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  1. #1

    Default 1975 Evinrude 70 hp has started stalling when revving in gear

    Hi to all boat folks, greetings from Sweden!

    My 1975 Evinrude 70 hp (model 70573B) has recently developed this issue where it stalls while putting into gear and revving the engine. You can see it happening in this video recorded earlier today: https://youtu.be/3IfztThmwsg.


    I've had this boat during 4 years and it has been running really good all the way, except for the last couple of weeks. It seems like an intermittent issue. A couple of minutes before this video was recorded I had it running normally, see this video https://youtu.be/7Jzbl2AJUk8. Then suddenly it starts hesitating under load, surges, and then I can only start in idle.


    The problem first arose after a 2-3 hour trip two weeks ago, quite heavily loaded 6 people onboard and packing for weekend on a remote island here in the outer Stockholm archipelago. Engine worked pretty good, no problems on the way out. The day after, I added fuel from my 2 times 25 litres extra cans I brought, to get us home. During this trip home the first signs developed, slightly hesitating but nothing serious at first. Since then the problem has worsened.


    Just before this summer season, I put in 3 new ignition coils (3 cylinder engine) because the old ones had cracks in them, changed as preventive measure. New spark plugs Champion J4C like the manual calls for. Engine running great after new coils installed.


    Now when this issue developed I first suspected carburetor issue or compression loss. Tested compression all three cylinders are at approx 130 PSI (132, 132, 130), nothing suspicious here. Then I turned my attention towards carburetors. I got the carb kits from Sierra and refurbished all three carburetors. No noticable dirt in any of them but cleaned them out good anyway and put new gaskets in, fine tuned float settings etc. Also put in new fuel line from the bulb on, to the engine. Inside engine housing I renewed all fuel lines from the incoming fuel connection to fuel pump, and from pump to main carb.


    At home with water hose it started right away, kind of did a high five and took it back to the water for a real spin. It ran pretty well after the carb service, about 10 minutes without problems then again it started stalling.


    As next step I have emptied the whole fuel tank, took out 50 litres, took the aluminium tank out of the boat, had it upside down, rinsed with fuel and shaking everything out to make sure nothing strange is inside the tank. Got everything back in place and now I'm holding my thumbs it will be running better than this...

    Does anyone have any previous experience or knowledge on this type of behaviour in Evinrude 3 cylinder two stroke from the seventies?

  2. #2
    Join Date
    Sep 2010
    Posts
    20,293

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    Well , J4C is not the correct plug.----I say it is not running on all 3 cylinders.-------Does spark jump a gap of 11 mm or better on all 3 leads.-----Sparkplug is not used during that testing.----Could also be a reed valve issue.

  3. #3
    Join Date
    Sep 2010
    Posts
    20,293

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    deleted

  4. #4

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    Hi. I have the original user manual for this engine which states it wants Champion L77J4 plugs, gap 0,96-1,09 mm (0.038-0.043 in). As I had understood this plug is obsolete 40 years later but the J4C is a suitable equivalent, using copper for better longevity. But, I admit it's difficult to be 100% sure, I certainly appreciate alternative plug spec from a verified working setup, which should I use instead?

  5. #5
    Join Date
    Sep 2010
    Posts
    20,293

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    J4C is the wrong plug.----Find the L77J4 or it's equivalent !

  6. #6
    Join Date
    Sep 2010
    Posts
    20,293

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    J4C is the wrong plug.---Find the L77J4 or it's equivalent !----Seems to be available here in North America

  7. #7

    Default Re: 1975 Evinrude 70 hp has started stalling when revving in gear

    Problem solved! Since last report I've made three changes so I'm not 100% sure what ultimately solved the problem but I believe it was the spark plugs, as racerone already mentioned. Here in Stockholm I could not find the L77J4 easily available but I did manage to buy NGK B7HS10 which I've read many have been using with good results. They certainly work well for me.

    Here is today's reward, nicely running engine 45 years old:
    https://youtu.be/8ZPn8Q2NP8E

    Summary: With fresh fuel from a newly cleaned fuel tank, new fuel lines all the way from tank to carburetors, cleaned carburetors refurbished with service kits, serviced ignition with new coils, plug leads and new plugs (NGK B7HS10), the 70573B engine is running like new again. Seems these engines were designed to last a lifetime. I'm happy it's running fine again, thank you for pointing me at the spark plugs!

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