petrol coming out of carb inlet (airbox - carb) connector

[ukjules]

I have just rebuilt a wreck of a gsx 250 and it is now tuned pretty good and
runs well.
Plugs ok, Coils ok, HT leads ok, Valve clearances ok, Timing ok, mixture set to 1.5 turns out and
is ok.
HOWEVER:
When i stop after running the engine for a few minutes on the RH carb petrol comes out it seems from the jet
at the air inlet end mouth ?
It starts coming out not immediately but after say 30 - 2 minutes.

It stops in the end but i have to use a rag to wipe it up !

What is this ?
I have had the carbs to bits many times and they are cleaned.
The tank is on when i do this.

please help ......

Jules.

[steveb922]

Sticky float valve?

[ukjules]

It only happens when it is turned off after running fine ?

I have had the carbs to bits and the float valve does not seem to be sticking !
they as clean as you can get. The same as the other one but that is fine.

[JTGS850GL]

It only happens when it is turned off after running fine ?

You have a bad petcock valve or it's in the prime position.

[ukjules]

I have yet to look at the petcock proper.
So its strip down petcock - ill do that first.

Just checked and it is coming out of both ! inlets.
It is just that the lh one takes longer to start coming out ?
It does not seem to stop either on the lh one - bike lent over to the left.

It is not set to prime when this happens by the way.
It is set to normal and not reserve

[sharpy]

Crap in the fuel? Thats a question, NOT a order. Worn float tip? Do you have a in line filter or at least those domed screens over ure needle jet? Also be carefull, flooded carb/airbox can also mean flooded combustion chamber. If you crank the engine over you run the risk of bending a conrod. Pull the spark plug out 1st before you start the engine after any flooding.

[ukjules]

How would crap in the fuel cause leaking ?
Float tip springy thing seems ok.

Anyway i have cleaned the carbs twice now - stripped down completely and
immediately the same thing happens - leaking only when stopped engine after a minute or so.
the second time i stripped them down there was no filth in them.

I have had to disconnect the tank from the carbs to stop the leak.

the leak is not from the petcock but i will strip that down tomoorrow if thought should
just to be sure all clean.

[hampshirehog]

Crap in the fuel means the float needle may not seat properly all the time. If your float needle is worn then again, it'll let fuel through when seated. It won't necessarily show when running as your bike is using the fuel that's coming through. Plus does the float needle seat sit in an o ring? That could be split and let fuel in.

[ukjules]

Needle valve:
I took out both and cleaned them - they both seem fine work on the bench.

the carbs are almost identical to the diagram below (a gpz 750)


I will check again though:

Clean carbs and needle valve
check float height (this issue may have always happened as i have only just got it going)
Check over the petcock but i will have to check i have not done that already.

carb layout similar to this !.jpg

[hampshirehog]

You have to inspect the needle valve with a magnifying glass. Tiny imperfections can let fuel through. plus if your carbs are the same as the diagram then you have that o ring. Check it's not split or perished.

You can do a bench test. Set the carbs up off the bike and fill with fuel down the fuel inlet hose. The hose should stay full for a good while (several minutes at least) - the needle valves are / should be very effective against letting excess fuel in to the float bowls.

[ukjules]

i will check the needle valve more closely and the thing it sits in with the seal.
(It could be that this issue has always happened !)

I have only had it for a month or so and got it going. goes fine by the way but
it might have some juddering when gaining speed 40 - 60. Was thinking this was the atu ....
This is not for now though.

ill study the needle valve tomorrow

Surely it simply has to be the needle valve ?
or (like the other chap said) the petcock - but off the carbs that does not leak ?

thanks

[JTGS850GL]

Guys, you missing the point of a bad petcock. He may have floats not sealing properly, but no vacuum operated petcock should allow fuel to flow once the engine is off. Unless the petcock has been replaced with a simple ON/OFF shutoff valve, the one in there is bad.

Don't attempt to rebuild the one you have. I've tried several times as have many on here and the success rate is very poor. Replace the petcock with a new one and most of your problems will go away.

[ukjules]

ok - the bike has been stood for ages and the petcock has not been touched.
So - I will do as you say and look at the petcock - first.

I will post pictures tomorrow - this is my hobby bike so not critical but i will
dismantle it as i have had recent success's with gpz750 and gpz600 petcocks.
if i bust it ill get another ... hopefully.

(but what about the tank not leaking when unattached to the carbs ?
ie petrol pipe and vacuum pipe off it and free of bike ?
does that mess up the theory ?
its late my brain has gone !

thanks - wil do this tomorrow

[ukjules]

Ok testing today:

1) External tank with feed direct into carb fuel line
vacuum line free / prime of course shut off
bike runs and leaks out after after 8 mins after stopping engine but fuel able to flow.
I can feel the vacuum pulses on the vacuum line when engine running

2) removed petcock and dismantled.
Very clean and i had cleaned it a few weeks ago. However
when i blew out the vacuum (with my diving cylinder) nozzle some crap did come out .....
The way this is made - it would have allowed some air to come out but the passage was semi blocked.

3) petrol out of tank and now cleaned up - not much filth in the tank and all
caught by the filter in the tank. There was some around the base of the filter.

4) Not that it was leaking but the petcock / tank seal is now creased and i have to renew it
(It leaks now)
so can test no further with the tank on and vacuum.

petcock repair kit ordered but will only put on the tanks seal first.
(Might try some instant sealant just to test it as i want to know what is happening here
anfd if i need to dismantle the carb again !

P.S the petcock is on / res and a screw for prime

[ukjules]

Carb repair kit ordered as the needle valve holders seal was perished.
It gave no seal and fell to bits at the first attempt to prize it out.

All else was clean as i had done this before but def missed the seal or indeed
ignored through inexperience the slackness of it !

float heights ok - at a quick masurement glance



GSX 250 carb seal worn.jpg