Still not running right

[recoiljunky]

I've been tring for a couple of months now to get this thing right but still no luck:

Stock 302, new Edelbrock intake, new Holley 470 TA carb, new Duraspark dizzy and control module, new plugs and new wires. NP435 transmission, 3.50 gears, 35" tires.

When you really get on it it breaks apart in it's mid-power range. If you let off the accelerator slightly it will recouperate. Initially I thought it was a bog (as in too much fuel) but now I'm not sure. It does this weather the motor is warm or cold.

I have adjusted the timing using a vaccum guage. It pulls a steady 20 psi of vaccum. The spark advanced is hooked to the correct, metered vaccum port on the carb. I have swapped in every vaccum secondary spring into the carb but they all allow the motor to break up.

I have suspected that it may be a fuel starvation issue. Maybe the bowls are getting sucked dry, then filling back up when I let off. The floats are set to the proper level, just at the bottom edge of the sight window. The fuel filter is clean and the line and tank are clean as well. I'm still running a mechanical fuel pump.

The motor idles fine and runs pretty good as long as you don't keep it floored for over 5 or 6 seconds.

Any ideas?

 

[Pa PITT]

Do you not have another carb or another bronco buddy to swap one off of to see if it'll run with another carb....I guess there is a million of those carb out there running good ..But I've read of a lot of them causing trouble ....But I fugure we're only hearing of the bad ones...
Keep us informed ......alway nice to hear of that stupid fix after a2 month trial .....

 

[broncnaz]

I would concur with the fuel starvation possibility. but have a few other concerns thatare more likely but first. Have you checked your jetting after a full or near full throttle run? a old or weak mechanical pump might not be able to keep up with the demand.
My other guess might be to much timing might try backing it off or unhooking the vacuum advance see if it make any differance.
I think this may be you biggest issue. Your overall gearing issue 35" tires and 3.50 gears are far from optimal. A small carb on a small engine in a heavy ill geared vehicle will cause the secondaries quicker that could be why even changing the springs makes little differance you might have to try putting in a heavy spring and a light spring to see if that makes any differance.

 

[Broncobowsher]

That sounds like fuel starvation to me as well.
If you can hook up a fuel pressure gauge at the carb and tape it to the windshield. Go flog it and see if the pressure drops off under load. I bet it does.

My boat had a similer problem. under load it would go into lean surge. Mechanical fuel pump wasn't up to the volume task (pressure was fine)

 

[br0nc0xrapt0r]

I know whats wrong the "Holley TA" part no really mine wasn't a TA but I had the same problem only far far far more severe I put on an edelbrock 500cfm started the truck without any adjustments and I never looked back.

 

[bax]

Can I ask what was done to the motor before you had this trouble?

 

[recoiljunky]

Can I ask what was done to the motor before you had this trouble?

I got it a few months ago and it didn't run right. I pulled the tank, cleaned it, replaced the fuel lines and filter, replaced the dizzy and control module, swapped the intake and carb, replaced the plugs and wires, ran a new vacuum line to the brake booster (which probably has a slight leak; I can hear it hiss when I shut the motor down.)

 

[recoiljunky]

That sounds like fuel starvation to me as well.
If you can hook up a fuel pressure gauge at the carb and tape it to the windshield. Go flog it and see if the pressure drops off under load. I bet it does.

My boat had a similer problem. under load it would go into lean surge. Mechanical fuel pump wasn't up to the volume task (pressure was fine)

I may give that a try today or I might just swap the pump; I haven't decided yet.

 

[recoiljunky]

I would concur with the fuel starvation possibility. but have a few other concerns thatare more likely but first. Have you checked your jetting after a full or near full throttle run? a old or weak mechanical pump might not be able to keep up with the demand.
My other guess might be to much timing might try backing it off or unhooking the vacuum advance see if it make any differance.
I think this may be you biggest issue. Your overall gearing issue 35" tires and 3.50 gears are far from optimal. A small carb on a small engine in a heavy ill geared vehicle will cause the secondaries quicker that could be why even changing the springs makes little differance you might have to try putting in a heavy spring and a light spring to see if that makes any differance.

I suspect it could be timing as well. I'm going to check it with a light today. As far as overall gearing, with the NP435 I don't see it as much of an issue. What would normally be considered 2nd gear is, in effect, 3rd gear for me (I just end up using Low as 1st gear.) Once I get the motor straightened out I will look into regearing the Bronco though.

 

[recoiljunky]

Do you not have another carb or another bronco buddy to swap one off of to see if it'll run with another carb....I guess there is a million of those carb out there running good ..But I've read of a lot of them causing trouble ....But I fugure we're only hearing of the bad ones...
Keep us informed ......alway nice to hear of that stupid fix after a2 month trial .....

