Merc Cruiser 350 trouble starting when hot

[glastron90350]

I have a 1990 Glastron Futura with a MercCruiser 350 stern-drive. The problem happens when I've been driving the boat for an extended period of time, usually 45 minutes to an hour, and I turn the boat off to relax, fill up on fuel, or take it out of the water. It simply won't crank for 10-15 minutes, and when it does, it takes some real effort. I turn the blower on and let it run before cranking, but it doesn't seem to help. The boat cranks perfectly when cold so, I'm perplexed. I'm the second owner, and have noticed this issue since I bought the boat two years ago. Pretty embarrassing with passengers...any ideas?

 

[bonzoscott]

Re: Merc Cruiser 350 trouble starting when hot

Welcome to iboats! I'm not clear on your description. "It won't crank" means nothing happens when you try to start, turning the key? Then, when it does crank, takes some effort - means it cranks strong but no fire up?
Clean both ends of the battery cables shiny. Then when it cranks good but no fire, check for spark at the plugs.

 

[glastron90350]

Re: Merc Cruiser 350 trouble starting when hot

Welcome to iboats! I'm not clear on your description. "It won't crank" means nothing happens when you try to start, turning the key? Then, when it does crank, takes some effort - means it cranks strong but no fire up?
Clean both ends of the battery cables shiny. Then when it cranks good but no fire, check for spark at the plugs.

I apologize. The engine turns over, but does not start. Battery is new and terminals are clean...I've suspected vapor-lock.

 

[Bondo]

Re: Merc Cruiser 350 trouble starting when hot

I apologize. The engine turns over, but does not start. Battery is new and terminals are clean...I've suspected vapor-lock.

Ayuh,.... Welcome Aboard,.... Is the motor Carbed, or Efi,..?? got a serial number,..??

Are ya workin' the throttle at all, or just turnin' the key,..??

Have ya had it Tuned Up, 'n Serviced in the 2 years you've had it,..??

 

[glastron90350]

Re: Merc Cruiser 350 trouble starting when hot

The motor is carbureted. Original carb from 1990. I don't have the engine serial right off hand, but I can find it. Where would it be located?

Aside from yearly oil changes and winterizing, I haven't done any tune-ups. Is there something specific that could be causing this?

 

[glastron90350]

Re: Merc Cruiser 350 trouble starting when hot

The motor is carbureted. Original carb from 1990. I don't have the engine serial right off hand, but I can find it. Where would it be located?

Aside from yearly oil changes and winterizing, I haven't done any tune-ups. Is there something specific that could be causing this?

Also, I am working the throttle when turning the engine over.

 

[ktbarrentine]

Re: Merc Cruiser 350 trouble starting when hot

I had a similar problem with carb flooding that was caused by a bad fuel pump diaphram, putting fuel into the carb via the sight flow tube. Wouldnt notice it when running, but caused it to have flooded symptoms when trying a hot restart. May not be your prob, but have you checked the sight-flow tube during operation?

 

[glastron90350]

Re: Merc Cruiser 350 trouble starting when hot

I had a similar problem with carb flooding that was caused by a bad fuel pump diaphram, putting fuel into the carb via the sight flow tube. Wouldnt notice it when running, but caused it to have flooded symptoms when trying a hot restart. May not be your prob, but have you checked the sight-flow tube during operation?

Hmmm...I have noticed a really strong smell of fuel when I try and restart the motor, and that's even before I try and give it gas when It won't crank after turning over and over and over...Is the sight-flow tube the clear tube that I see coming out of the carburetor? How would I check it during operation? And would that automatically mean that the fuel pump diaphragm is bad? Thanks for the response

 

[ktbarrentine]

Re: Merc Cruiser 350 trouble starting when hot

Hmmm...I have noticed a really strong smell of fuel when I try and restart the motor, and that's even before I try and give it gas when It won't crank after turning over and over and over...Is the sight-flow tube the clear tube that I see coming out of the carburetor? How would I check it during operation? And would that automatically mean that the fuel pump diaphragm is bad? Thanks for the response

Yes...it's the "clear" (although it seems to "yellow" with age) tube that leads to the back (aft) side of the airhorn. You can check it during operation by observing it while the engine is running to see if you can see flow. I went as far as removing my flash arrestor and could see the fuel coming out of the tube into the carb air horn. Pretty much nailed the diagnosis for me. It means the fuel pump diaphram is leaking (if not totally failed) and the tube directs fuel to the carb instead of into the crankcase where you would have much bigger problems (like.....kaboom!).

You'll see my rig is a 1990 as well... I've been told the fuel pump diaphrams do not like ethanol in the fuel. If it sits for long periods of time, it leads to cracking. At least that's what happened in my case. If this is the case for you, I recommend OEM for the new pump. I went sierra at first. They are made in china and it failed after about 8 engine hours. Best of luck!