Earlier in the year I helped a friend clear out her shed prior to a house move and came across an old red steel fuel can with what smelled like petrol, but slightly odd. I took it home and used it in a ratio of around 25% of this to 75% new fuel for my lawnmower - Standard 170cc Honda engine.
All went OK for a couple of mows (around 1/2 tank) then I started getting a misfire which got worse and worse. I stripped down the fuel system and although the thin, fine mesh in-line filter from the tank was clear I had a soft yellow waxy substance floating in the carb chamber and blocking the jet holes.
After a good clean and flush of the tank and fill with new fuel, all was OK again.
Just wondering what the contaminant could have been, and any possible reason there was the yellow goo was in the carb but not the filter. The chap who would have filled the can was a petrolhead going way, way, way back so there could have been any strange additive in there.
Surely ‘bad’ petrol is only because it’s lost its more volatile components over time and so less flammable. I can’t see any way that would cause the yellow substance I found. Also I’d have noticed this as soon as I added it rather than getting through half a tank of the stuff
If you’ve ever watched those TV shows by Henry Cole, the motorbike ones especially they come across blocked carbs regularly. It’s nearly always a yellow substance from stale petrol blocking the jets.
Ok, so it does look like there’s degradation of petrol due to oxidation over time (even more so with higher ethanol fuel), causing it to go yellow. I’ve just checked some that was left and it has a definite yellow tinge to it. As you say, Mike that waxy buildup is common with old fuel.
Thanks both.