fuel delivery - fuel pump issue...

[pheengurs]

hey all, I've got an oddball issue with my 64, and thought I'd share it to see if anybody's had a similar problem...

The motor is a 78 C10 - 355 (350 bored .030) - 4bolt mains, with mild cam, lightly ported, cast 2.02 heads, edelbrock airgap intake, edelbrock carb, double roller timing chain, flattop pistons... a solid, good running motor...

Anyway, here's my problem: The level in the fuel filter is just fine, until the motor warms up, (enough to cycle the cooling fans a couple of times), then the level in the fuel filter starts getting lower and lower until there's barely a trickle of fuel going into it... then the motor starts running funny, missing and popping and backfiring when you hold the accelerator past 1000 rpms...

when staring at the fuel filter, as the motor cools down, you can see it slowly fill up again, and then it eventually empties... I don't know if that's normal for an old setup that doesn't have a return line

I also noticed that when the motor is warmed up, then you shut it off, there is bubbling happening in the filter. Not alot (like boiling fuel or something), but some bubbling... Now I know for a fact my gas cap does not fully seal, but the design simply doesn't allow for more than a slight pressure fit. There are no threads or like what you see on a more modern gas cap, so perhaps that's why the gas drains, as the pressure releases from the gas cap ???

I've checked all the rubber fuel lines, and they are still nice and soft, no dryness or cracking at all. There is a hard line from the sending unit on the tank that goes through the floor. From there a 12inch rubber hose connects to a 5/16 steel line that runs along the frame to near the exhaust downpipe on the passenger side. From there it's rubber to a steel U line that sets up the angle properly for the rubber line to attach to the fuel pump. From the pump, there is a 3/8 steel line running upwards to the fuel filter. From the steel line, there's a short rubber hose, then the filter, then another 12 inch rubber hose to the carb. There are no leaks anywhere.

On both the old mechanical pump and now after borrowing a friends spare mechanical fuel pump, once the fuel inlet line is attached, fuel will dribble out the fuel pump via the outlet that is to feed the carb... When the main fuel line is removed fuel flows rather freely out of it, so there's no blockage.

I don't really understand what the problem is. How could the same problem happen with both pumps? How could fuel flow just fine until the motor is fully warmed up?

Right now the motor is timed at 8 degrees advance. I held the timing light on the balancer, and revved the motor a bit, and noticed the timing retards as I rev it... IS THAT NORMAL??

Also, since coming back from maylong, my vac gauge shows a steady 11-12 at idle, instead of a steady 15-16 as it was before, and should be reading. (I confirmed this reading by running a vac tester off the manifold vacuum port, which I'm not using and is currently blocked off) AND, when I unplug the manifold vacuum port off the intake, the idle speed increases by about 100rpm or so, but the vac gauge still reads 11-12...

(do you guys use your manifold vacuum port off the intake for anything? According to the edelbrock carb manual, everything is supposed to be run off the carb...)

I re-torqued the carb nuts, the intake and exhaust manifold bolts & exhaust down-pipe bolts, thinking this might be the cause of low vac, but it changed nothing... My engine rebuilding manual say low vacuum gauge readings are most likely a leaking carb to intake gasket...

I DID, make my own carb gasket out of gasket paper. Perhaps that is a factor?

So, I'm stumped. And unless you guys come up with something, I'm gonna throw money at it. I'll buy an electric fuel pump, and I'll buy a new carb gasket, and I'm also going to buy some 3/8 fuel line, and replace the old stuff. I dunno what else to do. This is a very weird problem...

also here's a pic of the truck (a work, of course, in progress...)

[pheengurs]

anybody have any ideas???

[Alan's Classic]

Old school Kid had a similar problem. he could run about 15 miles then it would die. Wait a few minutes then it would start up and run another 15 miles. I mentioned that he should check the pick up screen in the tank and he said it was nasty. He cleaned it and the tank and the problem was fixed. This is the only suggestion I have. Good luck.

