man-a-fre auxiliary tank venting question? (1 Viewer)

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recently I did a bunch of work on my auxiliary gas tank (see here) - but something that came up during all of that is that that model of tank (originally by Con-Ferr) had a little vent port just to the left of the fill neck located at the very top of the tank. this vent port came capped when I obtained the rig.

additionally, I had noticed some issues filling the tank which I related to no venting of the tank so pressure would back up making it a PITA to fill as the nozzle would always shut off quick like unless I held it just right to let air in/escape when filling.

so, to address this, I uncapped that vent and put a nice 1' long tube off of that that goes up the frame about 8-9" above the tank. problem solved....

BUT, the issue now is that I have seen gas leak out of the top of that tube! even under less than full tank, it will rise up that tube & flow over. not much, but it does.

WTF? Should I just recap it as it was when I first got it? I thought my idea would be a good solution and should likely have been there in the first place (or why even have the vent port). I can fill it faster easier now, but even running that vent tube higher than the tank and fluid (under pressure or heat or whatever) can still find it's way up that tube.
 
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Remove your filler neck, drill a hole the size of the breather on the tank, just behind the mounting flange of the filler neck. weld or braze a hard line in the hole. Run a rubber fuel line from the tank up to the new hard line. The tank will vent at the filler. Any excess fuel or vaper will then drip back into the tank. Look at the filler on the stock tank and you will see the same vent
 
kind of knew you would say this....

but if you route that vent hose back to the fill neck, the fill neck and 'new' vent hose/port are still under and will be covered by the rubber boot on the gas nozzle when you go to fill up so vapors, build-up will not be able to pass by and you will be back in the same boat as I was before I even opened the vent up.

it seems that what you reccomend is great IF there are other vent ports on the tank to let pressure and gas vapors out and let any run-off go up the tube and recycle back down the filler neck. but in this case, there is only 1 vent port and just sending it back to the filler neck still keeps the system closed and under pressure.
 
"e covered by the rubber boot on the gas nozzle ". The handle has a vent designed in it. It is designed to retrieve gas vaper from your tank. The reason your tank used to burp back at you was with the tube capped off the air in the tank being forced out had no place to go except back up the filler tube. Air going out gas going in same tube caused the problem. I have the same tank in my 78 and had the same problem untill I vented the take back at the top of the filler tube.
 
ditto on the above, I had this anoying problems for awhile and fixed it and it is all good now, it fills like stock now. I pulled the fill neck, drilled a hole, tapped some threads and found a brass fitting at the hardware store. I doubled up on it by using a bunch of jb weld around the fitting and in the threads, worked great. Make sure the tank is also vented up to your charcoal canister. It should have a port for the fill neck and one for the charcoal venting canister, this will help with the expansion/contraction of the vapors when going up in altitude, etc. Let me know if you need pics and I can take some tomm.

Noah
 
1973Guppie said:
ditto on the above, I had this anoying problems for awhile and fixed it and it is all good now, it fills like stock now. I pulled the fill neck, drilled a hole, tapped some threads and found a brass fitting at the hardware store. I doubled up on it by using a bunch of jb weld around the fitting and in the threads, worked great. Make sure the tank is also vented up to your charcoal canister. It should have a port for the fill neck and one for the charcoal venting canister, this will help with the expansion/contraction of the vapors when going up in altitude, etc. Let me know if you need pics and I can take some tomm.

Noah
If you have a supply line, return line and a vent line for filling the tank, which does not leave a port available to run to the charcoal canister. Normally the vent to the canister comes off the top of the tank, not the side, because you only want to put gas fumes into the canister. That is why Toyota has that plastic condenser above the tank. Maybe this would work if you tee off the fill vent line and ran that to the condenser tank and tee it in to an existing line.
 
1973Guppie said:
ditto on the above, I had this anoying problems for awhile and fixed it and it is all good now, it fills like stock now. I pulled the fill neck, drilled a hole, tapped some threads and found a brass fitting at the hardware store. I doubled up on it by using a bunch of jb weld around the fitting and in the threads, worked great. Make sure the tank is also vented up to your charcoal canister. It should have a port for the fill neck and one for the charcoal venting canister, this will help with the expansion/contraction of the vapors when going up in altitude, etc. Let me know if you need pics and I can take some tomm.

Noah

first, the metal fill neck is such a thin metal, how are you tapping any threads into it? I could see a 90 degree fitting (see image) with a hole drilled in the neck and than a bolt and rubber washer setup clamped around the fill neck hole like a sandwhich.

BEC72000.gif


second, on these auxillary tank, there is 1 vent. no option/need for a charcoal canister.
 
