Mercruiser 4.3 not starting when hot

[Jfreakman84]

Hello all,

I recently purchased a 1996 Bayliner Capri with a 4.3 Mercruiser I/O. The engine was replaced about 4 years ago by the previous owner who is a (car) mechanic and someone I trust to do things right. He used it for two years and said it ran great, every time. He had it running when I purchased it but it had been sitting at least one year. It was winterized before being stored. I've replaced the battery, impeller, and done several other things to help it along.

The first time we took the boat out, it started fine initially, very few revolutions before it caught and ran fine. We rode around a bit and went swimming. Boat took several more cranks the second time but still seemed to start fine. Went tubing, when I shut the engine off while loading new riders it immediately caught. Went swimming again and it was much harder to start but still caught. Went for a much longer drive and went to the ramp to load it up. It died at the ramp and I couldn't get it started. Got it loaded by hand and brought it home

Since the boat was about half full of old gas I thought that the fuel filter might have gotten a bit clogged; changed that and the boat started just fine in the driveway. Ran for about 30 minutes without any issue, waited a bit and restarted it with no issue. Took it to the lake today and had similar experience.

It died after idling for a bit and wouldn't start itself. I removed the flame arrestor and squirted a bit of gas down the carb. Took a minute, but eventually it caught and ran fine for another 30 minutes or so. Went swimming for maybe an hour and started fine after that.

Got it to the ramp, backed away from the dock, and it died. Would not start, even with gas in the carb. Floated around a bit fiddling with it, and finally got towed back to the dock by another guy at the dock with a wave runner. As he was pulling me, turned the key, and it started.

I don't understand what could cause this. Is it a fuel issue? Flooding? Not enough gas? Fuel pump?

It starts great when it's cold and in my driveway. It does not like the dock, apparently.

Thanks for reading this long post and for your help.

 

[dubs283]

You need to check for spark when the engine doesn't start. You've pretty much ruled out a lack of fuel but also, it could be too much fuel, e.g. flooded engine from faulty carb leaking down or something else

Bring an in line spark tester with you to check spark, needs to be bright blue/white and able to jump a decent gap

 

[Rick Stephens]

2 barrel or 4 barrel carb? If you have the 4.3LX with the 4 barrel then you have a Weber carb which has a history of dribbling fuel into the intake when shutdown. Floods the motor making restart tough.

 

[Jfreakman84]

You need to check for spark when the engine doesn't start. You've pretty much ruled out a lack of fuel but also, it could be too much fuel, e.g. flooded engine from faulty carb leaking down or something else

Bring an in line spark tester with you to check spark, needs to be bright blue/white and able to jump a decent gap

I have a cheap one which lights up. Each plug is lighting while cranking. Is there a way that I can see the color or do I need a different tester? Plugs look good, not burnt.

 

[Jfreakman84]

2 barrel or 4 barrel carb? If you have the 4.3LX with the 4 barrel then you have a Weber carb which has a history of dribbling fuel into the intake when shutdown. Floods the motor making restart tough.

I believe it is the 4 barrel carb. Is there a way to fix this or should I replace the carb with a different one?

I'm not a mechanic by any means, I can do small things but rebuilding a carb is way above my level.

 

[Rick Stephens]

I believe it is the 4 barrel carb. Is there a way to fix this or should I replace the carb with a different one?

I'm not a mechanic by any means, I can do small things but rebuilding a carb is way above my level.

If this is the issue, then a rebuild can help. Using an original Merc rebuild kit, or Edelbrock kit (the Edelbrock 1409 is a direct copy of the Weber) is the way to go. Quality needle valve and seat is the main goal here, Needle valve and seat is what controls inlet flow of fuel into the carburetor fuel bowl. That and CAREFULLY checking, double checking float height. Carb rebuilds are not *hard* particularly. They just take patience and attention to detail. A lot of help available here if you want to task yourself. Otherwise, might be a decent carb mechanic close to you.

Buying one is pretty tough. Either you get a new Edelbock 1409 and learn all about how to calibrate it for your motor, or get a maybe (small chance) correct rebuilt one off the market. Neither is particularly simple endeavor. I would personally find it LOTS easier to rebuild one that is already properly calibrated to my motor.

 

[Jfreakman84]

If this is the issue, then a rebuild can help. Using an original Merc rebuild kit, or Edelbrock kit (the Edelbrock 1409 is a direct copy of the Weber) is the way to go. Quality needle valve and seat is the main goal here, Needle valve and seat is what controls inlet flow of fuel into the carburetor fuel bowl. That and CAREFULLY checking, double checking float height. Carb rebuilds are not *hard* particularly. They just take patience and attention to detail. A lot of help available here if you want to task yourself. Otherwise, might be a decent carb mechanic close to you.

Buying one is pretty tough. Either you get a new Edelbock 1409 and learn all about how to calibrate it for your motor, or get a maybe (small chance) correct rebuilt one off the market. Neither is particularly simple endeavor. I would personally find it LOTS easier to rebuild one that is already properly calibrated to my motor.

Thank you. Ill look into that. Does the whole carb assembly have to come off the motor to do this?

 

[Bondo]

Thank you. Ill look into that. Does the whole carb assembly have to come off the motor to do this?

Ayuh,..... Welcome Aboard,..... Do you give it some throttle when yer tryin' to restart it,..??
If not, it might help,.....
If yer carb is dribblin', go to Wot when you try restartin' it, 'n it'll clear the flooded situation,...

To rebuild a carb, it has to come off, 'n be totally disassembled, cleaned, 'n then rebuilt,....

 

[Jfreakman84]

Ayuh,..... Welcome Aboard,..... Do you give it some throttle when yer tryin' to restart it,..??
If not, it might help,.....
If yer carb is dribblin', go to Wot when you try restartin' it, 'n it'll clear the flooded situation,...

To rebuild a carb, it has to come off, 'n be totally disassembled, cleaned, 'n then rebuilt,....

Thank you! I've been reading the forums for awhile now and they've really helped.

As far as giving it some gas, if I turn it off and turn it right back on (when we're tubing or in the driveway) it will fire right up. When it's cold I give it one pump of the throttle and back to neutral and it'll fire up. When it's hot, sometimes it will fire with the throttle about a quarter of the way and sometimes it won't... I'll try with leaving it wide open and see if that helps.

It doesn't have any of these problems in the driveway of course, so I guess I'll have to find a time when it's just me and wife to go. That way if I do get stranded it's not with all the kids.

Is there a way to tell if the carb is dribbling with it on the boat?

 

[Bondo]

Is there a way to tell if the carb is dribbling with it on the boat?

Ayuh,...... The symptoms usually tell the story,.....

To answer yer question,..... When ya shut it down, after a few minutes, pull the flame arrester, open the throttle plates, n ya may, or may not be able to see fuel puddlin' in the intake,....

Does it start hard after sittin' a week,..??

 

[Jfreakman84]

Ayuh,...... The symptoms usually tell the story,.....

To answer yer question,..... When ya shut it down, after a few minutes, pull the flame arrester, open the throttle plates, n ya may, or may not be able to see fuel puddlin' in the intake,....

Does it start hard after sittin' a week,..??

Not usually. I'll give it gas with the throttle and put it back in neutral. It may take a few more cranks but not nearly what I've been experiencing