4.3 Mercruiser cold start issues

[MichaelBC]

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

I always like good advice and if someone helps me to understand things.

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.

This was just an assumption. But what I can say is that my carb is is empty after a day or two. I have a transparent little fuel filter in line to protect the sender of the flow meter. So I can see that there is a good amount of fuel pumped in the carb when I turn on ignition and it stops when the carb valves get closed by the floats. So the carb bowls must be empty and as I do not think that the fuel is slowly dripping into the engine it must evaporate.

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

What you have done, despite your rationalisation, is very dangerous. You have a boat just itching to go up in flames...

OK, now it is getting interesting. I talked to quite few people here and half of them told me about the same as you do and the other half did already the same modification that I did for years.
I do understand that it is nice when the fuel pump only runs when the engine is turning. But if the carb bowls are full the pump works against the closed carb valves. As the pump can bring much more fuel as the engine takes, the pump also does this when the engine is running.

So can you give me one example what could happen that causes my boat to go up in flames ?

In the 80s, when cars had carbs, all european cars started the elctric fuel pump when you turned on the ignition. I remember that I could always hear it when turning the key before the radio came up.
So why is it so harmful on a boat when it worked for millions of cars in the past and very few of them did go up in flames ?

The pump original wiring was as it was for a reason.

This is exactly what I would like to understand. What is this reason ?
If this reason makes sense to me I will change the wiring back today. Seriuosly, I would like to understand why this setup is like it is and what I do not see so far.

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...

This was my bad, I didn't think about coast guard regulations as my boat runs in Europe. Should have thought about it as this is a US forum.

Here we do not have any regulations on boats, which is funny as we have much more regulations on cars than you have. Also the insurance company could only leave me alone if they prove to me that an illegal modification was the root cause of an accident. As there are no regulations this would be very hard.

Regards
Michael

 

[Scott06]

The difference between a boat and a car if you have a fuel leak in a car the fuel and any fuel vapors only goes out on the ground, in a boat they get trapped in the bilge of the boat So there is more fire and explosion potential in a marine application. This is the main reason both fuel and electrical components are designed for marine use.
it is wired through the oil pressure switch to prevent if the ignition gets bumped on or engine stalls and isnt running the fuel pump is not running and pressurizing the fuel system. Carb needle and seat have been known to stick open.

i also have this same issue that the carb bowl empties out when it sits for a while. Some folks have wired a momentary switch to bump the fuel pump for a short time.

 

[achris]

Plenty to unpack here, so It's going to be a long one. Best make yourself a coffee.

.... But what I can say is that my carb is is empty after a day or two. ...So the carb bowls must be empty and as I do not think that the fuel is slowly dripping into the engine it must evaporate...

Yep, I WATCHED the fuel bowl empty on that carb I had on the bench, in about 2 hours! I also tried another test (because I was think the same as you). I filled the carb but didn't run the engine (no draw of fuel through the venturi)... After a week, carb still full.

OK, now it is getting interesting. I talked to quite few people here and half of them told me about the same as you do and the other half did already the same modification that I did for years.

Just because 90% of people did a particular thing, doesn't make it right, it just make 90% of people wrong.

I do understand that it is nice when the fuel pump only runs when the engine is turning. But if the carb bowls are full the pump works against the closed carb valves. As the pump can bring much more fuel as the engine takes, the pump also does this when the engine is running.

So can you give me one example what could happen that causes my boat to go up in flames ?

Finally, an easy one. Your engine is happily idling away, you are attending to something else (like setting the anchor), and because you're at the front of the boat you can't hear the engine. Something (dirt, a flake of rust, a grain of sand, whatever) causes the needle in the carb to stick open, and as the pump (as you correctly surmised) can deliver more fuel than the carb could ever need, the float chamber floods, fuel then pours into the engine and the engine stalls due to being grossly over-rich. And because you have wired the pump to continue to run even after the engine stops, the open needle and running pump now start filling your engine with raw petrol. And once the engine is full, it starts flooding out of the engine and into the bilge. The fuel in the cylinders also leaks passed the piston rings and starts filling the oil pan with petrol. Congratulations, you have just created a fuel-air bomb, and put it in the bilge of your boat!

