Mercruiser Issues

[fcveazey]

Someone help! Got a 350 Chevy M/C. Background. Just purchased 5 months ago and ran poorly. Took it in and ended up replacing manifolds and risers, starter, waterpump, alternator, distributor cap and rotor, and had the timing set.Boat runs nice and cool now 125 130 tops, and runs like a top for 30 mins (you can almost set you watch to it ) then it starts missing a little, gets progressively worse till the point which it will not run or re-start. Backfires through the carb etc. etc. etc. After an hour tow back to the ramp it starts and runs fine to get on the trailer. Just had the carb overhauled and changed the water seperator filter ( no water or contaminants seen ) plugs and plug wires are brand new.
I'm leaning towards replacing coil next then fuel pump. Has anyone seen this before. It's driving me up the wall!!!! Its happened 3 times in a row now. I know all of the Sea Tow guys on a first name basis!! lol

 

[mkast]

Re: Mercruiser Issues

When the engine fails to start you will have to trouble shoot the problem, fuel or ignition. Think before you spend. Far more inexpensive that guessing.

 

[maxxman04]

Re: Mercruiser Issues

check the choke on carb. also, may want to have tank checked for vapor lock.

 

[pocrain]

Re: Mercruiser Issues

Someone help! Got a 350 Chevy M/C. Background. Just purchased 5 months ago and ran poorly. Took it in and ended up replacing manifolds and risers, starter, waterpump, alternator, distributor cap and rotor, and had the timing set.Boat runs nice and cool now 125 130 tops, and runs like a top for 30 mins (you can almost set you watch to it ) then it starts missing a little, gets progressively worse till the point which it will not run or re-start. Backfires through the carb etc. etc. etc. After an hour tow back to the ramp it starts and runs fine to get on the trailer. Just had the carb overhauled and changed the water seperator filter ( no water or contaminants seen ) plugs and plug wires are brand new.
I'm leaning towards replacing coil next then fuel pump. Has anyone seen this before. It's driving me up the wall!!!! Its happened 3 times in a row now. I know all of the Sea Tow guys on a first name basis!! lol

I'm not a trained tech but it certainly sounds like a coil to me, one thing I learned years ago is when installing a coil to be certain there is a space under the coil to stop heat tranfer as much as you can as heat shortens the life of the coil. You could check the fuel pressure if you are set up for it.

 

[fcveazey]

Re: Mercruiser Issues

Checked the vapor lock thing last time out..at least between the filler and the tank. If I'm not mistaken, the coil is sitting right on top of the intake (touching), thats a good point it may be transferring excessive heat. Thanks. As far as troubleshooting while broken down, I really don't know what else to try except buy a new coil, and replace the existing one with a new, cool one and see if she starts. Back to the vapor lock thing. when fuel heats up, it becomes less dense and expands. What are the possibilities that the pump is bad at a particular fuel density ie warmer less dense, but at cooler temps, it is pumping enough volume to keep the engine running? Just a thought.

 

[fcveazey]

Re: Mercruiser Issues

Additionally, as far as the choke goes, carb and choke were completely ohauled last week. What about the coil spring/heater that actuates the choke? Could that be bad. I heard theres a way to disconnect that and plug the holes with stainless plugs. Anyone ever heard of that? I live in FL, so I really don't think warming the base of the carb is necessary.

 

[bparsel]

Re: Mercruiser Issues

I really dont think it's a choke issue, besides all you need to do is pull the air element and look to see if its a choke issue when the problem occurs. Simply run the boat and watch the butterflys.

Also, overheating the coil doesnt make much sense either, you'll hit maximum operating temp well below that 30 minute mark and the heat transfer would take place. I would look more into a vapor lock situation from the timeframe you are describing.

Vapor Lock Service Bulletin

http://www.boatfix.com/merc/Bullet/99/99_07.pdf

 

[fcveazey]

Re: Mercruiser Issues

Thanks Bparcel. The Mercruiser Service Bulletin is awesome. I t definately gives me alot more to consider on the fuel side of the equation. I have to be honest, I was leaning towards the spark. Again, thankyou!

 

[wca_tim]

Re: Mercruiser Issues

if it's backfiring throug hthe carb from a fuel issue, it's leaning out. as mentioned above a fuel pressure gauge would be a good investment. You can pick one up that will fit in the line roight in front of the carb for very little at an auto parts store. That will at least tell you where to look

 

[Bondo]

Re: Mercruiser Issues

Just had the carb overhauled and changed the water seperator filter ( no water or contaminants seen )

if it's backfiring throug hthe carb from a fuel issue, it's leaning out.

Ayuh,... Hook it up to a remote tank at the fuelpump or fuel filter...

Sounds like either the Fuelpump or the Fuel Tank has Issues....

 

[fcveazey]

Re: Mercruiser Issues

Fuel tank sounds a little far out to me since one day I used it for 4 hrs with no prob, then the next time I used it, it started this missing thing.

 

[rbh]

Re: Mercruiser Issues

could you have any rubber fuel line thats old enough to compress/shrink as the engine heats up?
rob

 

[Bondo]

Re: Mercruiser Issues

Fuel tank sounds a little far out to me since one day I used it for 4 hrs with no prob, then the next time I used it, it started this missing thing.

Ayuh,... That speck of Crap had to find it's new home at some point,...
It sounds like that point was at the beginning of the last trip....

But,... Whatever.... Just keep Throwing Parts At It,...
Eventually you get it Right...
Diagnosis is for Poor folks....