Anyone have a factory 402 non-A/C set-up? Would like to put a rumor to rest.

[71CHEVYSHORTBED402]

There's a long-standing rumor the 402 with A/C had a fuel pump with a return line to the fuel tank. I know it's not true, not for a 1971 anyway, because they only offered one fuel pump for a 71 402 and A/C doesn't matter. The fuel sender has only one line as well. A return line applies to 1972 only.

Even the part houses are on-board with the confusion. I know because of the pump to carb. lines they offer.

I don't suspect a return line has anything to do with A/C. So my question is, does anyone have a 1972 factory 402 set-up, non-A/C, and does the fuel pump have a return line between the fuel pump and fuel tank?

[71CHEVYSHORTBED402]

After another peak, I can answer the OP. Despite the hearsay A/C makes no difference for a fuel pump on a 72 either. Here's a page out of the part's book that clears things up.

The return line has something to do with a TH transmission, which wasn't "required" pre-72. Other than perhaps an emissions experiment, I haven't a clue how a TH and return line are associated.

This came up because I needed a pump to fuel line. Many part houses make it a point to distinct between A/C or not, because they're misinformed. They sell the A/C line for a "long fuel pump". In reality it's for a tall pump on a 72 402 with TH. The other is sold as a standard line for "non A/C". In reality it's for a pre-72 BBC, and a 72 402 without TH.

Example of pre-72 fuel pump on BBC: https://www.amazon.com/ACDelco-40727.../dp/B000C9PXAQ

Example of 1972 402 fuel pump with TH: https://www.amazon.com/Spectra-Premi.../dp/B008M4RE6O

[Steeveedee]

Cars of that era with AC I believe always had the recirc line. It had to do with avoiding vapor lock. That's a 40+ year old memory, so don't hold me to it. In '71 Chevrolet started putting a two-row radiator in the big cars with the 400 SBC. We had so many warranty returns for overheating you just wouldn't believe it. Southern California in the summer, 105º in the shade (and no shade), those cars got hot, especially in traffic. First time I ever saw a blue torque converter. Needless to say, that trans was cooked, too. My '70 truck had a four-row brass radiator when new.

[71CHEVYSHORTBED402]

Originally Posted by Steeveedee

Cars of that era with AC I believe always had the recirc line. It had to do with avoiding vapor lock. That's a 40+ year old memory, so don't hold me to it. In '71 Chevrolet started putting a two-row radiator in the big cars with the 400 SBC. We had so many warranty returns for overheating you just wouldn't believe it. Southern California in the summer, 105º in the shade (and no shade), those cars got hot, especially in traffic. First time I ever saw a blue torque converter. Needless to say, that trans was cooked, too. My '70 truck had a four-row brass radiator when new.

You aware of a connection between a recirc line and TH transmission Steeveedee?

I can only speak for my Chevy's, both 402 with A/C. I suspected my 71 project had the short fuel pump. It was changed sometime after, the vapor line was connected to the pump. I confirmed it had the short pump when I pulled the tank. The original config. is consistent with the GM parts book. My 72 is per the book as well, it has the recirc line.

I'm rebuilding my 71 without the recirc line. Worst case scenario it vapor locks and I replace the pump, sender and fuel line.......Wow, what a bummer. See what happens. I don't recall the A/C ever blowing cold. Seems it was dry when I got it in 89, and I never charged it. It never vapor locked, hope it never does.

[Steeveedee]

I don't know of a link between the trans and a recirc line. Mine doesn't have it. Could have used it a few times. I've had it vapor lock on me even without the AC running. I need to fix some leaks in that. I was waiting to do that until after I got the hot running under control. I flushed the cooling system and put in a Cold Case radiator. Looks like that did the trick.

[davepl]

Here's one - riddle me this: why does the 265hp 396 come with a return line and the 350hp 350cid does not? Why would one vapor lock and not the other?

My only guess is that it was all big blocks, period. And my best guess as to the WHY is that the engine is much wider and has reduced ventilation and the fuel line is more sandwiched between the frame and exhaust manifold.

Anyone else know why the lowly 396 would come with something the top small blocks did not? Other than "part commonality to all big blocks" I can't think of one!

[71CHEVYSHORTBED402]

Originally Posted by davepl

Here's one - riddle me this: why does the 265hp 396 come with a return line and the 350hp 350cid does not? Why would one vapor lock and not the other?

My only guess is that it was all big blocks, period. And my best guess as to the WHY is that the engine is much wider and has reduced ventilation and the fuel line is more sandwiched between the frame and exhaust manifold.

Anyone else know why the lowly 396 would come with something the top small blocks did not? Other than "part commonality to all big blocks" I can't think of one!

396 with a return line.......Hmmmmm. What year truck?

[painterljp]

We are having problems with our 402 it has a return line tall pump. At about 40 mph seems starving for fuel. Has a new 2 line sending unit with return line. We disconnected and pulled the two saddle tanks. So those aren't issue. Sometimes it does it hot or cold motor. Doesn't do it all the time. Am gonna check the lines for any fuel supply issues. But question is what does radiator have to do with it. It came with a 3 core radiator we changed out to a 4 core Harrison. Doesn't get hot at all. It is an air conditioned truck but a/c stuff isn't on it at all yet. It has a short water pump factory. I must be missing something.

[HO455]

I would be more suspicious of what the vacuum advance is doing to start. Then it is OK then if you have access to an air/fuel ratio meter check the mixture, or bump the meter rods one or two sizes richer and see what happens.

[painterljp]

Will check it. The vacuum advance I think is ok it starts first time. Everytime. Normal two pump in morning then hits with key first bump. No cranking at all. It is a used distributor though new.cap and coil.
Am not any good with carbs. Will take it to my carb guy and get him to check it out. Figured it was a.fuel delivery problem though.

[HO455]

The vacuum advance won't affect the engine during startup. But it is common for an advance unit to need to be limited so it doesn't give too much advance in certain combinations. It is easy to check with an adjustable timing light. Set the light up, but leave the vacuum advance connected to the carb. then rev the engine up until the timing no longer advances. Then adjust the light so the flashing mark is on zero. Check the light for the reading. Not knowing your cam, converter, and rear end ratio I can only give a generic recommendation of 34 to 38 degrees max for the advance with the vacuum advance hooked up. If you find your at 36+/-2 try bumping the timing back several degrees to test if your problem disappears. If it does then you can work on limiting the advance and return your initial timing to where it was.

[painterljp]

Ok I have a non adjustable timing light. Will borrow a friends this week and see if that helps. Can't seem to figure it out. But will work on what you said to do. Dont know if timing advance has anything to do with tach bottoming out at 3500rpms either. Think we have a few more problems than I think. Dont know about converter but supposed to be stock. We rebuilt motor and tranny everything is supposed to be stock. At least that is what parts we asked for. Although had to pull granny twice cause 2nd gear went out after 50 miles. Burnt it up. Sorry for taking over your thread. Will pm you for more answers if these dont work. The rearend shouldn't be it cause we just changed ho52 for a Dana 60 3.54's. Did it with both rears.

[JDL]

Mine