Starting Carbureted engines

CARIBOU

CARIBOU

Member
Jun 4, 2019
56
Wiarton. Georgian Bay, Ontario Canada.
Boat Info
1989 340 Sundancer Humminbird Helix 7 6.5 Quicksilver Genny/ a/c / Central Vac/ Ice Maker.
Engines
Twin 7.4,s Shaft Drive
Hello there, 1989 340 Sundancer twin 7.4,s with carbs and mechanical fuel pumps. Any suggestions on starting procedure of these engines after boat sits for a few days. Im sure fuel is draining back out of carbs but without overhauling and changing fuel system to electric what can I do? I pump the throttles a few times then turn key but to no avail will it fire, after at least 10 -20 pumps it will then fire but stall then retry key and away she goes. There has to be a better and quicker way. Thanks for any help with this Steve.
 
Unfortunately not. What happens is the fuel drains out of the carb and the mechanical fuel pump takes forever to fill the carb back up after it has been sitting for a while. That's why pushing the throttles forward 10 times does absolutely nothing until the fuel gets back into the carb.

Once the fuel gets back to the carb....then it is about the choke to keep it running.

You can see it for yourself if you pull the spark arrestor off and have someone else advance the throttles and keep the choke open. No fuel equals no start.

To fix the problem.....you have a couple of choices:

1) The cheapest solution is to do nothing and live with it. Many have but that translates into replacing the starter at some point.

2) Next up is changing the fuel pumps to electric. This includes an oil pressure safety switch and a fuel pump block off plate. Around $250 per engine. I wire them up with a Prime momentary switch that energizes the fuel pump with the engine off to get fuel to the carb.

Once you have fuel at the carb.....you are good to go.
 
PlayDate said:
Unfortunately not. What happens is the fuel drains out of the carb and the mechanical fuel pump takes forever to fill the carb back up after it has been sitting for a while. That's why pushing the throttles forward 10 times does absolutely nothing until the fuel gets back into the carb.

Once the fuel gets back to the carb....then it is about the choke to keep it running.

You can see it for yourself if you pull the spark arrestor off and have someone else advance the throttles and keep the choke open. No fuel equals no start.

To fix the problem.....you have a couple of choices:

1) The cheapest solution is to do nothing and live with it. Many have but that translates into replacing the starter at some point.

2) Next up is changing the fuel pumps to electric. This includes an oil pressure safety switch and a fuel pump block off plate. Around $250 per engine. I wire them up with a Prime momentary switch that energizes the fuel pump with the engine off to get fuel to the carb.

Once you have fuel at the carb.....you are good to go.
Click to expand...


Unfortunately not. What happens is the fuel drains out of the carb and the mechanical fuel pump takes forever to fill the carb back up after it has been sitting for a while. That's why pushing the throttles forward 10 times does absolutely nothing until the fuel gets back into the carb.

Once the fuel gets back to the carb....then it is about the choke to keep it running.

You can see it for yourself if you pull the spark arrestor off and have someone else advance the throttles and keep the choke open. No fuel equals no start.

To fix the problem.....you have a couple of choices:

1) The cheapest solution is to do nothing and live with it. Many have but that translates into replacing the starter at some point.

2) Next up is changing the fuel pumps to electric. This includes an oil pressure safety switch and a fuel pump block off plate. Around $250 per engine. I wire them up with a Prime momentary switch that energizes the fuel pump with the engine off to get fuel to the carb.

Once you have fuel at the carb.....you are good to go.
 
So I should pump throttle twice to close choke, then just turn over engine (5-10) seconds until fuel pump catches up, and it should fire.
 
My 185 had a carbureted 4.3, here was my cold starting procedure.

1. Turn key and let engine crank 5-10 seconds. This would fill the carburetor bowl with fuel.
2. Pull neutral button, pump throttle 3 times. This pumps some fuel into the intake and sets the choke.
3. Set throttle to 1/3 open - crank - it usually fired right up.
 
