Fuel tap left in prime position.

[ianali]

I’m away from my ‘78’ Z1000 for a month or so. I took it for a spin last week and pretty sure I left the fuel tap set to prime, stupid I know. Can any here advise if this will cause a problem? Cheers, Ian.

[moizeau]

Depends how sealed your float valves are? It may not cause a problem at all, you may have an airbox full of fuel and stains on the bike. Worse case is that it fills the engine with fuel. You'll smell it when you return if it has leaked and check the 'oil' level before you start it.

[zed1015]

In the prime position the fuel tap is open.
This may lead to fuel weeping past the float valves and flooding the cylinders.
Worst case is that the tank will drain and fill the cylinders and crankcase.
If this happens drain the oil and spin the motor with the plugs out to clear the cylinders.
Fuel may also fill the exhaust so plugs back in and spin to blow it out the pipes.
Once cleared and left to air a while just fit a new filter and fresh oil.

[ianali]

Thanks for replies. Il get my lad to pop around then and close it. Hopefully a couple of days won’t have done any harm. Old age creeping up on me I guess...

[warren3200gt]

This may lead to fuel weeping past the float valves and flooding the cylinders.
Worst case is that the tank will drain and fill the cylinders and crankcase.

Has anyone ever actually experienced this? I never have and dont really comprehend the situation where this could arise. Anyone that can explain how this could happen for me please.

[moizeau]

This may lead to fuel weeping past the float valves and flooding the cylinders.
Worst case is that the tank will drain and fill the cylinders and crankcase.

Has anyone ever actually experienced this? I never have and dont really comprehend the situation where this could arise. Anyone that can explain how this could happen for me please.

Yes, on the Zeph11 I've recently bought. The carbs were flooding badly. Some was going into the airbox and some into the engine. When I drained the oil it was very fluid and smelled of petrol. There was 7 litres in there instead of 5. One advantage was that when I removed the drain plug instead of getting very oily fingers, a quick wipe and they were clean....but smelled of petrol.

[Mr Bump]

This may lead to fuel weeping past the float valves and flooding the cylinders.
Worst case is that the tank will drain and fill the cylinders and crankcase.

Has anyone ever actually experienced this? I never have and dont really comprehend the situation where this could arise. Anyone that can explain how this could happen for me please.

If you've got a full tank of fuel and an open tap the pressure or 'head' on each little float needle valve is quite high, so one or more could start leaking a little. The float needle valves are not a perfect solution and can be unreliable if worn or contaminated with dirt, which is quite likely if you have a rusty tank. Its enough of a concern that manufacturers put vacuum taps in to reduce the risk.

I'd have thought that it's a bit less likely that fuel would end up in the sump on those carbs as they have an overflow drain to pipes that divert excess fuel onto the ground. That would mean that if yr float valves are a bit weepy you could end up with fuel all over the garage.

But, there does remain a risk of the fuel rising up past a jet needle then trickling forward into the inlet tract, seeping past an open inlet valve and into the cylinder. It'll then work it's way down past the piston rings and find its way into the sump where it'll contaminate the oil. If it's left long enough a lot of fuel could very slowly find its way into the sump. If the oil is contaminated enough and nothing is done about it it could seriously damage yr motor when it's ridden, which makes leaving the tap on a very expensive oversight.

It can happen on CV carbs that don't have overflows (such as Z1100A) and I think it is a known problem on z1300's, but don't quote me on that.

Olly

[warren3200gt]

Okay, needle valve weeps or fails, overflow fails, carb bowls fill and the fuel starts to trickle to the carb outlet but.......
Before it gets to valve height it would pour out the carb inlet mouth then filling the airbox or back on the garage floor if using pods/stacks.
Bit unlikely all those alternative escape routes would fail before getting into the barrels/sump.
Hence my question has anyone actually experienced this occuring?
All my bikes run vm's so no experience cv's.

[zed1015]

Yes! had it happen on a Z400J with slide carbs and a Suzuki 600 SRAD ( cv's ) when the vac tap failed.
Both filled the cases and on the SRAD it filled the exhaust too.
Depending on which way the bike is parked fuel will follow gravity so it will either run into the engine via open valves or enter via the airbox and then down the crankcase breather tube and into the cases.

[Kwackman]

had it happen on a Z400J

A man of taste!

[warren3200gt]

Aahhh, of course, forgot about the crank breather. Ta v muchly, now it makes sense.

[MrDavo]

A member of the SOHC Hodna forum that I'm also in left his CB750 fuel tap open for a few days recently, when he came to start it the engine was full of petrol and locked solid.

He was worried that he'd bent a rod or the crank, as it still wouldn't turn over after draining the petrol out of the engine, in fact the torque of the starter had pushed the flywheel cockeyed on its taper and jammed it hard against the crankcase, so much less horrific that we first feared.

I've been spoiled by bikes with vacuum petrol taps for years, now two of my three bikes have manual taps, and I have an extra thing to remember. I used to know a lad in Salford who's 650cc BSA caught fire with the push/pull type fuel tap open, he had small circles with 'Pull On Push Off' branded (in reverse) several times into the palm of his hand as he struggled to bash the tap shut through the flames!