Guru's help me diagnose

As yall know I have a 78 bronco w/a 400. I'm having serious issues with a carb that is running rich. The truck runs great but it smells, and occasionally acts, like its getting too much fuel. The exhaust is the biggest giveaway as is the milage. 5.5mpg aint gunna cut it. I've been light on the throttle so a heavy right foot aint the issue. I notice that on a cold startup I pump it once and it fires up and runs great. After I shut it off, once warm, it rumbles to a start and kind of shakes. It always will start but it starts harder after its been warm and starts to cool down. My girlfriends dad is a certified mechanic and he guesses that a seal is warn out in my carb and extra fuel is leaking down from the manifold and resting in the pistons, causing the hard starts. (He also mentioned something to do with heat from the motor causing it) I'm not great at diagnosing things but before I ****k the carb up by retuning it, I was wondering what yall think is causing this?

Symptoms: hard starts after warm (and sitting for a while), occasional flooding of the engine when sitting at an idle for too long (engine nearly dies on takeoff-rare), sluggish off the line once stopped, smell of unburned gas in exhaust, shitty fuel milage.

The carb is a 600CFM edelbrock 4-barrell. I'm not sure of the exact age but it was installed between 1998 and 2000.

I really need help because it is severly limiting where I drive. I cant drive to the dump and back without going through 3 gallons of gas. Please help. Could it be a dirty needle? Bad tuning? Leaky gasket?

Other than this the truck runs very strong.

I had similar problems with a Holley carb with the electric choke. Mostly, it was not getting power and the choke stayed closed unless I jambed it open with a screwdriver or stick. If your Edelbrock has a manual choke, it could still be binding. If the butterfly doesn't open up after a bit, check the voltage at the elec choke to see if you're even getting power. And when the carb acts up on you (runs rough after warm-up), pull the air cleaner lid and see if the butterfly is closed or if it's open as it should be. JSM84

I agree, it sounds like the choke is working fine when cold but the choke thermostat is not pulling it off all the way.

If it were me I wet get rid of that old Holley carb and get an Edelbrock. I used an Edelbrock on my Bronco and it works great.

im having the same problem with my holley, look between the elec housing for the choke and the carb there is a plastic clip, red i belive, it might be broken mine is and i got the same problem

the carb does have some choke issues but nothing that would cause this. The choke is electric and tends to stick open and gradually increase the motors rpms. I dont care about that because all I do is tap the gas and boom, regular idle. I just really am struggling with this problem. This has been a grea carb and runs 10x better than the old holley we had (with a power valve :puke) this is just one issue and is holding back my motor in not only performance but mpg. I really need some help from the experts. What the hell would cause this?

did you get a look at that clip?

why don't you temporarily disconnect the choke, and see if it makes a difference?
i run the same carb on my truck, and never touched it.

the carb does have some choke issues but nothing that would cause this. The choke is electric and tends to stick open and gradually increase the motors rpms. I dont care about that because all I do is tap the gas and boom, regular idle. I just really am struggling with this problem. This has been a grea carb and runs 10x better than the old holley we had (with a power valve :puke) this is just one issue and is holding back my motor in not only performance but mpg. I really need some help from the experts. What the hell would cause this?

That helps narrow it down somewhat. Some of us 'old school' carb guys can listen to a carb while the engine is running, and tell what's wrong. Kinda hard to do over the web. Sounds as if your choke may be sticking a bit, but open rather than closed? I think you're on track with the problem being a flooding condition, or too rich an air/fuel ratio. Couple other things you can check. There are two idle adjustment screws on the front of your Edelbrock carb, assuming it's a 1400-series 600cfm. try turning one or the other (right one first) 1/4 turn to see if and how it affects your condition. you're not going to throw it completely out of tune unless you go like 1 or more complete turns of either screw. It will begin to stumble or stall if you go too far. your idle should be around 700-800 RPM. That's really the only adjustment I've had to make on my 1405 (manual choke) on the 85 Chevy truck. You can also call the technical hotline number: (310) 782-2900 and talk to an Edelbrock rep about your problem. JSM84

