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Gary Murray

Remove air filter screen?

7 posts in this topic

No, you don't. It will expose you to the risk of an air filter fire is the engine backfires, and it will bring you no benefit whatsoever in the course of it. The myth is that removing the screen will improve air flow into the engine, but the fact is that a clean, oiled element has more air resistance than the screen does, before adding dust.

In '03 or '04, Doug Henry's Super Moto tech crew did several dyno tests with different air box configurations and found that there was no detectable gain from removing the screen. My own flow tests indicated the same thing.

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No, you don't. It will expose you to the risk of an air filter fire is the engine backfires, and it will bring you no benefit whatsoever in the course of it.

I have heard this before... now the million dollar question for those of us (well, just me really) that don't understand why the 2T's don't have a screen? Is there no risk of back fire with the 2T? :ride:

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Even if a 2 stroke was to back fire the explosion has so many more places to disipate it's energy ( crankcase ) than a 4 stroke. Also the 2 stroke has reed valves that will stop most if not all of the backfire energy and flame from getting back to the carb and air filter area. A 4 stroke backfire on the other hand sends flames back through the intake tract, through the carb and releases the energy and flames into the oiled air filter if the spark arresting effect of the screen is removed. There are several stories of burned 4 strokes due to a backfire. Not to be too much of a wise a$$ , but I believe the screen removal is the same as wide open exhaust in that it is only psychological horsepower that you are getting. My humble opinion -- WR Dave.

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I have heard this before... now the million dollar question for those of us (well, just me really) that don't understand why the 2T's don't have a screen? Is there no risk of back fire with the 2T? :ride:
Pretty much no risk of backfire with a two-stroke, yes.

Since modern four strokes produce a spark at every TDC, there is the possibility of the engine failing to fire on the power stroke, then carrying that fuel over to the next TDC, where both sets of valves are open. If it ignites there, it's a straight shot out the intake, if the slide is raised, and it could be a fireball the size of a melon.

In two stroke, all the ports in the cylinder are closed when the spark occurs, and regardless of which direction the crank turns, the exhaust port opens first, then the transfers. Furthermore, in a non-reeded pinger, the fact that the transfer ports are open automatically means that the intake port is closed, and with a reed, the pressure would close it off, anyway, just as Dave said.

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My friend has a '95 klx 250 with out an airfliter screen, and the bike backfired casuing the newly oiled filter to catch on fire. It's pretty hard putting out the fire considering you had to unbolt the seat to get to the fire. Kind of scary knowing that there was 2 gallons of gas inches away from the fire. It is a real hazard, so do not remove the screen.

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If it ignites there, it's a straight shot out the intake, if the slide is raised, and it could be a fireball the size of a melon.

Jeez, makes me cringe when I think where the airbox is situated in relation to my private parts. :ride:

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