13sec83trans

First time this has happened to me i went to the drag strip for amateur night and on all 3 of my time trials i vapor locked hard. I've researched it for a couple hours and this is what I've gathered. first ill say what i'm running.

72 SBC 400
TH350 trans
750 quadrojet carb
stock radiator from the stock 170 hp motor (i know this is a issue)
forged flat tops at 10.5/1
485 lift cam
Stock heads

So i automatically run slightly hot from small radiator i want to get 190$ champion 3 core with tax check in spring. was already getting hot when i arrived at the track and i let it sit for a while with fans on and car off before i went and ran time trials at about 60 mph every time down the track it locked. all the fuel lines run real close to headers i have a few layers of 2000 Degree ambient tape covering them. I'm thinking that pushing the car up through line instead of keeping car on caused massive heat soak and vaporized fuel in the bowl. i bought a 110 gph fuel pump at 8 psi with no return line (i have return line on old stock one) i was reading that i could buy a fuel regulator with the return line setup and it would work better than running return line from fuel pump. would installing this 110 gph pump and regulator improve my vapor lock problem? I was also looking at carburetor heat shield how well would this work to help heat soak on the fuel bowl? also any other suggestions to fix problem? I am only 22 and first day on forum please help.

skinny z

Here's my take on the heat soak issue.
Without a return line on the typical mechanical pump system, dead heading the pump and waiting in the staging lanes will almost certainly create a boiling situation. After a pass, I can barely touch the fuel filter housing that's attached to carb side of the pump. That's hot. (Being right beside the lower rad hose doesn't help either. Neither does the fuel line close to the exhaust as you mention).

What isn't included in your post is why you think you have a vapour issue.

What do you mean exactly?

I have a fuel pressure gauge and can observe the fuel pressure drop to almost zero at the stripe. That's with a 110 gph pump (Edelbrock) that does not have a 3rd (return) line. This pressure drop doesn't appear during normal crusing when the car is at reasonable temps and I happen to get on it to the top of 3rd gear (or so).
I've picked up a Carter M6626 mechanical 3-line pump and will be testing with it later this season.

For what it's worth, all steps should be taken to ensure the car runs as cool as possible, as consistently as possible. Especially at the track. Big rad. Electric fans. Cold air intake. All of those will improve performance (and economy).

Something else to consider too, is the small fuel bowl on the quardrajet. Based on your engine specs, I doubt that you're physically running out of fuel (by drawing the bowl dry) but that is a problem with high consumption engines. There are remedies for that too.

PS. Welcome to 3rd Gen.

13sec83trans

Its never locked on me before this, but it always misbehaves if i'm running errands to a few places and i turn it off and on even if i leave big fan on. On every pass it would happen at top end of second right before shifting into third and shut down for around a full second and kick back in. i saw that carter pump mentioned in a few posts i'm going to try and return the summit racing one i got and get that. I'm thinking the problem was caused by sitting in line with the car off but with the small rad the temp keeps rising when just sitting there so that wasn't an option either. I am going back on the 23rd hopefully it will be cooler outside that day it was really hot when i went before. My dad had mentioned the small fuel bowl but he and myself felt like the symptoms where vapor lock. I just want to have a real pass on the 23rd without spending to much money trying to improve any heating problems as much as i can.

Night rider327

iTrader: (13)

Use a wooden of plastic 1/4" to 1/2" thicker spacer under your carb.
Re route the fuel lines away from block and rad. if you can.

An old temporary fix... Place wooden clothes pins on your fuel lines

Run a return line.. You can do this a few diff ways.
1) 3 line pump
2) or return style pressure reg
3) or 3 line metal fuel filter, placed close to the carb's inlet. These filters were stuck on a many older cars. It is the std 3/8" inlet/outlet but also has a 5/16" return line on the filter.
4) Make your own return fuel log type of line..

The stock little alum 1 core, plastic tank rad should do OK, not best but ok,
Look at a diff fan. The stock elec fans on these cars suck. I only run the 2 speed ford taurus / tempo 3.8L fans on all of mine. Those things moves ALOT of air plus has a nice shroud. On my S10 I have it wired with a temp switch to turn it on/off. With my camaro I have it wired to a on/off/on toggle switch.

