Guys, I really need help please......

[Kp]

Let me re-phrase.
The return line goes from the filter at the front of the intake manifold, and over the pass side valve cover, and back down to the frame rail, to where the mech pump was mounted.
It is not particularly close to the exhaust manifold at that point. It is just ABOVE the mnaifold, so a break up high would be pretty bad.
The fuel lines are relatively close to the manifold in the framrail though. That big block fills the space between the framrails from side to side, and the exhaust manifold is basically parrallel with the [ of the framrail. I will probably get a piece of tin to box that part of the framrail to shield the fuel lines there.
Carb has no elec connections at all.
The biggest problem with this, is that to re-create the problem, I have to hit the hwy. By the time the problem occurs, I am 15 miles from home, and its been hovering around 110 degrees here for the past week.
Leaning over a hot BBC in 110 degree heat, on the side of the road, really, really sucks.

 

[Kp]

UPDATE
Ok, the haynes manual has a method for checking flow from the stock pump.
It says to put the fuel line into a container, and crank for 30 seconds.
After 30 seconds, a pint of fuel should've been pumped.
So, the same volume should apply to the electric pump.
I would be surprised if it didnt pump a pint in 30 seconds tho......I know I can drink a pint in 30 seconds!

 

[southernspeed]

Boiling in the carb seems to be a normal condition. Even my lawnmower will boil the gas if you turn it off.

Yeah but your lawnmower has a blown 572 in it

. If I were you, I might look into other BBC pumps, see if you can find one with a return. That would alleviate the fuel filter issue.

I believe mid to late 70's BBC have a return line at the pump.

 

[Kp]

yeah, some of the pumps do have an outlet for a return, but that would be a mechanical pump.
I cant go that route. I think theres a problem with my cam eccentric, because the mechanical pumps make a knocking sound, and dont last very long.
Gotta stay electric.

 

[southernspeed]

Then I would suggest getting a high flow pump and putting in an inline FPR set to what your carb needs so it can return the rest to the tank. be carefull though. Theres quite an issue with aeriated fuel when you're returning a lot of it to th tank, this will cause you no end of problems as all you're doing is feeding bubbles to the carb.

 

[Kp]

Well, I just installed an electric pump, so I am trying to determine if it flows enough, because my problem is still there.
It says it flows 36 gph, which seems low by comparison, but I dont know what a stock trim big block needs?
i dont want to buy another pump if its not really the problem

 

[Kp]

Well, I had a little time to play with this yesterday, and it really looks like the problem is the gas in the carb boiling. I was able to make it stall, and quickly popped the hood and pulled off the air filter housing.
Sure enough, you could hear it bubbling like crazy. I hit the accelerator pump, and what looked like steam came out of the carb.
I guess I'll buy a carb spacer and see if that helps. I am really knd of curious about whats causing it though.
The engine temp never topped 190*, so why is the carb getting so hot?

 

[dyeager535]

Only thing I can think of is that your pump just isn't moving enough to keep the fuel cool, (via the return) and thus the carb is heating up.

Your case is obviously out of the ordinary, or every carbed GM engine would have an issue like this.

ONLY thing I've ever heard about GM having a problem with this, was a hot soak issue, where once shut down, the carb would stay hot enough to evaporate all the fuel in the carb, and it would be hard starting. ONLY on certain cars, and they ended up with a little cooling fan setup to run when the engine was off, directed at the carb. I think a phenolic spacer would be more effective.

 

[scotto0609]

I had a similar problem about a year ago with my truck. Could not use a mechinical pump because it would not work. The electric fuel pump on it didnt seem to keep up with eingine under load but would idle all day long. I changed the whole fuel delivery system over to a holley projection I had laying around. no change. Then I changed the coil in the hei and the pick up in the distributor .problem solved! So fi you have another good hei around give that a try. Hope this helps!

 

[Kp]

Thats interesting. I wonder why the HEI would cause fuel system problems?

 

[scotto0609]

I dont think it did ,my problem was disguising itself as a fuel problem. My filter was empty whenever it would stop running and I too would get the boiling sound. It was just another place to look,especially if you happen to have a extra cap laying around. good luck scott

 

[tumbleweed1002]

I don't remember reading were you mounted your pump, it should be mounted as close to the fuel tank as possable. a friend of mine with a burb running a 454 had the same problem his pump was mounted to the fire wall elect pumps push fuel 100 times better than pulling it any way he moved it back to the tank and all the problems dissapeard. just somthing to think about.

 

[broncoman6524]

If your pump isn't enough (which I have no idea how many GPH a stockish 454 needs) a full throttle run as long as you can hold the pedal to the floor should tell you. Should also be 100% repeatable. BUT if you lift from the throttle, and the problem doesn't go away, then it's probably not a delivery issue. When you get off the gas, fuel demand goes to almost nothing, and since an electric pump isn't governed by whether the engine is sputtering or not like a mechanical pump, it should recover almost instantaneously.

You may not be able to keep it at full throttle long enough to suck the bowl dry, but it's worth a try.
quote]

when you say this are you sayin to let it stall/die because of the lack of fuel? or would hte motor surge kinda thing...im having similar problems and wehn i let it wind out to 4k it starts surgin...i too am having problems with stumbling on acceleration. im getting annoyed/pissed this has robbed me of soem crazy power...

