Venting a non-vented gas tank cap

[MTGreen]

Have a Deere R70/R72 riding mower I recently refurbished. Has a gravity feed tank feeding a now 12hp single cylinder B&S.
Original gas cap was vented and in bad shape. I ordered a replacement part from Deere and got the part that superceded the original which fits but is not vented.
Didn't think much of it until I tried to troubleshoot why it would run great for 30 seconds to a minute then die. Runs great with the cap off but of course that's not a fix.

Thought about just drilling an 1/8" hole in the cap, or drilling a hole and epoxying in a hose nipple attached to some vacuum line.
Anyone have any better ideas?

 

[Tinhack]

That should work but don't just drill it straight through. Drill one hole on an edge of the underside then drill the top hole 180 degrees from that. A straight through hole might gush gasoline.

 

[beenthere]

Could just buy the vented cap too. Part # AM100289

My 4x2 Gator has a non-vented cap and never stalls out. Not sure why ?? Must vent some other way than the cap.

 

[CobyRupert]

Is there another part that goes into the underside of that cap that makes it vent-able?

 

[MTGreen]

Could just buy the vented cap too. Part # AM100289

My 4x2 Gator has a non-vented cap and never stalls out. Not sure why ?? Must vent some other way than the cap.

I had tried to order that part number and got the non vented substitute

 

[MTGreen]

That should work but don't just drill it straight through. Drill one hole on an edge of the underside then drill the top hole 180 degrees from that. A straight through hole might gush gasoline.

I'm trying to understand how this works? The only way I can see that air can get into the tank is through a hole in the top round center of the cap -anything on the sides is blocked by the filler spout.
I can see this would work if the top was double walled with an air space in between, but unfortunately this cap has just a single layer of plastic

 

[MTGreen]

Is there another part that goes into the underside of that cap that makes it vent-able?

I'm afraid what you see in the pics are it

 

[garry1p]

A small hole may not seem like much but gas fumes will escape wasting gas and possibly creating a dangerous situation stored in an enclosed location.

I suspect as gas exits the tank a one way vale allows air in.

 

[5030]

A much smaller hole is required. I believe even a number 50 wire size drill hole will work just fine.

 

[DarkBlack]

That should work but don't just drill it straight through. Drill one hole on an edge of the underside then drill the top hole 180 degrees from that. A straight through hole might gush gasoline.

180 degrees from the first hole would create a single straight hole.

I imagine you mean 90 degrees

 

[CliffordK]

Would you lose the cap if you unscrewed it 1/4 or 1/2 turn when mowing, then screwed it back down when finished?

I just searched E-Bay for "VENTED JOHN DEERE GAS CAP", and a bunch popped up, most with what looks like a hole in the middle.

 

[MTGreen]

Would you lose the cap if you unscrewed it 1/4 or 1/2 turn when mowing, then screwed it back down when finished?

I just searched E-Bay for "VENTED JOHN DEERE GAS CAP", and a bunch popped up, most with what looks like a hole in the middle.

Yes the cap would vibrate off immediately.
This mower doesn't take the standard thread cap, presumably because it's pretty old as mowers go

 

[Fuddyduddy1952]

I like to fabricate things. A one way check valve like this $11.99 one, brass for fuel & would work. Hole in cap, thread on nut so air goes in but won't let fuel out.

 

[slckeys]

I'm not affiliated with the seller, but a quick search found me this on eBay. Looks like a small hole middle underside. Might this work for your application?

Pardon Our Interruption...

 

[MTGreen]

I'm not affiliated with the seller, but a quick search found me this on eBay. Looks like a small hole middle underside. Might this work for your application?

Pardon Our Interruption...

Yes looks like it will work, thanks. Part numbers match. I wasn't looking aftermarket and apparently I should have

 

[Tinhack]

180 degrees from the first hole would create a single straight hole.

I imagine you mean 90 degrees

I hope you're never lost in the woods. My compas has 360 degrees. If North is 0 then 180 is South.

 

[Tinhack]

If you can't get a vented cap, make your own. Cut a round piece of plastic to fit tight to the underside on that seal area. Then put your holes in.

 

[ruffdog]

Most vent holes in caps were smaller than 1/8"....more like 1/16"

 

[Fuddyduddy1952]

Probably I'd just drill a hole, J B Weld a 2" piece of steel tubing in it & stick a couple ft. of rubber vacuum hose on it.