4.3L 4bbl hard cold start issue

[flynnhart1]

Regarding 4.3L engines with 4bbl carburetors being hard to cold start. I added this circuit to my 1997 Sea Ray 185 with an Edelbrock 1409 4bbl carb. The 1409 is basically an exact copy of the Weber 4bbl and the 1409 also seems to ?drain? the fuel bowls after long periods of sitting. This circuit supplies 12V to the the fuel pump for 10 seconds (adjustable) when the ignition key is turned on and then transfers the 12V to the normal fuel pump circuit (i.e. - via the oil pressure safety switch). With this circuit I don?t have to run the starter for the time necessary to fill the fuel bowls; I just turn the ignition key to the on position, wait ten seconds (fuel bowls fill) and then start the engine. A momentary switch will do the same thing, but I wired this into the ignition switch and the stock wiring harness and it is essentially transparent to the boat.

 

[Scott Danforth]

Re: 4.3L 4bbl hard cold start issue

if your fuel bowls are empty, you have a carb issue.

shouldnt matter if the fuel pump is running or not. with a full fuel bowl, your motor should run for 30-90 seconds depending on load, even when cold

 

[Walt T]

Re: 4.3L 4bbl hard cold start issue

Gasoline likes to evaporate over long periods of sitting as he said.

 

[alldodge]

Re: 4.3L 4bbl hard cold start issue

Regarding 4.3L engines with 4bbl carburetors being hard to cold start. I added this circuit to my 1997 Sea Ray 185 with an Edelbrock 1409 4bbl carb. The 1409 is basically an exact copy of the Weber 4bbl and the 1409 also seems to “drain” the fuel bowls after long periods of sitting. This circuit supplies 12V to the the fuel pump for 10 seconds (adjustable) when the ignition key is turned on and then transfers the 12V to the normal fuel pump circuit (i.e. - via the oil pressure safety switch). With this circuit I don’t have to run the starter for the time necessary to fill the fuel bowls; I just turn the ignition key to the on position, wait ten seconds (fuel bowls fill) and then start the engine. A momentary switch will do the same thing, but I wired this into the ignition switch and the stock wiring harness and it is essentially transparent to the boat.

View attachment 219213

Looks good and this will accomplish same task as EFI engines have (5 seconds), and I do like it.

Comments: Need to make sure to use sealed relays, and it could also be accomplished with a normally open push button switch. If it went bad no problem so long as it did not go bad in the normally closed position

 

[Bondo]

Re: 4.3L 4bbl hard cold start issue

Looks good and this will accomplish same task as EFI engines have (5 seconds), and I do like it.

Comments: Need to make sure to use sealed relays, and it could also be accomplished with a normally open push button switch. If it went bad no problem so long as it did not go bad in the normally closed position

Ayuh,.... I like it too,.... other than the leaky fuel bowls, I Love the AFB carbs,....

What'd ya use for the timed relay,..??

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

I got the interval relay from Ebay for $9. It came with a n.o. SPDT relay and I needed a n.c. one. I got a n.c. one from Digikey for about $2. Ten minutes with some solder braid and I had the relay swapped out. The relay is a fully sealed unit. I installed it under the dash right next to the ignition switch so it shouldn’t see much moisture. The interval relay circuit is is basically just a threshold detector that triggers an SCR to provide coil voltage to the relay. The adjustable potentiometer is part of the RC circuit that determines the trigger delay. Pretty simple circuit. I left the stock wiring to the oil pressure safety switch in place so that if there is ever a problem I can simply unplug the wires and re-connect the stock wires. 30 seconds at most to do that.

 

[Mark Bennett]

Re: 4.3L 4bbl hard cold start issue

Flynnhart1,

I really like this idea as well, I've lived with this issue for 15 years because I really like this engine and carb as well. How about a little more detail with regards to installation and components. It sounds like like you replaced the N.O. relay in the interval timer with a N.C. one, is a N.C. one available with the Interval Timer? I'm a mechanical engineer and can handle the installation, reading electrical schematics takes me a little while. I would really appreciate a little more instruction and pictures with regards to what to connect to what.

Thanks

Mark

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

The guy I got it from on Ebay told me he can pretty much make it any way you want it. Search for MINI TIMER SWITCH TIME RELAY 3 TO 110 SEC KIT. I didn’t mind modifying the one I got, I’m pretty good with electronics. I had to change out the relay and add the wires. You could ask him for a SPDT N.C. relay and to add the wires. There are 5 wires that need to be put on the relay, +12V, ground, C (relay coil voltage), N.C., and N.O. Since I put the relay under my dash I needed to make the N.C. and N.O. wires about 25ft long to get to the engine compartment. I made the +12V, ground, and C wires about a foot or so since they only needed to get to the connection points under the dash. I made a simple drawing of the hookup, I can try to clarify anything you need. Best regards, flynnhart1.

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

Slight changes to drawing……….

