hey guys i swapped from tpi to carb and now i think i have vapor lock. i will be driving along and the car sputters and dies. mostly after driving for 30 mins + or idling for a few minutes then giving it alot of throttle.

then to get it restarted i have to hold the gas pedal down some and crank it for like a minute to get it going again. and i have to hold the throttle too until it dsounds like it will stay running.

is this vapor lock? how do i solve it?

 

How did you set up your fuel delivery system for the carb?

(Sorry, I don't recall if you've said so in other threads - too many members out there to remember everyone's configuration.)

 

i have a rubber line running off the return line from the tank over by the washer bottle.

then it goes along the lower radiator support to a short piece of metal line into a mechanical pump on the block.

from the pump i have braided stainless line to a dual feed line into the holley 650DP with a plastic type 1" spacer.

 

What did you do with the stock in-tank pump?

 

i left it in there and i just draw from the return via the mechanical on block pump.

 

You need to drop the tank, remove the pump, use the pick-up line as a pick-up line (no pun intended), and the return line as a return line.

 

the pump i am using doesnt have a return line. i bought some shielding hopefully that will help. i will let ya know.

 

No return line is a very good way to promote vapor lock.

 

i found out what it was. the lower radiator hose i bought when i installed my griffen radiator was touching the hard line to the carb. i bent it in a tighter angle and wrapped it with shielding so after tomorrow i will know for sure if it is fixed.

 

solved

 

You should still have a return line. With it being August, it's gonna get hotter before it cools down, and then you probably WILL run into a vapor lock problem. We're already in the 100's here.

 

Carbed cars (i think) dont have a return line nor need one, or i have just never seen one with it. But i am intrested in knowing how you got your fuel pump to work, do you have any pics or any thing

 

3rd gen carb'd cars all came with a return line from the factory.

 

how do you run a return line when the fuel pump doesn't have ports for it? Just run a loop with a feed to the carb? seems like it wouldn't get enough fuel that way.

 

But they also had Q-jet carbs that were computer controlled, there is no way to put a return line on a holley 650 DP or a good aftermarket electric fuel pump, like a holley blue.

 

Being computer controlled had nothing to do with it. The return fitting was on the pump, not the carb.

Carter makes a high-flow return-style mechanical pump that bolts right on.

 

im not running a stock pump. im running one from a 78 with a carb.

i dont have wiring THANK ***. F.I. SUCKS!

i no longer worry about my car not starting or something not working like it should. even with the vapor lock my car restarts without fail.

carbs rule, fuel injection makes you a fool!

no sensors, no wiring mess, no blown fuses, no custom proms or tools, no expensive aftermarket crap just to be fast. why carb? i say WHY NOT?

 

Then replace the '78 fuel pump with an '82-'86 f-body mechanical unit. That will give you the return.

 

I have been running carbs for like 4 years now, never had a problem with vapor lock nor have i ever seen anyone have a problem with it. Mechanical pumps (in my opinion) are not what you need with running a high performance engine. There is no reason to have a return line in a carbed car. Nor is it possible with GOOD high performance parts. And it dont have anything to do with the computer but who runs a Q-jet i would rather run an eldebrock carb. Just my two cents for what it is worth.

 

And I disagree with everything you just said.

My $.02.

 

what did you disagree with, that most carbed cars dont have a problem with vapor lock, that most carbed cars dont have a need for return lines or that mechincal fuel pumps and Q-jets are junk.

 

But just to say, i do agree that running a fuel pump off of the return fuel line is not correct and i dont see how the fuel pump is getting the volume of fuel needed to run the engine

 

You didn't use "most" or "junk" in your original post...

 

most as in the factory third gens and junk as in mechincal fuel pumps

 

I've been running them for about 35 years now, I've seen it and seen others with the problem. 3rd gens in particular had enough of a problem that the factory came out with a dealer-installed kit to remedy it.
It is the least expensive, and very often, the most reliable. The only thing it won't do is prime the engine before starting. For the street, there's no reason to change from mechanical to electric. Of course, if you already have electric, there's probably also no reason to change to mechanical. And, a '78 350 probably doesn't fall into the HPE catagory, either.
The above reason is why a return line may be necessary. AC and stop & go traffic in hot weather is certainly cause enough. And, it is completely possible with a good street performance engine.
Here you are putting down what is argueably the best street performance carb out there, in favor of one that shouldn't be used in the same sentence with "high performance".

Enough already.

(At least we agree on the use of the return line for supply.)

