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Fuel tank Air vent.

LUKLA

Active Member
Just curious.
Is any one has done your air vent differently than just making #30 hole in the fuel cap on RV12 gas tank.
I have heard there is new way ppl are doing but haven't seen any picture or schematic or instruction.
input will be appreciate as always.

LUKLA
 
I think it is a very good idea to change the fuel vent location as Van's has suggested in 37-01 Rev 5 due the possibility of the hole in the cap being plugged or a new owner being unaware of the hole in the cap, losing the cap, replacing it with a new one without drilling the the vent hole. A possible cause of a disaster. I made the revision moving the vent to the top of the tank. Only problem was that I have an automatic shut off and when it shuts off, a small amount of gasoline would spew out the new vent onto the floor. Why, I do not know. I then moved the vent an inch or so below the top of filler neck and plugged the fitting on the top of the tank using the same vent outlet location on the bottom of the fuselage to solve this problem.
 
I recommend having both vents, the new tank and the cap. I initially built mine without the cap vent and was having variable fuel pressure when the tank was filled. Put a vent hole per instructions in cap and no problem the last 100 hours.
 
I recommend having both vents, the new tank and the cap. I initially built mine without the cap vent and was having variable fuel pressure when the tank was filled. Put a vent hole per instructions in cap and no problem the last 100 hours.

Very interesting....me thinks I'll try that as I've seen changing (lowering) fuel pressure as fuel is consumed (and I know my vent works as fuel runs out if I overfill tank)...

Scott...where would find instructions on how to drill vent hole in cap?
 
Actually I subscribe to the vented cap all by itself. I use 93E10 auto fuel exclusively and don?t want a lot of air exchange in the tank. Alcohol is very hydroscopic and will absorb moisture in the air. Also, octane rating for auto fuel will diminish if not stored in a sealed container.

So I run a cap with the small vent hole and have had zero problems in 258 hours. When I did the fuel tank SB I elected to not install the new vent system. Fuel pressure and fuel flow are rock steady regardless of fuel quantity.
 
Actually I subscribe to the vented cap all by itself. I use 93E10 auto fuel exclusively and don?t want a lot of air exchange in the tank. Alcohol is very hydroscopic and will absorb moisture in the air. Also, octane rating for auto fuel will diminish if not stored in a sealed container.

So I run a cap with the small vent hole and have had zero problems in 258 hours. When I did the fuel tank SB I elected to not install the new vent system. Fuel pressure and fuel flow are rock steady regardless of fuel quantity.

So verdict is Just make # 30 hole in fuel cap and it will do perfect !!!

Thanks a lot Folks.
Lukla
 
I have the Van's early plan's holes in the fuel cap. It seems to be working fine for me over 500+ hours. Just be sure that as part of your pre-flight that you remove the cap and blow air (breath) through the holes to ensure that they are free and clear of debris, bugs, etc. Also, during outside exposure to rain, I tape a piece of plastic sheeting over the cap that is positioned to keep rain out of the cap area yet would blow away in the prop wash if I were to forget to remove it before flight.
 
Double vent

I also have the new style vent system and the vented cap. I drilled mine to the tap size for 4-40 and then tapped both the cap and the lower plate 4-40, just in case I didn't like the results. I had a couple of flights when I smelled fuel on climb out before I vented the cap, and none since vented. Needless to say I have not had to block off the cap vent. 117 hours total, approximately 100 hours with both vents,no problems.
 
Doug,

If you are smelling fuel on climb out check your carburetor bowl gaskets for leakage. That was my problem. I was using the rubber (neoprene?) gaskets that were supposed to be reusable. The auto gas looks like oil on the drip pans.

Rich
 
In my experience, smelling fuel during a climb typically means that one or more of your carb floats is overweight. This causes fuel fumes to vent out of the carb bowl vent tube and into one's nostrils.

When new from the ROTAX factory, the carbs are equipped with thin cork bowl gaskets. These cork gaskets don't seem well suited for repeated use and can be awkward to properly reinstall. ROTAX parts dealers (e.g., Lockwood, CPS, etc.) supply a thicker fiber-based gasket which works well -- no leaks for me. :) I have heard that the rubber (silicone or neoprene?) gaskets are not happy with mogas/ethanol fuels.
 
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