choke cap inop

[Luke85]

I found the choke cap (aka choke heater) on my '85 GT to be inoperative. I have the proper 7.2 volts going to the connector, but the choke will never cut back from the initial 2000 rpm fast idle to the interim 1200 rpm without me blipping the throttle. The coil never gradually opens the choke plate. It will then never go down to regular idle unless I push the fast idle cam manually out of the way. The choke plate never fully opens and blipping the throttle will return to the interim 1200 rpm since the fast idle cam never gets the signal to release. The cap fails the resistance test and there is some corrosion inside. Basically the cap/heater/coil does nothing. I would like to have an automatic choke on the car (desired but not required), so I see three options:

1) Run with no choke. I've done this before and for a seasonal car is probably okay.
2) Replace the cap with an OEM unit that uses 7.2 volts. I can't seem to find one of these.
3) Replace the cap with one that uses 12 volts and is adjustable. If I opt for this I need to identify a 12v source that is only hot with the engine running. Anyone know where one is?

Is the OEM 7.2v choke cap available anywhere?

Thanks for reading.

[at_the_junkyard]

I'm not 100% positive but a while back I was researching the choke coil voltage on the 85 vintage stock 4180 carb and all indications I could find were that they operate on a 12 volt source for the coil (no hot air assist) ?

Also on my son's 80 cobra with an aftermarket carb (12 volt choke cap) I used a 6 volt auto relay and wired the relay coil to the old choke wire (7 volt). Then ran a new switched 12 volt source from the battery. Works good and only powers the choke when the alternator is turning as opposed to when the ignition key is on etc. Perhaps that may be an option for you using a 12V replacement cap.

Hope that helps

[Luke85]

I had to read your reply a few times, but I now understand. Have to find a 6v relay. Thanks.

[at_the_junkyard]

No problem. Just to clarify if your using a 12V source from the battery make sure it has a fuse etc.

So is this on a 4180 carb ? I'm curious now if they had a 12 volt or 7 volt choke coil ?

[Luke85]

It is the original 4180C carb on an 85 5-speed GT. The factory manual states the choke cap is controlled by a 7 volt (or thereabouts) source from the stator connector on the alternator. One of my checks was to verify the connector at the choke end is seeing it when the car is running. It is unique maybe to that year or maybe a couple of years, I'm not sure. I did a search on this site and found confirmation to that. That is also why it's so difficult to source a direct replacement. I have a spare carburetor but that part is busted (naturally).

Since I'm a little fuzzy on sourcing the correct relay I may just use a 12v cap and connect it to a circuit switched to the engine running (if I can), otherwise with the ignition key on.

[306gt]

You can power up a 12 volt cap right off the ignition switch. There are a couple of 12 volt spots open on the ignition switch connector. I saved some old dash harnesses for this reason. I pulled a wire out of the old switch connector. and spliced a new wire on to it for my son's Line loc. Plugged it right in to the harness connector. Locks in like factory. I then added a inline fuse for the line loc.

[at_the_junkyard]

OK interesting. I always thought the 7.2V choke caps were used as an assist on carbs with a hot air (from the exhaust) option and when they switched to electric only used 12 V. Not sure.

Here is a link to 6VDC relay very similar to what I used for your reference if you go that route etc. It should also fit in a standard automotive relay base.

https://www.amazon.com/TE-CONNECTIVI...s%2C786&sr=8-3

[gr79]

Installed a manual choke on my Holley.
Engine always wanted partial choke a bit longer than the automatic one gave.

Have p,ositive control over engine warm up knowing the choke plate can be adjusted as to engine need.
Not a predetermined time on for emissions or feeling choke curve is not working correctly.
Positive manual control over a certain window of fuel/air mix at all times.
Am not using fast idle cam. Coax cold engine when parked for a minute or two until engine idles on its own.
Rarely needs full choke for more than couple blocks of driving.
When engine starts accelerating flatly, gradually open choke for leaner mix.
Full open when engine is warm enough to drive normal accel onto main road.
Found my engine responds best when choke flap is closed a tiny bit angled toward the center of the carb boosters.
As if it were the sweet spot in the overall tune of carb and engine. Full power with cruising economy.
A notch sharper and smoother overall response than wide open choke or, of course, too much choke.
Gone is the tiny bit of hesitation when picking up speed after tuning a corner or from a standing start.

[Luke85]

I do have a 12v cap coming in the mail. When I hook it up I'll see if it responds in the way the motor wants, being mindful of gr79's experiences. If good I'll either drive it from a 12v source or use the relay from the link provided. If the response is not right I'll hook up a manual cable.

I did start up the car yesterday at full cold with the choke plate held open (the only way I can use the car until all these parts arrive), and it was a little reluctant at first but within a couple of minutes would idle by itself. I could go without a choke if pressed.

[Luke85]

I installed the 12-volt cap (sources from Mike's Carburetor Parts) and wired it to a circuit that is hot when the key is on (not just when the engine is running, couldn't find that). Located on the firewall, and using the same connector that did go between the cap and the alternator, it pretty much looks factory. With a car I'm trying to keep original and unrestored, that last feature, while minor in this case, is important.

Best of all I have a choke system that works now.

[erratic50]

I wired my electric choke to the 12V for my coil on my 74 Galaxie back in the day. Worked good. Well except for being a high school kid that thought he had to run a 360 degree rise Offenhauser on a daily driver ……. What a fuel puddling bitch that grumpy old 351W was when it was below zero outside