4V Choke electrical voltage

Hi Gentlemen!

Following this Powerman5K's thread
https://forum.garysgaragemahal.com/Mystery-hose-tp128472.html

I was referred to this reading
https://www.garysgaragemahal.com/chokes.html
in which Gary mentions:
«​I should point out that if you install an aftermarket 4bbl carb, like a Holley, Edelbrock, or Demon in place of a Motorcraft 2bbl and use the factory electric choke wire you are going to have problems.».

The fact is that Big Brother was born with a 351W 2V.
Later, the original engine was replaced with a used 351 Cleveland 2V.
I bought the truck from my father-in-law and after couple of years got serious problems with the Cleveland, so I decided to replace the engine again.
Found a good 351W 4V, ran it as is during couple of years, than decided to make it rebuilt in 2015.

I replaced the Motorcraft 4V carburetor with a 4V Holley last 2022.

I am wondering if I should have done some modifications when Big Bro got his first 4V...

How can I verify if voltage to the choke is the right one, and if not, how to correct the problem?

And what kind of problem is caused by a to low voltage?

Thanks!

The first and most important question is whether the choke is working well or not.  Does the engine start well in most, if not all, conditions?  If so, then I wouldn't worry about how the choke is wired.  If not, then it is time to figure out how it is wired.

There are really just two voltages that you'll usually find at the choke: 7V and 12V.  The 7V comes from the stator winding of the alternator so isn't available except when the engine is actually running, not just when the key is on.  But the 12V can be available either when the engine is actually running or when the key is just on, depending on how someone wired it.

So pull the wire off the choke and put your DVM on it and turn the key on.  Do you get a voltage?  If so, how much?  Then start the engine and check again.

Another check is to see where the wire goes.  It may well go to the alternator and if it does it should be a white/black wire.  In that case you know that you should get about 7V and only when the engine is running.  And I'll bet that's what you have given that the engine originally had a 2150 carb on it.

Oh, I missed the "what kinds of problems" question.  The problem with having 7V on a 12V choke would be that the choke takes a long time to come off.  And given that it will be a delicate balance between getting enough choke to start and having it come off fast enough not to cause the engine to be so rich it stumbles.

And if you have 7V to the coil and are having problems you may be able to use the choke heater from the 2150 carb in place of the 12V heater on the Holley.

Gary, I wasn't expecting to get an answer tonight!

Gary Lewis wrote

Does the engine start well in most, if not all, conditions?

Clearly, the answer is no.
In fact, I don't remember when Big Bro started well. I am now wondering if this behavior began with the 4V engine...  And more cold is the weather, more difficult is the start.

I will make the verifications you are describing, and will come back.

Tomorrow, not tonight.


Many thanks!

Gary is quick on the draw:-)  Like gary said, 12 volts on the choke.  Most of my stuff should be in today as to change out my intake on the 351L7 this weekend.

Why not just use the Holley choke cover for the 4180? It is made for the 7V supply. I have one I bought to use on a friend's project that never happened (we are very much afraid covid got him as nothing has been seen or heard in well over a year).

Another option (and I know it works) use a relay actuated by the 7V to switch on the 12V. Yet another, Chrysler used an oil pressure switch (NO closed by pressure) and so did GM. Chrysler's was to power the choke heater on the carbureted 4 cyl engines and GM's was to turn on the electric fuel pump on EFI engines.

Ok Guys, I made a voltage test.
But probably the wrong way:
- Unplugged the choke wire and plugged the tester in the wire.
- Other end of the tester on the battery positive pole.
- Turned key on "start" position.
- Got 2.75V DC (on the 10V scale).


The engine wasn't started, kept the ignition key 1 second, just enough to read the voltage.
Do I have to completely start the engine?

Jeff - You need to put the other end of the volt meter to the negative terminal of the battery. Then turn the key to Run and measure. If you have some voltage there record it. Then start the engine and record that.