Kevs87Z28;
Wouldn't surprise me at all if your problems return, unless you solved the real problem in the process of moving the line away from the radiator hose. I still think the use of the return line as a supply is not smart.

Did you replace the fuel pump, or just reuse what was on the used engine when you got it?

 

okay i know the problem now, Im 21 years old, that is the problem. I do know my stuff about cars but we have two different views, such as Q-jet carbs, your generation loves these things for some odd reason i dont understand it but my generation loves double pumpers. Q-jets never got them never will

 

All right, I'm gonna jump into a pit of snakes here, but:

It's not about being 21. Hell, I'm only 22. Big whoop. The fact is, the Q-jet is undeniably the best STREET performance carb. Period. It was built for streetable performance, as well as acceptable gas mileage, and they can take a beating. When I rebuilt mine, with no instructions and no idea what I was doing, it STILL ran, even with the check ball missing and gas overflowing out the top gasket. Try that with an Edelbrock. Didn't think so.

Mechanical fuel pumps are more than adequate for a daily driver that you take to the track every now and then, just to see what it will do. The return line is so that, should evaporation begin to occur, there is somewhere for the fuel vapors to return to so that the pump can continue pumping fuel, instead of trying to compress vapors. The great majority of us here who have done an engine swap use return-line style mechanical fuel pumps. It is typically necessary because unless you've completely re-routed the fuel lines fairly well back, somewhere the steel line is going to run near a hot header or collector.

Electric pumps are best for high performance applications where every ounce of horsepower helps. However, for a regular daily driver, it is simply a matter of preference.

True "good" high performance vendors make parts for any application.

I'm sorry if I seem to be butting in, but the age factor does NOT come into play here. Either you know what you're talking about, or you get ignored.

....that's all I have to say about that.

 

see that is my point the Q-jet is best mannered for the street, Correct? (BTW..i hate eldebrock carbs)The Q-jet was made for good fuel consomption. Well, i will spend the extra gas money to be faster than the guy with a Q-jet carb and i will stick with my Double pumper. im done.

 

That's good, because we've strayed way off topic.

If you think I prefer q-jets to double pumpers for racing, you haven't read enough of my posts.

However, the originator doesn't have and doesn't need a double pumper. That's not his vapor lock issue. Using the wrong line for fuel supply, having it too close to heat sources, and not having a return are vapor lock issues.

(FWIW: Last time I drove the '57 to the track, which does have a double pumper, it was a hot day, and it vapor locked just inside the track gate. Embarassing, to say the least. Once I'm inside and making rounds, no problem, because I take measures to cool it down. No fuel return on that car, by the way - pusher electric and return style reg at the carb are remedies I've considered.)

 

i do have a double pumper thank you very much.

i was told by someone one here that the return goes to the bottom of the tank so thats why i draw from that line. the pump is new. i am one of those people that doesnt re-use old parts. if it can be replaced within a reasonable amount of time and cash then i do it. i want reliable and using old parts is foolish. you ask for trouble doing that.

the problem is not totally solved yet. sometimes it does sputter. i am running a cheap flex hose from advance so thats why it touches. the stainless flex hose i have on the way will stay how i bend it and solve my problem.

i dont have ac or smog. i am running true dual 2 1/2 with hedman headers. its not close to the fuel line there. i didnt have a problem until that hose came into play.

debate what is what somewhere else, i dont want it in my thread and its childish and pointless to solve the task at hand.

 

well, i think your problem lies in your return line, there is just not enought volume of fuel to feed an aftermarket fuel pump, you may need a return line or it could be cativation. Cativation usally occurs when people try to leave the factory fuel pump in the tank as a puller and a aftermarket in the lines as a pusher.

 

do you understand my setup? i dont think you do.

stock pump is dead. it has no power, no ecm. i dont draw fuel from that line. i use a mechanical pump on the block to draw from the return line. i dont see why it matters if i take out the old pump and extend that line. it would be just as long as the return and do the same thing.

why would i need a return on a mechanical pump? a stock replacement for a 305 4 barrel wont flow enough for a 355 with a double pumper that revs to 6k rpm, it wasnt designed for that. and im not paying for a holley blue or whatever most are running on here. mechanical pumps are fine, no reason to ask for a electrical problem and the car not start.

so find a mechanical pump with a return and the lines pointing toward the frame rail on the passenger side under 50 and i will buy it. otherwise wait until the flex hose is on and see what happens.

im "old school" people i dont like electronics in control of my car and i like cheap, easy, and safe ways of doing things. that never hurt the "old timers" and it wont hurt me or my wallet either.

