Petcock Open = Drained Gas Tank

Hungry J0e · May 5, 2011

Finishing up some carb balancing on my Amals and accidentally left the petcocks open when I finished.

Came back to the garage two days later to discover the gas tank had totally drained into the engine and left side header... Fortunately there had only been about a gallon left in the tank. Drained everything out through the sump plug... gas had also migrated into the primary and drained that as well...

Obviously I would expect some leakage, but is this a normal amount? Suggested fix?

Cheers,

- HJ

swooshdave · May 5, 2011

Hungry J0e said:
Finishing up some carb balancing on my Amals and accidentally left the petcocks open when I finished.

Came back to the garage two days later to discover the gas tank had totally drained into the engine and left side header... Fortunately there had only been about a gallon left in the tank. Drained everything out through the sump plug... gas had also migrated into the primary and drained that as well...

Obviously I would expect some leakage, but is this a normal amount? Suggested fix?

Cheers,

- HJ

Do you have the Viton needle valves? What kind of floats?

Hungry J0e · May 5, 2011

swooshdave said:
Do you have the Viton needle valves? What kind of floats?

Viton needles, stay up floats.

Set the float level about 0.25" below the rim...

Cheres,

- HJ

maylar · May 5, 2011

Came back to the garage two days later to discover the gas tank had totally drained into the engine and left side header... Fortunately there had only been about a gallon left in the tank. Drained everything out through the sump plug... gas had also migrated into the primary and drained that as well...

Something is very wrong. For a carb to overflow into the engine means gas had to flow down the intake valve and past the rings. Gas in the primary means your main seal or the bolts holding the inner primary case are leaking from the crankcase. And how in the world did it get into the header?

No, this isn't normal. If the float and needle valve are working correctly you should be able to leave the petcocks on indefinitely. The only fuel loss should be by evaporation.

L.A.B. · May 5, 2011

maylar said:
Something is very wrong.

I can't see that there's anything seriously wrong? For some reason float valve didn't fully close so any fuel overflowing from the float bowl would simply drain into the engine through the inlet tract-unless engine just happened to stop when the inlet valve was fully closed.

maylar said:
For a carb to overflow into the engine means gas had to flow down the intake valve and past the rings.

I don't see how the fuel would have to flow down the intake valve? If the valve was even slightly open then the fuel would leak into the cylinder and drain through the ring gaps reasonably quickly.

bluto · May 5, 2011

also check the fit of the float within the bowl....when I bought my bike last year the PO had installed new floats and/or bowls and the fit was too tight, this made the floats stick and even led to a fire....I filed the sides of the float where the pivot pin holes are a bit and no problems since

pete.v · May 5, 2011

Hungry J0e said:
swooshdave said:

Do you have the Viton needle valves? What kind of floats?

Click to expand...

Viton needles, stay up floats.

Set the float level about 0.25" below the rim...

Cheres,

- HJ

0.25 = 1/4" The fuel level should be 0.25 below the rim, not the float. I would say that if the float was that low the tickler would not reach it to function.

My stay up floats are .020 above the rim pushing on the tang with something small to get a realistic reading, not to say that is universally accepted but that is what works for me.

As with many Norton things, no 2 are alike. I like mine just high enough to get a good tickle responce and a good positive seat when full, then tune accordingly.

I set my carbs up on a board vertically with a clear tube running from a fitting corked into the drain on the bottom. With the tube running up the side of the carb, it mirrors the level in the bowl. Running another tube from the banjo for filling. Leaking fuel from the bottom, you can see the level drop, fill, and stop. Sighting along the side, put a mark on the bowl where the fuel level is on the tube. Measure this distance to the top of the float bowl to get your fuel level. This does not tell you where your float is but tells you which direction you need to adjust.
Fuel level is what you really want to adjust. Float level is relative. I believe this is the meniscus method.

Hungry J0e · May 5, 2011

pvisseriii said:
0.25 = 1/4" The fuel level should be 0.25 below the rim, not the float. I would say that if the float was that low the tickler would not reach it to function.

My stay up floats are .020 above the rim pushing on the tang with something small to get a realistic reading, not to say that is universally accepted but that is what works for me.

As with many Norton things, no 2 are alike. I like mine just high enough to get a good tickle responce and a good positive seat when full, then tune accordingly.

I set my carbs up on a board vertically with a clear tube running from a fitting corked into the drain on the bottom. With the tube running up the side of the carb, it mirrors the level in the bowl. Running another tube from the banjo for filling. Leaking fuel from the bottom, you can see the level drop, fill, and stop. Sighting along the side, put a mark on the bowl where the fuel level is on the tube. Measure this distance to the top of the float bowl to get your fuel level. This does not tell you where your float is but tells you which direction you need to adjust.
Fuel level is what you really want to adjust. Float level is relative. I believe this is the meniscus method.

I think I'm going to have to do a similar setup to observe what is going on...

You are correct, my terminology was imprecise. The fuel level is 0.25" below the rim for the float to shut the valve when the bowl is level on a workbench. I had to set my level that low to get good response on the fuel/air mixture screw. Others have noted similar issues. I *do* get good tickler response from that level.

Regarding the fuel in the headers, I noticed that when kicking the bike over to see if I had hydraulic lock on the pistons. I assume the cylinders were full and the pistons pushed some fuel out the exhaust valves into the header.

Regarding fuel in the primary, I have known issues with migration of oil from case to the primary when wet sumping. So a gallon or so of gas no surprise some migrated over as well...

I suspect there may be something wrong with my seat. Definitely the needle/seat connection isn't working as advertised... any ideas for correcting this?

Cheers,

- HJ

comnoz · May 5, 2011

I always though that was the way Amals were supposed to work.

Actually they should shut off pretty well with Viton needles if there is no dirt around.

