4.3 Mercruiser cold start issues

[Whitej5]

I seem to be having a hard time starting my boat after it sits for a day or more. The boat starts right up if it been running. I pump the throttle between a half a dozen to a dozen times but it still takes a while to start. Towards the end of last year I even had to start using starter fluid to get it started. When I pump the throttle I do not see much gas getting sprayed in to the carburetor but more of a little drizzle. I am by no mean an expert when it comes to a Carburetor but if given direction I am more than confident I can fix it. Can any one provide a list of things to try?
Thanks in advance.

 

[QBhoy]

Hi. Is it the 4.3 that takes a feed of the oil pressure to run the fuel pump ?

 

[nola mike]

Hi. Is it the 4.3 that takes a feed of the oil pressure to run the fuel pump ?

Doesn't matter, on the initial start the bowl should be full. Pumping the throttle should give it enough gas to get started.

 

[Lou C]

Is the choke valve closing or mostly closing on a cold engine?

 

[achris]

Hi. Is it the 4.3 that takes a feed of the oil pressure to run the fuel pump ?

During normal running yes, but during cranking the circuit is powered up from a pole on the starter solenoid so the pump runs IMMEDIATELY the starter is cranking... And that's true for all the electric pumps on Mercrusiers, 4.3, SBC and BBC....

But here's the kicker with the later model 4.3 non-vortex engines. If you are running a Weber 9600 or 9666 carb, it will be dry after a few days of not running. Unfortunately there is a problem with those carb in that they 'dribble' after being shutdown, and the bowl is dry when you next attempt to start it. And you then have to keep cranking until the bowl fills.

The 'fix' is one of a few things. Replace the Weber with an Edelbrock, fit an outboard style fuel primer in the fuel tank bay (NEVER in the engine bay!) and prime engine before trying to start it. Or you could do as I did... (see my signature for my solution )

 

[Bondo]

I seem to be having a hard time starting my boat after it sits for a day or more. The boat starts right up if it been running. I pump the throttle between a half a dozen to a dozen times but it still takes a while to start. Towards the end of last year I even had to start using starter fluid to get it started. When I pump the throttle I do not see much gas getting sprayed in to the carburetor but more of a little drizzle. I am by no mean an expert when it comes to a Carburetor but if given direction I am more than confident I can fix it. Can any one provide a list of things to try?
Thanks in advance.

Ayuh,..... Welcome Aboard,...... I'm guessin' you've got the 4bbl. Merc/ Weber carb,..??

If so, achris has got yer answer,.....

 

[Lou C]

I’m wondering if these carbs have a welch plug or similar in the bottom of the bowl that could leak. This was a known problem with older Rochester Quadrajet carbs although I haven’t had this with mine. Even if it sits for the 6 month winter storage if I crank it over 3 times it starts. During the season one crank over or 2 at the most if it sits a couple weeks.

 

[QBhoy]

During normal running yes, but during cranking the circuit is powered up from a pole on the starter solenoid so the pump runs IMMEDIATELY the starter is cranking... And that's true for all the electric pumps on Mercrusiers, 4.3, SBC and BBC....

But here's the kicker with the later model 4.3 non-vortex engines. If you are running a Weber 9600 or 9666 carb, it will be dry after a few days of not running. Unfortunately there is a problem with those carb in that they 'dribble' after being shutdown, and the bowl is dry when you next attempt to start it. And you then have to keep cranking until the bowl fills.

The 'fix' is one of a few things. Replace the Weber with an Edelbrock, fit an outboard style fuel primer in the fuel tank bay (NEVER in the engine bay!) and prime engine before trying to start it. Or you could do as I did... (see my signature for my solution )

This explains a lot actually. I didn’t know that at all. My friend Has issues on his 93 4.3 Webber, exactly as you describe there chris !

 

[QBhoy]

During normal running yes, but during cranking the circuit is powered up from a pole on the starter solenoid so the pump runs IMMEDIATELY the starter is cranking... And that's true for all the electric pumps on Mercrusiers, 4.3, SBC and BBC....

But here's the kicker with the later model 4.3 non-vortex engines. If you are running a Weber 9600 or 9666 carb, it will be dry after a few days of not running. Unfortunately there is a problem with those carb in that they 'dribble' after being shutdown, and the bowl is dry when you next attempt to start it. And you then have to keep cranking until the bowl fills.

The 'fix' is one of a few things. Replace the Weber with an Edelbrock, fit an outboard style fuel primer in the fuel tank bay (NEVER in the engine bay!) and prime engine before trying to start it. Or you could do as I did... (see my signature for my solution )

Chris where do I see what you’ve done ? I’m useless at finding my way through forums. Thanks

 

[Lou C]

Chris where do I see what you’ve done ? I’m useless at finding my way through forums. Thanks

He installed a 4.3 with MPI instead of a carb!