Damon

You need cheap solutions here. So I'm not going to tell you to install an electric "helper pump" back by the tank (even though it would cure your problems, in all likelihood).

"Vapor lock" is a generic term that people use to describe two different but related things:

1. The mechanical pump draws suction on the feed line from the tank under heavy demand. If the fuel is already hot, and it sounds like yours is, the fuel instantly flashes to vapor inside the lines since the boiling point of the fuel goes down as the pressure drops. Fuel pumps can't pump vapor- only liquid fuel. And that's the end. If you add a low pressure "helper" pump it keeps the fuel line under pressure at all times and almost always cures these types of problems (plus the overall fuel system can move MORE fuel than either pump can by itself).

2. Pressurized, hot fuel in the line between the pump and the carb enters through the inlet valve (going from 6-7 PSI to 0 PSI) and hits the scorching hot body of the fuel bowl. And guess what happens? It flashes to vapor. Notice the similarity to #1? Drop in pressure combined with heat = problems.

Neither of these is necessarily like an on-off switch. You can get a little of both in some cases depending on how hot it is along the fuel line and the body of the carb.

SO.... you address both...

1. You know keeping everything cooler overall (better cooling system) is going to help, as you already suspect. Especially with a big 'ol cast iron 400. That's big block heat in a small block wrapper. It takes one righteous cooling system to keep it under control. Bigger rad, better fans is the cheapest route to victory here. The stock water pump is better than you'll ever need it to be (if in good working condition) so don't waste your money on a high dollar aftermarket pump. High tech thermostats also largely worthless. Just put a good quality Stant 160* stat in there if you do mostly track use and call it a day.

2. More heat wrap on the fuel lines. If one layer is good, two is better. Everywhere in the engine bay, especially near exhaust headers.

3. Heat shield and/or phenolic carb gasket. One little 1/16" thick paper gasket ain't gonna cut it. 5 stacked up would work better, on the cheap. A carb heat shield built into a gasket or in combination with a stack of other gaskets would be even better since it also helps reflect some radiant heat coming off the intake manifold. Finding one that fits a QJet isn't going to be as easy as for a Holley, though. Side note- if your intake has an exhaust crossover, block the crossover ports (many intake gaskets come with metal inserts to do this).

Oh, and you don't need a fancy radiator, either. I've found the HD replacement you can get at AutoZone, etc. works just fantastic. It's aluminum with plastic end tanks and will run you about $125. All your lines (like the trans cooler and overflow tank lines) will hook right up, too.

13sec83trans

Thanks for the advice guys, i do have a BIG fan in there thats wired to be on constantly or just with the key turned. I just noticed yesterday that there is a lot of space in between radiator and the wall on both sides for air to escape to nowhere, gotta get that plugged up.

to nightrider- Are you saying that putting clothes pins on the line would keep it pressurized while the car is off?

to damon - when you say replacement radiator from autozone you mean the stock one that came on a 400 motor? Before i posted this i looked for carb spacers with heat shield for my qjet and was not having much luck but i could probably stack a couple only problem is my air cleaner is so big that it already rubs on the hood insulation. I didn't know you can run a electric "helper" pump with a mechanical to keep it pressurized. If this continues to be a problem i am definitely looking into that

Wife'sCar

iTrader: (1)

The clothes pins won't keep it pressurized per say. They act as a heat sink, drawing the heat out of the lines and dissapating it through the wood. So the lines stay cooler and keep the fuel from hitting it's flash point.

I'm running a holley mech pump and a small Mr gasket electric helper pump near the tank on my 5.8 bronco, I was still getting vapor lock with this and ended up having to run a regulator with a return as close to the carb as I could get it as well as the two pumps. This keeps the fuel running through the lines in a cycle from the tank to the regulator that keeps the fuel much cooler. I've been running this for about a year now and have not had a single re occurrence. I have noticed that there was a big difference in the frequency of vapor lock between running ethonal and ethonal free fuel. I'm guessing the ethonal lowers the boiling point just enough that the low pressure from a carb fuel system doesn't keep it under enough pressure.

13sec83trans

That was another thing i saw in the research i was doing that ethanol fuel will screw with carbs but my piston compression is high to run lower octane. would it be better to run the 90 octane ethanol free or 93 with 10%?

