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Topic Summary

Posted by: SteveKfl
« on: August 28, 2019, 08:45:50 PM »

Good job, sounds like you've got it "covered", lol.  Safety first!
Posted by: aboyandhisdog
« on: August 28, 2019, 06:25:50 PM »

Good point, Steve.  The end of the vent line is at the back side of the driver seat, just below the top of the seat.  I installed a 1/4" fuel cut off valve in the line so I can open and close it.  I also cut a finger off an old leather glove and slipped that over the line so no rain or bugs or dirt can get into the line.  But really, the only time I'll have the vent open is when I'm driving or gassing up.  I think it will work great.  Appreciate the input!
Posted by: SteveKfl
« on: August 28, 2019, 08:02:35 AM »

Sounds like the stalling issue may be solved, but thinking out loud... two things come to mind, as it sounds like you have an "open ended" constant vent now.  If I understood that correctly, One, isn't it going to allow "evaporation" quicker and allow condensation in, especially if using Ethanol fuel?, and Two, aren't those constant supply of "fumes" potentially if "trapped anywhere", going to possibly create a "bomb" if a spark happens, like your electric pump use (depending on location) or even just static electricity?  One thing I learned in the service... "gas fumes" make an "explosion", not the gas itself.  You can throw a lit cigarette into a bucket of gas and it will put it out, but don't wave it or any flame/spark over the fumes.  It is more "expansive" than dynamite!!!  I suggest you make sure the fumes have an "exit" away from "trap spaces to accumulate".  Happy and SAFE motoring... 
Posted by: aboyandhisdog
« on: August 27, 2019, 06:04:00 PM »

It's all handled, Scout.  If you read my last two posts you can see I was sucking air in through the fuel pick-up in the tank (M38).  But thanks...any and all input welcome!
Posted by: scoutpilot
« on: August 27, 2019, 03:02:49 PM »

You've been through a number of carbs and a number of pumps. All with the same result. I have a few suspects that have already been mentioned. Have you tried removing the fuel pressure gauge from the system? Does the problem appear after a certain amount of time, or randomly?
Posted by: aboyandhisdog
« on: August 27, 2019, 01:18:45 PM »

Thanks Bob and BW.  So here is what I have discovered...The vents in the fuel cap (M38) and in the vent in the fuel pick-up in the top of the tank both work only for quite high pressure.  Neither vent was opening easily for make up air to get into the tank as I used fuel, so a significant vacuum was being created.  Now it never really seemed to affect fuel delivery, but I can't help but believe that it must have made the pump work harder.  I also found that the slightest bit of air getting in through a small crack in the (in tank) filter, or entering through a not-so-secure- hose clamp will indeed cut out the engine.  The 1/4" tube from the top of the pick-up is merely a cut 1/4" (cut to about 4") brake or fuel line and then the flared end screws in to the fitting at the top of the pick-up.  Part of the problem is that the cut end that the hose slips over is not flared.  So, a rubber fuel line slipping over the metal line relies solely on the hose clamps to keep air out.  A guy could take the line off and flare it, but they don't come that way from the mfg.

Now, here is another big improvement I made.  On the vent that is also located in the top of the pick-up, I removed the small metal flap that is supposed to open as you use fuel letting air into the tank.  This has the effect of letting air in easily and also letting air out easily.  To keep fuel from sloshing out, I installed a 1/4" line to the outside from the vent, ran it along the top of the tank, and then turned it up about 10" at the backside left of the seat.  So the pressure in the tank is now always the same as the outside air pressure.  I closed the vent in the cap as it is now no longer necessary.  This eliminates the vacuum inside the tank and also lets me get an additional 2+ gallons of fuel into the tank!  Finally, having the tank fully vented has solved several issues I was having. 
Posted by: Bruce_W
« on: August 26, 2019, 01:22:17 PM »

Tom,
   I believe the M38 fuel tank has a filter inside it. Maybe it's restricted.   BW

Oops. Didn't notice there was a second page to read before I posted. I see you know wbout the filter.

And yes, any air allowed into the fuel pickup or the line to the pump, will cause problems of varying degree, depending on the size of the leak, the fuel level in the tank, attitude of the jeep, etc.    BW
Posted by: Bob W
« on: August 16, 2019, 07:35:32 PM »

Quote
Here is a specific write up on a 3A cap.� I'm not sure how the M38 cap works in comparison.

http://www.cj3a.info/tech/gascap.html

Original M-38 fuel caps are unvented. Later M series caps have a valve inside so they can be changed between vented and unvented. Many M-38s ended up with later fuel caps on them. The venting on an M-38 fuel tank is in the assembly where the external vent line attaches to the tank. There are check valves in there very similar to what is inside and original CJ-3A fuel cap.
Posted by: aboyandhisdog
« on: August 16, 2019, 04:32:45 PM »

Okay, I think I discovered the issue.  On an M38 tank the pick up is in the top of the tank and goes down 73/4" to the bottom of the tank.  At the bottom of the pick up is an in line filter.  Last spring I changed this filter and just used what I had in the garage which was one of those plastic see through filters.  I liked that you can see what is inside it.  Trouble is it has a slightly tapered body so it doesn't secure squarely in the bracket that holds it in place. 