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this is the exact type of fitting I used, however you get it done is fine, I decided to tap it, yes, the metal was thin, not sure what fill neck you are using, this is why as I mentioned I doubled up on it by using some jb weld around the fitting.

My tank as I mentioned has 3 ports, not sure if yours is different, mine is from man a fre many years back, one for charcoal, one for fill neck vent and one for the supply fill line. It is necessary to vent the tank in order to have it setup properly. You will have issues if you go up and down in altitude as I mentioned the fumes need to expand and contract. You could vent it to the atmosphere but it is cleaner and a better solution to properly connect the fumes back to the engine for consumption.

noah
 
bsevans said:
If you have a supply line, return line and a vent line for filling the tank, which does not leave a port available to run to the charcoal canister. Normally the vent to the canister comes off the top of the tank, not the side, because you only want to put gas fumes into the canister. That is why Toyota has that plastic condenser above the tank. Maybe this would work if you tee off the fill vent line and ran that to the condenser tank and tee it in to an existing line.

the vent line/return line should be the same line, not 2 seperate lines. The vent line on my tank comes off an upper raised area on top of the tank, this is attached to the charcoal canister. The main supply line is hooked to the fill neck, next to it is the return/fill neck vent line which is tapped into the filler neck. The whole think is really fairly simple.......

Noah
 
1973Guppie said:
this is the exact type of fitting I used, however you get it done is fine, I decided to tap it, yes, the metal was thin, not sure what fill neck you are using, this is why as I mentioned I doubled up on it by using some jb weld around the fitting.

My tank as I mentioned has 3 ports, not sure if yours is different, mine is from man a fre many years back, one for charcoal, one for fill neck vent and one for the supply fill line. It is necessary to vent the tank in order to have it setup properly. You will have issues if you go up and down in altitude as I mentioned the fumes need to expand and contract. You could vent it to the atmosphere but it is cleaner and a better solution to properly connect the fumes back to the engine for consumption.

noah

I must have a different tank than yours. Mine seems even older than yours (made by Con-Ferr and sold by man-a-free). SO - I have only 2 'ports' in that tank. 1 is for the supply line out to engine (and that is actually a threaded port so maybe not even a 'port'). the other is this mini vent port to the left of the filler neck hole (so maybe theonly true 'port'). that is it. nothing more. nada. zilch. zero. and I got it from the PO with the vent hole covered - and has been for some time until I addressed some other issues with the tank recently.

I assumed it was plugged as vented gas caps are for this reason.. venting... but they seem inadequate.

anyway, I went and got some fittings I think that I can make work. a nice 90 degree (kind of like what you see above minus the hose fitting end which I will adapt) and a few others I will rig to work.

once I mod this thing, I will post up images as I think I have some good ideas - even using some JB Weld myself - to make this work.

photos of your setup would be nice just for reference.
 
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My rear tank has three threaded attachments. One for the supply line, one for the return line and one for the fill vent. On my 78, the tank vapor pressure bleed off is not part of the return line. It has multiple lines running from the tank to the vapor separator (that plastic canister above the tank with multiple lines attached) and a line from the vapor separator to the charcoal canister which has a check valve and outer vent control valve. These valves allow the vapor pressure from the tank through the vapor separator to flow through the charcoal canister. The check valve functions to bleed vapor pressure into the carburetor when the VCV is open or when the BVSV is open. Under those two conditions the vapor is dumped into the throat of the carburetor. When the outer vent control valve is open the vapors are dumped into the float chamber. These circuits have nothing to do with the return line. Without these connections to the fuel evaporative emissions control (EVAP) system the only pressure relief for the rear tank is through the gas cap which takes considerably more pressure to bleed. Individuals with rear tanks that do not connect to the EVAP experience pressure build up in the tank that increases with a less than full tank and an increase in ambient conditions as well as a long run on the freeway. You can hear the sides of the tank pop as they are pushed out do to the pressure buildup. Is it dangerous, I doubt it as long as you are aware of it and bleed it off slowly as you unscrew the gas cap. A self adhesive aluminized thermal blanket covering the side of the tank and the drivers front half (tank or skid, which ever is exposed) will help reduce the heat loading on the tank. Tying the highest point of the fill vent line to the factory vapor separator will bleed off the rear tank pressure. This will also subject the factory tank to the pressures of the rear tank which are higher than the factory passenger seat tank. My main concern is what this added pressure will do to the vapor separator canister. Personally, I bleed the pressure slowly and make sure no one is smoking nearby. I have the thermal blankets and a header wrap to put on the exhaust line from the muffler back. One of those projects that keeps getting reprioritized.
 