My last question is would running a return through a regulator after the carb be more effective than a return on the mech pump? or it doesn't matter

Wife'sCar

iTrader: (1)

The octane rating doesn't make a difference, it's the ethonal content itself. And if you get your pump and regulator setup right you can overcome the ethonal issue as well. The ethonal doesn't really screw with the carb itself, the old style fuel lines that came factory on carbed vehicles can't handle the ethonal, it eats away at the interior of the lines. This gums up the carb, but if you replace all the lines with new ethonal resistant lines, have a good pump setup, and a return style regulator, you can run ethonal fuel no sweet.

I run ethonal fuel in my bronco all the time now and it doesn't miss a beat. I love having the last year of the carbed broncos but didn't want to sacrifice drive ability or have to hunt for ethonal free whenever I go out on long trips with it so I did a ton of research into this myself about 3 years ago.

Damon

When I'm talking about a replacement rad I mean the HD version that fits your car, not an original 400 application (which would have been a truck or full sized car from the mid 70s).

Understood about hood clearance being at a premium in these cars. Just gotta do the best with what space you've got.

A "helper" pump would be a low-pressure in-line electric. Carter 5 PSI electric or Holley Red pump (6-7 PSI). The electric pump makes sure there is plenty of fuel for the mechanical pump to instantly draw in at the line as opposed to sucking through the long, skinny straw back to the tank. The mechanical pump does the pressure-regulation and the final push up to the carb. Sounds odd but the combination of the two does an EXTREMELY effective job moving fuel though small-ish stock fuel lines, while also keeping vapor lock under control (because the feed line is always under pressure, never suction). You don't want or need a high pressure pump- it could easily over-power the one-way valves built into the mechanical pump and push right through it, straight up to the carb.

I run the combination of a Carter 110 GPH mechanical street pump and a Carter 5 PSI electric pump back by the tank in my Malibu. Without the electric "helper" pump the supercharged 383 would EASILY outrun the little 3/8" fuel line and mechanical pump's capability to suck fuel out of the tank at higher RPMs. The motor would practically shut off at 4500 RPMs. Added on the electric "helper" pump, no other changes, still using the stock fuel line, and it pulls all the way up with fuel pressure so steady it's like the needle is painted on the gague face.

Wife'sCar

iTrader: (1)

I'm running a holley 110gph mech pump on my bronco with a Mr. Gasket 12S 7psi helper pump, and a Mr. Gasket return style regulator.

13sec83trans

damon- your last paragraph sounds exactly like what happened to me at the track and i am certainly getting a helper pump asap. im going to try running 90 ethanol free as well, luckily i got a station 2 miles from me that sells it. i've been looking at these helper pumps and on the 110 gph holley blue pump on summit racing with max psi of 14 says in the notes that it flows 70 gph at 9 psi so i would be looking at under 50 gph for 5 psi? and does that matter with the mechanical being rated 110 gph?

Damon

Flow INCREASES as the pressure it's required to produce drops. Inverse relationship.

Get the lower pressure Red pump and you won't even need a regulator. It's already designed for a 7 PSI max, similar to your mechanical fuel pump.

The Blue is designed for 14 PSI and will over-power the one-way valves in your mechanical pump, allowing 12-13 PSI to show up at the carb- way too much.

Wife'sCar

iTrader: (1)

The ONLY reason I ran a regulator was to be able to add a return line. The fuel wasn't moving fast enough between the mech pump and the carb and was boiling as soon as it hit the carb. I do agree with the psi being recommended, use pumps that pump the pressure you need. You want a helper pump to be smaller than the mech psi. That way it's doing exactly what it's name says, helping.

Some people can get away with just the mech pump and the helper pump. Not sure where everyone lives, but my Bronco is mostly my daily driver. On days in the high 90's I was still having boiling issues in the carb, so the return line helped cycle the fuel so it never sat in the engine bay to long. I do a lot of stop and go traffic.

By all means start by just adding a helper pump, a return reg can always be added later if needed.

I only used it for the return line, not to actually regulate the pressure. I do intend on replacing the helper pump with a stronger stand alone electric pump and ditching the mech pump all together so I will need the regulator for that.

13sec83trans

Thanks for all your advice guys you were really helpful! I bought the holley red pump and a wix 33041 filter w/ return. i hope the pump is not as loud as everyone says it is lol i should probably invest in a fuel pressure gauge to. I had no idea you could combine these pumps like that and either did my dad seriously thank you.