 

I apologize for all the non-related chatter and arguements. Perhaps I'll clean it up when I have some time.

Admittedly, I didn't ask for all of the details of your setup, although I did ask how the fuel system was set up. It took almost 30 posts to find out what kind of carb you have.

As for how much pump you need, think about this: You say you need more pump than a stocker, yet you think a smaller line than the stock feed line is good enough. Sorry, those are incongruent thoughts. A stock mechanical pump can handle more fuel than a 5/16" line can deliver. The Carter M6626 replacement pump is free-flow rated at 120 GPM, which is plenty for a double pumper'd 350 reving to 6k. If indeed your problem is vapor lock, the return will help keep the fuel getting to the pump cooler. But, it won't deliver 120 GPM with a 5/16" feed line.

 

You are getting alot of good advise here.

Why don't you take it.

 

AMEN !!

Auggie

 

Also being discussed here https://www.thirdgen.org/techbb2/sho...93#post2472993


Vapor lock is a two-fold issue - heat getting into the fuel line, and the reduced pressure in the supply line from the "sucking" action of an engine-mounted mechanical fuel pump (or even electric, if it's up by the engine). Please note two things specific to your use of a small supply line:

1) A smaller line will absorb heat more readily, because there is less mass to soak up a given amount of heat (if the only heat source is at the radiator hose, which I doubt, that problem may be reduced if your line is 3/8" there);

2) A smaller line will reduce the pressure at the pump more than a larger line due to line loss.

A pusher pump with larger line, along with a return, will eliminate the problem. A mechanical pump with return & larger supply line will reduce the problem by keeping the fuel cooler (return), providing more mass to absorb the heat (larger line), and increasing slightly the pressure at the pump inlet (reduced line loss with larger line).

If your problem really is "vapor lock".

 

Exactly. Maybe this pic will help. As you can see the large spring above the diaphram is very important. Engines that have high revs requier a stronger spring just like valve sp's. This pic dosn't show the shaft that runs from the cam to the pump arm but I think you can get the picture. When the pump arm is moved in the down position (lower pic) this is the suction stroke which seats the fuel outlet valve and unseats the inlet valve. When the pump arm moves back up the large diap. spring pushes the diap. down seating the inlet valve and unseating the outlet valve sending fuel to the carb. These pic's don't show the fuel pump return line which should have a restriction of around .090" to .125" to maintain pump pressure but will let fuel circulate through the pump thus keeping it cool and preventing vapor lock. Speaking of vapor lock how does this occur? If you will look at the bottom pic you will see the pump arm in the down pos. and on the suction stroke. As the large diap. sp. tries to move the diap. down to push fuel to the carb the needle may close on the seat (idling) and stop fuel flow because you can't compress a liquid, right. The pump arm will continue to move up and down in the slot on the diap. shaft (lower pic) but like I said before there is now no fuel flowing through the pump to prevent vapor lock. The heat in the pump builds and the fuel turns from a liquid to a vapor and when the needle opens to allow more fuel into the carb float bowl all you get is vapor. Cough, cough engine dies. A few years ago I bought a Carter Street Pump (M6900) and it came without a return line. I took the pump apart and drilled and tapped a hole in the fuel chamber (lower pic) and added the return line. The pump did not last long but thats another story. Schools out. By.

Auggie

 

ok so i see that you say the line is too small. i can agree with that. it was a temporary solution to get my car home from my uncles 3 hours away. i do want to take the old pump out now. do i just clamp some rubber line to the place it normally goes in the pump?

i am taking the info SDIF

i thought five7kid knew what i had because he has replied to numerous posts of mine (i have several because im new to carbs). i appologize for not mentioning it and i didnt think it mattered either but i guess it does.

so you think the new pump and nooking up the lines right will fix it? i have a heat shield under the carb and a sleeve on the line to the carb. should i remove the stock type fuel filter (tpi) from the line now that i have a carb?

 

I read through so many posts on different forums in a given day, I lose track of who's got what. Looking up what someone has said earlier takes even more time, so I rarely do that.

I keep forgetting about the in-line filter back by the tank for EFI cars. It should also be removed for a suction system, since it will further reduce the pressure at the pump inlet.

A piece of rubber hose sticking down to where the electric inlet used to be will work. Getting a sock filter on there somehow is also a good idea, although I can't help much with exactly how to do that. The '57 pick-up is a piece of tubing onto which a sock filter slips over. There's an AC part number out there for that sock, but I don't know off the top of my head what it is.