I give up 78 omc 225hp

[collision]

I have 78 omc 225hp. It will run great for 4 minutes in or out of water then loses rpm and will still run will not rev over 2500 rpms and dies when you try to put it in gear, after it sits for several hours it will run great again. every thing on the engine is new, carb, fuel pump, all ignition and still has not changed. I am lost

 

[NHGuy]

Re: I give up 78 omc 225hp

Try a separate fuel supply, use a portable tank rigged to your fuel line. You cold find that the built in tank has crud that slows the fuel way down.
I don't know if your boat has a version of this problem, but I know of at least one guy who cooled down his ignition amplifier with ice and that's how he found his was bad. When he kept the ignition amplifier sufficiently cooled the engine worked fine. When the amplifier was not chilled the engine would die out when hot.

 

[collision]

Re: I give up 78 omc 225hp

Before I put the carb and fuel pump on i check the tanks and vent tubes put new fuel line on thought it might be vapor locking. It has new points and condensor coil plug and plug wires. this has puzzled many good mechanics, usually i can fix anything but this. I had one boat mechanic say it could be a switch that kicks the rpms back when you put in gear, can not find that switch.
Can not think of anything enternal that could cause this.

 

[Howard Sterndrive]

Re: I give up 78 omc 225hp

I had one boat mechanic say it could be a switch that kicks the rpms back when you put in gear, can not find that switch.

1978 OMC does not have that system


when you replaced the points, did you have a look at the advance weights/springs in the distributor for rust or old, sticky gummy oil?

 

[collision]

Re: I give up 78 omc 225hp

I will check that thanks