New Problem with 1974 50HP Evinrude

[mstone1968]

I finally got my boat running good thanks to all of everyone's help on here. It has ran great for about a month & 1/2 with NO problems. However this weekend a new problem started. Motor fires up, idling great (in the beginning of that day), moving down the lake at a good speed, then all the sudden it was the same as if you had throttled all the way back then throttled all the way forward, then back and continued to do this the rest of the way in. Like driving a car and alternating your foot with the gas pedal and the brakes. Revs way up then down. Then was hard to start engine and when engine did start up, the idling would rev up then down continually. I took it home, took out the spark plugs, cleaned with sea foam and sprayed the sea foam into carbs and let set. When I fired it back up, it did smoke quit a bit for a couple of seconds, It seems to idle good then it starts to idle fast then slow then quits. Would anyone have any ideas on what to do next. It was running great for a while, then suddenly started acting up again? Any help would be greatly appreciated. I think this motor is still good and I'm hoping it is something minor. It seems like every time it starts running good, something else happens.

Things I have done recently:
1. New Spark Plugs on both cylinders
2. Removed carbs and had them thoroughly cleaned and with a new rebuild kit
3. New Gas Tank, Hose, and Bulb
4. Checked and cleaned fuel pump screen. Opened up the fuel pump and everything still looks good. Doesn't look dry rotted or anything.
5. Adjusted the carb needles as outlined on here.
5. Bought an original 1974 Evinrude Manual for this model. Read through it and adjusted the throttle linkages and fine tuned idling.

 

[jtexas]

Re: New Problem with 1974 50HP Evinrude

I suspect a cylinder's dropping out due to electrical malfunction.

Inspect the wiring from the stator to powerpack to coils, look for missing/burned/cracked insulation, corrosion. Also anything grounded to the engine block, clean the connection good & shiny.

Check for spark with a spark tester - look for a sharp blue spark across a 1/2" gap.

one more thing, unlikely as you just did the carbs - make sure the throttle plates and choke plates are all staying open when they should. and check that linkage between the throttle lever and timer base - it should have a plastic bushing (ball joint) on each end.

 

[mstone1968]

Re: New Problem with 1974 50HP Evinrude

Hello Jtexas,
Thanks for your help, I will look at the wirings, do spark test, and check linkage when I get home. I hope it is only a wiring problem.

p.s I see were you are from Texas. My wife is from Dallas, TX (originally from Garland TX) Her family still lives in Dallas and Plano/Mckinney area. She just returned from there this past week. We live in Kentucky but I have visited Texas on several trips. Thanks for your help.