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Gas Cap Conundrum

Marcus Boone

Marcus Boone

New Member
I successfully got the fuel tank back in, all hooked up and drove it today (woohoo). Currently i have no vents on the fuel system as I have not yet sorted a new vapor canister system. Per other threads, that means I think i need a vented fuel cap.

So I ordered one that supposedly fits. It's the same images/model number everywhere I look, pointing me to Motorad. So I purchased, but it doesn't quite fit. As in it doesn't seal in the slightest. Images of crown are similar. Do I somehow have a non-stock filler tube? See the images for 1) the motorad replacement cap 2) the current cap, that seals tightly with extra (longer) tabs 3) the filler tube.

any suggestions? thanks
IMG_1099 Medium.jpeg IMG_1098 Medium.jpeg IMG_1097 Medium.jpeg
 
That's the correct filler neck.
There's no other that looks and fits that way.

I expect there is no vented cap for a '73.
The '74 TSM shows all CJs that year got vapor recovery.
Your '73 TSM will show whether all CJs that year got vapor recovery - and a sealed cap.
They use cap Jeep PN 994739.
These parts were introduced for 1970-ish, and possible a non-venting cap existed for those first years.
I don't have a book that covers those years, but Faxon sells one.

Kinda think you are making this hard.
I would run a vent from the regular tank vents and use the sealed cap.
Common practice.
You can send the line to air through a cheap fuel filter at the vent end.
Run it up to wherever you can place the filter high enough not to spill.
 
in anticipation for getting the canister, I installed the liquid check valve behind the passenger tire (there's a metal panel there making a sort of gap between it and the back wall where the lights mount. both vents come off the driver's side of the tank and into the two lower connections. the single top connection is currently capped. I think what you're advising is to uncap that, put a small hose and fuel filter there and call it a day until i get the canister installed (i prefer not to have gas smell in the garage). here it is, camera facing towards front of jeep
IMG_1102 Medium.jpeg
 
Yes, I am familiar with that area, the hoses, the check valve, etc.
The original check valve was mounted there, shielded from debris off the tire.
That would work.

Or, you could run a hose to under the hood in anticipation of using that when you get your canister squared away.
Jeep used (bright green!) nylon for the vent lines as I recall; less than a dollar a foot at Amazon, maybe less elsewhere.
https://www.amazon.com/25ft-Nylon-Fuel-Line-Exceeds/dp/B07KWHHB9F
Use a short length of rubber hose at each end and spring clamps.
Run that from the check valve along the frame parallel to the fuel lines.
The fuel filter on the end is to keep bugs and dirt and such out of the open line.
 
Ugh...brings back bad memories...some '71 models have a bastard size cap (like mine). It's different than the '66-'70 and '72 and on.
Yours looks like mine.
I had to get a cap for a '77 IH Scout.
I think Rock Auto has an application / year error with this part.
 
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Marcus Boone said:
in anticipation for getting the canister, I installed the liquid check valve behind the passenger tire (there's a metal panel there making a sort of gap between it and the back wall where the lights mount. both vents come off the driver's side of the tank and into the two lower connections. the single top connection is currently capped. I think what you're advising is to uncap that, put a small hose and fuel filter there and call it a day until i get the canister installed (i prefer not to have gas smell in the garage). here it is, camera facing towards front of jeep
View attachment 102478
Click to expand...

Just put a hose and old filter on there. It'll be better than a vented cap.
 
Yes, you can make a cap vented by drilling through it.
A factory-vented cap contains a labrynth that (nominally) passes vapor but not liquid.
Only marginally effective IME.
I'd say you are much better off to vent up high if you can.
Vented caps will withstand slosh, but not full-on fuel immersion.
On a '70-up Jeep, Jeep Corp gives you the tank vent connections for this purpose.

My advice - don't ruin your factory sealed cap by drilling it.
 
thanks for the pointers - I'm going to run the hose to the front and connect to the canister and leave it there until I get the vacuum sorted.
 
Without the purge from the air cleaner connection, the canister will get saturated with vapor eventually.
I expect it won't hurt anything, but it won't block the fumes.
Just FYI.
 
Just closing out this thread with a follow up on the fuel tank cap. After installing a new canister, there was still a slight gas smell. Through some trial and error, i determined my gas cap does not have a tight seal - i suspect the gasket is dried out.

This sent me in search yet again of a replacement cap. I found this on eBay https://www.ebay.com/itm/1575018980...97&osub=-1~1&crd=20260226170749&segname=11051

I didn't think I needed a new neck, and I wasn't excited about paying $100 for a gas cap so I contacted the seller. He replied promptly with this:
The cap you need is no longer available which is one reason we manufactured this neck. Between 1970 and early 76 there were 3 different necks, all looking alike to the untrained eye. That means there were 3 different caps. 2 of the caps (most used) are impossible to get now. The 3rd one which you don't have was used least but is most available today. You've already found out it won't lock down on your neck. So you need to buy our kit. The other reason we came out with the kit is there are many who bought a project Jeep and the neck was missing. - Barney, Barney's Jeep Parts LLC

I don't know if all of this is factually accurate, but my continued search for a cap only was fruitless. So I puckered up and bought it. Should be here this week and hope to get it installed and finally have the fuel smell mostly addressed.
 
Marcus Boone said:
I didn't think I needed a new neck, and I wasn't excited about paying $100 for a gas cap so I contacted the seller.
I don't know if all of this is factually accurate, but my continued search for a cap only was
Click to expand...
Well that sucks as a solution. I went to rock auto and ordered a cap for my ‘71, the Motorad MGC705, which didn’t fit the ‘71, but it did fit my ‘73 perfectly.

Good luck
 
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