1984 Mercruiser 350 Issues

[Koa]

Hello all, thought I’d make it through the whole season without any major issues. I was sadly wrong.




This past weekend I went to start the boat and it wasn’t starting like it normally would, the starter sounds like it engages for about one second and then just spins. Ended up taking off the power steering belt and it fired up.




Then once I had idled out of the no wake zone and tried to bring it up on plane it bogs down and will stall out if I don’t back off the throttle. If I put it in neutral and throttle only it will go full rpm, but under load it will bog down and eventually stall.




It will then not start unless you allow it to sit for a little while. So I pulled it out of the water and checked the usual suspects.




I replaced the fuel filter, spark plugs (all of which on starboard side were badly fouled, port side looked clean), did an oil change, and checked the filter before the carb which was clean.




Now it starts up pretty easily ( I think the starter may still be bad). But it still won’t go WoT. You can’t even slowly ease it up on plane.




I’m not sure what the next steps should be, it appears to have enough gas going into the carb, but possibly a bad fuel pump? Or maybe something with the distributor? Gas in the tank is clean and fresh.

 

[Maclin]

The starter issue could be corroded connections. Clean the battery terminals and inside the battery cable terminals, also the connections at the starter, also the ground connection to the engine and any other related grounds.

The carb may be flooding. What are you doing with the throttle when it won't start? Is there a strong raw fuel smell at the engine?

Spark plugs, were they sooty as in carbon fouled? Or wet and clump like oil fouled.

Hopefully you are using the blower as safety measures prescribe.

 

[Koa]

With the throttle I tried starting it without giving it any gas. No luck, so then I tried pumping a few times and still nothing. Spark plugs looked carbon fouled. But it was just the one side. Yes, blower is running the whole time but there wasn’t a noticeable gas smell

 

[Rick Stephens]

A thorough carburetor rebuild would not be out of line.

I can't think of a simple reason one side of a motor should foul spark plugs and the other side is nearly clean looking. You should start right out with a compression check to see if we can find a cause.

 

[Scott Danforth]

clean looking on one bank only is water steam-cleaning it.....my guess either crack, bad elbow joint or head gasket

do a compression test.
check your manifold/risers for a breach.

 

[Maclin]

Well, if it is flooding then pumping it will make it worse. For flooded condition, remedy is to open the throttle past 3/4 and crank until it feels like it is clearing and trying to start.

 

[Scott Danforth]

if the clear/yellow tygon tube from the fuel pump to the spark arrestor has fuel in it, then your fuel pump has failed and is dumping fuel into the carb. Easy fix if that is the case, change fuel pump (and do an oil change)

also, another issue with rochester carbs is that the welsh plugs eventually leak, causing the motor to flood. that is an easy fix as well.