Bad Voltage Regulator
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
Bad Voltage Regulator
My truck has been in the restoration shop for almost a full year. The truck sat for about 6 months without being started at all. It is finally finished, and I drove it home last week with the following symptoms:
The carburetor would load up at idle and emit smoke. You can smell the over-rich mixture. In driving it home, it lacked power and the AMMETER was reading to the left of center, or on the "D" side. Both of the power windows worked, but they went up VERY slowly, and both of the turn signal blinked VERY slowly. When I got home, I discovered that the voltage regulator was defective, and so the alternator wasn't charging up the battery. The alternator itself was tested and it works fine.
Can this be why the truck is running rich and idling too low? As in, if the alternator isn't charging the battery, that would certainly explain the slow windows and blinkers. But would that also affect the ignition system, perhaps not firing the coil or the plugs completely, resulting in a richer mixture?
I checked the carburetor floats and they are fine, and the choke is working normally.
The carburetor would load up at idle and emit smoke. You can smell the over-rich mixture. In driving it home, it lacked power and the AMMETER was reading to the left of center, or on the "D" side. Both of the power windows worked, but they went up VERY slowly, and both of the turn signal blinked VERY slowly. When I got home, I discovered that the voltage regulator was defective, and so the alternator wasn't charging up the battery. The alternator itself was tested and it works fine.
Can this be why the truck is running rich and idling too low? As in, if the alternator isn't charging the battery, that would certainly explain the slow windows and blinkers. But would that also affect the ignition system, perhaps not firing the coil or the plugs completely, resulting in a richer mixture?
I checked the carburetor floats and they are fine, and the choke is working normally.
Laughing Gas
Joined: Nov 2011
Posts: 1,033
Likes: 11
From: Wausau, WI
Not sure if this is going to help you or not, but have a quick story.
Few years back I bought a new car. Shortly after, I noticed dim headlights on the way home from work. Turns out the alternator quit working and the light on the dash never came on. When I got home, I tested the voltage at the battery with the car idling. It was just a bit over 5 volts. The car still ran fine with all of the electronics in it.
The next morning, I threw a charger on it for almost an hour and took it to the dealer to have it replaced under warranty, about a 10 minute drive. By the time I parked there, it was barely running. Don't know how far down the battery was at that point, but must have been really low.
If the battery had enough juice to work the power windows, though slow, I wouldn't think it would cause much of an idling or loading up issue. BUT, anything is possible.
Few years back I bought a new car. Shortly after, I noticed dim headlights on the way home from work. Turns out the alternator quit working and the light on the dash never came on. When I got home, I tested the voltage at the battery with the car idling. It was just a bit over 5 volts. The car still ran fine with all of the electronics in it.
The next morning, I threw a charger on it for almost an hour and took it to the dealer to have it replaced under warranty, about a 10 minute drive. By the time I parked there, it was barely running. Don't know how far down the battery was at that point, but must have been really low.
If the battery had enough juice to work the power windows, though slow, I wouldn't think it would cause much of an idling or loading up issue. BUT, anything is possible.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Where low voltage shows up in a carb'd engine is a weak spark. And a weak spark will let an engine idle fairly well, but it won't let the engine develop much power. (What actually happens is that the effective cylinder pressure goes up as the load on the engine goes up, and at some point the spark won't jump across the gap in the spark plug.) So, I don't think low voltage is causing the rich mix and loading up. Instead, you have a carb problem. It could be as simple as the gas has gone bad, and gas today goes bad quickly. It can gum up the needles and seats such that they don't seal and the float level goes high.
How much have you driven it? Is the gas low enough that you can freshen it up with a bunch of new gas? Drive it out and refill?
How much have you driven it? Is the gas low enough that you can freshen it up with a bunch of new gas? Drive it out and refill?
Thread Starter
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
Where low voltage shows up in a carb'd engine is a weak spark. And a weak spark will let an engine idle fairly well, but it won't let the engine develop much power. (What actually happens is that the effective cylinder pressure goes up as the load on the engine goes up, and at some point the spark won't jump across the gap in the spark plug.) So, I don't think low voltage is causing the rich mix and loading up. Instead, you have a carb problem. It could be as simple as the gas has gone bad, and gas today goes bad quickly. It can gum up the needles and seats such that they don't seal and the float level goes high.
It idles well, just a little low. I had the idle set to 500 RPM in gear when it was running correctly, but now it dips just below that. Anything less than 500 RPM and it almost wants to stall. The idle is around 450 - 475 RPM right now in gear, which is too low and the engine is struggling.
Should I drive it like this, or is there a problem I need to look into? Because of the charging problem (I am correcting that), I have only driven it about 5 miles or so since.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Spark voltage doesn't change the fuel/air ratios. Those are completely separate variables. However, a weak spark does have a harder time firing a really lean mix.
The regulator went out on one of my trucks once, and I didn't notice it until it started missing as I accelerated. It idled fine, but got gradually worse at accelerating or running in top gear. Shift down and it was ok - until the voltage went further south.
Anyway, if you have good gas then something is amiss in the carb. Perhaps the accelerator pump or power valve died while sitting. The PV could easily do that.
The regulator went out on one of my trucks once, and I didn't notice it until it started missing as I accelerated. It idled fine, but got gradually worse at accelerating or running in top gear. Shift down and it was ok - until the voltage went further south.