As is my practice to over tighten things, I secured it so it wouldn't shift.  Wouldn't you know, it had a small crack in it as a result and I believe it was probably sucking air in when the fuel would slosh around or especially when the level was low and on hills.  I'm guessing a little bit of air entering the line would be just enough for my pump to lose it's prime.  Anyway, everything is back together and filled with fuel and now to see if we have victory.

Thanks to you all for your ideas...fingers crossed...
Posted by: MikeP
« on: August 16, 2019, 07:16:00 AM »

so ive been following/reading this post and my advice (complete novice but still can figure out crap :) )would be to start from the original setup of the jeep as in no fancy pumps and different carbs etc and that way you can rule out stuff by having the original setup and then re add items that you want to it and try to recreate your issue also there may be a likely chance your carb could be malfunctioning in some way whether its clogged or something not lifting or releasing etc
Posted by: aboyandhisdog
« on: August 15, 2019, 10:44:15 PM »

Yes it is inline, and no it does not starve the mechanical pump.  It is a flow-through design and I've had it on board for about 9 years without an issue.  In fact it has saved me many times when there is vapor lock, boiling fuel, crud in the carb jet, or the issue I am having now. 

I just came in from another drive with the new fuel pump and had the same thing happen, so I'm certain I don't have a pump issue.  Tomorrow I'm tearing out the tank and flushing it and will get a couple of feet of new fuel line on order.  If this doesn't do the trick, I'm out of ideas!
Posted by: SteveKfl
« on: August 15, 2019, 08:01:18 PM »

Is that electric fuel pump inline with the regular pump?  I don't remember hearing of that before.  Could it be restricting the flow by having to pull the fuel thru the Electric pump mechanism starving it?
Posted by: aboyandhisdog
« on: August 15, 2019, 06:11:47 PM »

An update:  The fuel cap I used which is "open" (hole but no valve) makes no difference, as the jeep died again today - only to be revived by my turning on my elec. fuel pump when it began to stumble.  That was one of the best mods. I ever made to my fuel line.  Anyway, just installed my third fuel pump - a new Airtex.  Should know tomorrow if it is successful or not.  If not, about all I've got left is the possibility of bad rubber line or gunk in the tank.  Beyond that, I'm completely out of ideas.

Forgot to mention, installed a different carb. too and it still died. 
Posted by: aboyandhisdog
« on: August 11, 2019, 10:19:20 AM »

Thanks, Steve.  We don't have RV gas here, at least I've not heard that term.  Occasionally an obscure station will have non-ethanol gas but they are few and far between and not an option for me.  I do use Sta-Bil Marine additive in every tank which is supposed to counteract ethanol and even prevent corrosion in a metal tank.  Been using that for years.  Right now I am playing with some other gas caps that I have as I do believe the one I was using was, in fact, defective (the valve seems frozen).   Just came in from a drive with a different cap and had no whoosh when I got home and opened the cap.  I sure appreciate your input!
Posted by: SteveKfl
« on: August 11, 2019, 09:20:37 AM »

... but for your problem, it isn't "pressure" in the tank, it is IMO a "tank side vacuum fighting the pump" that may be your problem (hopefully solved that simply as a cap).  The "swoosh" you described I'm guessing was "sucking in air" not releasing pressure, or you would smell the gas fumes.  Key words in both articles... The other valve allows air into the tank as fuel is removed by the engine... thereby preventing a vacuum from forming inside the tank.  While looking for symptoms of a "bad vented cap article", I came across one chat box that the guy was saying his gas tank actually was caving in with a thump on long drives, so when he heard it, he pulled over and released the cap to pop it back out, and to release the vacuum before it stalled the car.  That is a strong vacuum (it was a 50s Chevy not a Willlys).  PS, if you're using Ethanol fuel, the rubber hose gets eaten very quickly on the inside, plus condensation can form in the tank in storage/non-use.  When replacing the hose, I'd suggest a "bio-fuel hose capable hose" with a PVC inner liner to fight the appetite of the alcohol in the fuel.  I use RV GAS a non-alcohol fuel for my low mileage equipment and vehicles.  Costs more at the station, but the "fuel related repairs" have stopped, including replacing my in-tank fuel pump in an Astro/GM product.  It is well worth the extra money IMO.