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OMC 260 GM 5.7L with 800 Stringer drive - Dies once under load

HiZ

HiZ

Member
Okay What I have is an OMC 5.7L GM 350 260hp
Equipped with a 800 Stringer drive

the boat is a 79 IMP INCA

Low hours and looks great
Now for the running issue

Took it out for the first time and it ran great accept when warmed up under load
Runs all day on the ears on land.
About 10 min run time and it will loose power and die out, not totally die. But come off power and you can come to an idle and it will run

So, Looking it over I found the intake gaskets seeping and pulled the intake, replaced them, cleaned the carb, and adjusted idle to 8deg BTDC


Took it back out tonight and it purrs like a kitten, runs well.
But upon acceleration it bogs and then hits.
Let's say you are getting on plane or are on plane and smack the throttle, it will die then take off....

Accelerator pump is working and carb is clean

When the power comes on it is fine again, so cruising for about 10 min and it starts to stumble and fall off power

I came off plane can idled back, it shifts fine and works great when at idle/low rpm


Where do I go from here? I'm not much for points and condensor so any help or a direction to go would be great


It seems to stumble, as if it's missing and it does it only when under load and only when running after a few min say 5-10 under load normal cruising RPM

anything?
 
Check tank vent line - try a run with fuel cap off etc.

Fuel filter?

If the filter is new, I'd tee a pressure gauge into the inlet on the carb and watch fuel pressure when it's acting up under load - should be 4-7 psi

If not 4-7, could be weak fuel pump or a clogged anti-siphon valve at the fuel tank connection.
 
Fuel filter at the carb is good!
What is the fuel/water sep on the side under the manifold
I saw it and it looks greek to me, how does that come apart?
It has a metal canister and is pre the fuel pump

Fuel pump is new and was just replaced by previous owner, not that it makes a bit of difference. I will check running loaded PSI
 
Compression is good ? If yes...

Run it on a fresh external tank of fuel straight to the new fuel pump. Make sure the vent is open.

If the issue repeats pull the plugs on the esa module.

If that fixs the problem post back we will go from there.
 
HiZ said:
What is the fuel/water sep on the side under the manifold
I saw it and it looks greek to me, how does that come apart?
It has a metal canister and is pre the fuel pump

Fuel pump is new and was just replaced by previous owner, not that it makes a bit of difference. I will check running loaded PSI
Click to expand...

lefty-loosey
inspect the canister -it is steel and says to replace it with filter
I don't replace it every time, but if has had water in it, it can rust -pinholes = exploding boat when the bilge fills with gasoline.

I would tear that crap original deathseeking design off and mount the popular spin on Sierra or Mercury water sep/filter on the bulkhead of the engine compartment like all boats have had for the last decade or so.

Previous owner said fuel pump was changed = first thing I would be looking at.
 
Master mechanic said:
Compression is good ? If yes...

Run it on a fresh external tank of fuel straight to the new fuel pump. Make sure the vent is open.

If the issue repeats pull the plugs on the esa module.

If that fixs the problem post back we will go from there.
Click to expand...

Okay, fresh sep tank an same issue
Pull plugs from the ESA? is that the module on the shift system on top where it adjusts?
Looks like there are 2 pig tails up there?
Let me know I will try that this weekend.
 
not necessarily, no ESA originally, but some 79-81 boats were updated to full mech lowers under a program by OMC dealers
 
Master mechanic said:
I seem to remember something like that.

Maybe we can get a picture of the drive sideways.

Then we will know for sure whats on the boat.
Click to expand...
What do I need to take a shot of?
Drive turned all the way to port and stbd?
What section am I looking to take a pic of, transom assembly?
 
BACK FROM THE DEAD!
See how far you get when you leave for work and come back to it being cold out
Okay, So side shot of the drive. I am going to pull the thing out this weekend and get it going.
May be out there tomorrow and roll with it, what do you need a pic of, sideways picture? what angle?
IE: side profile shot of the drive?

How do I service this thing? There is fluid in the drive side and in the transom assem, Correct?
 
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