PDA

View Full Version : stupid carb question/problem



Moose
05-03-2005, 11:45 AM
i've got an edelbrock 400 bolted onto an edelbrock 1400 in my '78 bronco w/a 6.6L engine. the problem started as soon as the weather got warmer last month (so the old people say), after i went through my first tank of premium gas w/OUT a lead additive, and after installing a new set of rebuilt heads w/new hardened valve seats. as soon as i filled the tank with gas and an STP lead additive, at idle in drive, the engine would stutter. rpm got real low like it wasn't getting enough fuel. stalled a couple times. won't stall as long as i keep my right foot on the gas, and left foot on the brake. driving, it does fine, unless i'm going under 25 mph.

one afternoon of frustration, i floored it, the stutter went away. that evening i drove it 25 miles, no problems. then it started again the next day. had a guy from work that knew about carbs re-adjust it, fixed the stutter again. that was a month ago, no problems since then. same tank of gas. this morning, tried to drive it to work, started stuttering again.

i was told:

1) maybe the lead additive burned the fuel pump diaphram

2) the fuel filter was dirty (replaced, nothing changed)

3) unscrew the two idle adjustment screws in the front, spray carb cleaner in there and blow it out with compressed air, and pull a couple star bolts on the top and spray carb cleaner in there too

4) i got water in my gas; use "dry gas" or "heet"

5) vapor lock; loosen fuel cap (this could be an option since every time i top the tank off, this happens, and it usually goes away after i drive it a couple miles. and it's the original gas cap)

6) not enough fuel pressure (if so, then why does it come back alive every other time)

7) sending unit strainer clogged

and don't tell me to trash the edelbrock carb. it's run in this truck for a year, no problems.

jerryg79
05-03-2005, 11:57 AM
is the carb 400cfm, I ran a 650 4barrel on my 351M, is that 2-barrel or some ****. Why are you using lead additive, I never used it on mine, it seems like you like to waste your money on extraneous things.

Have you thought about rejetting it, I always needed to do that, mine would backfire through the carb, if you really got on it.

I think it was James that used to get Vapor Lock real bad on his 400, i think he routed the fuel line way out around the motor to keep it out of the heat.

I'm assuming you did away with the mechanical fuel pump?

mudtoy67
05-03-2005, 11:57 AM
Why are you running lead? Very high compression? The only people I see running lead are race cars running race fuel. The race fuel has a lot more octane than regular gas. I'm wondering if adding lead to regular gas may be causing some of the problem.

stx4wheeler
05-03-2005, 12:28 PM
a two barrel will run fine on that motor cause thats what im running in the 7.5L, i would think as well that it is the lead additive messing something up, as jerry said is the fuel pump electirc or manual if manual your pump could be trashed.

jerryg79
05-03-2005, 01:56 PM
a two barrel will run fine on that motor cause thats what im running in the 7.5L,

What is the world coming to when we use YOUR Bronco to guage what will and will not work......

:flipoff2:

BMFScout
05-03-2005, 02:40 PM
I think the solution is for you to sell me the camaro...cheap.

If you put in hardened exhaust seats, I don't understand the lead additive, not necessary. I say it's the carb, but heck if I know what's wrong.

Helpful as always Fred, what a d!ck...;)

Moose
05-03-2005, 03:41 PM
is the carb 400cfm, I ran a 650 4barrel on my 351M, is that 2-barrel or some ****. Why are you using lead additive, I never used it on mine, it seems like you like to waste your money on extraneous things.

Have you thought about rejetting it, I always needed to do that, mine would backfire through the carb, if you really got on it.

I think it was James that used to get Vapor Lock real bad on his 400, i think he routed the fuel line way out around the motor to keep it out of the heat.

I'm assuming you did away with the mechanical fuel pump?

thanks for the reply jerry,

the carb is a 600 cfm 4bl edelbrock.

well, the machine shop told me to... sort of. before i rebuilt the heads for the 2nd time, the valvetrain went to shat. i brought them to him, and he told me he just put regular seats in there, and i should have used a lead additive (i didn't know that). so he rebuilt them for nothing the second time with hardened seats and said now i won't need a lead additive. but because of the lack of an additive the first time, i'm phobic w/out it. so i asked if i could still use the addititve with the hardened seats. he told me it wouldn't hurt, if anything it will help.

why would i do away with the mechanical fuel pump? the heads were only ported around the exhaust seats to allow for a little more fuel/air to go around the valve when openned. the chambers and cam are stock size.

Moose
05-03-2005, 03:46 PM
Why are you running lead? Very high compression? The only people I see running lead are race cars running race fuel. The race fuel has a lot more octane than regular gas. I'm wondering if adding lead to regular gas may be causing some of the problem.

bryan,

lead: see above post.

i'm starting to think maybe the additive is causing the problem. i'll call the machine shop and see what he says.

jerryg79
05-03-2005, 03:47 PM
Maybe I'm dumb, if you have a mechanical fuel pump, you dont have a sending unit do you? I thought that was for electrical in-tank fuel pumps. I thought the whole unit for a mechanical fuel pump was attached to the side of the block minus an in-line filter. Hence the vapor lock. Maybe I'm wrong.

