for $12? They have needle & seats and o-rings.

[Macmatic]

Did you fix it yet or would you like me to find the web site where you can get partial kits for $12? They have needle & seats and o-rings.

https://www.cycleorings.com

Great guy to deal with, and QUICK! I placed my order around 8pm on a Thursday, had confirmation that night and my o-rings Saturday.

/\/\ac

[Giblet]

Did you fix it yet or would you like me to find the web site where you can get partial kits for $12? They have needle & seats and o-rings.

https://www.cycleorings.com

Great guy to deal with, and QUICK! I placed my order around 8pm on a Thursday, had confirmation that night and my o-rings Saturday.

/\/\ac

I got a set of o-rings from www.cycleorings.com too. Quick service. Now if I can just find a spare set of carbs to rebuild. I needed to change needle & seat too. https://www.partsnmore.com/ sells kits that only have the float bowl gasket, needle & seat & three o-rings.

[gs650gt]

I think You should also check the fuel petcock. If it's leaking along with the needle valve seats, the result will be overflowing gasoline.

But if either of them is working, it should be enough to stop the flood...

[ccratin]

I just got my 85 450L running dealing with the same issue. Make sure you check your float needles to ensure that the spring loaded pins inside are not stuck. Both of mine were which makes the valves not shut well at all and makes adjusting the floats properly impossible. After two weeks with gas in the tank, about a gallon was inside the crankcase. Fortunately, when I decided to get back on the project, I check the oil just in case! Good luck.

[Tighthead]

Partnmore.com is a cool site, and thanks for the reference, but I couldn't find anything for a 450, and as best as I can tell, parts from the 550 (which they do have kits for) won't work.

I ordered new valve needle seats and o-rings from crotchrocket.com. I was hasty and when I got the floats off I grabbed the needle seats with pliers and turned (they're threaded, unlike the ones in the excellent carb rebuild series on this web site), deforming them so much that the needles won't fit in them anymore. Dumb rookie mistake, I know. And at ~$30 a piece for new ones, a little costly. But it never hurts to get new parts, I guess.

The spring loaded doohickies on the needles themselves are nice and smooth. Actually, everything inside the carb looks pretty clean.

Let me ask you all this about the petcock: when I took my tank off, the petcock was obviously still attached to it. If the petcock was leaking, wouldn't I be able to see gas dripping out of the petcock as I hold the tank up?

'Nother update: I got to thinking, and since my fuel tank is sitting just outside, I tried it: I held it up, sloshed it around, and I couldn't get anything to come out in the ON position. Then I switched it to PRIME, and sure enough, here comes some gas. Switch it back to ON and nothing comes out. Is this fairly conclusive? The petcock seemed to be working just as expected.

[ccratin]

Sounds like your petcock is working as designed. If it were leaking in the "On" position, you'd need to be worried. Those o-rings were the likely culprit. Look closely at your float needles for wear. The seat and needles wear as a unit, so they may not seat well with the new seats.

[Billy Ricks]

The size o-ring that comes in kits to repair pump up style garden sprayers is the perfect size for the seats.