One thing I have seen as a common problem is fuel leaking around the needle seat. It is just a press fit into the bowl and if there is a scratch or two on the od of the seat or in the hole it is pressed into then the fuel just leaks between the seat and bowl. You can push the seat out and re- install it with a little blue locktite to cure it. Jim

pete.v · May 5, 2011

comnoz said:
I always though that was the way Amals were supposed to work.

Actually they should shut off pretty well with Viton needles if there is no dirt around.

One thing I have seen as a common problem is fuel leaking around the needle seat. It is just a press fit into the bowl and if there is a scratch or two on the od of the seat or in the hole it is pressed into then the fuel just leaks between the seat and bowl. You can push the seat out and re- install it with a little blue locktite to cure it. Jim

A gallon in 2 days? That's quite a scratch. That may aquaint to a gallon in 3 to 6 months, maybe. I'm thinking human error or perhap a simple rebuild needed.
Joe, if you have been fiddling in there recently then it's probably something you did or did not do. Anyhow, you still need to get in there and eccess.

L.A.B. · May 5, 2011

pvisseriii said:
I'm thinking human error

The human error was not turning the taps/petcocks off! :roll:

DogT · May 5, 2011

You can make the needle valve/seats so they don't leak. Lookey here leaky-float-bowl-seat-t8025.html?hilit=float%20bowls to test, all you need to do is make the rod that holds the float so it doesn't come off when you fill the float from the filler and bolting it to a flat piece of metal will do. You can even leave the float visible like I did and adjust it while watching the gas level. Don't put up with leaky carbs and petcocks, they start fires.

My petcocks were dripping about 3 drips a minute and that drained about a gallon overnight into the float bowls, but mine just evaporated from there it was so slow. The OB BAP petcocks are $17 ea. and they seem to work. Not sure about the ethanol though, I use avgas because of the F/G tank.

Dave
69S

maylar · May 5, 2011

L.A.B. said:
I don't see how the fuel would have to flow down the intake valve? If the valve was even slightly open then the fuel would leak into the cylinder and drain through the ring gaps reasonably quickly.

I meant through the open valve. And ya, I suppose gasoline would go by the rings quickly.

But in all the Amal overflows I've seen gas never filled the engine. I would expect it to come out the tickler and dribble on the floor.

DogT · May 5, 2011

I would think a leaky petcock would just allow the gas to evaporate from the float, but a wide open petcock would certainly flood the carbs if the needle/seat is leaky enough and they usually are pretty leaky if not correct, but usually only enough to drip down the side of the float bowl and drip off the bottom. But I have heard of flooding the engine with fuel.

Dave
69S

L.A.B. · May 5, 2011

maylar said:
But in all the Amal overflows I've seen gas never filled the engine. I would expect it to come out the tickler and dribble on the floor.

If it was a full-on gush of fuel from a stuck float with the valve open, then yes, the head of fuel would rise as far as the tickler, however, a trickle of fuel through the float valve would escape into the carb bore because the drillings are lower than the tickler outlet, and the Amal Mk1 float bowl doesn't have an overflow as most carbs do.

comnoz · May 5, 2011

Yes I have a small selection of bent rods in my shelf from people trying to kick the bike over with a cylinder full of fuel. One of them is from my bike. Jim

BillT · May 5, 2011

maylar said:
But in all the Amal overflows I've seen gas never filled the engine. I would expect it to come out the tickler and dribble on the floor.

The bottom of the intake manifold is lower than the top of the vent in the tickler. A slow leak will run through the manifold and into the cylinder head.

I saw, firsthand, the damage caused by exactly this.

My local Norton guy had a customer come in about a year ago, who had gone for a ride on his Commando, and forgot to close the petcock when he got home. About three weeks later, he went for another ride, not realizing about 1-1/2 gallons of gas had leaked through a carb, into the cylinder and crankcase, and eventually into the primary. He rode about 20 miles before the bike stopped.

He was pretty upset that it cost him close to $2000 to fix the damage. The engine was OK, but all the gas in the primary wrecked everything inside except the alternator.

swooshdave · May 5, 2011

BillT said:
He was pretty upset that it cost him close to $2000 to fix the damage. The engine was OK, but all the gas in the primary wrecked everything inside except the alternator.

But it was clean inside! :mrgreen:

Hungry J0e · May 5, 2011

Setup a rig similar to Dog T. I used rubbing alcohol as a surrogate for gasoline, as they have similar specific gravities.

You could easily see when the needles were seating, and all seemed fine, but I let it sit for awhile while I cleaned up the shop for a bit.

Coming back 10 minutes later both floats were noticeably higher when sighting from the side. I used a bamboo skewer in a drill chuck with some polishing compound to polish both seats.

Set the rig back up and repeated. This time I kept an eye of the floats the whole time. The right hand carb was good now, but by sighting along the left hand float you could observe it very slowly rising. I tried polishing some more but no joy, so I boiled the bowl, pushed out the seat (came out surprisingly easy), and reinserted it with blue thread locker as per Jim's suggestion (would have used red but had none on hand).

Will go back tomorrow and see what comes of it.

Cheers,

- HJ

swooshdave · May 5, 2011

comnoz said:
Yes I have a small selection of bent rods in my shelf from people trying to kick the bike over with a cylinder full of fuel. One of them is from my bike. Jim

No wonder you wanted a bike you could start with your hand. :mrgreen:

Petcock Open = Drained Gas Tank

Hungry J0e

swooshdave

Hungry J0e

maylar

L.A.B.

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bluto

pete.v

Hungry J0e

comnoz

pete.v

L.A.B.

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DogT

maylar

DogT

L.A.B.

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comnoz

BillT

swooshdave

Hungry J0e

swooshdave

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