1973 evinrude 18hp fastwin surges

[B.johnson1993]

I recently bought a 1973 evinrude 18hp fastwin, it starts up good, runs good, but when I accelerate it surges, it doesn't surge in reverse, just forward. It will run good if I'm going slow, but when I open the throttle to go faster it starts to surge and slow down, the boat will speed up then slow down, eventually it'll kill, if this has any correlation with the issue, the two times I've done this when experiencing the surging, I'll put it into reverse then go back into forward and it seems to not surge for me and works how it should at wide open throttle, any advise or comments will help, thanks

 

[hardwater fisherman]

Make sure the water pump is working well. If motor is new to you and you dont know when it was last changed. You should at least install an impeller. After that check for good spark. Also you can try pumping the fuel bulb when it starts surging and see if that helps.

 

[B.johnson1993]

I will try that, thanks

 

[geoffwga1]

Spun Prop.

 

[spacemonkey77]

May check the fuel pump. My 1979 evinrude had similar symptoms. I read that a pinhole in the diaphragm can cause surge. I replaced the pump and no more issues

 

[racerone]

If the engine speeds up and the boat slows down it likely is a problem with the propeller.-----Try a new / different propeller.-----Or is it a short shaft motor on a 20" transom ??

 

[B.johnson1993]

Is there a way to check if the prop spun? And if it did spin is that expensive? Or just replacing the prop will fix it if that's what it is.

 

[B.johnson1993]

Also when the surging happens the engines rpms slow down when the boat slows down, it's not like the rpms are high and the boat is slowing down, if that's makes sense

 

[racerone]

Mark the hub of the prop and the outer aluminum part.----Run the motor as before.--If it acts up check to see if marks are still lined up.-----Also test run with a different tank and hose.

 

[tomhath]

May check the fuel pump. My 1979 evinrude had similar symptoms. I read that a pinhole in the diaphragm can cause surge. I replaced the pump and no more issues

The fuel pump sounds like it could be the problem. Speeding up is a sign it's running lean, then starving out. Try pumping the priming bulb while it's running to see if that makes it run better.

 

[spacemonkey77]

My engine would run fine when cold. When it would warm and I get up on plane it would start to loose power and surge. Almost like bogging down and loosing rpms. Eventually I couldn't stay on plane. Fuel consumption was higher too. A new fuel pump solved it. Sounds to me like this is your issue.

A spun prop would sound more like the prop is cavitating. Reving up rpms, but loosing power. That does not appear to be your issue!

 

[B.johnson1993]

Figured it out, the guy before me must have tried to replace the spark plugs, I had it running with the cover off and noticed one of the spark plugs was loose, pulled it out and the threads came with the plug, put a heli coil in it and it runs great. Thanks for the input on my problem