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| Fuel tank vent lines...etc. | Rating: 
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| Posted: 04-23-2009 04:56 am |
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1st Post |
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dixiedog Member
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Hi, I'm kinda new to this board so please bear with me... putting my JH back together now and I have the dreaded Jorge fuel tank, didn't leak when I filled it with fuel out of the car, and after looking at every picture I could find I see no one has put the anti-syphon line off the "T" from the fuel pump to the tank pressure relief valve. Do I need it ? Thanks.
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| Posted: 04-23-2009 05:04 am |
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2nd Post |
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JodyKerr Member 
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Take a look at the following: http://www.theymightberacing.com/Projects/FrameOff/JH74G/FuelSystem.aspx I have a Jorge tank and have tested it it pressure wise. I put the tubing in as was described in the parts catalog & manuals. I've not completely decided it'll work as is, but that adjustable once the car is running. I asked about specialty anti-syphon t's, but didn't get any real response. Jody
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| Posted: 04-24-2009 03:00 am |
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3rd Post |
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Gary Martin JH 15371 Member
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I just finished installing my Aluminum tank, also by Jorge, in to my JH. I hooked it up as Jody explains, except I did not install the anti-syphon line with T section. My setup comes from the tank to a filter, then to the pump, then to a pressure regulator (more about that in a min), then to the fuel line to the carbs. The larger line on top of the tank connected to the brass pressure valve runs down the right side of the tank, through a hole and vents out under the car. This leaves the two pipe stubs on the top of the tank, one small and one larger. On my car I used the larger pipe stub for the line to the charcoal canister. As Jody explains there is a special rubber hose that adapts the larger 3/8 pipe stub to the 3/16 line for the canister. I could not get my hose adaptor to go on, since the pipe stub bulges out to 1/2 in at the end, so I cut that bit off. Then went on fine. The smaller pipe stub is most likely for this anti-syphon system which I did not put on. I capped of the small pipe stub. I don't see how Jodys return setup works, since it seems using a T would just pump gas right back to the tank and not supply enough pressure to the carbs. It seems there should be some sort of restrictor on the anti-syphon line back to the tank. Strombergs only need about 2.5 or 3 PSI. I think my pump was putting out a bit more than this, causing the car to run rich, so I installed the fuel regulator which seems to have helped. Also the Jorge tank comes with a thick plastic ring to use in place of the stock rubber seal. Do not see how in the heck that would ever seal. I used the stock rubber seal, but the fit is loose when installed. So what I did was take an extra locking ring for sending unit, and grind off the tabs and lip. Then used it as a shim under the lock ring to give more pressure to the seal. So far so good, but I have not filled up the tank that far yet. Gary Last edited on 04-24-2009 03:09 am by Gary Martin JH 15371 |
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| Posted: 04-24-2009 12:27 pm |
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4th Post |
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Jim Ketcham Member
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This has been covered somewhere on this board before. The original line from the T to the tank has a one-way check valve in it. It is actually hidden in the line itself, so often it is thrown away when someone replaces that line. Check valves were common on that era car and can be found and adapted if you lost yours. Anti-syphon is needed only when a vehicle's tank fuel level is above the carbs and the head is enough to force the carb needle valve off of its seat. While not common, it has happened. Jim
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| Posted: 04-24-2009 05:05 pm |
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5th Post |
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JodyKerr Member
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Jim, Do you have any idea of a part number for the check valve? It's not noted in any of the Jensen-Healey reading materials I have around. As to the two fittings on the top of the tank, the smaller diameter one is for the emissions line and the larger intended for the anti-syphon line. This was one of those scenarios where I knew there was something "missing" for the documentation, but without evidence from someone else I wasn't able to do anything about it. Jody
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| Posted: 04-24-2009 05:30 pm |
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6th Post |
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Jim Ketcham Member
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Hello Jody, Unfortunately, for the JH, the actual valve was part of the "anti-syphon hose assy" p/n 97183 for later models. Earlier models had it as an interim service modification (I guess anti-syphon was not originally on the JH) and called it P/N 94102 "pipe assy (includes tee piece, one-way valve...). I infer this from the parts manual. I can attest to the fact that the valve is hidden in the later models as I have cut them out of the hoses and installed them in new hose for several cars. If you can't get the original, you can find anti-syphon check valves used on other cars that splice in. Hope this helps, Jim
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| Posted: 04-25-2009 08:22 pm |
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7th Post |
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JHRV8 Member
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Upon reading the Jensen of England internet site, I read that the antisiphon valve is a must as when you park the car with the nose down on a steep slope, you can get run-off of the fuel into the carbs and massive flooding and subsiquent fire hazzard, so I believe the anti-siphon valve or another that works the same is a must......regards, JHRV8
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| Posted: 05-07-2009 06:06 pm |
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8th Post |
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JodyKerr Member
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Jim, Thanks for the information. I went spelunking through my array of spare JH bits and found an old line with the Check valve in place. I've cut it out of the old line and will end up updating my article on the subject. In addition, since I'm at the local NAPA on a regular basis I'll check their books to find a replacement part that matches. Jody
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| Posted: 02-05-2019 11:25 pm |
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9th Post |
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Rick in Miami Member
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Jody, Did you find a suitable NAPA replacement part for the anti-siphon valve?
