Crom Cruach Posted June 9, 2023 Share Posted June 9, 2023 trying to fix suspected vapor lock. I want to fit a 3 way filter close to the quadrajet, so I have to bypass the metal fuel line. Also fitting a small inline fuel pressure gauge. I'm confused trying to figure out the various fittings, so many options! Can anyone confirm the thread size for the fuel pump and carb inlets? I think fuel pump inlet is 7/8 inch x20 threads female and the quadrajet fuel inlet is 5/8 inch x18 threads female is this correct? I have to order these parts from the States, so I can't just bring the metal line down to my local motor factors! Thanks Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted June 9, 2023 Share Posted June 9, 2023 Not sure why you feel you need a fuel pressure guage most stock or light modified engines don't need them. I used a k&n in line fuel filter on mine. The line is either 3/8 or 5/16 on mine it is between the fuel pump and carb near the carb. I can't get to the car to get a picture right now but here is a picture of the filter. I got it from Amazon they list it now for $8.50 it works well. Never use a plastic fuel filter use either glass or metal. And remember there is also a filter in the carb to (or is supposed to be) that is the large nut on the carb. Quote Link to comment Share on other sites More sharing options...
Crom Cruach Posted June 9, 2023 Author Share Posted June 9, 2023 Thanks Steve. What I’m really after is the thread size & pitch of the fuel pump and carb - I need a connector to replace the metal fuel line Quote Link to comment Share on other sites More sharing options...
Canuck Posted June 9, 2023 Share Posted June 9, 2023 Some will simply cut the metal fuel line and have short rubber lines clamped on with the filter in between. I personally just use the factory filter in the carb for all the Montes I’ve had and don’t have an issue. 1 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted June 9, 2023 Share Posted June 9, 2023 Paul, You could always just cut the metal tube, re use the threaded ends and the few inches of the tube with the flair, and go with rubber tubing (fuel safe) and clamps to plumb the fuel lines. Just like the old days. Scott Quote Link to comment Share on other sites More sharing options...
Scott S. Posted June 9, 2023 Share Posted June 9, 2023 2 minutes ago, Scott S. said: Paul, You could always just cut the metal tube, re use the threaded ends and the few inches of the tube with the flair, and go with rubber tubing (fuel safe) and clamps to plumb the fuel lines. Just like the old days. Scott Quote Link to comment Share on other sites More sharing options...
Crom Cruach Posted June 9, 2023 Author Share Posted June 9, 2023 I don’t know if I want to cut the original line. Feels a bit permanent! I think it’s the ethanol making the fuel boil, but also the line is so close to the block it’s actually touching at one point. Not ideal (see photo). Ok research I think it’s actually 7/8 inch x 20 fuel inlet till 1971, 1 inch after 72. https://www.carburetion.com/CarbNumber.asp?Number=7042202 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted June 9, 2023 Share Posted June 9, 2023 You could always order a completely new steel line to replace it..... Or order thread by clamp fittings and run the whole thing in hose. If I remember right, I believe it's a 3/8" NPT thread, which is a 18/per inch pitch. And tapered. But I'm getting old.... Memory slips from time to time. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted June 9, 2023 Share Posted June 9, 2023 That does look like 3/8 to me 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted June 9, 2023 Share Posted June 9, 2023 1 hour ago, Scott S. said: If I remember right, I believe it's a 3/8" NPT thread, which is a 18/per inch pitch. And tapered. But I'm getting old.... Memory slips from time to time. They don't use tapered NPT (National Pipe Thread) fittings for fuel lines. The fuel line itself is 3/8", but the fitting that is coming out of that fuel pump in the picture above is an inverted flare (SAE J512). That flared junction is the sealing surface, unlike a NPT tapered thread which uses that taper to seal. Don't use Teflon tape or thread sealant on an inverted flare fitting either, it's pointless. The thread pitch for a 3/8 inverted flare fitting is: 5/8-18, which is a straight thread pitch. Also, for fuel and brake lines, you're going to want a double flare on the tubing end as well. Scroll down to 'Inverted Flare' in the links below for this conversation, but a lot of good reference info in general. https://www.titanfittings.com/us-thread-chart_a/342.htm https://www.hydraulicsdirect.com/Fitting-Thread-Chart-s/1934.htm Found this chart too: 3 Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted June 10, 2023 Share Posted June 10, 2023 Joe that's a whole lot of information there, I guess I didn't realize there was that many different fittings. Glad our cars just use a couple of them 🤣 2 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted June 10, 2023 Share Posted June 10, 2023 19 minutes ago, cny first gen 71 said: Joe that's a whole lot of information there, I guess I didn't realize there was that many different fittings. Glad our cars just use a couple of them 🤣 Newer cars expand on that with a whole slew of different styles for brake, fuel, hydraulic and EVAP lines. Don't forget the 45 degree, and 37 degree AN, banjo, O-ring Boss, metric bubble, and push connect fittings too. 3 1 Quote Link to comment Share on other sites More sharing options...