I guess I could put the factory 2 barrel back on it but it's not really a "known good."

 

[bax]

How did you get the motor? how old is it? Do you think it has been apart?

 

[recoiljunky]

How did you get the motor? how old is it? Do you think it has been apart?

It came in the Bronco when I bought it a few months ago.

I'm sure it has been worked on. The Bronco is a '76 but the 302 has the large spark plugs (older heads.) Also, when I pulled the stock intake the rtv looked new, as if the PO pulled an aftermarket intake off and threw on the old stocker.

The motor pulls good vaccum, doesn't smoke and generally runs good except for the breaking up at mid power thing.

The timing marks seem to be missing from the engine (unless I'm just not looking in the right spot.) The motor does not drag on start up, as if the timing was advanced too much.

I'm thinking I'll just replace the fuel pump and see if that helps. A new one is sitting in the truck waiting to be installed.

 

[recoiljunky]

I would concur with the fuel starvation possibility. but have a few other concerns thatare more likely but first. Have you checked your jetting after a full or near full throttle run? a old or weak mechanical pump might not be able to keep up with the demand.
My other guess might be to much timing might try backing it off or unhooking the vacuum advance see if it make any differance.
I think this may be you biggest issue. Your overall gearing issue 35" tires and 3.50 gears are far from optimal. A small carb on a small engine in a heavy ill geared vehicle will cause the secondaries quicker that could be why even changing the springs makes little differance you might have to try putting in a heavy spring and a light spring to see if that makes any differance.

Well, my motor doesn't have a timing mark on it and the fuel pump I just bought appears to be the wrong one, so I gave unhooking the vaccum advance a try. It seemed to improve things a lot. I'm guessing I need to back off of my timing some. I wonder if I have the right advance in my dizzy. Any way to tell? It's a Duraspark.

 

[bax]

Can you check your compression. Just on one cylinder. I am wondering how down it is. Can you tell if the front of the motor has been off.

 

[Gummi Bear]

I'd do a compression leak down as well. Mine ran like poo, and created more vacuum when I lost compression on a couple of cylinders.

Do some checking around, and find a new timing pointer, it's just a simple bracket that bolts on. If your balancer is painted like mine, use a crayon, to fill those marks with a color that's highly contrasted to the color it's been painted.

 

[recoiljunky]

Can you check your compression. Just on one cylinder. I am wondering how down it is. Can you tell if the front of the motor has been off.

I don't have a compression guage.

Front of the motor? If I had to guess, I would say that it has all been taken apart at one time or another.

Fiddling with the timing is changing the condition. I plugged the vaccum advance and it started to run better. I backed off of the initial timing a grunt and it ran even better. I backed off a little more and it started to run ragged at the bottom end. I advanced the timing just enough for the bottom end to have power and the mid-upper end will break up if the vaccum advance is hooked up.

The vaccum advance is hooked up to the correct port (Holley carb, passenger side, high up near the front bowl.) Replacing the dizzy is the first thing I did when I bought this and I actually let someone else do that. I am not certain it is the right dizzy for this application (I am not familiar with which distributor goes with which application.) It is a brand new Duraspark pointless distributor with a new control module.

I guess I need to get a pointer for my timing so I can see what exactly is going on but I can't see maks on the balancer either.

 

[recoiljunky]

I'd do a compression leak down as well. Mine ran like poo, and created more vacuum when I lost compression on a couple of cylinders.

Do some checking around, and find a new timing pointer, it's just a simple bracket that bolts on. If your balancer is painted like mine, use a crayon, to fill those marks with a color that's highly contrasted to the color it's been painted.

Truthfully, I don't want to know that the compression is low. Low compression would jive with falling oil pressure at warm up, huh?

If the bottom end is wore out, I'm going to need to tune it to compensate and run it for a year before I drop that 408 stroker in it. Anyone know a good source for crate motors?

 

[airman]

I had a similar thing happen and it was timing and a primary float that was too low. It eventually blew a head gasket.

Are you missing the timing marker or do you just have a dirty balancer?

 

[recoiljunky]

I had a similar thing happen and it was timing and a primary float that was too low. It eventually blew a head gasket.

Are you missing the timing marker or do you just have a dirty balancer?

Timing marker missing and balancer dirty.

 

[Bucky]

Recoiljunky,
Mine was kind of doing the same thing. I just changed my squirter on the Carb. I guess the TA 470 comes with a 35, I happened to have a 31 in an older Carb. Changes it and it made all the difference in the world.