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Author Topic: carburettors and diesel  (Read 3403 times)
Ivan
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« on: April 05, 2015, 10:10:35 PM »

I mistakenly poured diesel into the quad bike petrol tank. It ran half-heartedly, then I realised from the smoke emitted that someone had muddled up the petrol and diesel cans (not me, but I should have checked). I drained down the petrol tank and refilled with fresh petrol. I tried to drain down the carburettor float bowl, but for some reason the drain screw doesn't seem to work. So I thought it would probably just dissolve and everything would be ok. Indeed, the engine fired up ok, but the carburettor started flooding. I shut off the fuel, and the engine continued to run ok, and I drove it about 1/2mile and it ran perfectly (on what was in the overfilled float bowl). But as soon as I turn on the fuel tap, it overfills and starts dumping petrol from the overflow.

Any idea why? Is there any way the diesel could damage the plastic float or the needle valve? I'll strip it down tomorrow, but was hoping to spend my bank holiday doing something less tedious.
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Ivan
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« Reply #1 on: April 05, 2015, 10:33:02 PM »

PS I checked the densities - if there is residual diesel in the carb bowl, then it should make the float more buoyant rather than less so - so it's not that.

I wonder if the diesel, being oily, could lubricate the needle valve somehow, making it less likely to seal. Or perhaps it's made the plastic float swell slightly so that it interferes with the casting of the float bowl?
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jotec
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« Reply #2 on: April 06, 2015, 08:47:31 AM »

It could have a rubber tip on the needle valve that the diesel has affected?
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biff
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« Reply #3 on: April 06, 2015, 09:37:59 AM »

The diesel does affect the petrol rubber gaskets and diaphragms.
                           Biff         
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Ivan
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« Reply #4 on: April 07, 2015, 01:24:15 AM »

Removed the float bowl and manually pushed the needle valve/float fully upwards. Petrol still poured out. So I stripped it all down. No rubber seal on the needle valve, no sign of any dirt or debris. So I cleaned it all, let it dry and blew through the fuel line into the needle valve. After, I tested the needle valve to see if it would seal when I blew air through - seemed to, so I reassembled and it no longer floods. Still don't know why! It's running again, though I had to retune it as the idle was all messed up. Running acceptably, but not perfectly - but that's good enough.
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