Why is there fuel coming out my air filter? by Doc
[hr]
its called
fuel stand off....and it gets little specks of oil all over the bike plus fuel drips out of the air cleaner.
"FUEL STAND OFF'....this is a characteristic of a internal combustion engine with a carb on it. It has nothing to do with your jetting or acceleration pump
intake leaks or timing......it's a pulse wave that happens when a column of air(intake) traveling at 650 feet per second into a cylinder THEN the valve closes on this column of air. The column of air with a charge of fuel in it just doesn't stop, (who was it that said for every action there is a reaction?) any way when the valve closes the charged column of air traveling at a speed of 650 fts bounces off that valve and makes it's way to the other head where it bounces off that closed valve and the column makes it's way out through the carb....now here is where this gets interesting...the carb isn't too smart, It doesn't realize which way the air is traveling so as it goes over the venture it picks up more fuel in the column of air that already had a charge of fuel in it....when the column of charged air hits the atmosphere it's like hitting a brick wall so the air is reflected back into the engine as a little weaker pulse wave but since the fuel is much heavier than air the fuel continues out into the atmosphere soaking your air filter and the whole right side of the bike depending on how long you have the bike under a load at high throttle positions.
To witness this you can take off your air filter and do a few runs on the dyno and watch this STAND OFF happen before your eyes....a plumb of fuel will hover out side the mouth of the carb up to 8' away depending on the displacement of the
engine, cam overlap, and exhaust system used.
Now when you take the time to set up 'Intake Track Tuning' this waisted gas can actually be pulled back into the engine and used instead of washing your air filter. Intake Track Tuning is using the pulse waves of the intake to assist in cylinder fill by timing the wave to hit the intake valve as it is starting to open.....these are the things you do on motors that need the the EDGE to be a winner.
Hope this helped you to understand whats going on with your
bike, you don't see or smell this gas on a bike with a stock air filter because it's all tightly sealed, nor will you see STAND OFF in a EFI bike because there is no fuel to pick up on the way out.
If you continue to have a problem with the fuel on your bike and/or clothes take one of your wife's (or girl friends), light day pads and place it in the bottom of the football A/C cover....this will absorb all the fuel and oil from the breather, the fuel will evaporate and the oil will be trapped in the pad. Now one more piece of advice...........................change out the panty shield every 28 days.
Go on and laugh but this really works....don't use the pant shields with the WINGS.... the wing will stick out the cover and drip on the engine.
I got to take a nap now....but first here is how you figuer out intake tuning for those of you who have inquiring minds.
Intake track tuning is done by lengthening the distance from the middle of the intake valve to the atomosphere....ie if you add a 5 or 6' velocity stack to the end of your carb that would be extending your intake track. The intake track on My Pro Modified Drag Bike is 19 3/4' long, a stock [URL=http://www.v-twinforum.com/f
Fuel spray back into air filter