 

[QBhoy]

He installed a 4.3 with MPI instead of a carb!

Hahahaha...that would sort it out, right enough.

 

[achris]

I’m wondering if these carbs have a welch plug or similar in the bottom of the bowl that could leak. This was a known problem with older Rochester Quadrajet carbs although I haven’t had this with mine. Even if it sits for the 6 month winter storage if I crank it over 3 times it starts. During the season one crank over or 2 at the most if it sits a couple weeks.

Yes I know of the Rochester welch plug issue. There are no welch plugs in that location on the Weber. When I had my 4.3LX I did a lot of testing. The conclusion I came to is that the drilling between the fuel bowl and the main Venturi cluster is too small and can allow fuel to track along it due to capillary action. After shutdown you can easily see the fuel dripping off the cluster.

Chris...

 

[Whitej5]

Hi. Is it the 4.3 that takes a feed of the oil pressure to run the fuel pump ?

I’m not sure how can I tell?

 

[achris]

I’m not sure how can I tell?

What year is the engine? (Engine, not boat!)

 

[nola mike]

This is only applicable to electric fuel pumps...if you have a mechanical pump there isn't an oil pressure switch.

 

[QBhoy]

It sure sounds like Chris has the answer...outside the usual auto choke issues that are common. I’ve had two of these engines and was actually out on a Friend’s boat with one yesterday that has the same issue. What chris is saying makes total sense. Spot on. Can’t believe I didn’t know this about these particular engines of that age. Also had a VP version of the same engine with a Rochester carb. Never had an issue similar at all.

 

[achris]

Also had a VP version of the same engine with a Rochester carb. Never had an issue similar at all.

The Merc 4.3s with the Rochie carbs also didn't have the problem. At one point I was seriously considering changing the carb to a Rochie (on the 4.3LX).

 

[Lou C]

The Quadrajet is an excellent carb if you can start with an unmodified core. Even though they have not been made in 30 years you can still get most parts

 

[MichaelBC]

I had the same configuration, 4.3 pre Vortec with Carter 9600S carburetor, and I had the same problems. The previous owner installed a can of starting fluid with a hose in the flame arrestor and pressed this once every time he started the engine. I didn't like this solution and had a look at the system.

After running the boat the carburetor sits on top of a hot engine. In my oppinion this makes the fuel evaporate from the fuel bowls in the carburetor. So before the engine can start the fuel pump has to fill up the carburetor and it does this only while the starter cranks the engine.

I thought over it, but could not find a reason that makes sense to me, why the fuel pump has to be wired via an oil switch or the starter. So what I did was to change the wiring of the fuel pump from the oil switch to ingition plus. By this way the pump starts to fill when I turn on the ignition and if the inlet seats are ok it will not pump more than needed. Since then my engine started on the first turn of the key. If the engine is not running with ignition turned on, I have this alarm that starts after a few seconds. So there is no danger that I could forget it and have the pump working against the closed valves for long time.

So it works perfect for and is a little cheaper than changing to an MPI engine.

 

[achris]

You're not going to like what I say, but it needs to be said...

....After running the boat the carburetor sits on top of a hot engine. In my oppinion this makes the fuel evaporate from the fuel bowls in the carburetor...

Incorrect. It's not heat that is causing the problem. I suspected the same thing, it was a nice day around 24 degrees, so I pulled the carb and set it up on a bench. I blew compressed air down one venturi and fuel was drawn through. I then stopped the air and refilled the float chamber (as a running fuel pump would have done). Fuel continued dripping from the venturi until the float chamber was empty. This issue has nothing to do with heat.

.... I Ihought over it, but could not find a reason that makes sense to me, why the fuel pump has to be wired via an oil switch or the starter. ...

The reason is so that the fuel pump CAN NOT run unless the engine is turning. And should the engine stall, the pump stops running.

.... So what I did was to change the wiring of the fuel pump from the oil switch to ingition plus. ...

And in doing that you have violated coast guard regulations. If ANYTHING happens on that boat, regardless of whether it has anything to do with the fuel pump wiring, your insurance company is going to wipe their hands of you, and any injured 3rd party will sue you out of existence... What you have done, despite your rationalisation, is very dangerous. You have a boat just itching to go up in flames... The pump original wiring was as it was for a reason. I strongly suggest you return the wiring to original.

What you could add is a MOMENTARY switch on the dash (mark it as 'Fuel prime') that is wired from the ignition switch purple wire to the fuel pump wire.. that would achieve the same thing, when you turn the key ON you press the switch until the carb is primed, take your finger off the switch and crank the engine.

Chris...