[70 Suburban]

you may have one of two filters in the inlet. one is a paper and the other is a stone.... look at that. also I would put the carb gasket on anyway. along with fuel lines. usualy if your fuel runs back to the tank with the key off then you have a leak in the fuel line.. you could aslo have a float sticking in the carb not letting the fuel in or only trickle in...

[pheengurs]

thanks guys. I forgot about the pickup on the sending unit in the tank! I'll check it out. And I'll pick up some carb cleaner too, in addition to the rest of the parts...

thanks!

[mikie 1954]

first time for this . what you discribe sounds like vaper locking . if you have headers running close to fuil line you might be getting it too hot turning the fuel to vaper. try moveing line or insulating it . if i remember right that was one reson they moved fuel pump back to tank . anyone know if i am right or wrong ?

[TheDark1]

In the early '90's I worked at used car lot and had a mid '80's Chevy truck that would run for about 15 minutes and die. Once it cooled off , it would run again. Finally changed the fuel pump and problem went away. On my '65, evertime I would rev past 5000 rpm I would lose a fuel pump a day or two later. Went with a holley red electric pump and no more problems other than the noise they make. Could be vapor lock like mikie 1954 said ,too. Check that first since it's free. Hope this helps.

[protrash64]

I had a cobbled sending unit on my 'burb tank and air would leak in the fuel lines and cause the fuel to run back into the tank. It would take forever to get the truck started, and most of the time I would have to dump fuel in the carb. Once everything was replaced it worked great.

[justbad]

Electric fuel pump will fix your problem,also will fix starting problems after long periods of non use

[sixfour4x4]

my headers create an issue with my mechanical vapor locking, but typicaly only effects my re-start. electronic pump will fix that, but my guess is sending unit or filter is your issue. hows that edelbrock carb treat you 4wheeling? i hate em only 4barrel carb i've ever found decent for wheeling is the old rochester qjets.

[aerotruk63]

May I add, nice truck!

[pheengurs]

hey thanks everyone!

so I'm sorta still having the same issue. here's what I've done thus far:

-replaced mechanical fuel pump, with a Holley Red electric Fuel pump..
-replaced carb base gasket (old one was soaked with gas!)
-replaced steel fuel line except the sending unit pickup line and the line connected to it that runs down & out of the cab. I also bent it to stay farther away from the exhaust.
-removed & cleaned (varsol & airgun blodry) steel fuel pickup screen in tank
-replaced rubber fuel line at rear with braided fuel line
-added another inline fuel filter -before- holley electric pump
-added fuel pressure gauge & new see-thru filter after holley electric pump
-confirmed no other filter in edelbrock carb unit...

after doing all of that, the fuel filter now shows a steady 1/3 full instead of going empty after it's warm... I do have a connector leak at the fuel pressure gauge, so I'll probably ditch it for now...

before calling it quits last night, I swapped in a spare edelbrock carb of the exact same type...and that base gasket was wet with gas too... I wonder if that is normal? It wasnt wet all the way around like the homemade one I had on there before... but my vacuum gauge still reads lower than it should (around 11 instead of 15)... Perhaps there's just something wrong with that carb??? I dunno I'm grasping at straws here, this problem makes no sense to me...

If the other carb makes no changes, I'm gonna yank the pickup filter in the gas tank, and see if that helps the flow... I dunno what else to do...




(hey sixfour4x4, I have to agree with you on the edelbrock... they do not like steep angles, that is for sure... so you prefer the rochesters? I have a couple in the garage, maybe I'll switch the linkage on one and try it out, or do you have any mods to make em better for wheeling???)

[ob1monkey]

If you don't mind I have a fuel related issue that may be related to this. I'm running a 3 to 5 psi electric universal pump and I think the carb is starving for fuel. when I get on it thru the first three gears it tends to bogg out in thrid until I let off for a few seconds then it's fine, alsol if i roast the tires about 20 feet in it starts bucking until I let out and then it fine. If I drive it normal no playing then it will go for hours with no problem. I've got a pretty healthy 350 supposed to be making close to 380hp,418torque. Am I running to small a pump for this. As for the problem above sounds like you are getting to much fuel if your vacumm is low try leaning out the carb with a vacumm gauge. that may help.

