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Jelly in my carb


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I hope some kind soul might be willing to share their knowledge or experience... after five long weeks of wind, rain & snow, with night temps down to -10C on occasions, I got my motor (Bailey 175 four stroke) out of the shed on Saturday to prepare for another lesson - and maybe my maiden flight :lol:

After fettling and safety checks I stuck the battery in & fired her up. She started second attempt which is fair enough, but immediately there was fuel pissing out from the carb.

I soon whipped the carb off, removed the float chamber and found this inside:


(Apologies for the crap phone camera focussing...)

It can only be described as yellow jelly, and while there wasn't much it had gummed-up the little inlet valve, thus too much fuel was being pumped to the carb and it wet itself.

Easily cleaned and reassembled, it now runs as sweet as ever - but what caused the jelly? The fuel had sat in there for the last five weeks, had it reacted to the cold temperatures? The float chamber gasket appears a little tired, maybe the seal wasn't perfect... could this have triggered the jelly???

Any suggestions would be appreciated, hope to put my mind at rest before the thousands of hours I plan to fly come Springtime :)

Thank you in advance xx

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Hi Bob.

Take a look at the state of your fuel lines – especially the one inside the fuel tank. They are consumable items! I’ve seen jelly substance coming from cheap fuel line inside the tank. Replace all of them with Tygon, or even better Bing Blue Alcohol resistant line. The alcohol in petrol wreaks havoc with old lines, diaphragms, seats etc. Clean carb with carb cleaner and blow through all jets, and holes.


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In both carburetors and fuel injectors, fuel is metered through small, carefully calculated orifices. Over time, fuel evaporation and volatilization gradually can cause a buildup of gums and varnishes in these openings, and if left unchecked can block them, restricting fuel flow and compromising engine performance.

What kind of problems can occur from old gas?

In storage, gasoline immediately starts to oxidize and deteriorate. The older it gets the more it deteriorates and the more likely it will cause hard starting, performance issues and gum deposits that clog the fuel system.

If the gasoline in your fuel tank and carburetor has significantly deteriorated during storage, you may need to have the carburetor and other fuel system components serviced or replaced.

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Thank you all for your speedy replies...

The motor last ran (without issue) at the begining of January, so the fuel is probably 8-9 weeks old. I didn't drain the carb cos I didn't plan to lay the machine up - just week after week of inclement weather saw to that :(

I suspect the fuel lines are the culprit; on close examination this evening several appear opaque in places - I have a horrible feeling they're the originals. Yellow lines = yellow jelly... :roll:

Remedial action: replace all fuel lines, carb cleaner to clean the carb "properly" and fresh petrol! Thank you all again, no doubt this'll sort the problem once and for all 8)


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