In the 80s, when cars had carbs, all european cars started the elctric fuel pump when you turned on the ignition. I remember that I could always hear it when turning the key before the radio came up.
So why is it so harmful on a boat when it worked for millions of cars in the past and very few of them did go up in flames ?

Hey, we're on a roll here. A second easy one. Reason cars with constantly running fuel pumps don't blow up? A car engine isn't in a boat bilge. Car engine floods and fuel leaks out. Simple, the fuel (and vapour) falls out the engine bay and is gone. Fuel leaks out of a boat engine and it collects in the bilge. It has nowhere else to go! It takes an incredibly small amount of energy to ignite petrol vapour.

This is exactly what I would like to understand. What is this reason ?
If this reason makes sense to me I will change the wiring back today. Seriuosly, I would like to understand why this setup is like it is and what I do not see so far.

The fuel pump on a marine engine must be wired such that it CAN NOT run continuously when the engine isn't turning. The reasons are as I outlined above, to stop boats exploding.

This was my bad, I didn't think about coast guard regulations as my boat runs in Europe. Should have thought about it as this is a US forum. Here we do not have any regulations on boats, which is funny as we have much more regulations on cars than you have. Also the insurance company could only leave me alone if they prove to me that an illegal modification was the root cause of an accident. As there are no regulations this would be very hard.

It's ok, I'm not in the US either But where I am, while they don't enforce the USCG regulations directly, but if an insurance company can dodge a claim by saying that you have modified the engine outside of manufacturer's recommendations, THEY WILL! And changing the pump wiring IS a modification outside the manufacturer's recommendations.

I would recommend you change the wiring back to standard, and add the MOMENTARY switch I suggested...

Chris....
(in Australia.)

 

[MichaelBC]

Thank you for explanation. But I am still struggling to accept that. If the carb needle would stick open then the carb would be flooded also when the engine is running as the pump delivers much more fuel than the engine can use.

As I wrote already, I have this alarm horn that starts to sound about 10 seconds after ignition is turned on. It is so loud and annoying that I immediately switch of the ignition key. So the pump will never run more than 10 seconds without engine running.

As mentioned also I talked to a lot of people here in Germany to hear if there is one realistic scenario where this oil pressure switch would prevent anything. The only scenario that we found would be when the boat flips over and swims upside down. Then the pump might continue to run and pump fuel into the sea. But in this case this would be my smaller problem because this will only be a small amount cause the fuel tank will also be upside down then and the pump will pull air.

Don’t get me wrong. I am not stubborn at all if someone gives me one example that I can follow. But for now people tell me that it so dangerous and the boat will explode. But I never got one single scenario how this could happen.

 

[MichaelBC]

Hi Chris,
I am about put in a brand new engine with e brand new Edelbrock carb. So I will connect that via the fuel pump as it should be and see if this also empties out like the Carter carb. I guess it will because they are the construction. Then we will see what I do.

Regards
Michael

 

[achris]

Thank you for explanation. But I am still struggling to accept that. If the carb needle would stick open then the carb would be flooded also when the engine is running as the pump delivers much more fuel than the engine can use.

Yes, the carb floods, the engine stalls, and the oil pressure drops to 0 (because the oil pump needs a running engine to pump oil). When the oil pressure drops to 0, the switch opens, and stops power going to the pump, pump stops.

As I wrote already, I have this alarm horn that starts to sound about 10 seconds after ignition is turned on. It is so loud and annoying that I immediately switch of the ignition key. So the pump will never run more than 10 seconds without engine running.

