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First engine mods;


Phil_P
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Today I've been working on the engine of my Adventure F3. I didn't like the look of the standard air filter, apart from anything else, the mesh of the foam has such huge openings in it, I doubt if it would filter out a small dog, never mind dust. A filter like that is just asking to accelerate piston and bore wear. I have had good experiences with K&N filters from my motorcycling, and I managed to pick up a couple of brand new ones off fleabay that looked like they'd do the job. Fitting it however wasn't just a simple slip on job.

Once I discovered the retaining screws for the original filter were accessed by sticking an allen key through the foam of the filter, the removal was straightforward. It's a really crude system though, with the air intake into the carb throat being a simple flat plate, with the filter foam glued to the plate. This is probably the least efficient intake shape that there is. As luck would have it, I had a big chunk of delrin (acetal plastic) bar that was just the right diameter to fit into the K&N filter opening. I cut about a 30mm length of the bar, and marked it up and drilled it for the mounting screws. I then bored through the centre to the exact diameter of the carb throat intake. Left like this, I would have still have had the same 'flat plate' intake however. The next job therefore was to flare out the inlet hole in the delrin into a smooth trumpet bell shape. I then machined some grooves in the outside surface of the delrin to give the rubber round the mouth of the K&N some purchase when the retaining jubilee clip was tightened.

I also found that there was a 'step' in diameters further on in the inlet tract, between the metal and plastic inlet manifolds. I cured this by again machining a smooth transition between the two parts.

As it's now getting a little late and I don't want to disturb the neighbours, I will have to wait till tomorrow to find out if any of this work has produced any benefits. The worst case scenario is that nothing will have changed in performanc, but at least I will have a decent high efficiency filter keeping some of the c**p out of my engine

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