Moose
05-03-2005, 03:51 PM
a two barrel will run fine on that motor cause thats what im running in the 7.5L, i would think as well that it is the lead additive messing something up, as jerry said is the fuel pump electirc or manual if manual your pump could be trashed.

kevin,

it actually does pretty good on gas. performance is good. i'm gonna leave well enough alone.

i'll try to replace the fuel pump this weekend.

73bronco
05-03-2005, 05:14 PM
sounds like the carb isnt adjusted right to me. try swaping another carb on and see how she runs

stx4wheeler
05-03-2005, 05:34 PM
kevin,

it actually does pretty good on gas. performance is good. i'm gonna leave well enough alone.

i'll try to replace the fuel pump this weekend.


the first part of my reply was for jery when asking if it was a two barrel or four,
i dont have that much of a performance motor either and i would run an electric pump on it, it isnta whole lot more expensive(orieley brand) than a mechanical, and i noticed alot better starting(after periods of the truck setting a couple weeks) and a little better running when i went from mechanical to electric. plus it was pretty dang easy to install.
if you need i can get you the part # of my electric pump if you wanna go that route. good luck man

agjohn02
05-03-2005, 06:02 PM
Maybe I'm dumb, if you have a mechanical fuel pump, you dont have a sending unit do you? I thought that was for electrical in-tank fuel pumps. I thought the whole unit for a mechanical fuel pump was attached to the side of the block minus an in-line filter. Hence the vapor lock. Maybe I'm wrong.


its the thing in the tank with the fuel gauge on it. it "sends" to the gauge. its also got a sock on it for filtration.

fbronco86
05-03-2005, 06:26 PM
get fuel injection

robertf03
05-03-2005, 06:40 PM
don't need no gas

Graystroke
05-03-2005, 09:14 PM
first, you don't need lead additive as jimmy pointed out if you have hardened seats. It's to keep the exhaust valves from burning if you didn't have hardened seats. I'm suprised ferd still had unhardened seats in '78..but it is a truck and that was about the time everything was starting to switch over to unleaded.
the mechanical pump is fine. don't listen to these yahoos and start throwing money at it until you figure out the problem.
you said it happens when you top off the tank. check the vent line for blockage. the pump may be oveworked if there is no vent.
also check the lines for cracks or dry rot. may have a split somewhere which would cause your mechanical pump to suck air. if these don't fix it check the pick-up on the tank.

Moose
05-04-2005, 08:17 AM
first, you don't need lead additive as jimmy pointed out if you have hardened seats. It's to keep the exhaust valves from burning if you didn't have hardened seats. I'm suprised ferd still had unhardened seats in '78..but it is a truck and that was about the time everything was starting to switch over to unleaded.
the mechanical pump is fine. don't listen to these yahoos and start throwing money at it until you figure out the problem.
you said it happens when you top off the tank. check the vent line for blockage. the pump may be oveworked if there is no vent.
also check the lines for cracks or dry rot. may have a split somewhere which would cause your mechanical pump to suck air. if these don't fix it check the pick-up on the tank.

this sounds more logical. vent lines? you mean the emissions hoses? i took 90% of those off when the EGR was blocked off when the intake was swapped long before i owned it. the only vent lines i can think of would be on the drivetrain. is there one on the tank? i'll check on the pickup. thanks.

jerryg79
05-04-2005, 08:21 AM
this sounds more logical. vent lines? you mean the emissions hoses? i took 90% of those off when the EGR was blocked off when the intake was swapped long before i owned it. the only vent lines i can think of would be on the drivetrain. is there one on the tank? i'll check on the pickup. thanks.

there's a vent line on the gas tank, it lets the air out as you fill up the tank, else gas would shoot out as you displaced the air in the empty tank.

But dont listen to us yahoos, I mean fuel pump quite the off the wall suggestion, cause they dont suck at all on those motors :flipoff2:

Moose
05-04-2005, 11:03 AM
drove it last night to see if maybe it'd go away like it's done before (didn't have much time after work). nope. it did backfire a little on take-offs. and now, i can smell gas... like the choke is sticking?

agjohn02
05-04-2005, 12:30 PM
i had venting problems with my tank before i put the pump in it. it never affected the way the engine ran, but it would push fuel out when the tank got warm from sitting in the sun. oh yeah, and jerry's right, it'll shoot fuel at you when you fill up.

the choke idea sounds pretty good to me.

73bronco
05-04-2005, 01:54 PM
I dont even have a vent on my tank and no problems and if its carb there should be no return lines.

Violentv8toy
05-04-2005, 03:48 PM
sorry to hi-jack, but what happens if you do have a return line for a carb?

i've always had a little bit of fuel problems, and i run a return line. Should i block it off?