bsevans said:
My rear tank has three threaded attachments. One for the supply line, one for the return line and one for the fill vent. On my 78, the tank vapor pressure bleed off is not part of the return line. It has multiple lines running from the tank to the vapor separator (that plastic canister above the tank with multiple lines attached) and a line from the vapor separator to the charcoal canister which has a check valve and outer vent control valve. These valves allow the vapor pressure from the tank through the vapor separator to flow through the charcoal canister. The check valve functions to bleed vapor pressure into the carburetor when the VCV is open or when the BVSV is open. Under those two conditions the vapor is dumped into the throat of the carburetor. When the outer vent control valve is open the vapors are dumped into the float chamber. These circuits have nothing to do with the return line. Without these connections to the fuel evaporative emissions control (EVAP) system the only pressure relief for the rear tank is through the gas cap which takes considerably more pressure to bleed. Individuals with rear tanks that do not connect to the EVAP experience pressure build up in the tank that increases with a less than full tank and an increase in ambient conditions as well as a long run on the freeway. You can hear the sides of the tank pop as they are pushed out do to the pressure buildup. Is it dangerous, I doubt it as long as you are aware of it and bleed it off slowly as you unscrew the gas cap. A self adhesive aluminized thermal blanket covering the side of the tank and the drivers front half (tank or skid, which ever is exposed) will help reduce the heat loading on the tank. Tying the highest point of the fill vent line to the factory vapor separator will bleed off the rear tank pressure. This will also subject the factory tank to the pressures of the rear tank which are higher than the factory passenger seat tank. My main concern is what this added pressure will do to the vapor separator canister. Personally, I bleed the pressure slowly and make sure no one is smoking nearby. I have the thermal blankets and a header wrap to put on the exhaust line from the muffler back. One of those projects that keeps getting reprioritized.

much of what you describe on yours, I simply do not have on mine. I have owned it for a while now and ran it with the vent port closed off as the PO had it (and in hot desert conditions) as I never knew the system until I recently worked on it. so it only recently came about as I was doing other work on it (cleaning it and adding a sending unit) - so I never thought about it. now that I correlated the backup pressure when filling the tank (and thus, wasting 10 minutes trying to fill it) with the fact that that vent has a plug (something I never noticed on the rig due to it's somewhat hidden placement), I am looking for a solution that makes MY setup more safe and reduces the PITA of filling the tank.

so, it seems - with only 1 port available to work with here - it must be 'the' intended vent port and running it back to the fill neck will make the PITA go away and allow pessure to vent off better. agreed?

why the PO had it capped I do not know. maybe he thought the gas cap was doing it's job and venting enough so no worries.
 
noah -

gonna knock it out.

I am curious, and it woud be good for reference I think, to snap a few photos of a view looking down inside the filler neck and on the outside of the filler neck. I am curious how far into the filler neck your setup sticks? does it hinder the nozzle as it is likely not flush? I kind of have an idea that would make the entry into the nozzle flush rather than a nut sticking up.
 
wantatlc, here are a few pics, no the fill neck has no problems, it just goes past the vent mount, which is the way you want it to sit as you don't want a flow of gas going down that vent tube but past it and into the tank. Mount it as high as possible on the fill neck and you should be ok, I think I mounted mine about an inch or so down from the top of the fill neck. As far as venting, as long as you have a vented cap you should be ok. The tank is not in the interior so fumes should not bother you, I would say with the stock tank it needs to be vented properly because of the fumes that are created in the cab when going up and down in elevation, etc. HTH, Noah
fj40 fill neck 001.jpg
fj40 fill neck 002.jpg
fj40 fill neck 003.jpg
 
yep - pretty much what I envisioned, but good to see confirming photos. I will post mine up when I finish it.

hard to tell from last photo, but is the thread like 5-6 threads exposed so about a centimeter of the fitting just juts out into the filler neck? I might try (if I cannot pull off my first flush fitting idea) to build up JB weld to smooth that out. like a volcano.
 
if you are talking about inside the filler neck I wouldn't worry about it so much, the gas nozzle won't get in the way, like I said just make sure the nozzle passes the inlet so gas doesn't go down that way. I just screwed mine in a bit and jb welded a bit in the threads and a bunch on the outside, it is very secure and works great, no more "click" again and again at the pump.

Noah
 
finished......

so, here is the final product as told by animated imagery. at the 11th hour I decided to change my design away from copper fittings to a cleaner, more simple fuel line tubing setup just to see if I could pulll it off and make it a bit more flush on the inside of the fill neck - and to more mimic the setup on the front tank. so far so good with a weekend of driving. toughest part was waiting for the JB weld to dry for 15 hours.

vent.gif
 
Nice tech pictures! One question: what's the size of the big gas hose from the filler to the tank? Where you got them? My original Confer hose that came with kit collapsed since it didn't have the steel ribs inside.

Thanks.

/td
 

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