Q-Jet 454 - Choke electric vs mechanical

Beech2000

Beech2000

Active Member
Jul 11, 2015
253
NW Georgia USA
Boat Info
1990 Sundancer 350
Engines
2020 454 gen VI
Hurth V-Drive's
7.1 KW Kohler 5ECD
Hi All,
I have both of my 90 454's out of a 39.5 350 in for rebuilds. My engine builder recommended upgrading carbs to electric chokes. Any advantages?
 
I did mine 6 years ago when I had my engines rebuilt. The advantages are they are easily adjustable and they open much more quickly than the old thermal chokes. I recommend doing it.
 
Thanks for the reply,
How about wiring provisions? Does the Mercruiser engine wiring harness have an available provision for electric choke?
 
They normally just pickup 12 volts from the ignition switch side of the ignition coil.
 
hughespat57 said:
They normally just pickup 12 volts from the ignition switch side of the ignition coil.
Click to expand...

Because I have HEI ignition I believe mine pick up 12 volt off of the slave or starter solenoid. They don't draw much power.
 
Unless you have an aftermarket ignition system merc never used HEI, you may be confusing this with merc Thunderbolt ignition system which is also electronic. Purple wire in engine harness is 12 ignition on when key is in run position. This will feed positive side of coil, ignition module, and on newer ones electric fuel pump and choke
Splice into this to supply 12 v+ to electric choke, you will have much better and consistent operation of choke.
 
Okay, I understand. I was planning on blocking off the fuel pump port and going with electric. Looks like I'll have a stack of wires on purple side of coil. Thanks
 
Beech2000 said:
Okay, I understand. I was planning on blocking off the fuel pump port and going with electric. Looks like I'll have a stack of wires on purple side of coil. Thanks
Click to expand...

If I were you I'd stay with a mechanical pump as they are more reliable than electric and need to be wired just right or they are dangerous.. People change to electric for faster starts which is a double edge sword. I'd rather crank my engine a few revolutions to build up some oil pressure prior to engine start. JMHO.
 
Electric fuel pump doesn’t lead to faster starts on a carbed engine. Injected will be faster.

If my carb bowl is dry from sitting for a week or two I’m cranking to get fuel pump to run to fill fuel bowl. Fuel pump get power from the starter during cranking, then off the purple wire through an oil pressure switch when in run. You could wire a momentary switch to bump the fuel pump prior to start but that seems like a lot of work to me. Personally I’d leave the mechanical pump if that’s what you have, they generally work for years. Even merc still uses mechanical pumps on their reman carb engines like the 357 alpha and bravo.

Most of the guys upgrading to electric are doing it because during a repower they are upgrading to a newer block that doesn’t have a mechanical fuel pump provision.
 
Okay, I understand Mechanical fuel pump recommended with electric choke... correct?
Now is the time to make a decision as I'm currently ordering parts to reassemble the 454's.
Question: Has anyone used National Marine Carburetors? They're prices seem somewhat fair.
 
Last edited:
So another question. I'm shopping for fuel pumps. The OEM mercury's are $159each and made by carter. I see carter fuel pumps on-line for less money. Whats the difference between carter and carter sold by mercury?
 
Beech2000 said:
So another question. I'm shopping for fuel pumps. The OEM mercury's are $159each and made by carter. I see carter fuel pumps on-line for less money. Whats the difference between carter and carter sold by mercury?
Click to expand...

The Merc. pumps probably have the fitting for the hose that goes up to the carb/spark arrester to prevent fuel spilling into the bilge in the event of a diaphragm rupture.
 
I should quit trying to save money. $159 each for such an important item should be my last concern. Thing is I will have over $20K with engine rebuilds, all new OEM exhaust risers and manifolds. Carburetor exchanges, new fuel lines, oil coolers, ignition, raw water pumps and closed circulation pumps. Ouch :( Trying to go all OEM as best as possible.
 
Beech2000 said:
I should quit trying to save money. $159 each for such an important item should be my last concern. Thing is I will have over $20K with engine rebuilds, all new OEM exhaust risers and manifolds. Carburetor exchanges, new fuel lines, oil coolers, ignition, raw water pumps and closed circulation pumps. Ouch :( Trying to go all OEM as best as possible.
Click to expand...

I agree 100%. Stay with US made OEM on these fuel pumps. I've seen many aftermarket mechanical pumps bad right out of the box.
 
techmitch said:
The Merc. pumps probably have the fitting for the hose that goes up to the carb/spark arrester to prevent fuel spilling into the bilge in the event of a diaphragm rupture.
Click to expand...

I found the answer. Mercury uses a Carter M60601 pump. Then they supply the correct fittings and supply a new fuel line on the inlet side. Lastly, they protect the exterior material by epoxy primer and black urethane paint. All this for about an additional $40 from actual price of M60601 from Summit or Jegs.
 
In addition to the actual choke there are weighted cams with vacuum pull offs. They must be functioning properly for the choke to function properly.
Then there is the problem with the float bowl on rochesters that leak down so the problem may be more than just a choke coil be it electrically controlled or otherwise...
 
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