[fleetsidelarry]

pheengurs make sure you have a vented gas cap. vacuum advance should retard briefly when you accelerate (to stop engine from pinging). when you say timing is set at 8 degrees initial, you do mean with the vacuum advance unplugged, right?

ob1, friend of mine with a 454 was using an el-cheapo electric pump and experiencing the same problem, had to upgrade to a better pump, is your pump mounted back near the tank or up front?

[ob1monkey]

It's mounted about half way. It was a mr gasket pump that was there when I bought the truck. It ran great for the first three years until it pooped out on me. I then purchased the behind the counter universal part number 8012 for autozone,after which I punched the motor with 58 cc 305 head and a heavy cam 477/488 lift now I am running into the problem. sry that I jacked the thread. my tank is well vented and the inline filter(before pump is clear. the tank is only been in for about two years(custom no screen in tank).

[pheengurs]

ob1 - from what I've read, carbs need 5-7psi to run properly... if you're running 3-5, then that's not enough and your instinct is correct regarding fuel starvation... I'd test with another pump I know is up to par, or just save the hassle and upgrade to a better pump, considering you are running what I would consider a high performance 350...

how do you use a vac gauge to lean out a carb?


fleetsidelarry - my gas cap is an LMC truck chrome vented unit for the 64-66 year range (don't recall part#)... I know that if I park with the sideways angle pointing downward toward the gascap, it will leak out around the keyhole...so I guess it vents!?!

as for the timing, yeah, 8 degrees advance, with vac-advance off carb, and carb port temporarily plugged for the timing... and thanks for answering my question regarding the timing backing off under revvs...that makes sense.

I'm hoping to get into the garage tonight and finish this up... I want to conquer this problem already!

[ob1monkey]

there are two ways I know of to lean/adjust the carb. first is to tighten the air fuel mixture screws (while running) until it starts dying then loosen them just a bit so it smooths back out. the other is to hook a vacum gauge up to the manifold and adjust the screws back and forth to get the best vacum. I personally have used bothmethods and have had several people coment on how well my carbs are tuned. the vacum method should aslo help with the gas mileage.

I did some research on my fuel issue and found that I did purchase a 5 to 9 psi pump. I installed a fuel pressure gauge yesterday and found that it would barley hold 5psi at idle and as soon as I opened it up a bit and held it it would drop to almost 1psi. So the carb is definitly starving. I am going to move my pump further back almost on top of the tank and replace it while I'm at it.

[SIR]

...also remember that electric fuel pumps are designed to PUSH NOT PULL so get it as close to your fuel supply as you can...nice truck,good luck...

[aerotruk63]

I remember this post, dam that must have been frustrating all this time.

[aerotruk63]

Like your truck by the way, building one presently.

[protrash64]

Wow; my 'burb had the same problem and acted differently. The fuel would drain out when sitting and then would not start. Once started it would run just fine. Once it sat for about a day, no go. My fuel sender was cobbled together at that line also.....found it after replacing the fuel pump, filter and every piece of hose along the way.

Glad you found the problem.

[pheengurs]

yeah, it was super frustrating.. and costly.

but it's fixed for now...actually I ran it for quite a bit last year with that silicone goo fix...

a good thing to the cost factor however is now I've got nice shiny AN fittings an inline fuel pressure gauge and steel braided line in the engine bay...

of course the 'simple' look of the 64's engine bay in my truck is fast becoming more complex than I want it to be... She's got dual fans, and now the electric fuel pump... I'm gonna have to do something to waterproof the relays and wiring connections and/or move those to the cab...

anyway, thanks to all for their ideas and help and to the forum for being here, as it'd sure be a helluva lot harder to have this hobby without it...

[protrash64]

BTT for OK.............