 

[dyeager535]

Yes. It won't die, because the fuel pump is either still running (electric) or pumps every time the cam rotates. (mechanical)

On the Q-jet, I just got leaner secondary rods, and the problem went away.

 

[mosesburb]

Well, I had a little time to play with this yesterday, and it really looks like the problem is the gas in the carb boiling. I was able to make it stall, and quickly popped the hood and pulled off the air filter housing.
Sure enough, you could hear it bubbling like crazy. I hit the accelerator pump, and what looked like steam came out of the carb.
I guess I'll buy a carb spacer and see if that helps. I am really knd of curious about whats causing it though.
The engine temp never topped 190*, so why is the carb getting so hot?

Just out of curiosity, have you tried pinching off the return hose and see if your symptoms change?? Reason I ask is that the stock pumps (3 ports) don't return all that much fuel and if you're using a commonly available inline filter with a return line on it (typically a Chrysler original application) the return port is pretty much free flow so you may be returning too much fuel to the tank and if I read it correctly, you had this filter on the mechanical pump also (yes/no??). I had a stock big block in a Sub (Gen V with no mech pump provisions) and I ran an electric pump on in and I had to regulate the fuel pressure back down to about 4psi or it would overpower the float. By pinching off the return you may create another issue (over-pressure), it might not, but mine sure didn't like it. If it does you may need to add a regulator, but it would be an easy test to see if too much feul is going back to the tank.

I have run into mechanical pumps making noise and failing quickly before. The cause ended up being a small block pump on a big-block. They appear very similar, share the same mounting configuration, but will not last long. Not saying that's what you had going on, but might be something to ponder.

 

[Kp]

Well,
the pump is mounted to the framerail, as close to the tank as I could get it, which is basically under the rear passenger door. It's about 2 ft away from the tank.
I did a few full throttle runs, and it will pull all the way to a pegged speedo(85+), UNTIL, it gets hot.
Basically, if I went out and got in the truck right now, I'd be able to run it up to faster than that big ol truck should go. BUT, after a little while of driving around, it would stall upon any type of acceleration.
I havent tried pinching off the return, for fear of flooding, dumping gas into my crankcase, etc. Also, with no return, the possibilty of vapor lock in the lines comes back, because there is no fuel circulation.
The filter is the same one I had on the mech pump, and is the chrysler design that you mentioned. The return is free-flowing just like you said. Only the smaller outlet would limit the flow, and that probably wouldnt limit it much.
I am hoping to pick up the carb spacer this weekend, and if that still doesnt work, then I may pinch off that return line, and see what happens.
I really appreciate all of the suggestions guys. I wish I didnt have to keep buying parts so I could buy a membership here!!!

 

[kirkallen143]

How good is your power supply to the pump? Usually on that long of a run of wire from the battery, one needs a relay so you have a constant supply of voltage all the time.
Making sure your pump is big enough, heres the equation:

Fuel needed = Hp (horse power) * BSFC (brake specific fuel consumption)

fuel needed = 350 Hp (guessing here) * .55 (average for a BBC)

fuel needed = 192.5 lbs/hr (divide by 6, because gas weighs @ 6 lbs/gal)

fuel needed = 32.1 gal/hr (this would be for an engine rated at 350 horsepower, lesser Hp = lesser pump needed)

So your 36GPH pump is enough from the equation above if you only put out 350Hp.

And don't rule out the ignition, alot of fuel problems thought to be ended up being ignition problems. The module and/or pickup coil in the dizzy will act like this, once it gets hot the engine will die on you. It has happened to me before.

Good luck,

Kirk

 

[Kp]

Thanks Kirk!!!
I'd be surprised if that engine in stock trim with the 236(peanut port) heads is putting out more than 300hp.
I have pretty much convinced myself that the fuel pump is not the issue. I popped the line to the carb when the truck was having problems, and it was flowing fine.
Also, I had the same problem with the mechanical pump before I put in the electric.
Ignition is definitely on the list, but I've got to exhaust all of the low dollar possibilites before I throw any more big $ at it.
I have been eyeing some MSD HEI parts in the summit catalog tho.....

 

[kirkallen143]

No problem. I would stay with the stock ignition parts, the stock items will suffice for a stock build. The HEI already puts out enough electricity even for a slightly modified engine. A stock module and pickup coil are cheaper, and readily available and every auto parts house.

Kirk

 

[Kp]

Just wanted to say thanks to everyone who posted, and let you know that the truck is fixed.
I picked up the carb spacer,(Mr. Gasket # 3406), and put it on on Saturday.
Drove the truck about 40 miles in the heat of the afternoon, and it never stalled out, even on full throttle accelerations.
I did have two problems with the Mr. Gasket kit though.
First, one of the studs they supplied was fubar'd. It was turned down so far that the supplied nut just slid over it. The other 3 were fine, but that one was no good. I had to make my own .
Also, I had to grind the spacer for clearance at the throttle shaft. On the pass side, opposite the linkage. The shaft goes thru the carb, and there is an adjustment there that hit the spacer. Couldn't even crack the throttle. I just used the grinder to take the spacer back to flush with the carb body. Now it clears just fine, and seals fine too.
Truck runs fine. Thanks again!
Now I just need to charge my A/C...................