I'm at a loss as to what to do. I've ordered a couple different gas caps (one from CJ Pony Parts that was vented and one from LMC that was supposedly for trucks without the vapor canister). The one from CJs has a very loose fit, doesn't really feel like it seals, and leaks liquid gas down the side of the truck while driving. The one from LMC is a very tight fit, seals good, but over time will build up pressure in the tank as if it's not venting. Both seem to have their issues but don't know if one is more desirable that the other. Anyone experience the same thing and have any solutions?

 

Been running these for years without issues. The secret to keeping the gas in the tank is not to fill it up. I never have mine past 3/4 unless I plan on driving some of it out, and don't park on a sidehill with the driver side down.
Bob Drake Reproductions 01A-18416-A Bob Drake Locking Gas Caps | Summit Racing

 

​​​​​​Thanks for the response and suggestion. Would love to be able to get a full tank every time but might just have to sacrifice. Do you notice a gas fume smell when driving at all? I notice it heavily with the CJ one, especially with a full tank

 

I had some problems once. I replaced the dried up gasket for the sending unit on the tank, changed the short hose between tank and throat (and it’s two hose clamps) and finally bought an NOS Motorcraft locking(vented) cap, and tossed the Bob Drake reproduction one. Once the handle clicks off I don’t add another drop. Not sure which item, or combination of items did the trick, but the problem is solved.

 

Thanks for the response. I've already don't the rubber hose and hose clamps, still need to do the gasket.

Do you have the link to the cap you purchased? Does it build pressure when the truck is sitting for a period of time?

 

Same here on when the gas pump clicks off not putting any more gas in the tank and it put a stop to gas leaking from the cap/filler neck.

 

Is what you've tried one of these? Stant 10623 or Gates 31623?
https://www.oreillyauto.com/detail/c...cap/sta4/10623
This type works for me. I get a bit of gas smell on a full tank going around a corner - but its not leaking gas - just fumes coming through the vent it seems. I fill it until it clicks.
I cleaned up all the inside stuff as well - I was getting a lot of gas smell from an older fuel level sending unit.

 

Yes that looks like the one from LMC. Does your tank get pressurized when it's sitting? Mine did just over the course of a 55 degree night last night. If that's how it supposed to be then fine, I just don't want it hurting anything

 

I have experienced some pressure differential occasionally, but nothing that got me too concerned. Not sure why it was only apparent occasionally.
Did it build pressure or vacuum? A cold night would nominally reduce the air volume and create a vacuum. The tank vent needs to allow air in when the fuel pump is pulling gas out. People have fuel starvation problems linked to poor venting

 

It seemed like it was pressure, could feel it trying to push the cap off as I took it off. Happened again on my drive to work just now, about 80 degree weather. Seemed like it was causing a starvation problem with my electric fuel pump towards the end of the trip too (using electric pump because of my sniper EFI unit). Truck would bog down for a second then pick back up

 

Most of the replacement caps are only vented in one direction. They let air in but not out. Drill a .040-.060 hole in the check valve that's enough to stop building pressure in the tank. The problem with pressurizing the tank is more than just a bad smell. If your needle and seat in the carb isn't perfect, it can cause fuel to drip into your engine if it sits for a few days. Ever raise the hood and smell gas and couldn't figure out why?

 

And since you are running a Sniper, the tank needs to be well vented for pressure, so that the return line flows easily back into the tank. I believe the proscribed install for Sniper is to have a dedicated air vent, rather than rely on a vented cap. So keep an eye out for pump or fuel delivery problems related to that. I installed a dedicated vent, and can send photos if you'd like.

 

Yeah please do. I haven't had any issues with the gas cap from CJ (the one that was leaking gas and heavily leaking fumes) because I'm assuming it was ventilating enough for the sniper like you said. But I'd love to see how you have yours set up

 

Don't mean to hi-jack, but how is the Sniper coming along? Ready to go up against a 120 MPH 352 5-spd? LoL

 

Here are the tank mods. Welded in bungs for pump feed, pump return, vent. I Wanted 3/8” line for feed, so I did not use the stock fitting/straw. Could have used that for the return, but did not. My original fitting is now capped. The vent has no straw – just a hole at the top of the tank.

Here’s the routing from the tank. Black is the return, blue is the feed, the vent is blue and obscured behind the copper. Also some pics of the pass-through holes in the cab floor. I used the stock pass through for the vent, and did not use a bulkhead fitting for that – just bent the tube in a way that I can fish it in and out of place.










Here is the finished vent. Always pointed downhill, so I don’t create a p-trap for any fuel that might get in the tube. Added a sintered plug to keep the tube from getting plugged somehow.


Here is the detail in the cab. The vent tube needs a large vertical loop so that fuel does not slosh into it and pour out the end. (You could alternately consider a check-valve approach) My first effort was a continuous 3/8 hardline that looped up behind the cab corner gusset. I did not get that loop tight enough to go high enough up back there, and fuel was sloshing over the loop and coming out the end. I cut out that portion of the hardline and replaced it with ¼” hardline which was much easier to build a loop that went high enough and worked. This is ni-cop. I formed the basic 180 degree turn on the bench, then I just pushed it up behind the sheet metal while also bending it bit-by-bit to create the bend along the long axis. This allowed me to create a loop that can be installed/removed. I cut it to length and spliced it into the 3/8 hardline with compression fitting adapters.













Simple carpet does a fine job in covering the mess