That helps narrow it down somewhat. Some of us 'old school' carb guys can listen to a carb while the engine is running, and tell what's wrong. Kinda hard to do over the web. Sounds as if your choke may be sticking a bit, but open rather than closed? I think you're on track with the problem being a flooding condition, or too rich an air/fuel ratio. Couple other things you can check. There are two idle adjustment screws on the front of your Edelbrock carb, assuming it's a 1400-series 600cfm. try turning one or the other (right one first) 1/4 turn to see if and how it affects your condition. you're not going to throw it completely out of tune unless you go like 1 or more complete turns of either screw. It will begin to stumble or stall if you go too far. your idle should be around 700-800 RPM. That's really the only adjustment I've had to make on my 1405 (manual choke) on the 85 Chevy truck. You can also call the technical hotline number: (310) 782-2900 and talk to an Edelbrock rep about your problem. JSM84
What is the baseline setting for those idle screws? In case he goes too far & doesn't keep track of how far he has turned it.

Do you run them in gently till closed & then open 3 turns?

Poor mileage COULD be too big primary jets or your choke butterfly is not opening fully which would cause the motor to not be getting enough air. 5.5 MPG is not good.

Last point. The fast idle cam is a different issue. It is of course related to the choke but it doesn't nescessarily mean that your choke is malfunctioning.

It is clear you don't have the skills to overhaul the carb yourself. Try & find an old school mechanic to do it for you. I would strongly caution you to not use the GF father.

In the old days you could find small garages who worked on electrical, brakes timing carbs etc.

Nowadays it's all big shops like Sears auto centers & Meineke. I'll bet you can find a carb guru if you look hard enough.

Ranger - his carb is Edelbrock!!!

Yep ,about 3 turns from closed. I only suggest small increments of 1/4 turn to smooth out the idle. one step at a time. Edelbrock also has a website to go to for tech help.

If I could I would like to avoid tuning until I elminate the possibility of other problems, or is that just not an option...

Remember too that the Edelbrock Performer carbs are some of the most easily tunable carbs ever made. If you bought the carb used, are you sure the PO didn't royally screw it up? Tuning kits are affordable and readily available, once you make sure the mechanical stuff like the choke and floats are good, it's time to dig into tuning.

Just so you're aware, the power valve springs, enrichment needles, main jets, secondary air valve, floats, needles and seats, and air bleeds are all tunable and easy to get to, which means they're also easy to get wrong. You might want to check with Edelbrock tech to find out what the stock tune is so you know you have a good starting point.

Bronco Kid has a Holley carb.

The idle adjustment screws are 1 1/2 turns out or 3 full turns. I would try to adjust those by 1/2 turns. Screw them in and count how many times that it takes to turn them in till they seat. don't crank them down hard and use a small screwdriver.

Also make sure the choke is coming off all the way. Double check to make sure the flap is open all the way once warmed up.

You may also want to check the timing, make sure it is on. Check the timing chain as well by turning the harmonic balancer bolt back and forth and watch the dizzy rotor to see if there is any slop in it.

I doubt if the heat is playing any affect on the carb.

LMAO

As yall know I have a 78 bronco w/a 400.

The carb is a 600CFM edelbrock 4-barrell. I'm not sure of the exact age but it was installed between 1998 and 2000.



:doh0715:

its edelbrock. asked my dad and he said it was 2003 or so. I thought it was on I took the air filter off today and cleaned it because of how shitty my truck is running. Talked to a few people and both the mechanics I know said I should try playing with the metering rods (try some larger and some smaller). Both happened to have a spare 600cfm edelbrock carb layin around and they said they would give me the metering rods and help me play with tuning it. Hopefully I can get to 7mpg. 8 is my goal. 10 would be a godsend. Either way I will keep you updated.

Do what Ranger suggested first or you're just chasing your tail!

Especially if the carb has been on awhile and used to run fine.......you don't need to play with metering rods.

how does it run at WOT or higher RPM's? If it is getting too much fuel under these conditions also then it will be hesitant and sluggish you will still probably smell raw fuel and performance will be lacking; However, im guessing it would run fine under those conditions b\c your throttle plates will be wide open and you should have a decent mixture (air & fuel). im thinking u should stick to the old "guru's" on here and seriously check out that choke situation.
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