Bronco doesn't stay running after warm up

[gladrich]

Left the Bronco in the barn for the winter. Started it up a few times over the winter with no problem. Needed to get inspection done so I started it up and it ran for about 3 minutes. It was running rough and then died. I started it back up and it died imediately. So thats where it stands now. I let it cool down then start it up and it runs rough and dies then I restart it and it dies imediately. when I removed to air cleaner I noticed some mouse droppings on the intake manifold but I didn't see anything in the carborator. I checked all of the hoses thinking maybe a mouse chewed one and caused a vacuum leak but they all look OK. I then statrted tracing wires to try and see if they had bitten through any but I didn't see any. I started it up in the dark and looked for sparks, didn't see any. I checkeed the timing when it was running for the three minutes and it was right where it should be. I then changed the fuel filter, checked that I was getting spark on all the cylinders, did a compression test on all the cylinders. Non of which made any difference.
It is a 302 with Edelbrock manifold and a Holley street avenger carb. Compression test ran anywhere from 120 to 100. Most were at 118. Only 1 at 100.
I'm not sure what to do next so if you have any ideas please let know. THANKS!!

 

[blade]

Was the fuel filter clogged? If it was you could possibly have junk farther back in the line that is creating a restriction. Possibly on the pickup tube in the tank. Is there a second filter inline somewhere?

 

[blade]

If you only have a filter on the carb then it could be junk in the fuel pump.
I recently went through the same thing on my wifes 69 mustang, Same symptoms, it was varnish from old fuel blocking everything up.

 

[gladrich]

I don’t think the filter was clogged. The only filter I know of is right at the carb. It is clear plastic and I can see that it is full of gasoline.

 

[Slowleak]

What is the choke doing thru all this? Is it opening, staying shut?

 

[blade]

Did you check the fuel level in the tank, if it's dual tanks is the switch on the right tank? Thought I would ask just in case.

 

[gladrich]

The choke is opened just a little And opens a little more as it runs the 3 minuets. it has been hot here and probably 85-90 in the barn.
I’m pretty sure that I am on the right tank. I’ll move the switch to make sure. I really appreciate your input guys.

 

[Slowleak]

Three minutes is a long time at those temps. By then it should be fully open. If not, as the engine warms it will run rich and die. In cold weather it might run fine. Crank it up, let it run a little, open the choke, and see what happens…..my choke is fully open in about 45 seconds.

 

[Bitch'nBronco]

Did you look down the carb while it was running, if its been sitting a while there's a chance your floats are sticking and it started to flood as the bowls filled back up.

 

[gladrich]

So the choke is pretty much open from the git-go since it is so warm. By the time it shuts down the choke is definitley open all the way. I have not looked down the carb when it's running. I'll give that a try. It's also backfiring before it shuts down. When I start it up it runs at about 1500 RPM then after a minute or so it starts dropping to about 1000 then goes down to near nothing and back up to 1000 about four or five times (backfiring several times) then dies. I can try to keep it running with the excellerator but it hesitates alot and still shuts down.

 

[gladrich]

I pulled the carb off , dismantled and and cleaned it up. New gaskets etc... Wasn't really much to clean. Reinstalled and still have th eproblem. I then replaced the fuel pump...same issue. I am noticing some water coming out of the exhaust pipes (More on the drivers side). and I am wondering if that might indicate a blown head gasket. Is there any way to confirm that it is or isn't a head gasket issue without ripping everything apart?

 

[73azbronco]

Do a leak down pressure check of cooling system, you can rent the tools at autozone

 

[DirtDonk]

How much water? Could just be condensation because not running long enough to evaporate normal condensation in the exhaust.

Before you replaced the pump did you look down the throat to make sure your carb had no fuel in it?
No reason to replace a perfectly good fuel pump with a possibly bad new one from the store. Not till your certain fuel isn’t pumping to the carburetor.
Which you know it is, because the engine still starts semi reliably at first.
Maybe it does fail after a few minutes running, but gas doesn’t just get there without the pump at least working initially.

So you should be checking things like that long before replacing parts.
Or did you do the diagnosing and just didn’t mention it before the latest update?
You mentioned watching the choke open up, but what happens when you partially close it again while the engine is still running?
Just wondering if it’s going too lean.

I think you mentioned being able to keep it running if you work the throttle? I’ll have to go back and read it again, but if you did that and could keep it running then you have gas.
If not, then let us know what you found when looking down the carb when it dies.

 

[73azbronco]

I'm tending to think bad gas, water in the gas as a first easy fix, drain tank, start over. Cleaning carb is a good start, but unless you have good gas, your just putting water back into the float bowls. Unless your tank was filled to neck, every night temps drop, water condenses on tank walls, and there is one drop of water, do that all winter, lots of water.

 

[YNOTBOB2007]

I've had similar problems because mine is a truck that I keep in a different location, so it only gets started every few months. It's ALWAYS been because of the carb (and fuel lacquering up the carb inlets). You might not be cleaning the right parts of the carb.....just replacing gaskets won't fix it. Make sure to remove the 2 brass jets at the base of the bowl and clean/soak those. You don't even have to remove the carb. Be careful though....the jets are soft...don't strip...use a wide blade. Also be sure the float is positioned correctly....if not, the bowl starves for fuel or floods the carb. If you plan on having times of non-use for months, I've gotten into the habit of running my carb dry by switching the tank selector to the middle....takes about 2 minutes of run time. Also, after you start it when it's not been used for awhile, get it warmed up, then floor it on the highway.....it can dislodge some tiny stuff that might be cloggomg the jets.

 

[gladrich]

I took the carb back off and replaced the accelerator pump parts and the power valves. The Bronco starts up and runs now. I have the RPMS at about 1000 when it's warm. Now when I put her in gear she really bogs down and sometimes stalls out. Not sure what I need to adjust to fix that. If I turn the idle screw up it gets a little better but I don't want to idle at 2000 RPMS.

 

[YNOTBOB2007]

I took the carb back off and replaced the accelerator pump parts and the power valves. The Bronco starts up and runs now. I have the RPMS at about 1000 when it's warm. Now when I put her in gear she really bogs down and sometimes stalls out. Not sure what I need to adjust to fix that. If I turn the idle screw up it gets a little better but I don't want to idle at 2000 RPMS.

I don't know much about the Holly carb, but the symptoms still sound like something in the carb plugging. Try this: warm up truck, take off air filter. Slowly close the throttle plate and increase the throttle at the same time It will want to die...that's normal...just keep increasing the accelerator as you slowly close the plate. This will create a huge vacuum in the carb and possibly push through a pesky granule. This works better than flooring it on the highway to clear it out. If that doesn't work, did you remove the brass jets at the bottom of the bowl and clean them? That's important. If so, then the last thing would be a complete soak of the carb (overnight) per the rebuild instructions. Do you have a PCV valve on your engine? Shake it to be sure it's rattling. If not, they are cheap so just replace it.

 

[gladrich]

I do have a PCV valve and it does rattle. No I did not remove the jets and clean them. I'll try the throttle plate trick. If that doesn't work I'll check out the jets. Appreciate the help.

 

[gladrich]

So I kept tweeking the carb and finally got it running ok.

 

[DirtDonk]

Congrats! It’s always a dance with carburetors and points ignitions.
Lots of back-and-forth and allemande left and do-se-does. But eventually things come together.