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| Posted: 02-07-2019 05:12 pm |
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10th Post |
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Tom Bradley Member
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Rick, McMaster-Carr has reasonably-priced anti-backflow valves that are rated for gasoline and can be spliced into the tubing. The 0.5PSI pressure required to open the valve for forward flow should also help prevent gas from coming out of the carbs on a forward slope. They also have high pressure versions that require 2PSI to open up forward if you are dealing with really steep slopes. https://www.mcmaster.com/catalog/125/538
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| Posted: 02-07-2019 08:09 pm |
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11th Post |
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Esprit2 Member
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I've just read through this thread. There are two functions & parts being discussed in different posts, and it appears to me that some people are confusing the two. Maybe it's me that's not following the messages, and everybody else is on track; but just for the record: 1) When the car is parked nose-down on a steep hill with the tank/ fuel level above the carbs, the in-line anti-siphon check valve prevents fuel from flowing to the carbs, flooding them, perhaps to the point of over-flowing and causing a significant fire risk. 2) The fuel by-pass from the main output fuel line/ T-fitting back to the fuel tank, along with it's out-of-sight, 0.046" ID in-line restrictor orifice, functions as a "poor man's" dumb fuel pressure regulator. Under ONE set of factory-stock conditions, it bleeds off enough fuel to drop the stock fuel pump's "too high" output pressure down to the required ~2.5 psi measured at the carbs' inlets. Change anything, and the dumb regulator can't maintain the correct pressure. For instance, install a different pump with a different output pressure, install it higher or lower in the car, or install a different fuel tank that somehow alters the elevation of the fuel mass relative to the carbs, and the fuel pressure at the carb inlet will change. The ‘dumb’ fuel pressure regulator can NOT preserve the correct fuel pressure in the face of change. Period. If you make one of those significant changes to the fuel system (typically, an aftermarket fuel pump), then also delete the T-fitting, restrictor orifice, and bypass line back to the tank. Replace it all with an in-line, adjustable fuel pressure regulator, mounted as close to the carb inlets as practical, and set it to 2.5 psi. When you're deleting all that stuff, be certain to keep the Anti-Siphon check valve. Regards, Tim Engel Last edited on 02-13-2019 10:26 pm by Esprit2 |
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| Posted: 02-07-2019 11:13 pm |
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12th Post |
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Rick in Miami Member
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Thanks Tom & Tim. Tim, when 'deleting all that stuff' where is the anti-siphon check valve installed? Wasn't it originally installed in the bypass hose going from the t-fitting back to the tank?
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| Posted: 02-13-2019 11:20 pm |
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13th Post |
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Esprit2 Member
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Rick, Sorry to keep you waiting... I don't visit the JHPS site every day. I'm a Lotus guy who tries to help with 907 issues from time to time, so I don't know every inch of a JH. My fuel system comments are based more on a general understanding of how fuel systems work than inch-by-inch knowledge of where the anti-siphon valve is in the JH. I can't help you with that, and will have to defer to one of those who have been there before. Jody, In the article on your website, you mention that the 0.046" ID orifice is no longer available. A machine shop could make one, and it would help if someone who has one handy would measure and post the overall & stepped lengths, and the stepped diameters. Or... On a similar but different topic on a Lotus Excel forum, guys are using Dellorto Idle Jets in lieu of an restrictor orifice in a vacuum hose. Just a thought. 0.046" would equal a 116.8 jet (1.168mm ID), well out of the range of Idle Jets, but Main Jets cover that size. There are 115, 118 & 120 Dellorto DHLA Main Jets available, and 115, 117 & 120 Weber DCOE Main Jets. 115 = 1.15mm = 0.0453" 117 = 1.17mm = 0.0461" <<<<<< 118 = 1.18mm = 0.0465" << 120 = 1.20mm = 0.0472" I've not tried using Main Jets for a fuel return orifice, and I may just be blowing smoke. I'm just laying it out there as an option to consider. Regards, Tim Engel Last edited on 02-13-2019 11:24 pm by Esprit2 |
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| Posted: 02-14-2019 09:08 am |
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14th Post |
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chrisl Member 
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This may help (sorry about the three posts; I can't figure out how to do them all in one...) Attachment: jh_fuel1a.jpg (Downloaded 137 times)
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| Posted: 02-14-2019 09:08 am |
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15th Post |
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chrisl Member
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And the drawing referred to: Attachment: jh_fuel3.jpg (Downloaded 134 times)
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| Posted: 02-14-2019 09:09 am |
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16th Post |
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chrisl Member
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The sequence got messed up (sorry) bu this is p2 of the service bulletin referred to above: Attachment: jh_fuel2.jpg (Downloaded 133 times)
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| Posted: 02-14-2019 02:04 pm |
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17th Post |
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Rick in Miami Member
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Thanks Chris - Great info.