Yeah, I hear this a lot. And I still don't buy it. Nothing says the alarm can't fail, or you are doing something out of earshot. Or you sell the boat and the new buyer doesn't know what it means, ignores it (as they usually do), or cuts the wires because of the annoying sound

As mentioned also I talked to a lot of people here in Germany to hear if there is one realistic scenario where this oil pressure switch would prevent anything. The only scenario that we found would be when the boat flips over and swims upside down. Then the pump might continue to run and pump fuel into the sea. But in this case this would be my smaller problem because this will only be a small amount cause the fuel tank will also be upside down then and the pump will pull air.

Having worked in an offshore environment for over 30 years let me just say this... If your boat does swim upside down, the very LAST thing you want in the water with you is fuel. Fuel, especially petrol!, in the water takes an already bad situation and elevates it to a whole new level of disaster.

Don’t get me wrong. I am not stubborn at all if someone gives me one example that I can follow. But for now people tell me that it so dangerous and the boat will explode. But I never got one single scenario how this could happen.

Nobody ever gets a single scenario, until they do, and then they REALLY wish they'd listened to the people who said 'don't mess with a manufacturer's safety measure. It always ends badly'....

Just as an aside, I was asked to help out with an investigation into a boat explosion. The 2 guys on board survived, but will never walk again. Please, don't be those guys. (Petrol flooded into the space between the hull and the floor. When it ignited it blow the floor up so fast it smashed all the bones in their feet, ankles and lower legs.)

 

[MichaelBC]

Hello Chris,
thank you for your patience. My boat is 20 feet long and even it is very unlikely that I could not hear the buzzer or the engine I do accept your arguments and value your expertise. I also don't want to kill myself on the boat.

I do not like this manual carb fill button. What would you think if I put in a timer relay switch that gives voltage to the fuel pump for maybe 5 seconds every time I turn the ignition on and then switches back to the oil pressure switch. So if the engine is runnig it is the oil switch only and if the engine stalls the fuel pump would be off. But every time I turn on ignition it gets a short push. Would that be acceptable ?

Regards
Michael

 

[Scott06]

Hi Chris,
I am about put in a brand new engine with e brand new Edelbrock carb. So I will connect that via the fuel pump as it should be and see if this also empties out like the Carter carb. I guess it will because they are the construction. Then we will see what I do.

Regards
Michael

I find the same issue with my edlebrock 1409 as well given common lineage between the carter, Weber and edlebrock carbs I think you will
Not see improvement

 

[MichaelBC]

I find the same issue with my edlebrock 1409 as well given common lineage between the carter, Weber and edlebrock carbs I think you will
Not see improvement

I also do not expect any difference.

 

[achris]

Hello Chris,
thank you for your patience. My boat is 20 feet long and even it is very unlikely that I could not hear the buzzer or the engine I do accept your arguments and value your expertise. I also don't want to kill myself on the boat.

I do not like this manual carb fill button. What would you think if I put in a timer relay switch that gives voltage to the fuel pump for maybe 5 seconds every time I turn the ignition on and then switches back to the oil pressure switch. So if the engine is runnig it is the oil switch only and if the engine stalls the fuel pump would be off. But every time I turn on ignition it gets a short push. Would that be acceptable ?

Regards
Michael

It appears that it doesn't matter what I say, you have a counter argument. So I will leave this as my last comment on the situation. Good luck with whatever you decide to do.

Chris....

 

[Scott06]

I also do not expect any difference.

It does not bother me so much because otherwise the boat performs really well. my dad lives on a lake so i keep the boat there, he is retired so maybe with too much time on his hands bothers him more. He sprays a little staring fluid in the flame arrestor this runs the engine until the carb fills...
for me i cannot carry the starting fluid... beer in one hand, bag of ice in the other.

 

[nola mike]

It does not bother me so much because otherwise the boat performs really well. my dad lives on a lake so i keep the boat there, he is retired so maybe with too much time on his hands bothers him more. He sprays a little staring fluid in the flame arrestor this runs the engine until the carb fills...
for me i cannot carry the starting fluid... beer in one hand, bag of ice in the other.

When I was trying to tune it last summer, there was fuel in the bowl every time I took the top off to change the jetting on my 1409. Out of curiosity, how long do you need to crank before the bowl fills/it starts?

