jacob80 Posted January 3, 2009 Author Share Posted January 3, 2009 Alright, so here is the information I've attained. The 5/16 lines will be fine. It is not mandatory to run a surge tank, just as long as you keep the tank above 1/4 full, and replace all rubber hoses and clamps to fuel injection spec. Does this sound right? And one more question, we are thinking about putting a surge tank set up on the fire wall. Would it be possible to cut those lines by the firewall? Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 6, 2009 Share Posted January 6, 2009 the stock 240Z return is 1/4", and is on the passenger side along with the feed. The other 5/16" line is on the driver side and goes to the top of the expansion tank above the gas filler. Whether you use a surge tank or not, you still need a return. In fact, you need two returns with a surge tank, one back to the main tank, and on one back to the surge tank from the regulator. Pete Actually the stock 240 return line is 3/16", smaller than the 1/4" mentioned. I used the vapor recovery line connected to a high point vent as return on my 73 EFI conversion. My tank venting was accomplished with a 'high loop' up near the vapor tank, and then vented through a small K&N filter outside of the cabin. The stock fuel feed line was used on the outlet of the pump from the surge tank, the stock tank pickup was used with the Bendex Style Ticker pump to fill the surge tank, with the bleed off the surge tank being bled back through the tank's 3/16" line as a high point 'bubble bleed'. Later I incorporated the vapor line return line to the top of the surge tank, and then to the top of the main tank where it was before. I had no issues with either setup. The reason the stock return line always leaks is people think it's 1/4" and use the wrong line, and try simply clamping down the hose tightly. Use 3/16" line and it fits like it should and won't leak. but if you use that small line it will overfuel at idle with close to 45-50psi in the rail because of the phenomenon Pete mentioned. Running it through the vapor line though was fine, same as in my 260. I put the whole mess on an aluminum plate back by the tank, and used the factory mounting holes for the electric pump to mount it. Some spacers to move it off the frame and clear the moustache bar links and you can have a big mounting plate back there to mount everything. Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 6, 2009 Share Posted January 6, 2009 The reason the stock return line always leaks is people think it's 1/4" and use the wrong line, and try simply clamping down the hose tightly. Use 3/16" line and it fits like it should and won't leak. I never actually measured one Tony, just a guess. I guess because I never actually left one in a car. Pete Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 6, 2009 Share Posted January 6, 2009 Useless knowledge from 'The Vault'... Quote Link to comment Share on other sites More sharing options...
jacob80 Posted January 6, 2009 Author Share Posted January 6, 2009 Thank you Tony D. Also, is there a reason my tank only fills about half full? Does not having an expansion tank have something to do with this? We bought the car without one. Quote Link to comment Share on other sites More sharing options...
Derek Posted January 6, 2009 Share Posted January 6, 2009 Thank you Tony D. Also, is there a reason my tank only fills about half full? Does not having an expansion tank have something to do with this? We bought the car without one. Did they vent the tank to the filler neck? If not this may be a problem. Derek Quote Link to comment Share on other sites More sharing options...
jacob80 Posted January 7, 2009 Author Share Posted January 7, 2009 No, I do not believe it is vented to the fuller neck, should I just run a line to it from the small feed on the tank? Quote Link to comment Share on other sites More sharing options...
Derek Posted January 7, 2009 Share Posted January 7, 2009 No, I do not believe it is vented to the fuller neck, should I just run a line to it from the small feed on the tank? It's been a while since I did mine but there's a large diameter (3/4" i think) nipple on the top od the tank. I ran a 3/4" fuel hose from that through the car and into the filler neck. Derek Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 7, 2009 Share Posted January 7, 2009 The vent lines are grossly oversized for what they need to be. I have replaced several vent hose setups using 8 and 10mm lines aas opposed to the factory 15mm lines. I use nylon barbed adapters to change from one size to the other at or near the tank. This allows you to use as little '5/8"' Gasoline Vapor hose (expensive) as possible, substituting normal carburetted fuel line in 3/8" or 1/4" to do the venting. This has worked well. All you need to do is make sure the high points on the tank all have a clear unobstructed vent. Many times I have dropped a tank and found those 5/8" heater hose blockoff caps on there! If those high point vents are obstructed then you get a BIG air bubble at the top of the tank and will not be able to get a good fill to full capacity. The smaller lines are easy to route, and in some cases you can fit them all through one opening in the deck out back, allowing you to 'cap' the other ones in the rear of the car's decking with the aforementioned heater hose cap---positive seal against exhaust fuem entrance! I use a JDM filler neck on one of my cars...it simply had a 1/4" dump behind the right rear wheel for any gasoline expansion. It's sooooo non-evap compliant! Actually, putting a later mode EVAP cannister back there, or one from a Geo Metro (really small one!) would work on the one where I made that high point loop and K&N filter setup. I just have run out of stock on Geo EVAP cannisters. They fit nicely in the wheel well of a 260 to 'clean up' the engine bay as well...keeping us all green and clean and happy long-term. The tank needs to be vented to allow for filling (as you have experienced) and to prevent the tank filler and stuch from being sucked down like a crushed beer can during long highway runs where the fuel level changes considerably. I've seen filler necks sucked down FLAT from electric pumps pulling fuel out of the tank! You need some sort of vent for the system to function properly. Those that say otherwise, or claim to not have one usually have vent hoses so rotted they can't hold any pressure in the tank if they tried! They have an uncontrolled vent and just don't know it. You need an external vent to accomplish this. The venting of the top of the tank to the filler neck will allow complete filling, but will not accomodate for fuel expansion and the draw that happens whiledriving down the road---with a filler neck high-point venting, you would still need an external vent for makeup air and to allow for offgassing. Venting to a small EVAP cannister would prevent the 'raw gas smell' after shutdown if all is corked up properly. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted January 7, 2009 Author Share Posted January 7, 2009 Ok, so, I'll run a vent hose up to the filler neck and then, I will run another hose to a canister from the tank, correct? Quote Link to comment Share on other sites More sharing options...