Thanks Gary!

Start crank = 3V

Engine running = 7.8V

Jeff - I looks like you are seeing the stator voltage. Given that I think you have three options:

1. Use It: You may be able to get the choke to work on that voltage, but I don't think it'll be easy or perfect. I've gotten it to work on an Edelbrock carb that expected 12V, but haven't tried it on a Holley. It sorta worked on the Eddy but it took a lot of adjusting to get it to work at all, and even then it didn't work all that well. And since you see very wide temp swings in the frozen North I don't think this will work well for you.
2. Different Choke Heater: A heater intended for stator voltage will work. Bill suggested that the heater for a 4180 is set up for that, but I think the 4180 I have is a 12V heater. So you should look to see what yours says on it. On the other hand, I suspect the heater on the 2bbl that was on the truck was designed to work with the stator voltage and should fit the Holley. In any event, a heater that's designed to work on stator voltage will work great.
3. Relay: Or you can install a relay that is pulled in via the 7.8V from the stator and supplies battery voltage to the 12V heater presently on the Holley. That the setup the 351HO's and 460's used and will work well.

Like Bill said, just swap out your old Motorcraft cap for the two spade choke cap that comes on the Holley
I see you've already cut off the female bullet connector though....

Ford uses stator power so the choke spring only gets heated if the engine is turning.
Some model year H.O. engines did have a choke relay as stock

The relay setup works well on the Edelbrock on my 351W, pulled in by the stator wire.

Thanks Gentlemen, I'll take a look to my old carb tomorrow (we had friends for dinner tonight, I wasn't able to work on the truck).
Looking at the picts that I took last summer, is it possible to confirm the model?

Talked with another friend today, about that investigation.  He said that a higher voltage will open the choke flap faster, which is not necessarily desirable under our cold weather...  Any advice about this theory?

BigBrother-84 wrote

Thanks Gentlemen, I'll take a look to my old carb tomorrow (we had friends for dinner tonight, I wasn't able to work on the truck).

Isn't that illegal in Canada?  Did you fry them?  Boil them?  Or what?  

I don't know Holley carbs so I'll let the others respond to that.  But the real question is what the black plastic choke heater says.  12V?

As for the flap opening too quickly, I don't think that will be an issue as the choke system was designed to use whatever voltage is stated on the heater.  But if you want to try to dial the choke in using the 7.8V you have now it might work.

When the engine is cold loosen the three screws holding the choke heater, but only just enough to rotate it.  With the throttle held off the idle stop a bit rotate the choke cap until you get about 1/16" of gap between the choke butterfly and the carb body.  In other words, you want the choke to almost be closed, but not quite.

Put the air cleaner back on and take the truck for a drive.  See how easily it starts and how it drives.  If it starts easily great, but if you have to pump the throttle several times to get it to start then you'll need to reset the choke to close a bit more when cold - but only a bit.  Use drill bits to gauge it.

As you drive and the coolant temp comes up note whether the engine "loads up", meaning it acts like it has too much choke.  It might even blow black smoke out the exhaust.  If that's the case then the choke isn't coming off fast enough, which is caused by too low of voltage.

On the other hand, it is remotely possible that you don't have enough choke and the engine doesn't want to run w/o pumping the gas.  I doubt that will be the case, but watch for it.

Jeff, you have a Holley for Motorcraft 4180-C carburetor.
You can tell this by the Ford part # E6HE-9510-GB. and Holley for Motorcraft on the front of the bowl.
Unfortunately there doesn't seem to be a little aluminum calibration tag affixed. This is usually under one of the secondary diaphragm cover screws.

Choke coils are a unit onto themselves.
Motorcraft covers are calibrated for the ~7V that comes from the stator coil.
Holley universal chokes (with two spades) are set up for 12V from some other source.

Holley used to have all the list numbers under the technical files on their website, and probably still do, but my old bookmarks are 404.
Build number shows as 28th day of 1987 so it must have been swapped for a remanufactured OEM emissions carb at some point.

