OMC 5.7 no power after rebuild

[PGATOO]

I have a 1989 Bayliner Ciera 2655 with a 5.7 OMC motor and a King Cobra outdrive. End of last season had no RPM or Horsepower. Did a complete rebuild of the engine and now still have the same problem. Can only get about 3500 RPM and 24 mph at WOT. Trouble shooted so far, timing, compression, coil, Alternator, cleaned carb, everything ok so far. Thought it might be gear ratio but even when not in gear rev hits 4000 backfires and will shut off. I am able to restart immediately. My next step is to do a conversion kit for electronic ignition but troubleshooting by buying new parts is getting expensive. I have a 15 x 15 prop. Any ideas are appreciated.

 

[alldodge]

when not in gear rev hits 4000 backfires and will shut off.

First start with a know good hand held tack and verify the rpms

 

[Scott Danforth]

in addition to above

look at the fuel side of the boat.

what is the fuel pressure of the pump?
is your anti-siphon valve working or plugged?

what is the compression numbers?

 

[kenny nunez]

I wonder if there is a restriction in the exhaust like one or both internal flappers are out of place. This same symptom can happen on an auto with a collapsed catalytic converter or on older models that had 2 piece exhaust pipes where the inner pipe would fold and block the system.

 

[PGATOO]

thanks, everyone for the quick response, my mechanic only visually inspected the fuel in the carb and said there was plenty that is why we ruled the fuel side out. We did replace the two backflow flaps in the exhaust and I did notice they were stiff but we kind of ruled that out because it also happened in Neutral with no load, i will inspect though to ensure one or both arent jammed shut. We will inspect them on the weekend and report back. I will also inspect the anti-syphon valve.
Thanks again for all the suggestions. I will report back next week.

 

[Scott Danforth]

if you had the problem before you rebuilt the motor and you still have the problem. rule out the stuff that you rebuilt....what is left.

fuel system and anything ignition or carb related that you did not fully go thru.

did you set the points and timing? if not, start by filing the points, gap them to 0.018, verify gap with a dwell meter - adjust as needed, set timing, then go from there.

 

[Bondo]

if you had the problem before you rebuilt the motor and you still have the problem. rule out the stuff that you rebuilt....what is left.

Ayuh,..... Welcome Aboard,...... This, is key,..^^^....

To rule out the boat's side of the fuel system, hook a remote tank of fresh clean gas, right to the fuel filter,.....

 

[PGATOO]

An excellent idea will do that first!