1973 65hp Evinrude cuts in and out at full throttle

[V1 Rotate]

I have a 65373R 1973 65 hp. When you give it the full throttle it cuts in and out like one cylinder is cutting in and out. The coils were all cracked and fairly old so I replaced them all. The fuel pump has been replaced. Sometimes it does run good and then it runs as if it loses one cylinder. Sometimes if I back off a little on the throttle and then give it the gas it comes on strong for a couple seconds and then dies again. All the fuel is new the tanks are new the fuel lines are all new. Spark plugs are new as well. Compression after warming it up and at WOT is 130 130 128.

Just wondering if anyone has any ideas before I take it to the marina.

 

[shipwreck]

Re: 1973 65hp Evinrude cuts in and out at full throttle

Did check your float , need and seat , and high speed orifice on carb?

That's a 3 cylinder motor , you replaced coil did check the spark plug wires for h with a ohm meter or ( contituny checker ) to make sure that when replaced the coil unit and hooked the the spark boot coil that sank into the wire securely , it could be loose. or did use old wire and just buy the coil?

 

[V1 Rotate]

Re: 1973 65hp Evinrude cuts in and out at full throttle

all new coils and wires boots etc. It did the same thing before I changed the coils. The old coils were all cracked and pretty bad looking so I was going to replace them anyway. All connections are tight. The way this thing cuts in and out makes me think it is electrical since it turns itself on and off like a switch. But carbs are the next thing on my list. I'm just wondering if it could be another part of the electrical system.

 

[shipwreck]

Re: 1973 65hp Evinrude cuts in and out at full throttle

so , you have to restart the motor , dose firer up right away every time after the problem or is there a problem restarting the unit?

Dose the unit have a timing belt , i can tell from the schematic i have ?
possible a messed , Neutral start SWITCH ASSYwhich i beleive is in your control box ( shifter).

 

[jtexas]

Re: 1973 65hp Evinrude cuts in and out at full throttle

did ya do a spark test after replacing all those ignition parts? spark tester, couple bucks at car parts store, set gap at 7/16", look for strong blue spark.

if you have good spark all round, I'm with shipwreck - carb float - you can check the operation of the float valves by blowing through the fuel inlet (best to take carb off engine & drain the bowl first ), premixed fuel is an acquired taste. Held upside down no air should pass, rightside up should be very little resistance. If its been awhile since last carb rebuild, I'd go ahead with that.

 

[V1 Rotate]

Re: 1973 65hp Evinrude cuts in and out at full throttle

I'll do the spark test today. I have really no history on this motor so the carb rebuild is what I will try next. I first thought is was electric since at WOT the one cylinder just cuts in and out but the engine never dies. It starts up real easy everytime.

 

[walter w]

Re: 1973 65hp Evinrude cuts in and out at full throttle

Had the same problem with my 72 merc 65. It was a float bowl seat and needle problem worked fine at half but at full she would ease off for a bit and get back for 10 secs or so after I replaced the seats and needles no more problems. try looking at that.