Gas leaking out of one of the carb vent tubes. Doesn't look like any float issues.

[lettuceman44]

Hey guys, looking for some advice on what to look for. This is for a 1982 Suzuki GS450L

So one of my carb vent tubes is leaking a lot of gas when the bike is RUNNING. Only when running. So I don't think its a petcock issue.

It also leaks a lot of gas when the petcock is set to PRIME.

So my initial guess was a float issue. I opened up the float bowls, but nothing seems stuck, and the float needles seem fine. Also very clean. Also checked the needle jets, and no gunk.

So I'm going to take apart the rest of the carb. What I want to know is, what should I be looking for? What else in the carb equation can cause fuel to be leaking?

Also, the strange thing was this was not happening yesterday when I was turning the bike on. Just today. Prior to yesterday, it hasn't been turned on in a long time, as I wasn't able to work on it for half of last year. I'm wondering if something in the fuel tank gunked something in the carbs.

Again, the float bowl itself was very clean.

Pre emptive thanks to anyone who gives me some info or advice.

[Rijko]

has the petcock been overhauled ?
Especially avoid the K&L set with yellow label.

If it leaks a lot, hopefully the diagnose is easy.
Better than a single drip once every fortnight i mean.

Easiest and quickest check is to remove the vacuum line from
the petcock and see if gas comes out of the petcock through this pipe.
Try this with petcock on all 3 positions.

Next, connect a hose to the vacuum pipe and suck on it.
You should feel the vacuum system shut and close the connection.
Mouth full of gas ? Try this with petcock on all 3 positions.

Next remove the fuel line from the petcock and see if it leaks when set to
normal/res.

If no to these questions, the carbs are next in line to check.

Old or dirty floats may stick, see if they move easily on their axis.
Think you already did this and they are clean and move freely.

Old float needles may stick now and again, sometimes just once in a while.
This is hard to diagnose or reproduce, but is usually the cause of leaking.

Hope this helps

[lettuceman44]

Hey Rijko, thanks for the response.

Petcock all checks out. Works as needed. (tried everything you mentioned. No gas in mouth, just fumes :P)

I'm fairly certain it is a carb issue.


Now here is the weird thing.

I went to turn the bike on today for more troubleshooting, and no gas is leaking out. Tried it again, and nothing is leaking out.

I don't understand lol.

So day 1 it went from no leaks, day 2 it was leaking like crazy from one of the carb vent tubes, day 3, no leaks.

[Rijko]

i have the same issue with one of my bikes since last month.
Only leaks sometimes, sometimes during driving, sometimes
when moving the bike in the garage, sometimes just while parked.
Sometimes a little p*ss stain on the floor, sometimes it will pour out
like it needs to empty a full blatter like me after a bar visit
Teaches you not to forget to take the petcock OFF prime though.
Ask me how i know.

Known issue, 99% it's old float needles and seats.
Replacing those will solve the issue, i'm sure.

[Nessism]

Your bike is 35 years old. Go through the carbs and make sure everything is right. Replace all the O-rings since they are sure to be hard and deteriorated. Basscliff's website has a 450 specific carb rebuild tutorial.

And check the Newbie Mistakes thread linked in my signature to see if there is anything else you should be tending too like adjusting the valves. Maintenance is the way forward and the best way to assure your bike is reliable.

[lettuceman44]

Your bike is 35 years old. Go through the carbs and make sure everything is right. Replace all the O-rings since they are sure to be hard and deteriorated. Basscliff's website has a 450 specific carb rebuild tutorial.

And check the Newbie Mistakes thread linked in my signature to see if there is anything else you should be tending too like adjusting the valves. Maintenance is the way forward and the best way to assure your bike is reliable.

Sorry if I misrepresented this the wrong way, but I didn't just start working on the bike. I started last year.
All the O-Rings are already replaced, and the Carbs are cleaned.
Valves are already adjusted (although there is one that needs a shim closer to optimal)

This is a new issue.

[lettuceman44]

i have the same issue with one of my bikes since last month.
Only leaks sometimes, sometimes during driving, sometimes
when moving the bike in the garage, sometimes just while parked.
Sometimes a little p*ss stain on the floor, sometimes it will pour out
like it needs to empty a full blatter like me after a bar visit
Teaches you not to forget to take the petcock OFF prime though.
Ask me how i know.

Known issue, 99% it's old float needles and seats.
Replacing those will solve the issue, i'm sure.

What is the float seat exactly?

Like I said, I checked my needles and they seem fine. Do you know what the characteristics of a good one is, or how can I tell if one is bad?

[hillsy]

There is an o ring under each of the float valve seats - if they are split or pinched it will pass fuel through straight into the carb bowl bypassing the float valve.

The thing that the screw is holding in is the float valve seat:

[Rijko]

What is the float seat exactly?

Like I said, I checked my needles and they seem fine. Do you know what the characteristics of a good one is, or how can I tell if one is bad?

like Hillsy said .... the o-ring is important too.

here's another pic, the copper part is the seat.
Yours may look a little different but you get the idea.
Since GSR only allows 1 pic per post i will have to post more than 1 answer

mikuni-needle-valve-with-viton-tip-for-spigot-flange-mount-carburetors.jpg

[Rijko]

sometimes you can see wear on the needle

wornneedle.jpg

[Rijko]

10.jpg

sometimes the needle point has little visible wear, but sticks to the copper
seat on the long side of the needle, not the tip.

The issue is worse with bio-ethanol added to the fuel, leaning the mixture
and creating more friction between needle and seat

I have always had succes with this issue by replacing the needles
and seat as a pair.

[hillsy]

From memory all the GS float valve seats are press in (not screw in). Be careful pulling them out as you can easily distort / fubar the seat where the valve enters. If you squeeze them out of round the valves can stick. A squirt of WD40 or similar will help loosen the o ring.

Anyway, drain the carbs, take them off, take off the bowls, hold the carbs upside down, get a longer piece of fuel hose on there and blow into it. If the valves or seats are leaking you will be able to blow air through them and hear where it is leaking from.

ALWAYS bench test your carbs for leaks before you put them back on.

[Rijko]

From memory all the GS float valve seats are press in (not screw in).

the CV series has the pressed seats, the VM series are the screwed type afaik.
VM 26mm, 27mm, 28mm, 29mm have them

If you're lucky, you can find transparent float bowls and see what's going on

s-l1600.jpg


sometimes the needles have a bit of damage on the sides and
polishing that away solves the issue

[hannibal]

VM26 with screw in seats here. I forgot to tighten a valve seat and that (obviously) led to a leaky carb.

A clear bowl is brilliant!

[lettuceman44]

Thanks for the help guys. I'll take a look at these suggestions, and check the o rings to be sure.