Wife'sCar

iTrader: (1)

Get a square of rubber or one of those universal exhaust hanger rubber pieces and mount that. Between the pump and whatever you bolt it to. Use a locking nut or loctite so it doesn't back out. That will help noise level a lot.


And good lord I didn't know a filter existed with a return port, I'd have used that instead of a return regulator! Might order a few of those just to keep ready in the future!

Damon

My thanks to Wife's Car for confirming what I've said. His experience and recommendations are exactly like mine.

Yeah, noise is why I recommended the Holley Red over the Carter electric.

I have the Carter in my Malibu and even with the (supplied) rubber isolator mounts it sounds loud- even audible over my Flowmasters with axle-dumps. Mine's set to key-on with the ignition and before the motor is fired you REALLY hear it. Buh-Rrrrrrrrrrrrrrrrrrrrrr. Despite how noisy it is, it's definitely built to last. It's been in 2 different Malibus and has a combined 15 YEARS of driving under it's belt with ZERO issues. I truly believe it can not be killed.

You WILL hear the Holley Red, but it's not nearly as loud and the quality of the sound is much more agreeable to the ear. Like an electric pump, not like it's grinding rocks. I've installed 3 of them on friend's cars over the years in exactly the arrangement I described above. The oldest one is probably 6 years ago and so far none of them have failed, so it seems to be pretty durable as well.

A quick word about wiring them up.... You do NOT need a relay, big cables, or battery-tapped power connections. These aren't like massive high-pressure/high flow EFI pumps or race pumps. They draw MAYBE 3-4 Amps of current. Feel free to attach the power wire directly to any "IGN" (ignition-hot) terminal that's free in your fuse block. The stock fuse will be more than up to the task of powering it. I would recommend running a decent-sized wire from there back to the pump so you don't have voltage drop over that long run. 14 ga. is fine, 12 ga. is better. I've had mine wired like that for the whole 15 years and I've never had a single issue.

If you want to incorporate things like qualifying it's operation through an oil pressure switch or some such nonsense then, yes, you'll probably need a relay and a more complex wiring system. I prefer simple. Key-on, listen for the pump running, turn the key and drive it.

Through factory 3/8" fuel lines I've run cars deep into the 11s with this simple setup. It will support anything under 500 HP without breaking a sweat, including the roughly 450-470HP 383 blower motor currently in my Malibu.

skinny z

Care to offer up a part number for a return style regulator that's spec'd to work with a mechanical pump only? Anything I've looked for (although admittedly my search hasn't been all that thorough) says specifically in the literature "not for use with mechanical pumps".
I had been using (with my Holley Blue) a Holley regulator with 3 lines and I had mistakenly thought the 3rd line was a return when it actuality, it's a supply for 2nd carb. Seemed to work ok as I never had the same problem as I do now (simimlar to the OP) but I couldn't stand the noise of the electric pump.
Thanks.

skinny z

And while the OP seems to be on the right path for correcting his fuel delivery problems, for what it's worth, I still haven't manged to get the Carter M6626 3-line mechanical pump installed. Too much going on here however when it IS in place, I'll report back just to offer up the results.

13sec83trans

Thank you damon for additional advice on wiring it, i will be going to IGN in fuse block. Seems like it will be moderately easy to install. I got my red pump and filter from summit today man i love living 40 minutes from there warehouse always 24 hours shipping. Gonna try and get it installed tommorow.

Wife'sCar

iTrader: (1)

Oh my god if I lived that close I'd have a parking spot with my name on it....

skinny z

Yeah!

13sec83trans

Its been a long time since i logged on thought i would just update real quick. never got it installed went to the strip anyways and just put 60$ cam2 in it and hoped that would be enough. there was over 300 cars there (last night for amateur grudge matches) took over an hour and a half for first pass and just left right after. i was in lane 3&4 and i watched this truck in 5 go three times before i got to get 1 trial i was so mad. It ran a 13.8 with .1 reaction on street drag radials i thought it was going to be faster but i'm happy with it still beat the car i was up against. Decided to return mechancial pump i got and stay with the smaller one that already has return line. It has been put away for the winter and will get the holley red pump installed soon along with a long list of other things. thank you everybody