Derek Posted January 7, 2009 Share Posted January 7, 2009 I was looking at my gas cap the other day and I noticed that it has a one way flapper valve in it allowing air in the tank but not letting anything escape. Don't know if it works or not as I have a vent line on mine but that's the design of the cap. there are 2 ridges that run across the cap. I used to think these were strengthening ribs but upon closer examination they are the vents. Derek Quote Link to comment Share on other sites More sharing options...
lgoodson@pacbell.net Posted January 19, 2009 Share Posted January 19, 2009 Gee I don't know but I have a 71 240Z. It has a 5/16" line and a 3/16" line on the passengers side. One is the fuel feed and the other is I believe the canister line (evap). On the drivers side there is a 1/4" line at one fuel block. I believe this was for the return line for the twin carb set up. The engine was already gone when I got the car. For my LT1, the factory pipes are 3/8 and 5/16. The return line needs to be able to handle the return fuel without building up presure at low RPM's but not be too big so as to keep the fuel pump from building enough presure when the engine needs it at high RPM. I will be converting my prsure line to a retun line and adding a new 3/8" presure line. I will also have to change the lines into the tank which I will be changing to a FI tank as soon as I find one. Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 19, 2009 Share Posted January 19, 2009 The 1/4" line on the 'driver's side' is for the EVAP system. The 240's all used crankcase accumulation for EVAP control. That line went through a flow-diverter valve and either vented pressure from the tank to the crankcase through a fitting on the big line in the side of the block, or allowed makeup air from the filtered side of the air cleaner to go back to the tank to accomodate the dropping fuel level. I have not investigated the 'vented cap' but if it was a one-way valve that may well be workable under EVAP restrictions at the time. It for sure could not let anything vent out. And from an early 71 240 I personally witnessed suck down the filler neck flat...it has to be the gas cap 'with ears' that has that kind of device present. I just don't know why they would bother with the EVAP Filtered Air setup if that was the case though---a one way diverter valve would have been much cheaper, as the makeup from the cap would be more than enough. Quote Link to comment Share on other sites More sharing options...
Derek Posted January 19, 2009 Share Posted January 19, 2009 I have not investigated the 'vented cap' but if it was a one-way valve that may well be workable under EVAP restrictions at the time. It for sure could not let anything vent out. And from an early 71 240 I personally witnessed suck down the filler neck flat...it has to be the gas cap 'with ears' that has that kind of device present. I just don't know why they would bother with the EVAP Filtered Air setup if that was the case though---a one way diverter valve would have been much cheaper, as the makeup from the cap would be more than enough. Here's more info for the "wiki" I never knew they were vented either. I was looking for alternatives to the way I was currently ventiing so I investigated the cap. Derek Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 19, 2009 Share Posted January 19, 2009 I wonder how that works when the bayonet is engaged? Perhaps the valve is a 'suction/vacuum break' that is activated when the bayonet is being removed from the filler neck allowing for easy removal of the cap. While fully engaged on the filler neck--perhaps it's sealed. That would make sense. In the 240 with the flat filler neck there was a 'woosh' when the cap was disengaged---the reason the neck sucked down was they had plugged the EVAP line up front. The Vacuum Break Theory sounds like the explanation that would be most plausible in that case. I always assumed it was air rushing past the outer rubber section of the cap, but an internal relief would make sense. Pull a filler neck and check engaged and disengaged moveability of the center flap, Derek! LOL Quote Link to comment Share on other sites More sharing options...
Derek Posted January 19, 2009 Share Posted January 19, 2009 Pull a filler neck and check engaged and disengaged moveability of the center flap, Derek! LOL I'll get right on it! Derek Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 19, 2009 Share Posted January 19, 2009 Cast a filler neck! Muahahahaha! Quote Link to comment Share on other sites More sharing options...
jacob80 Posted January 20, 2009 Author Share Posted January 20, 2009 As a conclusion: Can I use the stock lines, the big one on the passenger side (not the 1/4) as the feed to the surge tank, filter, HP pump, then to the rail, back to the surge tank, and then use the return on the driver side? I will also drop the tank and run the vent line to the filler neck, but I still don't have an expansion tank, is this ok? Quote Link to comment Share on other sites More sharing options...
Derek Posted January 20, 2009 Share Posted January 20, 2009 Here's how I plan to do it. 5/16" hose from fuel tank drain plug conversion to lift pump. lift pump to surge tank. surge tank to high pressure pump. high pressure pump to 5/16 metal line passengers side. 1/4" return to surge tank. 3/16" line becomes atmospheric vent for tank. The vent to the filler neck is there for refueling only.You would need to T into that 3/4" line at the filler neck and run that either to the front of the car via the 3/16" line or vent it to the atmosphere in the rear of the car. Not a great idea as the fumes may find their way into the cabin. You should also add a rollover valve at the T. If you come up with on let me know as I haven't found one yet. If you don't T off of the filler neck and just use one of the extra fittings on the tank every time you fill up fuel will find it's way through the vent line. If it's in the 3/4" line at the neck it's mostly above the fuel level. This part I know from experience! Derek Quote Link to comment Share on other sites More sharing options...
jacob80 Posted January 20, 2009 Author Share Posted January 20, 2009 A diagram would benefit that greatly, anyone have one? Quote Link to comment Share on other sites More sharing options...
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