Ford 3000 missing under load

[RedDawg]

I got a 1968 Ford 3000 gasser last year but this is the first time I’ve had a chance to put it under a good load. I went through it when I first got it replacing fluids and adjusting things. It only got used a few hours bush hogging and such. Yesterday and today I was pulling a Ford 2-14 plow through this heavy clay soil up here on my ridge. The first hour yesterday went great. Lots of power and smooth. Then under load I started losing power. It wasn’t firing on all cylinders. It got to the point that from a dead stop I couldn’t let the clutch out and get rolling even with the plow up. It was missing so bad it died. I tried restarting it and all I got was a ‘click’.

I opened the hood and a simple touch of the positive battery cable showed it was loose. I had run as far as I could since it wasn’t charging the battery. I have the original generator and all the original ignition components. (I do have an electric fuel pump.) So, I hooked up the trickle charger and let it sit last night. I went out and fired it up this morning and it ran great. About an hour in it started doing the same thing. I quickly checked the battery cables and they were fine. The generator was putting almost 16 volts to the battery.

I was able to finish my plowing since it didn’t get as bad as the day before. But under load it was missing. When it wasn’t under load it was smooth and firing on all cylinders. I’m thinking the coil might be getting hot and start getting intermittent. But, before throwing parts at it – and since I have to run it for an hour before I can get it to do it again – how should I diagnose this? Thanks for the help.

 

[old]

Check the spark at all 4 wires the center wire on the cap then the 3 spark plug wires. Make sure you have a good blue/white spark that jumps a 1/4 inch gap or more at all 4.
Then take it out and run it hard and as soon as it starts to miss check the spark and make sure it is still that good blue/white spark that jumps that gap. If you still have good spark try removing the gas cap and see if it runs good that way. You might have a clogged gas tank vent. Also when you open up the gas cap listen for a suck to blow sound when you take it off. A sound like either will say the vent is clogged up

 

[RM-MN]

Check that you have a good flow of gas to the carburetor too. My Ford has a glass bowl with a filter in it and that filter will restrict the flow of fuel just enough to make it run low when pulling hard.

 

[RedDawg]

Old and RM-MN, thanks for the ideas. I didn't mention that I did check the gas flow right away. There was no vapor lock on the gas cap. And I had good flow at the carb.

As for checking the spark, I'm trying to figure out how to do that since when it isn't under load it runs smooth as if all plugs are firing. It only happens when it is good and warm and it is under a heady load (an hour of plowing heavy clay). I got my plowing done so I'll have to find another project to put it under load and carry a spark plug when that happens and quick jump off and try each wire.

Hope I can figure it out. I got the 3000 because the old 640 was having a fit with this clay up here.

Thanks again.

 

[old]

A good running 640 should be able to keep up and do with a 300 does all day long. Have you also pulled the carb drain plug and made sure you have a steady flow of gas for 3 minutes that will fill a pint jar in less then that time?

 

[RedDawg]

(quoted from post at 16:41:17 02/14/16) A good running 640 should be able to keep up and do with a 300 does all day long. Have you also pulled the carb drain plug and made sure you have a steady flow of gas for 3 minutes that will fill a pint jar in less then that time?

Nope, I pulled the line from the electric fuel pump to the carb and checked there. I'll pull the plug on the bowl and try that.

The 640 runs good but that 2-14 plow and this clay is a struggle...

 

[old]

I understand the clay problem. I have a 841 and a 2-16 plow and it does not like the heavy clay I have here in Missouri.

 

[Sean in PA]

(quoted from post at 19:46:19 02/14/16)

Nope, I pulled the line from the electric fuel pump to the carb and checked there. I'll pull the plug on the bowl and try that.

The 640 runs good but that 2-14 plow and this clay is a struggle...

That 3000 did not come from the factory with an electric fuel pump. It came with a mechanical fuel pump mounted up on the front of the engine. Perhaps the electric fuel pump that is on there cannot supply quite enough fuel when the engine is under a heavy load for an extended period. The carburetor is controlled by a governor, and the governor will cause more fuel to flow for a given rpm when the engine has more load, so a fuel pump that otherwise is supplying plenty of fuel might not be able to keep up when the engine is running at high rpm's under a heavy load.

 

[RedDawg]

(quoted from post at 17:27:18 02/14/16)

(quoted from post at 19:46:19 02/14/16)

Nope, I pulled the line from the electric fuel pump to the carb and checked there. I'll pull the plug on the bowl and try that.

The 640 runs good but that 2-14 plow and this clay is a struggle...

That 3000 did not come from the factory with an electric fuel pump. It came with a mechanical fuel pump mounted up on the front of the engine. Perhaps the electric fuel pump that is on there cannot supply quite enough fuel when the engine is under a heavy load for an extended period. The carburetor is controlled by a governor, and the governor will cause more fuel to flow for a given rpm when the engine has more load, so a fuel pump that otherwise is supplying plenty of fuel might not be able to keep up when the engine is running at high rpm's under a heavy load.

I know the 300 didn't come with that fuel pump originally which is why I made mention of it in the original email. And I'd relplace it if I could fine the original lines again. I appreciate the insight and am still open to it being a fuel issue however I fail to understand how it could keep up for the first hour of heavy work but not the second hour.

I know the first day was an electrical problem with the loose battery cable. That's why I'm more convinced it's an electrical issue but I'll investigate everything.

Keep it coming.

 

[RedDawg]

Good steady flow of fuel from the bottom of the carb for several minutes. I'm going to see what the electrical components look like.