Anyway, if you have good gas then something is amiss in the carb. Perhaps the accelerator pump or power valve died while sitting. The PV could easily do that.
Thread Starter
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
Spark voltage doesn't change the fuel/air ratios. Those are completely separate variables. However, a weak spark does have a harder time firing a really lean mix.
The regulator went out on one of my trucks once, and I didn't notice it until it started missing as I accelerated. It idled fine, but got gradually worse at accelerating or running in top gear. Shift down and it was ok - until the voltage went further south.
Anyway, if you have good gas then something is amiss in the carb. Perhaps the accelerator pump or power valve died while sitting. The PV could easily do that.
The regulator went out on one of my trucks once, and I didn't notice it until it started missing as I accelerated. It idled fine, but got gradually worse at accelerating or running in top gear. Shift down and it was ok - until the voltage went further south.
Anyway, if you have good gas then something is amiss in the carb. Perhaps the accelerator pump or power valve died while sitting. The PV could easily do that.
I have a spare carburetor ready to go, but I don't want to run bad gas in a freshly rebuilt carburetor. Is there a way to know if the gas is bad?
I thought about the power valve. Is there a way to test it?
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
The only way I know of to test a power valve is to pull it, suck on it, and see if it leaks.
I don't think you'll hurt anything to drive it the way it is. Yes, it is running rich but that just builds up a little carbon. So, maybe it'll clean up with driving. However, if it doesn't you could put the other carb on and see if that helps. It isn't going to ruin the carb.
I don't think you'll hurt anything to drive it the way it is. Yes, it is running rich but that just builds up a little carbon. So, maybe it'll clean up with driving. However, if it doesn't you could put the other carb on and see if that helps. It isn't going to ruin the carb.
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Lead Driver
Joined: Nov 2013
Posts: 7,180
Likes: 1,174
Okay...now I am confused. Wouldn't a weak spark from low voltage result in a richer mixture?
Should I drive it like this, or is there a problem I need to look into? Because of the charging problem (I am correcting that), I have only driven it about 5 miles or so since.
I would certainly correct the one known problem (low voltage) before worrying about the rough running. I'd be willing to bet large sums of your money on the low voltage causing poor ignition performance. That would give the same symptom as a rich mixture (gas smell in exhaust, etc.) but wouldn't actually affect the air/fuel ratio delivered by the carb.
If you really want to put your mind at ease while waiting on the repair of the voltage regulator, charge the battery fully and then see how the truck runs. It should run fine for at least a half hour off the battery. That would help you know if further troubleshooting is needed.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Was the battery sitting for that six months, and how old was it before this? Remember a defective battery presents a tremendous load to the charging system and can ruin alternator stators and roast regulators, etc.
Also consider thick coats of paint (you mention a restoration) and corrosion commonly cause all sorts of problems with charging and voltage drops, bad grounds etc where connectors and cables need clean, tight connections to bare metal.
http://aimpartsonline.com/reduce%20warranties
http://www.aa1car.com/library/voltage_drop_testing.htm
http://www.aa1car.com/library/charging_checks.htm
Also consider thick coats of paint (you mention a restoration) and corrosion commonly cause all sorts of problems with charging and voltage drops, bad grounds etc where connectors and cables need clean, tight connections to bare metal.
http://aimpartsonline.com/reduce%20warranties
http://www.aa1car.com/library/voltage_drop_testing.htm
http://www.aa1car.com/library/charging_checks.htm
Tuned
Joined: May 2015
Posts: 318
Likes: 13
From: Baltimore
A lot of Fords use stator voltage from the alternator to open the choke. If the alternator's not working, the choke would be slow to open. They also use a heat tube off of the exhaust manifold assuming it hasn't rotted off. fix the charging system first and go from there. Keith
Thread Starter
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Cargo Master
Joined: Dec 2004
Posts: 3,362
Likes: 22
From: Florence, SC
The voltage regulator was indeed bad, and that was causing the battery to discharge. A new voltage regulator fixed it, so that problem is solved. 
HOWEVER, my engine is still loading up at idle. I checked the choke and it is completely open when the engine is fully warmed up. The air filter was dirty so I replaced it with a brand new one. It runs great at every speed except for idle - and then it runs VERY rich.
As I said before, the idle speed was a little low, so I turned the idle speed screw a quarter turn to bring it back up to 550 RPM in gear. After driving it around for a good long time, the idle speed went right back to where it was before: 450 - 475 RPM....and chugging. It is still VERY rich.
The verified the mixture screws are still where they were before: 3/4 turns out on the left side, and 1 turn out on the right side.
I *suspect* I have a bad economizer valve. What do you think?
HOWEVER, my engine is still loading up at idle. I checked the choke and it is completely open when the engine is fully warmed up. The air filter was dirty so I replaced it with a brand new one. It runs great at every speed except for idle - and then it runs VERY rich.
As I said before, the idle speed was a little low, so I turned the idle speed screw a quarter turn to bring it back up to 550 RPM in gear. After driving it around for a good long time, the idle speed went right back to where it was before: 450 - 475 RPM....and chugging. It is still VERY rich.
The verified the mixture screws are still where they were before: 3/4 turns out on the left side, and 1 turn out on the right side.
Originally Posted by Gary Lewis
Anyway, if you have good gas then something is amiss in the carb. Perhaps the accelerator pump or power valve died while sitting. The PV could easily do that.
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