Where to pick up power for electric choke?

[2550SX]

1992 Chaparral 2550SX with the 7.4 and Bravo1
Engine SN: OD717696

I am removing a webber carburetor with a divorced choke and replacing it with a Rochester carburetor with an electric choke. Where do you guys like to pick up 12v to supply the choke?

I think if I run a wire to the purple on the coil I would get 12v when the key is on but the engine not running.

I think if I run a wire all the way to the AC tap on the alternator at least the choke would only get 12v when the engine is running.

Thoughts?

Interesting thing I learned today. I bought this boat 3rd hand and although was not surprised to see a squarebore webber carb on the 454 but when I removed it I was surprised to see an adaptor plate with a spreadbore manifold. Someone changed it right? I'm not too sure, it looks like in Mercruisers part catalog this is how it came. Maybe the engines they bought from chevy with spreadbore manifolds already installed but you could no longer buy spreadbore rochesters in 1992. That's my guess, does anyone know?

Thanks

 

[GA_Boater]

What is in the PDF files? If you are using PDF to add pictures, don't expect a lot of views. Put pictures in your post, not PDFs which are not always trustworthy.

 

[Scott06]

The purple wire to the ignition is where mercruiser picks up power to the electric chokes.

i think the adapter is factory. you can plug your serial number in on some parts sites and the parts breakdown drawings show an adapter between the manifold and carb that look like spread bore adapters. I suspect you are right that manifold was a q jet holdover but the q jet was no longer available

 

[Scott Danforth]

the same purple wire coming from your key switch that goes to the choke also goes to the coil.

dont try to re-invent what works for millions of boats.

i also agree, dont post PDF's (IT 101, PDFs normally contain malware) embed your pics

you can still buy spread bore carbs and manifolds and square bore carbs and manifolds.

 

[2550SX]

So millions of boats use the purple wire?

That's why I signed up to the forum, to ask questions I do not know.

The PDFs are not pictures. The PDF's are pages from my mercrusier manual showing a purple wire go to the coil but not the choke. If the manual showed a purple wire going to a choke I would not be asking this question. Additionally I do not know why mercruiser manuals would contain malware.

I am aware you can still buy carburetors as I just bought one.

Thanks

 

[Lou C]

OMC and Volvo engines all used the AC tap on the alternator. This is advantageous because it only puts out voltage when the engine is running. Otherwise as soon as you turn on the ignition the choke will open up, probably too early for good drivability. I was going to convert my Quadrajet over to an electric choke but decided to keep the simple divorced manifold heated choke. It opens slower, but no issues with wiring, etc. It responds directly to engine temp via the heated exhaust crossover. The main thing with these manifold heated chokes is making sure your thermostat does not stick open or else the low engine temp will keep the choke from ever opening. That's one advantage of the electric choke, it is independent of engine temp.
I'd recommend starting the engine, and see what the voltage reading is on various outputs on the alternator. Ideally you want one that only puts out charging voltage with the engine running.
I'm not sure I'd use the coil because the draw of choke heater might reduce voltage to the coil, in fact instructions provided by Holley and Edelbrock both mention this.

 

[GA_Boater]

So millions of boats use the purple wire?

That's why I signed up to the forum, to ask questions I do not know.

The PDFs are not pictures. The PDF's are pages from my mercrusier manual showing a purple wire go to the coil but not the choke. If the manual showed a purple wire going to a choke I would not be asking this question. Additionally I do not know why mercruiser manuals would contain malware.

I am aware you can still buy carburetors as I just bought one.

Thanks

You say they are Merc manuals. We don't know where they came from. Been burned once, it won't happen again. I will not open PDFs in any forum unless I know the source.

 

[Reserector_]

My OMC is connected to the AC tap just as Lou C explained. Running to a key-switched source will work, but as soon as you turn the key on (with the flame arrestor removed) you can watch the choke slowly open. That's how it is with my Holly. Rochester may have a stepped cam that prevents it from moving until the throttle is stroked, and that may be why Merc runs theirs to the coil. I can't really say.
If you don't have an AC tap, you don't have that option.

 

[2550SX]

OMC and Volvo engines all used the AC tap on the alternator. This is advantageous because it only puts out voltage when the engine is running. Otherwise as soon as you turn on the ignition the choke will open up, probably too early for good drivability. I was going to convert my Quadrajet over to an electric choke but decided to keep the simple divorced manifold heated choke. It opens slower, but no issues with wiring, etc. It responds directly to engine temp via the heated exhaust crossover. The main thing with these manifold heated chokes is making sure your thermostat does not stick open or else the low engine temp will keep the choke from ever opening. That's one advantage of the electric choke, it is independent of engine temp.
I'd recommend starting the engine, and see what the voltage reading is on various outputs on the alternator. Ideally you want one that only puts out charging voltage with the engine running.
I'm not sure I'd use the coil because the draw of choke heater might reduce voltage to the coil, in fact instructions provided by Holley and Edelbrock both mention this.

Thank you for answering. I sort of thought the same thing. Dont draw from the coil and dont hook up to the key but hook up to a spot that would give power only when the engine is running. With no wiring diagram but the one I attached to go off of I was more inclined to use the AC tap. I know on older GM cars they used 12v off the oil pressure switch for just that reason.

 

[2550SX]

My OMC is connected to the AC tap just as Lou C explained. Running to a key-switched source will work, but as soon as you turn the key on (with the flame arrestor removed) you can watch the choke slowly open. That's how it is with my Holly. Rochester may have a stepped cam that prevents it from moving until the throttle is stroked, and that may be why Merc runs theirs to the coil. I can't really say.
If you don't have an AC tap, you don't have that option.

Thank you as well. I think the back of my mando alternator has the AC tap. I need to verify with my multi-meter when the engine is both off and on.

Thanks guys.

 

[Lou C]

What you will find is that the AC tap puts out both AC volts and DC volts, but the choke will work fine that way.

 

[johnkom]

I wired mine to a relay controlled by the oil pressure. Choke and hour meter work when there is oil pressure.

JK

 

[Scott Danforth]

if you sit around long enough with the ignition on prior to firing up the motor, you have other issues than your choke.

your ignition coil does not like to be on and the engine not running. it turns that sucker into a toaster element.

doesnt matter what OMC did, because they are no longer here. and on many motors over the years, they ran a wire from the coil to the choke just like Mercruiser. just like volvo did on the SBC that was in my boat back in 1988...

and yes, millions of boats and billions of automobiles have the ignition wire wired to both the choke and the coil.