- Joined
- Oct 13, 2004
- Messages
- 611
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- 16
- First Name
- Grahame
In a reply in another thread, Four Stroke Torque, I mentioned that I use multiple fuel filters and thought that an explanation as to why would not go amiss, so here goes:
I used to only have a fuel filter in the feed pipe to the carburettor but one flying session was cut short because the engine died when pulling up for a loop. Doing a full throttle / nose up test the engine leaned out and no matter how much I opened the needle valve I couldn’t get it to run satisfactorily; obviously a serious “plumbing” fault I thought.
On stripping every thing down at home the problem was solved; the fuel filter was virtually blocked with fine grass cuttings and this was restricting the fuel flow. The flying site hadn’t been mowed recently and the model had done a good impression of a “strimmer” on the take off run, the ends of the prop becoming stained green. As fuel was sucked from the tank, air and in this case grass, was drawn in through the tank vent to take its place. The answer is a fuel filter in the tank vent line, each time the tank is filled the filter is “reverse flushed” so keeping it clear.
This started me thinking; as the piston moves down the contents of the crankcase are expelled via the crankcase breather, as it moves up it sucks air into the crankcase. It is normal practice to extend the breather with a pipe exiting the bottom of the cowl, right in the contaminated air. Another filter required.
If debris can get into the system through a vent pipe or breather just imagine what the carburettor could suck in, the RC car boys always use an air filter, I know their models are (nearly) always on the ground churning up dust, but for the price of an air filter I can’t understand why every body doesn’t fit one.
One thing to be aware of if you use the fuel feed line to fill your tank, make sure you fill straight into the tank and not through the filter. If you do the latter any bits in the fuel will be held on the engine side of the filter to be sucked straight into the carburettor as soon as you start the engine.
I used to only have a fuel filter in the feed pipe to the carburettor but one flying session was cut short because the engine died when pulling up for a loop. Doing a full throttle / nose up test the engine leaned out and no matter how much I opened the needle valve I couldn’t get it to run satisfactorily; obviously a serious “plumbing” fault I thought.
On stripping every thing down at home the problem was solved; the fuel filter was virtually blocked with fine grass cuttings and this was restricting the fuel flow. The flying site hadn’t been mowed recently and the model had done a good impression of a “strimmer” on the take off run, the ends of the prop becoming stained green. As fuel was sucked from the tank, air and in this case grass, was drawn in through the tank vent to take its place. The answer is a fuel filter in the tank vent line, each time the tank is filled the filter is “reverse flushed” so keeping it clear.
This started me thinking; as the piston moves down the contents of the crankcase are expelled via the crankcase breather, as it moves up it sucks air into the crankcase. It is normal practice to extend the breather with a pipe exiting the bottom of the cowl, right in the contaminated air. Another filter required.
If debris can get into the system through a vent pipe or breather just imagine what the carburettor could suck in, the RC car boys always use an air filter, I know their models are (nearly) always on the ground churning up dust, but for the price of an air filter I can’t understand why every body doesn’t fit one.
One thing to be aware of if you use the fuel feed line to fill your tank, make sure you fill straight into the tank and not through the filter. If you do the latter any bits in the fuel will be held on the engine side of the filter to be sucked straight into the carburettor as soon as you start the engine.