Crom Cruach Posted June 10, 2023 Author Share Posted June 10, 2023 OK I could buy a spare 'fuel pump to carb' steel line and customize it, but the open end won't be barbed to hold the hose properly, so I think plan A is to get an inverted flare fitting. Check out this, it looks like it would fit both carb and pump, but do I need a section of double flared line to go inside, and act as a kind of washer? Brass Straight Tube Fitting, 3/8" Hose x 5/8"-18 Male Inverted Flare Swivel Straight Brass https://www.amazon.com/gp/product/B01BH74JOC/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1 or this: Edelmann 821660 Inverted Flare to Hose Barb, Straight, Brass, Natural, 5/8-18 in. Quote Link to comment Share on other sites More sharing options...
jft69z Posted June 10, 2023 Share Posted June 10, 2023 Either one of those will screw into the fuel pump or carb fitting with nothing additional needed. 1 1 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted June 11, 2023 Share Posted June 11, 2023 I've been connecting NTP threads to fuel lines for decades on diesel generators, and other than teflon taping the threads, I've never had any issues.... As long as it's not the flared ended tubing being used. Pre made braided hoses or clamped fuel lines are approved by the equipment supplier. Dorman carries a variety of fittings just for this application. On 6/9/2023 at 5:02 PM, jft69z said: They don't use tapered NPT (National Pipe Thread) fittings for fuel lines. The fuel line itself is 3/8", but the fitting that is coming out of that fuel pump in the picture above is an inverted flare (SAE J512). That flared junction is the sealing surface, unlike a NPT tapered thread which uses that taper to seal. Don't use Teflon tape or thread sealant on an inverted flare fitting either, it's pointless. The thread pitch for a 3/8 inverted flare fitting is: 5/8-18, which is a straight thread pitch. Also, for fuel and brake lines, you're going to want a double flare on the tubing end as well. Scroll down to 'Inverted Flare' in the links below for this conversation, but a lot of good reference info in general. https://www.titanfittings.com/us-thread-chart_a/342.htm https://www.hydraulicsdirect.com/Fitting-Thread-Chart-s/1934.htm Found this chart too: On 6/10/2023 at 10:11 AM, jft69z said: Either one of those will screw into the fuel pump or carb fitting with nothing additional needed. Quote Link to comment Share on other sites More sharing options...
jft69z Posted June 11, 2023 Share Posted June 11, 2023 2 hours ago, Scott S. said: I've been connecting NTP threads to fuel lines for decades on diesel generators, and other than teflon taping the threads, I've never had any issues.... I worked in the chemical industry for a lot of years, with a lot of nasty stuff. We tended to use the right fittings in the right place, without exception. If you're saying you mated a male NPT thread with a female NPT thread, then yes, a wrap and a half or two of teflon tape is correct. In the above case with Paul's fuel line, using a tapered NPT fitting in the fuel pumps straight threaded port as you suggested, is not correct. 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted June 12, 2023 Share Posted June 12, 2023 For our cars gm used double flare fittings for that line. No exception. If you try to use a NPT tapered fitting two things will happen. You’re going to bottom it out or you’re going to get it started and it will start to stress ( swell) the part you’re attaching it to ( carb inlet or fuel pump). If you’re starting with an NPT hole then yes as in the case of a water temperature sender or oil pressure sender. I have seen NPT fittings used in wrong applications. Can it be done, yes but I wouldn’t. With proper negotiation skills you can put a square peg in a round hole but it’s so much easier to use the correct parts needed for the application. 2 Quote Link to comment Share on other sites More sharing options...
Whons Posted June 13, 2023 Share Posted June 13, 2023 Here is what I did on my 70 Monte with an Edelbrock carburetor. 2 Quote Link to comment Share on other sites More sharing options...
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