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| Posted: 02-14-2019 03:25 pm |
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18th Post |
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CDA951 Member
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Rick in Miami wrote: Thanks Tom & Tim. Tim, when 'deleting all that stuff' where is the anti-siphon check valve installed? Wasn't it originally installed in the bypass hose going from the t-fitting back to the tank?Hi Rick, My J-H does not seem to have any sort of anti-siphon valve, but it had already been converted to Dellortos and thus the fuel return line/"pressure regulator" orifice had been deleted. The anti-siphon check valve is installed in-line between the tank and the carbs to prevent flow unless its pressure rating is overcome (usually around 0.5 PSI from what I have seen). Otherwise the only things keeping the carb fuel bowls from overflowing with fuel when parked nose-down are the needle and seat valves. Anti-siphon devices are required by the US Coast Guard for marine applications to keep fuel in the tank in case of a fuel leak elsewhere in the system. As I am currently finalizing my fuel system, I plan to walk to my local marine store this weekend and pick one up! Chris
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| Posted: 02-14-2019 04:56 pm |
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19th Post |
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redracer Member
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I'm not sure why all the confusion: earlier gas tanks only had 2 vent tubes where the pressure relief valve is screwed in, whereas the later tanks(I do NOT know what chassis # this started from, even though I looked through all my info)has 3 vents. This 3rd vent runs to the "T" in the diagram with the anti-siphon valve just before the "T". This had a clip on the hose to attach it to the highest part of the tank. The valve itself is about the size of a 22 bullet; it is spring loaded to push a small ball inside it into the conical end when fuel pressure is turned on. After the engine is shut off the weak spring pushes the ball backwards to allow air in to prevent the siphoning. I have never seen this "Technical Bulletin" even though I thought I had all of them and have never heard of "T.I.Royal"? Maybe he was the Australian branch? Here is a link to a cheap viable option on Amazon https://www.amazon.com/attwood-Universal-Anti-Siphon-Valve-Fitting/dp/B00E21PVE8?th=1&psc=1
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| Posted: 03-04-2019 10:39 pm |
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20th Post |
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Rick in Miami Member
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After trying to rescue my pin-holed fuel tank with various sealers, it just turned out to be too far gone. The obvious pin holes soon turned into many more not so obvious ones. The bottom surface looked like a really bad case of acne – a really, really bad case. I bit the bullet and sprang for the aluminum tank on ebay - $399.95 w free shipping. Ordered it on a Wednesday evening and received it the following Wednesday morning. Not only was the shipping free, it came packaged in a very sturdy plywood crate. This tank is very nicely constructed. It fits very well although I had to trim the ends of the fat filler nozzle hose so the sealing gasket could be installed more easily. The take off for the ¼” anti-siphon hose was 5/16” but not a difficult work-around. I found the original anti-siphon valve in the original anti-siphon hose but it had been mistakenly tee’d into the pressure relief hose. I’ve attached a couple pics of the valve (its .25” diameter) as well as the restrictor for the emissions tubing. When installing the sender, I used an original rubber seal instead of the nylon one supplied with the tank. I also had to use 2 spacer rings between the metal sealing ring and outside surface of the sender to take up some slack. I cut these rings from the side of a plastic milk/water jug . To be on the safe side I also spread a thin film of Permatex anaerobic gasket maker on both sides of rubber seal. Pressure tested before installing. No leaks. Attachment: valve 1a.jpg (Downloaded 101 times)
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