Mercruiser 470 Second Start

[saltydogjeff]

I got my boat out on the water, and initially, it runs great. I can steadily run with no problems (longest being about 20 minutes at 3000 rpm). Then I stop and go fishing for a little bit. I've noticed after the last two times, after I break, I start up the engine, idles fine, but then when I get up to cruising again, the engine will stall out unless I go into low revs. I think it has something to do with the gas, because it is the same tank of gas that was in the engine when I bought it, and I believe it is about a year old. I would say its the gas, but also, when I hear the engine running, I hear the carb spraying fuel into the intake, and it sounds like when I try to run higher revs and it is having a tough time getting power, that I don't hear fuel spraying through the carburetor. I think this could be a fuel filter problem, because I removed the fuel filter on the fuel pump previously because of fuel delivery. Maybe something in the lines is getting clogged. Has anybody run into this issue before?

 

[saltydogjeff]

Re: Mercruiser 470 Second Start

Update. I forgot that the electrical line from the carburetor broke. Maybe that?

 

[carguy001]

Re: Mercruiser 470 Second Start

The wire is for the choke need to verify the choke is opening once motor is at temp, that would cause it to not get enough air. Also need to make sure you have the correct fuel psi some where around 7-12 pounds (I think). Ensure there are no blockage in the fuel line from the tank to the pump and same from pump to carb. Other things to check is points, plugs, wires,cap&button, also the coil, the ignition system can become heat soaked and not perform as they should. If the boat had old gas in it might look at rebuilding the carb.

 

[yamhoss86]

Re: Mercruiser 470 Second Start

Its the gas, Since the gas has been sitting for sometime, the octane in the gas is low.
My suggestions is you get a portable gas tank to run the engine for a few mins, then switch gas tine to the gas tank and run the bad gas out.

 

[saltydogjeff]

Re: Mercruiser 470 Second Start

I took the boat out again today, after trying to run as much of the fuel out as possible previously, and putting fuel stabilizer, and diluting the fuel with more fuel. So, I think I ran into the same problem, where things run great, then after starting it back up, it has power issues.

Now, I think I have solved the problem, but I need help with correcting it. So, the reason I assume it is a dieseling, or pre-detonation problem is when I ran the engine the second time, when I shut the engine off, I heard a cylinder fire again with the ignition off. This causes me to think the engine heats up, then begins to diesel not igniting at the correct position, via TDC instead of 8 deg TDC, therefor causing the slack in power.

What do I need to do? Should I take off the intake manifold and file it to remove the carbon and clean up the block? I saw the video of the guy filing the block for a flat surface, and also read a couple of threads over this issue. I had a compression test done, and I forget the exact numbers, but it was something like 165, 180-185, 180-185, 180-185, where the first cylinder was low, but all the other cylinders tended to have a high compression.

 

[saltydogjeff]

Re: Mercruiser 470 Second Start

I think I'm going to try pouring water down the carb, and then using sea foam.

 

[Bt Doctur]

Re: Mercruiser 470 Second Start

What do I need to do? Should I take off the intake manifold and file it to remove the carbon and clean up the block

You dont really know what your talking about let alone trying to tell you how to do it. This link will get you to the manuals that you need to read BEFORE starting any kind of work.They say "Ignorance is Bliss" bit it can get very expensive.
Take yorr time to read up about these motors first, then attempt working on them.

 

[NHGuy]

Re: Mercruiser 470 Second Start

Dieseling will happen if the motor is really hot on shutdown, and it happens when the idle is too high. And it is sometimes exacerbated by overly advanced timing. So check that your idle is down low, and run it at 11 or 1200 rpms for 30 sec or a minute to lower your engine temp before you bring it down to idle and then shut it down. If it still diesels lower the idle more. I have stopped dieseling car and boat motors by turning off the ignition and then putting the shift into gear too.
Dieseling is bad for the motor, you need to get rid of it.

 

[saltydogjeff]

Re: Mercruiser 470 Second Start

After further thought and discussion, I think it could be vapor lock. I replaced the fuel line when I replaced the carburetor. I am going to insulate the fuel line, and also do the seafoam in case it is dieseling/pre-igniting. Hopefully one of those will fix the issue.