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1988 5.7 270 Engine loses power

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onthjug

New member
I have twin 1988 5.7 270hp Crusader Engines. Just recently the Starboard engine will lose power and seem to miss,lose power and bogdown after running 30 minutes under load. It runs fine in Neutral or low power to 1500 rpms. When this happens you can push the throttle up and it will start to climb in rpms for 5 seconds then will bog or stutter like losing fuel. Seems to run a tad rich also. Carbs are old and so is fuel pump but all ignition parts including coil are new. If it sits for awhile it will run up to almost 3000 but never where it should and then start to slow down and lose power then bog. 1500 is about all she will turn. No overheating. When this started at 2800 rpms I heard what I thought was spark knock or pre ignition until I throttled back. My thoughts are fuel pump and or Carb issue. What throws me about carb is why would it wait till under load after time? Possible fuel pump issue?

I have a new pump and was going to install. Carb I would say no matter could stand to be replaced/rebuilt
 
Your first question presupposes the issue is in the carb...

Pump, maybe but not likely....

I'd suspect a restriction in the supply line, likely the screen on the pickup tube... best way to tell is to plumb a vacuum gauge into the fuel line at the inlet to the fuel pump.
 
With that what would explain it running almost ok till it has been running 20 mins or so? I will ck that along with fuel quality for sure. It throws me that a line issue would not be "All" the time under load.
 
Heavy load = more fuel needed....crud suspended in fuel collects at screen on pickup tube...fuel flow is reduced and engine suffers....engine is shutoff and "crud" floats away from nozzle...cycle repeats....

could also be deteriorating fuel (old) but without any water contamination....
 
I had a similar problem with the fuel tanks-crud etc had them cleaned twice but same problem.when boat comes up on plane all the crap runs down to the lower end in tank where the pick up tube is.it gets clogged and bango stalls. I cut into the rubber fuel lines and added barbed tee on the tank side of the fuel shut offs. then using air I would hit the trigger once or twice and actually hear the crap blow off and the fuel bubble.Ran fine until the same thing happens.Mine had a third tank which I removed a while back but I replaced it with a new 58 gal and have eliminated the old tanks altogether.I siphoned all the old fuel out of the old ones and into the new and ran it almost out-now I use only ethanol free clean and nice looking fuel both engines on one 58 gal tank.
 
Its been one thing after another. I replaced fuel pump ordered carb replaced. Went to start engine starter died. Replaced starter new carb has problem and is dumping fuel flooded out rear 4 cylinders. Waiting on replacement carb. I want to inspect tank they are 130 gal failrly mewish aluminum tanks. Guess I need to run out 60 gals first since they are half full
 
back in the sixtys I had a cutless w/ a 4 barrel carb.my buddy got a re-built one in the auto parts store and it still would not run flooding etc.I heard of an old german guy who was a carb spe******t and went to see him.I still remember his words in broken english / german "never,never buy a re-built car-ber-ratttter-alvays re-build ZA-old-Vone!!!!
he did and it ran fine.
 
onthjug said:
......... When this started at 2800 rpms I heard what I thought was spark knock or pre ignition until I throttled back.
Click to expand...
Spark knock or pre-ignition is a different phenomenon from that of Detonation. If your engine is detonating, you'd best catch this ASAP.

Common contributors to Detonation:

Lean fuel/air ratio.
Excessive cylinder temperatures.
Too much ignition spark lead and too early. (see your OEM specs and check your progressive and TA per RPM)
Any/all of the above in a Marine engine load scenario.
 
Update************************************
Removed tank pickup to find plugged with sediment. Elbow was so full im surprised engine ran. Thanks to added extra spin on filters by the tanks nothing has gotten past them into the engine filters.
 
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