 

[Lou C]

And that's the advantage of a mechanical fuel pump, the engine stalls, pump stops, if the pump diaphragm leaks, the gas goes into the yellow overflow hose. Too bad modern GM small blocks did away with mount for the mechanical pump. And the pump will not fail to run if there is a wiring issue, corrosion, etc. Cheaper and at the same time more reliable. IMHO better for a carbed engine.

 

[MichaelBC]

It appears that it doesn't matter what I say, you have a counter argument. So I will leave this as my last comment on the situation. Good luck with whatever you decide to do.

Chris....

I am sorry, I did not mean to offend you.

I did write that I will follow your recomendations to wire back to original and just wanted to hear your expert oppinion about my idea with the 5 second timer relay switch. I thought I was asking in a friendly way so I can not really understand your reaction. But maybe used wrong words as I am not a native english speaker.

Thank you for all your input.

 

[Scott Danforth]

'nuff said in the picture below

the great thing about the factory wiring. there is a feed line from the crank circuit. when you crank the engine, the bearings and cam get some oil and the carb gets fuel.

 

[achris]

I am sorry, I did not mean to offend you.

I did write that I will follow your recomendations to wire back to original and just wanted to hear your expert oppinion about my idea with the 5 second timer relay switch. I thought I was asking in a friendly way so I can not really understand your reaction. But maybe used wrong words as I am not a native english speaker.

Thank you for all your input.

Not offended. I have explained the situation, and the whys and wherefores, but you seem to keeping coming up with reasons not to listen, so....

5 seconds may not be enough. What's the problem with a momentary switch?

 

[achris]

.... staring fluid ...

Great way to stretch head bolts!

 

[Scott06]

When I was trying to tune it last summer, there was fuel in the bowl every time I took the top off to change the jetting on my 1409. Out of curiosity, how long do you need to crank before the bowl fills/it starts?

Maybe 25-30 seconds. It seems like a long time when cranking and the buzzer is going off. I think not only is it refilling the bowl but getting gas through the idle circut passages again.

 

[nola mike]

I started last week for the first time this season. I did jump the pump for a few seconds before attempting to start, and it literally took 1 crank (couldn't believe it). It's now sat a week, and I need to drain the block tonight (groan). I'll start it and see how long it takes to fire first.

 

[Rick Stephens]

Hello Chris,
thank you for your patience. My boat is 20 feet long and even it is very unlikely that I could not hear the buzzer or the engine I do accept your arguments and value your expertise. I also don't want to kill myself on the boat.

I do not like this manual carb fill button. What would you think if I put in a timer relay switch that gives voltage to the fuel pump for maybe 5 seconds every time I turn the ignition on and then switches back to the oil pressure switch. So if the engine is runnig it is the oil switch only and if the engine stalls the fuel pump would be off. But every time I turn on ignition it gets a short push. Would that be acceptable ?

Regards
Michael

Michael,

I gotta say this thread has made me very uncomfortable. Setting things up as workarounds to basic safety features is not my comfort zone. The logical simplicity of the fuel system in gas powered boats is necessity for safety. Yeah, you can get away with bending rules for the most part, until one day you can't. Boats and fuel leaks don't wait long to go boom. Happens often enough to give anyone pause. Strict quality control and maintenance on the entire fuel system and none of those features matter - not running the blower, not the safety interlocks built into fuel pump power, not carb venting. But it only takes one leak.

I have a 4.3L that I built the entire system from the ground up. It has the Edelbrock. And it had the problem of emptying all its fuel out when left sitting. Been pretty well minimized with one way check valve and a go through on the carburetor. But I still have to prime the carb by manually powering the pump if it sits for more than a week, or crank for 20 or 25 seconds, which I dislike.

I take jobs working on boats all the time. Mostly welding on aluminum hulls used in rocky rivers. If I see the fuel safety systems bypassed I won't work on them, even unrelated repairs. Boats burn really well.