Rebuilt carbs leaking like a sieve

[oblique]

These carbs have been months in the making. Im about to roll this bike from a cliff. 1980 Gs750L...quite certain its all original.

The first rebuild I stripped them completely and dipped in the Yamalube carb stuff for 24 hours then boiled for 15 minutes. Put everything back together with new bowl gaskets (aftermarket light-colored ones) and fresh o-rings for the following:
needle valve seats
fuel interconnect fittings
breather hose fittings
drain plugs

Also new were intake boots and clamps, PCV tube and hoses.
The bike refused to start...BUT the carbs did not leak...at all.


I tore into the carbs again and realized I forgot to remove the pilot jets from the bodies. 2 were clogged...I cleaned them all and replaced the rubber caps as well.

This time I got massive fuel leaking from the carbs...I got not for the life of me tell where it was coming from...it was dripping from all over the place...the connecting plates were wet and it was impossible to see the source.


I figured bad needle valves or improper float height. I ordered replacement needles and reset the floats. This time it leaked worse. From the the breather hoses as well as the previous areas..but the bike ran!!! It actually started and ran with no choke, although the idle was steadily climbing and I turned it off when it hit 4000.

I am not sure how to proceed...do I need to replace the bowl gaskets everytime I remove them? How could they leak like this?

 

[chuck hahn]

Well since you dont tell us what bike it is....The only "CLUE" is that you mention valve seat orings so you must have CV carbs. Heres the turutorial. Be sure to use new pilot jet rubber plugs so they seal tight or they will leak too mush fuel via the pilot jet circuits.

http://www.mtsac.edu/~cliff/storage/gs/mc_maint/GS_CV_Carb_Cleaning_Series.pdf

 

[chuck hahn]

Maybe find a manual here.

http://members.dslextreme.com/users/bikecliff/

 

[chuck hahn]

One other thought..IF, by chance, you used pliers to pull the seats out you stand a good chance of squishing the holes out of round...thus the float needles jam up and wont shut off / allow fuel flow. either way its a bad thing to squeeze the seats. Good news is that new seats are available here. Scroll around and youll find them on one of these pages.

http://www.siriusconinc.com/search_...art=1&partno=&x=20&y=13&search=search&start=0

 

[mikerophone]

You don't need to replace the bowl gaskets unless they are torn or come off in pieces. I re-use mine several times. Did you measure the float hight (22.4mm +/- 1mm IIRC) WITHOUT the gaskets in place?

Aftermarket gaskets - any chance the floats are hanging up on these gaskets?

If you haven't already, check out Nessism's carb tutorial. Very worthwhile, especially the part near the end where he illustrates putting the carbs in a vise and checking full height in the bowl with a drilled out drain bolt.

 

[Tiny]

That tutorial is awesome!!!

 

[mikerophone]

Yes it is! Thanks to Ed for making it.

Here's the other (older) one that has some helpful tips in it too, I like that page about 2/3rds of the way in where it shows all of the components "exploded" and the wire bristle in the match is a great trick too.

 

[londonboards]

You really ought to be able to see where the fuel is coming from. Otherwise you are simply guessing as to the cause. On these carbs there are probably 10 reasons (although I can only think of 6 right now) for them to leak.

You do have the the hoses correctly fitted to the right place - don't you?

Drain the bowls, dry everything up, replace bowl plugs. Take the bike outside. Take the seat off (may help you see the middle carbs a little easier). Get a helper to look on one side and you look on the other side. Both of you have torches to look into the dark areas. Open petcock to prime and see where it comes out. You have to be able to see where it's coming from.

When searching for oil leaks I think some people spray the suspected engine parts with talcum powder. This immediately turns dark when it gets wet. You could try this trick on the carbs too.

Greetings

 

[Guest]

Tap on the bowls to seat the float needle.

 

[oblique]

I have been very thorough in checking the carbs the second time around and did take some cues for the guide while doing so - this is not my first rodeo, however...I've rebuilt a number of sets from different bikes.

I did indeed try tapping on the floats.

I simply cant see where theyre leaking. The bike is completely bare (no tank, no seat) and I am fuellign with a temporay container. I was pouring gas in and shining a maglite while they leaked and could not locate the source.

Is there a way to test for leaks with the carbs out? Do I have to use gasoline or is there a less toxic option?

 

[GateKeeper]

Test them on a bench, I see no difference if they are in the bike or otherwise, just make sure they are level, and hook up your lines, if the floats are working and the valve seats are seating then you should have no leaking

 

[eil]

If they're leaking as badly as you say, I see no reason that putting them up on the bench and testing with plain old water wouldn't work.

It's probably something silly. You'll find it.

 

[JTGS850GL]

This may seem silly, but are you sure you're connecting the fuel to the fuel inlet and not one of the vent lines? It's been done before. Don't ask me how I know...

 

[oblique]

Fuel intake connected to middle nipple and vents on either side. Have not changed arrangement of these.

I will be pulling the carbs...again...to bench test.

 

[oblique]

Carbs leaking from the circled ports. They leak here first then from the vent hoses.

 

[Guest]

You're filling your float bowls too much or are leaking from the float needle and seat.
That is your main air jet and is directly connected to the main jet. When the bowls overfill that is the first place it come out.
You either have torn O-rings on the float seat (inlet valve), the float adjustment is way off or the needle and seat are not sealing.
Check for a ridge on the tip of the needle that you can catch your fingernail on. Did you happen to mix up the old needles and seats? They wear as a pair.

 

[oblique]

Thanks for this. It never occurred to me that the seats might be worn as well - I do indeed have new needles against old seats. Much appreciated.

 

[JTGS850GL]

I'd replace all 4 seats with new needles. Lots of aftermarket options as the OEM seats/needle assembly is VERY expensive.

Here's where I got mine:
http://www.partsnmore.com/

 

[Guest]

I have some good stock needles and seats I'll put in the ultrasonic cleaner and send to you.

 

[JTGS850GL]

Now that's even better.