Graystroke
05-04-2005, 09:20 PM
I meant don't listen to the crap about putting on a electric pump. Also, does you carb have an accelerator pump that can be blown out like Holley's? It only takes one backfire through the carb to blow the diaphram.
I had a sticking choke on a Holley I had on my old '63 Chevy. The choke would hang if it backfired and you had to beat it loose w/ a hammer! It was a manual choke...if this is the case it shouldn't run at all.
it's easy to check the pump...disconnect the line at the carb, add some hose and aim it where you can see it squirt and crank the engine w/ the coil wire removed. it should squirt across the driveway.

Moose
05-05-2005, 08:44 AM
alright. i'll check that stuff. it sticks shut. shut means lack of air, too much fuel; therefore the smell of gasoline, right?

Moose
05-05-2005, 04:58 PM
don't laugh. summit sells the parts i have, so i emailed them basically the same thing i wrote at the top. this is what brad had to say:

Discussion Thread
---------------------------------------------------------------
Response (Brad) - 05/05/2005 12:45 PM
Two quick things here.
1) You don't need the lead additive since you have hardened seats now.
2) Don't use higher octane than what the engine requires.

That said, I think you answered your own question;

"5) vapor lock; loosen fuel cap (this could be an option since every
time i top the tank off, this happens, and it usually goes away after i
drive it a couple miles. and it's the original gas cap"

Now, let me explain vapor lock. Vapor lock usually happens after a
short stop, or long idle period, and shows up as a sag on acceleration,
which usually stalls the engine. Cold weather doesn't do it. Look for the
following;

*No black smoke from tail pipe.
*No fuel pressure.
*Dry carburetor air horn.
*No accelerator pump discharge.

Now, there is also fuel foaming. This happens after a fillup of fresh
fuel, when cold fuel hits a hot carburetor. It will show as a sag, or a
series of short jerks on acceleration, also stalling the engine.

Look for the following;

*Black smoke out tail pipe
*Normal fuel pressure
*Normal accelerator pump discharge
*Engine starts after a long, wide open throttle crank.

Want more?

Alcohol mixtures and octane boosters effect the volatility of the fuel,
with hard starting, and driveability issues.

How to fix it?
*An electric fuel pump near the tank pressurizes the fuel lines, and
prevents vapor lock. A mechanical pump has a vacuum, which causes the
fuel to more easily turn to vapor.

*Insulate the carb, and fuel lines from heat sources.

*Eliminate any sharp bends or kinks in the fuel supply lines.

*Use a vapor separator filter, and a return back to the tank. (rarely
done)

*PICK YOUR GAS STATION BASED ON EXPERIENCE WITH THEIR PRODUCTS!

*Avoid alcohol, and octane boosters.

Hope that helps.

Brad

Auto-Response - 05/03/2005 12:55 PM
Technical Support

i already replied with some of the same things discussed here. it's starting to basically sound like i just need to shoot some carb cleaner in there.

it was interesting to see what he had to say about the electric fuel pump.

uglyota
05-05-2005, 07:14 PM
wow...and I thought the Summit employees were all Wal-mart castoffs

Moose
05-08-2005, 07:50 PM
it's the electric choke. after a medium or more throttle, the flap thingy wants to stay open too much. so, i can either swap it or use it for a cool paper weight that smells like gas or adjust the choke (http://www.edelbrock.com/automotive/index.html) or adjust the float (http://www.edelbrock.com/automotive/index.html). neither of which i know how to do. looks like i have to go to school again dammit!

73bronco
05-09-2005, 04:42 PM
choke isnt hard to adjust. While your engine if off and cool just losen the 3 screws that hold it down and turn it until the flap is almost closed. You're all set just make a few minor adjustments later for how you like it.

Moose
05-13-2005, 08:09 AM
choke on the edelbrock carb was a b!tch to adjust. they want you to unbolt the cap, measure how much the wing thing falls... no more than a 1/4 inch...? the pictures were terrible. their drawings looked nothing like the carb.

so i swapped it for a holley. NIGHT AND DAY! runs like she did before i left well enough alone, except w/out the blown head gasket. it's easy to adjust too. the response time after adjustments are none. if i turned one of the screws on the edelbrock, nothing would happen, so i'd turn another screw, then nothing would happen. then something would happen, and i didn't know which adjustment changed something... nightmare. it was so out of whack by that time... had to start everything back over again.

i'm an idiot mechanic and even i can adjust this thing. edelbrock should have just stayed in the air transportation department and left fuel delivery alone. now i know what everyone is talking about when they're discussing float bowls, sight levels, and jets, etc.

only thing is: now i know why carbs (at least holley) are so bad for off-highway vehicles. those float bowls are kinda sensitive. if you stop too hard at a stoplight/sign, she'll tend to drop in rpm, then pick back up after stabilization. the edelbrock didn't have that problem. that's why it was such a b!tch to adjust the floats on that one. but i already know how to fix the holley. but holley already sells a jet kit for off-road.