 

[Mark Bennett]

Re: 4.3L 4bbl hard cold start issue

Thanks Flynnhart1, that is exactly what I was looking for!

Mark

 

[Mark Bennett]

Re: 4.3L 4bbl hard cold start issue

Flynnhart1,

I was reading my manual and it said the fuel pump was energized when the ignition switch is turned on, I'm wondering if mine already does what the interval switch would do?

 

[Bondo]

Re: 4.3L 4bbl hard cold start issue

Flynnhart1,

I was reading my manual and it said the fuel pump was energized when the ignition switch is turned on, I'm wondering if mine already does what the interval switch would do?

Ayuh,.... That's only true on the Efi/ Mpi motors,....

 

[Mark Bennett]

Re: 4.3L 4bbl hard cold start issue

Thanks Bondo

 

[Mark Bennett]

Re: 4.3L 4bbl hard cold start issue

This looks like it would work, any thoughts?

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

That needs a separate external trigger signal to start the timer delay and it is not clear to me how it is reset. The interval timer I used does not need a trigger. Supplying the +12V (turning ignition on) starts the timer delay function and removing the +12V (turning ignition off) resets it. Perfect for the application.

FYI, here is the principle of operation:

Relay starts out in the normally closed position. When the ignition switch is turned to the on (not start) position three things happen:
1) Timer delay function starts
2) +12V is supplied directly to the fuel pump from the relay’s N.C. contacts which will run it and fill the carburetor with gas.
3) After 10 seconds, the relay switches to the N.O. contacts which then supplies +12V to the oil pressure cut off switch. With normal engine oil pressure the o.p. cut off switch will be in the closed position so that the +12V will go to the fuel pump.

The timer delay is adjustable from 3 − 150 seconds (mine is set to 10). The operation of this circuit is basically transparent to the boat operation. The carburetor will be full of gas by the time the delay period ends and the relay switches and the during the momentary period while the relay is switching (fuel pump is momentarily off) will not affect anything as the carburetor is already full and doesn’t need any more gas at that moment.

Turning the ignition off resets the timer function.


Starting and Operation procedure:
If the boat has been sitting for awhile and the engine is cold, it is assumed the carburetor is empty (evaporation, drainage somehow, whatever). I turn the ignition key on and wait ten seconds before turning the engine over. During this 10 seconds the carburetor fills and the engine usually starts up right away. The timer can be set for longer or shorter delays depending on the need.

When the engine has been run and is shut off the carburetor will be full and it is not necessary to wait the 10 seconds before restarting the engine. Just turn the ignition key to the start position, and start the engine. The Interval relay circuit will still go through it’s timing cycle but it will be transparent to the boat operation.

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

If the engine is carbureted, the fuel pump is energized with +12V via the oil pressure cut off switch. The fuel pump will only receive the +12V when there is normal oil pressure and the oil pressure cut off switch is closed. The engine has to be running or turning over (cranking) to produce oil pressure to close the cut off switch. This is why I believe some carbureted engines are so hard to cold start. They must be cranked over long enough for the fuel pump to fill the float bowls with gas before the engine will start.

On EFI/MPI engines, the fuel pump runs when the ignition key is turned to the on (not start) position.

 

[fen-isl]

Re: 4.3L 4bbl hard cold start issue

I have done the momentary switch. It works well just ran a wire from batt thru a fuse to a momentary toggle switch to fuel pump so while checking oil level i just hit switch for 1-2 seconds Boat starts on first crank. I have 2 bb carb. Also works great for winterizing i pull plug to fuel pump run carb dry, then install adapter in top of fuel pump which allows me to pump out all of the gas for the winter.

 

[bruceb58]

Re: 4.3L 4bbl hard cold start issue

If the engine is carbureted, the fuel pump is energized with +12V via the oil pressure cut off switch. The fuel pump will only receive the +12V when there is normal oil pressure and the oil pressure cut off switch is closed. The engine has to be running or turning over (cranking) to produce oil pressure to close the cut off switch.

Typically, there is another connection from the fuel pump to the start circuit so that while cranking(even with no pressure) the fuel pump will operate.

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

No so on Mercruiser 4.3LH and LX carbureted engines. They have one +12V wire supplied from the ignition switch that goes to one side of the oil pressure cut off switch and there is one wire from the other side of the oil pressure switch that goes to the fuel pump. Refer to items 7 & 8 in the ‘B’ block in the wiring diagram on page 4E-4 of Mercruiser Service Manual #18 or page 4E-8 of Mercruiser Service Manual #25.

 

[flynnhart1]

Re: 4.3L 4bbl hard cold start issue

Yes, a momentary switch works fine as I stated in my first post. I believe Bondo posted a long time ago that is what he did. I wanted to make it part of the ignition system so that anyone could cold start my boat without having to find/push a switch. It’s like starting a diesel, you just turn the key on, wait 10 seconds, and start it. :happy: