4.3 v6 mercruiser late 80's engine problems at full throttle.

[Tyraz34]

Hi everyone- new to iboats, new to forums. Forgive me if I come off stupid ahead of time...
Here's my issue, hoping someone can help with some advice.
Started with a hole in the oil pan. Pulled engine replaced the pan, everything seemed fine.
Took the boat out and it runs great at slow speeds. Starts up fine, sounds good.
Once you open up the throttle, it picks up speed, planes out fine runs great. Then shortly after, it began to lose power. If you keep the throttle down you can hear this loud click from the engine compartment. The first time out the boat would sputter and pop then sometimes stall out. If I bring it back down to low Rpm it goes back to normal and I can open it up again with the same problem.
Took it home did some digging. Found one of the plugs on the dist cap wasn't seated properly, or at all for that matter. Took the fuel line off of the carb inlet and found what looked to be a small amount of sand in the filter.
Took the boat out again this weekend and the same problem happened, but it did seem to run better and take longer before it lost power. The clicking sounds like something flapping almost. Any quick trouble shooting methods out there to try? Should my first step be get an external tank and see if I have the same problem? Has anyone had this kind of problem? Engine info below.
Mcm 176
B627270
262 cid 4.3 l v6
1985-1987

Appreciate any advice and help.

 

[Scott Danforth]

welcome aboard

start by cleaning your tank and your carb (your running out of fuel because something is plugged) its called a lean sneeze

the crud in your fuel line that you found is a tell-tale indicator of crud in your tank

 

[Tyraz34]

Seems to be the common theme I'm seeing. Thanks Scott.

 

[alldodge]

Suggest emptying the filter into something clear like a baggie, and see if anything is in there besides gas. If filter has not been changed, change it now. Then run it as you mentioned on a gas can without the anti siphon valve. If it still does it check the lines and fuel pressure, then the carb

 

[Scott Danforth]

Seems to be the common theme I'm seeing. Thanks Scott.

most people dont run their boats enough to turn the fuel enough times to keep the fuel system clean

sitting ships go to shi#

 

[harleyman1975]

I think you disturbed some sitting crud someplace in the fuel system either in a line or in the carb itself. start at the tank and check/change lines, anti syphon valve, water/fuel separator, and then carb. why carb last? so that it does not get re-contaminated by a dirty fuel system.

 

[Bondo]

The clicking sounds like something flapping almost.

Ayuh,..... Welcome Aboard,..... That's Detonation, probably from a lean condition,....

Don't keep runnin' it when ya hear that noise, as that's the motor consumin' itself,....
It don't take very long to hole a piston, or burn the valves up,....

 

[Tyraz34]

Thanks everyone- think I need to know what to do. One question- how do I know if the boat is equipped with fuel water separator? Is the filter inside the pump? Also a pickup filter assuming? The fuel line runs straight to the pump then straight to carb. Thanks

 

[alldodge]

Thanks everyone- think I need to know what to do. One question- how do I know if the boat is equipped with fuel water separator? Is the filter inside the pump? Also a pickup filter assuming? The fuel line runs straight to the pump then straight to carb. Thanks

My bad, your filter is part of the pump. Just connect the hose going to the pump into the gas can

 

[Tyraz34]

Ok have some more questions guys.

So I took the fuel pump off the block. I took the top cover off and there is a small round cone shaped porus rock type thing inside and it was gunked up. First question, what is that? I also started pumping fuel out of the gas tank and it looks fairly clean. Is that some kind of filter?

Side note, should I just replace the pump? Looks to be the original if not it's old as hell anyway. The rock filter thing has a small chip in it where it looked like all the gunk was forming/stuck.

 

[Tyraz34]

Here is a picture of it

 

[alldodge]

The stone is the pump filter part number 35-8M0046752. From the look of the pump and filter I'm thinking your gas may be OK
http://www.mercruiserparts.com/bam/s...y/31472/919/80

 

[Tyraz34]

Ok I bought a new filter and cleaned all that crud out. Are you saying you think the gas would be ok because the pump is so gunked? Or it doesn't look that bad either? Thanks

 

[alldodge]

Once you open up the throttle, it picks up speed, planes out fine runs great. Then shortly after, it began to lose power. If you keep the throttle down you can hear this loud click from the engine compartment. The first time out the boat would sputter and pop then sometimes stall out. If I bring it back down to low Rpm it goes back to normal and I can open it up again with the same problem.

This was telling me you were running out of gas, not bad gas. Now that you found a pretty much clogged filter it could be you will be fine, so long as the pump can pump all the way to WOT between 4-7 psi.

 

[Tyraz34]

Yeah once I found this I thought that had to be the problem. But where did the crud come from? That's my concern and will it happen again in the near future...

 

[Tyraz34]

Also, when putting this thing back on is there anything special I have to do? I.e. Put gas it it, lube something, etc...

 

[alldodge]

The crud probably came from many years of no filter changing. I'm using your comment that the fuel is clean and smells like gas, so if that is the case, just flush the line then go.

So far as installing the pump just slide the pump rod back into the motor and make sure the pump arm is on the end of the rod and not on the side of it. Your not going to be able to prefill the filter, so it will take a bit more cranking to start

 

[Tyraz34]

Awesome thank you for your help.