The experienced owner of a large petrol engine model aircraft sought Dave Wilshere’s help
in diagnosing the issue that was causing his engine to run inconsistently.
The engine had become difficult to start and sometimes stopped without warning. The
owner had checked various engine related components and could not find anything
wrong. He was about to remove the engine and begin a strip down which would
have taken some hours.
Talking Dave through the checks he had completed on ignition and fuel related
items, the owner mentioned that he had removed the engine for unrelated maintenance.
The problem appeared to be fuel supply related, but
obvious failure or
problems were apparent.
The problem to Dave appeared to be fuel supply related, He checked the fuel system
and its installation and found no obvious failure or problems.
He asked the owner to talk him through the precise steps he took when refitting the
engine. Dave noted that when refitting the fuel tube to the carburettor the owner had
simply pushed the existing tube onto the carburettor – a very obvious and
natural thing to do.
Dave immediately checked the ‘fit’ of the tygon tube over the carburettor nipple and
found that he could easily rotate it back and forth. This meant that a firm seal had
not been made and air could, and was, leaking into the carburettor and
causing the inconsistent running.
Over time, tygon tube hardens where it meets the carburettor and, as a result, loses
its flexibility. So the solution to the problem was simply to trim back the fuel tube
to a more flexible piece. This then will flex over the nipple and form a
tight seal. Problem solved.
Elapsed time to solution – 10 minutes.
40 plus years of experience really does make a difference when time is money, the
amount of money available is not infinite and ‘time to market’ is everything.