Why turn off petrol taps

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lawman

lawman

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I have just bought a 73 Commando 850 and I was told that you have to turn off the petrol taps when the bike is parked. Could someone please tell my what the consequences may be if you don't turn them off.

Also do you have to turn them off every time you park or only if you leave the bike for a while like overnight.

I have never owned a British bike before so I am just learning about them.

Thanks

Frank
 
If a float sticks while its parked, you could dribble petrol all over the driveway.
And, leaning on the sidestand, it can be on enough angle that a float HAS to stick.
When you go to ride off, the tank is empty.

And if the petrol dissolves the bitumen under your sidestand, you may come back and find your pride-and-joy on its ear.
Seen it done...

Can also fill up a cylinder, which makes it tricky to kickstart.
And dangerous.

Good practice to ALWAYS turn off your taps when stopped.
If you see what we mean...

Also seen all of the above with oriental bikes.
Even though some of them have turnoffless taps !
 
Unlike most of the Jap bikes built since the mid-70's, our Brit bikes don't have "automatic shut-off" petcocks, in that they aren't controlled by engine vacuum like the later, mainstream bikes. Add that into the fact that the period Amal carburetors aren't much more than a controlled leak, and you set yourself up for a flooded engine at the next start-up, and/or all of your precious fuel poured out on the ground. Trust me; keep them closed when you're not riding.
 
I've lost fuel this way before, seems to happen quicker when the sun (remember that) has heated the petrol tank up.
 
lawman said:
I have just bought a 73 Commando 850 and I was told that you have to turn off the petrol taps when the bike is parked. Could someone please tell my what the consequences may be if you don't turn them off.

Also do you have to turn them off every time you park or only if you leave the bike for a while like overnight.

I have never owned a British bike before so I am just learning about them.

Thanks

Frank
Click to expand...

Turning them off while you stop for a few minutes is probably overkill
 
Welcome to the world of British bikes. Hate to mention the next issue - Are you sure the petcocks really turn off when they are turned off. Worth checking...
 
Thanks for all the advice and I will definitely act on the side of caution.

Frank
 
batrider said:
Welcome to the world of British bikes. Hate to mention the next issue - Are you sure the petcocks really turn off when they are turned off. Worth checking...
Click to expand...
Yes, I drained a whole tank of avgas overnight because I didn't realize my petcocks were leaking, luckily the fuel evaporated out of the float bowls and didn't dribble on into the crank case. Lesson learned, get some good petcocks and check them out, fill the tank and leave it on a table overnight with a can or paper towel under the petcocks.

You should also check your float bowls to make sure the needle valve doesn't leak too.

Dave
69S
 
All good, but probably the most important reason to keep your valves off while parked for any length of time is, if gasoline leaks past the float valves and down into the cylinders, it will work its way past the rings into the sump and fill your crankcase, contaminating your oil. Not good.

If you find start noticing your oil levels getting higher, or your primary's oil level is rising more quickly than a wet-sumped motor would normally manifest itself, sometimes it's worth taking a sniff to make sure no gasoline has made its way into your oil. Usually it's very obvious.
 
In the event that you forget to turn the taps off, it is a good idea to have the fuel system as tight and dry as possible.
Original Amal carbs often had plain nylon float needles. There is an upgrade to a Viton tipped needle, cost a few bucks each and really work well.
I often forget to turn the taps off with the Vincent, sometimes it sits that way for weeks. It is gas tight and the floats have never stuck (Amals). With the Norton, I have had a recent problem with the float sticking. As Kenny describes above, the gas filled the crankcase and migrated into the primary. It also made a puddle of gasoline about six feet in diameter around the bike, which was in a building and connected to a battery charger!
I have since changed to Viton needles and the sticking problem has not reoccurred.
I do need to remember to shut the taps off as a safety measure, however.I have also had this same sticking float problem with a near new Mikuni on another bike.
I replaced the float, the needle valve and the seat, but the problem persisted. Finally I changed the carbs for some new larger Mikunis and they have been fine so far.
Glen
 
Holmeslice said:
All good, but probably the most important reason to keep your valves off while parked for any length of time is, if gasoline leaks past the float valves and down into the cylinders, it will work its way past the rings into the sump and fill your crankcase, contaminating your oil. Not good.

If you find start noticing your oil levels getting higher, or your primary's oil level is rising more quickly than a wet-sumped motor would normally manifest itself, sometimes it's worth taking a sniff to make sure no gasoline has made its way into your oil. Usually it's very obvious.
Click to expand...

This is very sound advice and a great example of why this forum can be so valuable. I had a Royal Enfield 250 café racer with a down draught head (just like a Cdo.) One morning I found I'd left the tap on, but no sign of a leak anywhere. Was just turning it over slowly prior to starting it and heard some strange gurgling noises from the breather pipe. Didn't think anything of it. Gave it a healthy kick and was soon rather amazed to observe a stream of very diluted, petrol-smelling oil pumping out the breather pipe and all over the shed floor... Didn't go for a spin that day...drained the sump instead. I lost a gallon of petrol I'd only bought the day before... learned the lesson to turn petrol tap off ... :oops:
 
It's always good practice to turn off the tap on a gravity fed carb. It can't do any harm and may avoid a disaster. Turning them on is part of the starting ritual, along with the tickle. It soon becomes automatic. If you forget do do it one day when you're out, probably no harm will come from it but if you never do then sooner or later, things will go wrong.
 
Holmeslice said:
All good, but probably the most important reason to keep your valves off while parked for any length of time is, if gasoline leaks past the float valves and down into the cylinders, it will work its way past the rings into the sump and fill your crankcase, contaminating your oil. Not good.

If you find start noticing your oil levels getting higher, or your primary's oil level is rising more quickly than a wet-sumped motor would normally manifest itself, sometimes it's worth taking a sniff to make sure no gasoline has made its way into your oil. Usually it's very obvious.
Click to expand...

This happened to my ride-on lawnmower. Not exactly a Norton but same principle.
I transported it about 20 miles on a box trailer to a work site. When I went to top up the tank before starting work it was completely empty. Strange.
I checked the oil level and it was WAY over full. Probably due to road vibration causing the float valve to leak as I hadn't shut off the fuel tap.
I had to take it back home to drain and re-fill the sump.
That would be more difficult if you're out touring on the bike.
We are creatures of habit. Shutting off the fuel every time you stop the bike is a good habit to get into.
 
Viton Tipped Float Needles are a good idea .

Why turn off petrol taps


But still turn the fuel OFF .

http://www.google.com/imgres?imgurl=htt ... CDIQrQMwAw
 
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