Fuel tap, turn off when parked?

[Richh]

Afternoon all.

My old bike didn't have a fuel tap at all and I've never ridden another bike with one, so, as daft as it might sound, I'm not sure on how I should use it correctly.

I'm intelligent enough to know it needs to be open (pointing up) while riding, but when I'm parked do I need to turn it off? It was turned off when the bike was delivered which makes sense with the bike rattling around in the back of a van, but it's been on ever since.

Is that good/bad?

The main reason I've left it on is that I'm not in the habit of checking the tap every time I get on the bike, so I'd be afraid of leaving it off and juddering to a stop with a confused look on my face. But, if it's better to turn it off, I guess I'll learn one way or the other.

Ta,
Rich

[tigerclaw]

I'm not 100% sure of the issue, but I suspect the risk is that the needle and seat in the carburettor may not be happy and that the carbs / float chambers overfill, the fuel then may overflow into the cylinders... this can get fuel in the oil (after seeping past the rings) which is obviously a bad thing and you can also have the problem that the bike doesnt want to start because the motor wont crank over due to the petrol stuck above the piston (in the combustion chamber).

So I think if all is happy and healthy its not an issue but for safety sake / to avoid the risk it is better to turn it off... and if you forget to open the tap it doesnt die immediately so you have time to reach down and open it (it happens )

As I am writing this I figure that Carb cars dont have this because they tank doesnt sit above the carbs so if the petrol pump is not pumping fuel doesnt run into the carbs it usually runs back to the tank (different on a bike)

[superv500]

I always do, but then as well I always flick the kill switch as well, just in case anyone wants to jump on it and ride off!

I left my dummy petrol tank on once by mistake, it overfilled the carb bowls, filled up the cylinders and then the bike wouldn't crank, had to remove all the carbs, and then syphon the petrol out of each cylinder and then cranked it over to clear it's throat.

On the Superfour the Petrol tap is activated by a vacuum tube from cylinder no1, so when the engine isn't running, fuel isn't being delivered from the tank to the carb. Turning the tap off shouldn't really make a difference, but it's good practice to get to turn it off just in case you get a fuel tap issue.

[Richh]

Thanks for the tips you two, I've started closing the fuel tap and so far I've managed to remembered to turn it back on each time. Started flicking the kill-switch too, sounds like good advice - even if it only confuses down a potential thief by a few seconds it's worth getting into the habit I reckon!

Rich

[tigerclaw]

Its also fun just pushing the button and while I was being stupid typing that I thought its probably a good habit to be used to hitting it in case you ever needed to do so in a hurry

[brod]

hi
was just about to ask the same question, i think my carbs need a service thing is even if you turn your tap off
theres fuel in the float chamber which might leek into the engine, smell your oil if it smells excessivly of fuel then your carbs are leeking. this might be a good way to test if you do have a problem, run bike and turn off turn fuel tap off then start again run bike for 2-5 mins or until it runs out of fuel, next run bike with tap on turn bike and fuel tap off and leave for a few hours or over night, start bike and see how long it runs for if it runs for a shorter time then before then your float chambers loosing fuel (somewere). but smell your oil fuel in oil =possible engine failure i am going to have to change my oil cause ive got ocd.

[chricol]

the cb400 manual clearly states that you do not need to turn it off unless you will have the bike in storage. If you use the bike daily, you can leave the tap on (provided everything is in working order). There is a secondary valve that is operated by vacuum pressure from the engine and will only open when you are cranking to start the engine and will automatically shut when you turn off the engine.

Even if you disconnect all the hoses and remove the fuel tank with the tap on, fuel will not come out until you apply vacuum (suck on a pipe :p ) to the automatic valve

[brod]

maybe wont take my carbs off after all then, she runs super. if the float valves faulty then surely it will leek fuel from the fuel bowl into the engine
my oil smells slightly of fuel thats just normal i think, the odd thing is the last owner told me to make sure i turn the fuel off when not usng the bike dont know why but if i leave the tap on the bike smells of petrol.
cheers.....

[Superjack44]

maybe wont take my carbs off after all then, she runs super. if the float valves faulty then surely it will leek fuel from the fuel bowl into the engine
my oil smells slightly of fuel thats just normal i think, the odd thing is the last owner told me to make sure i turn the fuel off when not usng the bike dont know why but if i leave the tap on the bike smells of petrol.
cheers.....

Just a thought but perhaps someone has removed the vacuum diaphragm from the tap and so its possible for the fuel to be permanently on and thats why the previous owner suggested turning it off.
Only way to find out is turn the tap to the off position disconnect the fuel pipe and turn the tap on if fuel flows the diaphragm has been removed.

[brod]

cheers good tip will try that later looking at the other things the last owner said your probably right, it wobbles at hight speed realy meant the front wheels buckled and the suspensions like a rock .
cheers.......