Welcome to my world. - I'll echo what Bill said for the most part...
Don't bother pumping the throttles until you have cranked the engine for about 5 to 10 seconds - it takes that long to get the float bowls filled back up.
Then I'll pump the throttles about three times quickly - If no signs of life, I'll let the starter rest for about 10 seconds then try again pumping from go.
Usually the engines will fire at the end of step one.
Occasionally, I have to go to step two.

If the carbs have not been rebuilt in a while, I'd seriously consider doing it
 
I really appreciate all ideas I will follow your directions and hope for the best. Up here on Georgian Bay its winterization time so I will definitely give it a try this week before Haul out. Steve.
 
First of all, where do you think that fuel in the float bowl is going?? It's NOT going backwards through the mechanical pump and back to the tank!! The float bowls fill from the top, so there is no way for any siphon effect to pull the fuel out of the bowl. If the bowl is empty, then it's either evaporating (which should take a LONG time) or it's draining into the intake manifold and down inside the engine. Quadrajets were "famous" for doing this and there are many theads about how to get this resolved the right way.

Pumping the throttle with empty bowls does nothing. Like trying to flush a toilet that has no water. First crank the engine for at least a few seconds. THEN pump the throttle once or twice. This does two things... one, it resets the choke to a closed position (some engines will do that without moving the throttle. Second, it injects a bit of gas using the accelerator pump. Since these pumps (usually) draw from the lowest part of the bowl, you only need a little bit of fuel to make them work. If you're not squirting in fuel (because your accelerator pump is defective) it will make cold starts even harder. Most boats don't even need an accelerator pump for normal operation because you virtually never snap the throttle open like you do in a car when you punch the throttle, so you likely would never know that the pump is faulty, except for really hard cold starts.

If you are having cold-start problems, first check that the choke plate is indeed closing all the way when the engine is cold. Second, check that the accelerator pump does indeed squirt fuel into the carb when the throttles are advanced.
 
km1125 said:
First of all, where do you think that fuel in the float bowl is going?? It's NOT going backwards through the mechanical pump and back to the tank!! The float bowls fill from the top, so there is no way for any siphon effect to pull the fuel out of the bowl. If the bowl is empty, then it's either evaporating (which should take a LONG time) or it's draining into the intake manifold and down inside the engine. Quadrajets were "famous" for doing this and there are many theads about how to get this resolved the right way.

Pumping the throttle with empty bowls does nothing. Like trying to flush a toilet that has no water. First crank the engine for at least a few seconds. THEN pump the throttle once or twice. This does two things... one, it resets the choke to a closed position (some engines will do that without moving the throttle. Second, it injects a bit of gas using the accelerator pump. Since these pumps (usually) draw from the lowest part of the bowl, you only need a little bit of fuel to make them work. If you're not squirting in fuel (because your accelerator pump is defective) it will make cold starts even harder. Most boats don't even need an accelerator pump for normal operation because you virtually never snap the throttle open like you do in a car when you punch the throttle, so you likely would never know that the pump is faulty, except for really hard cold starts.

If you are having cold-start problems, first check that the choke plate is indeed closing all the way when the engine is cold. Second, check that the accelerator pump does indeed squirt fuel into the carb when the throttles are advanced.
Click to expand...


This is a very common problem with pre TBI and pre EFI 454s. Virtually everyone of them behaves this way if they have the original Quadrajet and mechanical fuel pump. Most owners get used to cranking their engines for 10 seconds on a cold start.

Some don't and replace the fuel pump and carb so they can have turn key starting.

I personally don't like cranking a starter for that long.
 
Rebuild the carbs and reseal the well plugs when rebuilding. Convert to electric chokes and be patient getting them set correctly. I did this to my 454s along with Racor fuel filters and even after sitting all winter they start without pumping the throttles. They will crank for 3-5 seconds but I prefer that in order to get the oil circulating prior to starting.
 
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