4.3l mercruiser no start when hot

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TMcDaniel

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Motor will not start when hot. I have been reading other posts for months and trying to solve my issue. Engine starts great when cold but will not start after it has warmed up. I have been through the vaper lock scenario, tried starting with WOT, batter is good, have cleaned all +- connections, rebuilt carb, new ignition coil, new ignition module in distributor. I have taken the hood off ran it on the muffs at home and still will not start after it’s warm. I have spark tester from the coil to distributor and I am getting spark. The only way it will start after it’s warm is with starting fluid and will run fine until I turn it off again. Please help. Mercruiser 4.3 thunderbolt V 2 barrel carb.
 
rolmops

rolmops

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It sounds to me that the fuel level in the carburetor is being drawn down by the engine running and when you try to start there is no fuel available.
What happens if you try to push to full gas a couple of times before trying to start? And what happens if you allow the engine, when hot, to run at an idle rpm for a minute or two? stop it and then try to start?
 
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TMcDaniel

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It’s a 2001. I don’t know the serial number. The sticker on the flame arrestor is blank. I’ve tried pumping the throttle a couple times and it does not help. The boat is in my driveway on the muffs so it’s at idle the entire time. And if I shut it down and try to restart 5 minutes later it will not start. I have the spark tester hooked up and I am getting spark. 12v to the coil. I’ve tried running a wire directly from the battery to the coil with the same result.
 
Scott06

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TMcDaniel said:
It’s a 2001. I don’t know the serial number. The sticker on the flame arrestor is blank. I’ve tried pumping the throttle a couple times and it does not help. The boat is in my driveway on the muffs so it’s at idle the entire time. And if I shut it down and try to restart 5 minutes later it will not start. I have the spark tester hooked up and I am getting spark. 12v to the coil. I’ve tried running a wire directly from the battery to the coil with the same result.
Click to expand...
When you pump the throttle look down the carb to see if any fuel is shot out from accelerator pump circuit, just trying to figure out if fuel bowl is dry . Thinking fuel leaks down into intake when you shut it off.
 
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TMcDaniel

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When I pump the throttle I can hear the accelerator pump but I’ll check to see if anything is coming out. Any other suggestions in the meantime?
 
alldodge

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TMcDaniel said:
I have spark tester from the coil to distributor and I am getting spark. The only way it will start after it’s warm is with starting fluid and will run fine until I turn it off again.
Click to expand...
Assuming spark gap tester, what is the gap set at and what color is the spark?
 
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TMcDaniel

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Cap and rotor are new wires are only a year old I’ll get a new fuel filter today. It idles around 700rpm without fail.
 
Scott06

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TMcDaniel said:
When I pump the throttle I can hear the accelerator pump but I’ll check to see if anything is coming out. Any other suggestions in the meantime?
Click to expand...
Thinking the fuel bowl is dribbling empty down into intake, leaving engine flooded but carb bowl dry. I get this and hot restart issues on my edlebrock carbed 5.0 ( merc webber same issue), need to open throttle wide to clear the overly rich condition.

If it fires on starter fluid would think there is no gas not too much... again would look in there see if there is a bunch of fuel in intake or if no gas is coming out of the carb. try with choke wide open.

As AD suggested re look at spark quality. Should be nice blue and jump a large gap at least 3/8". If orange would ohm the coil
 
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TMcDaniel

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Scott06 said:
Thinking the fuel bowl is dribbling empty down into intake, leaving engine flooded but carb bowl dry. I get this and hot restart issues on my edlebrock carbed 5.0 ( merc webber same issue), need to open throttle wide to clear the overly rich condition.

If it fires on starter fluid would think there is no gas not too much... again would look in there see if there is a bunch of fuel in intake or if no gas is coming out of the carb. try with choke wide open.

As AD suggested re look at spark quality. Should be nice blue and jump a large gap at least 3/8". If orange would ohm the coil
Click to expand...
I’ve looked in the intake and do not see any fuel dripping out when it’s not running. When trying to start it hot I’ve tried throttle wide open and choke wide open. If the bowl was running dry why would it start right up after cooling down for a couple hours.
 
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TMcDaniel

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Scott06 said:
Thinking the fuel bowl is dribbling empty down into intake, leaving engine flooded but carb bowl dry. I get this and hot restart issues on my edlebrock carbed 5.0 ( merc webber same issue), need to open throttle wide to clear the overly rich condition.

If it fires on starter fluid would think there is no gas not too much... again would look in there see if there is a bunch of fuel in intake or if no gas is coming out of the carb. try with choke wide open.

As AD suggested re look at spark quality. Should be nice blue and jump a large gap at least 3/8". If orange would ohm the coil
Click to expand...
I’ll take the tester off and try looking at it with the wire off see how far I can get it off before it won’t jump.
 
Scott06

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TMcDaniel said:
I’ll take the tester off and try looking at it with the wire off see how far I can get it off before it won’t jump.
Click to expand...
can you adjust the gap on the tester? I have one like this that you can


 
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TMcDaniel

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Scott06 said:
can you adjust the gap on the tester? I have one like this that you can


Click to expand...
The one I have is like this.
 
Scott06

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TMcDaniel said:
I’ve looked in the intake and do not see any fuel dripping out when it’s not running. When trying to start it hot I’ve tried throttle wide open and choke wide open. If the bowl was running dry why would it start right up after cooling down for a couple hours.
Click to expand...
that would point more to heat soak on an ignition component. Starting fluid lights off easier

Test the spark with an adjustable gap tester when it wont restart and ohm the coil

Have you tested spark at plugs, post 1 only mentions spark at coil to distributor. could be loosing spark in dist or wires
 
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TMcDaniel

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Scott06 said:
that would point more to heat soak on an ignition component. Starting fluid lights off easier

Test the spark with an adjustable gap tester when it wont restart and ohm the coil
Click to expand...
I tested the new and old coil yesterday the new one was tested when the engine wouldn’t start. Both tested at 1.2ohm.
 
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