You also don't have the bowl vent elbows attached to the float bowls so I'd imagine the carb dries up in a couple of days and would require extended cranking to get primed.
The side effect of this is lots of crusty residue ends up in the bowls.
Dried out gasoline, air in contact with the pot metal....

Gary Lewis wrote

Isn't that illegal in Canada?

Unfortunately not!  Had two full Holidays weeks, there was so much people here, coming in & out, lunch, dinner, sleeping, playing... had lot of fun, but I admit Big Bro was a bit neglected.


Anyway, last kid went back to school and last friends are gone, we're going back to normal life.

Gary Lewis wrote

As for the flap opening too quickly [...]

I remember my youth when I was driving a Renault 5.  Flap choke was manually operated by a cable, life seemed simpler.


Should find some time for Big Bro today... before going back to my office next Monday.

Thanks so much for your support!

ArdWrknTrk wrote

Jeff, you have a Holley for Motorcraft 4180-C carburetor.
You can tell this by the Ford part # E6HE-9510-GB. and Holley for Motorcraft on the front of the bowl.
[...]
Build number shows as 28th day of 1987 so it must have been swapped for a remanufactured OEM emissions carb at some point.

Jim, thanks for this info.  I tried to find the answer by myself, from Holley's web site, but I admit I was rapidly lost.

ArdWrknTrk wrote

You also don't have the bowl vent elbows attached to the float bowls so I'd imagine the carb dries up in a couple of days and would require extended cranking to get primed.

That could explain why Big Bro was always difficult to start and needed pumping to crank.
But I was expecting that giving him a new carb would fix this behavior...  This is unfortunately not the case, I still have to pump after a long parked delay (couple of days).


I hope that fine tuning the choke issue will help!

Holley used to have scans of their paper books in the technical support section.
IIRC the 4180's were across the top of pgs. 56 & 57, but alas you now have to punch in a list# and yours comes up "nothing found"

My truck has a mechanical fuel pump so it takes a lot of cranking if I let it sit too long.
Sometimes (if I know it's been a week) I resort to using a syringe to fill the bowls through the primary vent tube sticking up in the choke horn.
This saves wear and tear on my starter and battery.

The 'Hot Fuel' 460's with electric pumps bypass the oil pressure safety switch and prime while the starter is engaged.
I expect this is the case for 351's with electric pumps as well, but can't be certain without looking at the EVTM.
I have to look now....

'pumping' an empty bowl may give you something to do while the carburetor fills but I doubt it really accomplishes anything.

ArdWrknTrk wrote

My truck has a mechanical fuel pump so it takes a lot of cranking if I let it sit too long.
[...]
'pumping' an empty bowl may give you something to do while the carburetor fills but I doubt it really accomplishes anything.

Wow! Jim, that is very interesting.
Big Bro is also equipped with a mechanical fuel pump.  Never thought about it, but it's logical:  If the engine is off and not cranking,  pumping the pedal doesn't push fuel to the carb.  The engine must be turning to activate the fuel pump and provide fuel to the carb.

So, the full-pedal-to-the-floor move before cranking is only to close the choke flap, am I right?

The cam eccentric is what actuates the fuel pump lever so if the engine isn't turning the pump isn't filling the carb.

Certainly, when stone cold one press of the pedal will set the choke.
If there's still gas in the primary bowl, multiple pumps of the pedal will push raw fuel into the plenum and provide the very rich mixture you need for the engine to catch (because the fuel doesn't want to atomize and condenses on the floor of the intake manifold)

If the truck sat long enough for the bowls to evaporate, then yes there's nothing for the accelerator pump to push.
Pumping like mad will be sure to catch those first drops and get them into the intake.

This is the reason for the exhaust crossover that heats directly under your carb.
Obviously the engine has to get running for that to have any effect....