Fuel in oil (again) - Kawasaki Balius/ZR-250

[Cynos]

Okay, so a while back, I had a bundle of petrol in my bike's oil, and at the time, I put it down to me being a tard and leaving my fuel switch on prime while my bike sat for a long time. But, it's happened again, and it seems to be worse, and it seems to actually be causing flooding issues for my bike after running at high speed. And I'm definitely not leaving the switch on prime this time.

To elaborate, my bike's fuel switch is vaccuum operated. It has three settings, main, reserve, and prime, the last being a gravity feed for when you drain the carbs after running out of fuel. My thinking is that the diaphragm in the fuel tap is poozed, and getting more so, but that's entirely unscientific. Is there anything else that could cause it to malfunction? I'm wondering about the vaccuum it gets from the carbs, but as far as I understand (which is, very little) it'd have to be getting too much, and I can't see any way that's possible, but I am the mechanical equivalent of the guy who clicks the blue E to open the internet.

Any help welcomed.

[vifferman]

It's entirely likely that the diaphragm is 'poozed', and also entirely likely that the replacement is either unavailable, or if it is, you have to replacet the whole petcock mechanism, rather than just the bit(s) you need.
It's easy enough to tell - remove the fuel hose from where it enters the carb, and see if fuel dribbles out when it ought not to.
Although the vacuum-operated petcocks are (in principle, at least) a good idea, in practice they're just another complication looking for an excuse to fail.
I had loads of fun with the one on my VF500 - it was periodically either allowing extra fuel to be sucked into the inlet manifold of the cylinder (#1, IIRC) it was attached to (and thereby make it run really rich), or the vacuum hose would crack or fall off, causing that cylinder to run really lean and for the fuel supply to be compromised.

There is another potential problem at work here: even if the petcock is faulty, fuel should not get into the engine, unless the carb(s) allow it: the float in a carb is attached to a little valve that is supposed to stop the fuel running into the carb bowl once it's full. If it's not doing that, either the float is faulty (set to the wrong height or is punctured, so it doesn't float high enough), or the valve isn't seating properly (worn seat and/or valve seal). Fuel then continues to dribble into the carb, and through the valve into the inlet manifold, and from there into the inlet valve, and from there into the engine (if the inlet valve is partially open or not sealing against the valve seat).

[Cynos]

Yeah, I'm looking to buy a fuel tap from a wrecked Balius at the moment - and the float valves, I had a look at them, and I think two of the floats may be punctured. *sigh* I'm going to have to revisit my whole fuel system.

[Cynos]

Actually, ooks like I was wrong - I drained the oil and can't see any fuel in the oil (I presume it'd form a separate layer), but I did find a large hole in one of my vaccuum tubes, so will be replacing tonight, see if it helps any.

[malcy25]

Actually, ooks like I was wrong - I drained the oil and can't see any fuel in the oil (I presume it'd form a separate layer), but I did find a large hole in one of my vaccuum tubes, so will be replacing tonight, see if it helps any.

Worst case scenario. Block the vaccuum hose and fit an inline tap in the fuel line....

[davereid]

Im not sure I can make sense of this.

For fuel to get into the oil...

If the petrol tap is ON, and the carb float is faulty.. fuel will build up in the carb until it is higher than the main jet top, at which time it will spill into the venturi.

Then it will go forward towards the head and backward towards the air filter. Only if there was a massive leak, that totally filled the air filter would the fuel level reach the valve, and then it would only leak in if the valve were open.

But then, if there were that amount of fuel involved, it would fill the cylinder and you would have a hydrolocked motor, not just dodgy oil...

have I missed sommat ?

[cheviot]

Im not sure I can make sense of this.

For fuel to get into the oil...

If the petrol tap is ON, and the carb float is faulty.. fuel will build up in the carb until it is higher than the main jet top, at which time it will spill into the venturi.

Then it will go forward towards the head and backward towards the air filter. Only if there was a massive leak, that totally filled the air filter would the fuel level reach the valve, and then it would only leak in if the valve were open.

But then, if there were that amount of fuel involved, it would fill the cylinder and you would have a hydrolocked motor, not just dodgy oil...

have I missed sommat ?

get into the oil via the breather pipe in the bottom of the airbox. It seems to be a kawasaki thing. My ZR has done it once and there was quite a lot of fuel in the oil as well as the airbox.

[7mmWSM]

The fuel taps on these are bad at failing and only work on Prime alot of the time.
I wouldn't think this is your problem though.
I would think its leaking float needles in your carbs allowing fuel to enter the engine and ending up in your oil sump and also flooding the motor.

[CookMySock]

Actually, ooks like I was wrong - I drained the oil and can't see any fuel in the oil (I presume it'd form a separate layer)

Not usually. The fuel will mix really well with the oil if the engine has been run at all.

Remember if the vacuum fuel tap diaphragm has a hole in it, the fuel will be drawn straight into the vacuum source - probably the inlet manifold, bypassing the float valve completely. Try drawing a vacuum with your mouth (or otherwise) against the fuel tap vacuum port and see if you get fuel from there.

Steve