Wooger Posted July 7, 2017 Report Share Posted July 7, 2017 Hey guys, I have what appears to be a late 1969 gas tank in my 2-door 510 with two ports on top. Currently, the larger of the two (on the passenger side) is connected to the filler neck which appears to be correct. But the smaller port in the far driver side corner is also connected directly to the filler neck. Am i missing an evap tank? Anything wrong with the way it is currently set-up? I also have a non-vented gas cap. Thanks in advance, appreciate the help. Quote Link to comment
datzenmike Posted July 7, 2017 Report Share Posted July 7, 2017 If you have a non vented cap you must have a fuel tank vent line to the engine compartment in addition to the fuel line to the pump. It connects to the flow guide valve which collects fumes that are drawn into the carb to be burned and... allows air into the tank to replace the gas as it is used up. If the tank is not vented it will collapse as the tank empties. Quote Link to comment
Wooger Posted July 7, 2017 Author Report Share Posted July 7, 2017 Thanks for the response Mike, forgot to mention the car has a ka24de swapped in so no carbs. Only tubes coming out of the tank are the two connected red to the filler neck along with feed and return lines. Maybe I'm having a brain fart and this setup is correct? Quote Link to comment
Draker Posted July 7, 2017 Report Share Posted July 7, 2017 68/69 tanks do not connect to an evap. They don't have a vent line that runs to the engine bay either. They just had a clear tube that ran under the car. That's it. Quote Link to comment
Wooger Posted July 7, 2017 Author Report Share Posted July 7, 2017 Gotcha, appreciate it Draker. So now I guess the question is if I should re-route the smaller tube going from the tank to the filler neck to just vent to atmosphere under the car. Getting ready to install a surge tank set-up in the trunk and want to minimize as much of the fumes as possible. Thanks again for the help. Quote Link to comment
Draker Posted July 7, 2017 Report Share Posted July 7, 2017 If you run it back to the filler tube, the tank won't breath at all. If your filler cap has a good seal you might vapor lock the tank. Later models had a tiny hole in the cap to prevent this. Quote Link to comment
Draker Posted July 7, 2017 Report Share Posted July 7, 2017 I just ran a new line under the car.. only problem is.. if I or the fuel attendant tops off the tank it will syphon right out that vent.. lol. Just until the tank level drops.. so I don't top it off. Quote Link to comment
datzenmike Posted July 7, 2017 Report Share Posted July 7, 2017 Tank must be vented then. Air has to get in to replace the gas sucked out. I've collapsed a tank before. 2 Quote Link to comment
Wooger Posted July 7, 2017 Author Report Share Posted July 7, 2017 Tank must be vented then. Air has to get in to replace the gas sucked out. I've collapsed a tank before. I agree, it must be venting from somewhere, maybe a leaky filler neck/collar? I should probably look into that haha. I will probably just route the smaller tube from the top of the tank out the bottom of the trunk as mentioned by Draker and seal off the leftover inlet at the filler neck. Quote Link to comment
Wooger Posted July 7, 2017 Author Report Share Posted July 7, 2017 Now that i think about it, if my gas tank is not vented correctly (in its current state), would it create a sort of vacuum that would lower my fuel pressure under load? The reason I'm asking is my fuel pressure will sporadically drop significantly when i get on the throttle which leads to hesitation and bucking. My first thought was fuel slosh and a surge tank or sump set-up was in order, but now I'm thinking the bad gas tank venting is affecting my fuel pressure. Perhaps air isn't entering the tank at a fast enough rate to replace the fuel that is being consumed? But if that was the case i wouldn't be able to explain why the tank hasn't collapsed yet. Thoughts? Appreciate the insight everyone. 1 Quote Link to comment
mrbigtanker Posted July 8, 2017 Report Share Posted July 8, 2017 Is it venting through the cap. Also I thought the 68/69 vented through the cap hence none of the other crap. Shit I am wondering. Quote Link to comment
datzenmike Posted July 8, 2017 Report Share Posted July 8, 2017 Loosen the cap and drive it. If not venting you will get a huge whooosh sound when you take the cap off to refill. 1 Quote Link to comment
Wooger Posted July 9, 2017 Author Report Share Posted July 9, 2017 Is it venting through the cap. Also I thought the 68/69 vented through the cap hence none of the other crap. Shit I am wondering. Pretty sure the cap that's on right now is not venting, big "non vented" printed on it haha. Will keep you guys posted once I get back on the road. The intake manifold is currently off on the ka while I'm changing out the heater hoses. 1 Quote Link to comment
edekalil Posted July 9, 2017 Report Share Posted July 9, 2017 Loosen the cap and drive it. If not venting you will get a huge whooosh sound when you take the cap off to refill. Would the whooosh be going in or out? It seems I have had pressure come out of the tank. 1 Quote Link to comment
datzenmike Posted July 9, 2017 Report Share Posted July 9, 2017 As fuel level lowers air tries to get in if not vented. Not so noticeable if you take a week to use up a tank full. Gas will just evaporate to fill the void. On long trips where the tank is emptied in a few hours there is a huge whoosh of air going in. Air puffing out can only be a non vented partly filled tank in very hot? weather. Gas evaporates and builds some pressure. Normally these gasses are fed to the engine crankcase through the vent hose and the flow guide valve for storage. Next time the engine starts they are drawn out by the PCV valve and burned. The flow guide valve also allows air back into the tank as it is emptied while running. Newer cars use activated charcoal canisters for storing fumes. These are sucked out by engine vacuum the next time it's started. 1 Quote Link to comment
Wooger Posted August 8, 2017 Author Report Share Posted August 8, 2017 Just a quick update. It seems like the gas tank was not vented properly. I unhooked the smaller hose that was going to the filler neck and let it vent out below the car (capped the leftover hole at the filler neck) and now no more loss of fuel pressure. I still have no idea my the tank didn't collapse in on itself. Seems like problem solved for now. Thanks for all the help on this one. Quote Link to comment
Draker Posted August 8, 2017 Report Share Posted August 8, 2017 It doesn't sound like the way you routed it is correct either.. but I guess if it's working. ok? Quote Link to comment
Wooger Posted August 8, 2017 Author Report Share Posted August 8, 2017 It doesn't sound like the way you routed it is correct either.. but I guess if it's working. ok? I'm all for getting this right haha, especially if there are only two hoses coming out of the top of my tank. What would be the correct way to route the hoses? Thanks. Quote Link to comment
Draker Posted August 8, 2017 Report Share Posted August 8, 2017 tan/clear tube just runs under the car Quote Link to comment
Wooger Posted August 8, 2017 Author Report Share Posted August 8, 2017 Thanks for posting that Draker, that is almost exactly how mine is currently set up. The only difference is the vent bung on my tank is located on the far corner instead of the center. Quote Link to comment
D52E Posted August 12, 2017 Report Share Posted August 12, 2017 Info from parts manual at carpartsmanual.com Early fuel tank without evaporative emission controll: late vehicles with evaporative emissions: Early fuel piping: Late Fuel piping: 1 Quote Link to comment
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