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    1970 25hp deceleration after run at WOT

    Took out the boat today. After thoroughly cleaning the carb, clearing out fuel lines and connectors with compressed air, and replacing the fuel pump gasket it runs like a top. Ran great at WOT and seems to be running better. Thanks for all the suggestions. My guess is some junk clogged up the...
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    1970 25hp deceleration after run at WOT

    I’ll check the cap next time I’m out on the lake. Good idea , thanks
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    1970 25hp deceleration after run at WOT

    It’s the old style cap. Simple screw with hole and o ring . It vents when you unscrew the top screw like the cap on my old Johnson metal tank-manual vent. I have a plastic tank that I put this cap on. Vents like old style metal tanks (not pressurized). Check online reviews for the cap I...
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    1970 25hp deceleration after run at WOT

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    1970 25hp deceleration after run at WOT

    The new gas caps do suck. I ended up buying the old style cap with simple vent screw on top on eBay last year. They are harder and harder to find. The vent on the cap was open. Hopefully I can get the boat out in the next few days. Weather has put a delay on taking it out....it’s been raining
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    1973 johnson 25hp 25R73A

    Great motors when they run good. I liked my 71 so much I picked up a 70. The early 70’s 25hp OMC’s are super light weight and even when they “act-up”…they sill managed to limp back to the dock.
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    1970 25hp deceleration after run at WOT

    Rebuilt the carb today and cleaned out all fuel lines. Forecast calls for rain tomorrow but will take it out on the next clear day and try pumping the bulb and test using timing light.
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    1970 25hp deceleration after run at WOT

    Thanks. It runs great for few min then starts slowly decelerating. If carb rebuild doesn’t solve it, I’ll try pumping the primer bulb before rebuilding the fuel pump to see if power increases. Also will test with timing light before and when it starts losing power. Thanks for all the input...
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    1970 25hp deceleration after run at WOT

    Thanks. Got the carb rebuild kit today and carb is nice and clean. Will plan to take it out for test ride soon. I did test the fuel pump again by doing the “blow test”. I noticed I can blow somewhat into the outlet -it’s not completely blocking the entry of air. Curious if this is a sign it may...
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    1970 25hp deceleration after run at WOT

    Ok I checked spark as recommended using open air spark tester. Both leads jumped gap greater than 1/4”. Also noticed bright blue sparks. I checked fuel pump diaphragm by blowing into inlet side and heard a “horn” sound. Blew into outlet and it was solid. Although the gasket appears bit old and...
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    1970 25hp deceleration after run at WOT

    Racerone, I think your talking about the control lever pin. If so, that was a good idea to check that. However I just checked it and that “plastic” pin is still in one piece as well as the impeller pin. Thanks Racerone
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    1970 25hp deceleration after run at WOT

    Yeah it’s weird, the same motor (70 vs 71) but the 70 sounds like its running way higher top end RPM’s. I’ll borrow a timing light and read up on how to test it with light. Forgive my ignorance recerone, but could you provide me with a part reference number or another description for the...
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    1970 25hp deceleration after run at WOT

    And yes running 50.1 OMC outboard oil
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    1970 25hp deceleration after run at WOT

    Thanks for the responses. I will plan to check the fuel pump, I have a 71 25hp that runs good and I had replaced that motor’s fuel pump last year with a new OMC one. I’ll swap that fuel pump on the 70 that’s giving me issues and see if that works. I replaced the fuel line and new primer bulb...
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    1970 25hp deceleration after run at WOT

    I replaced the impeller and checked the fuel pump screen few months ago. I’ll check the fuel pump again. I will also plan to pull the thermostat (recently replaced) once it warm and make sure it’s getting water….
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    1970 25hp deceleration after run at WOT

    Hello, I have a 1070 25hp Johnson that’s been running great. Recently when I took it out, after running it for 5-10 min at WOT I noticed it began to decelerate. It didn’t seem like it was missing but instead just felt as though I was turning the throttle down. After I dropped the throttle and...
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    Slow speed needle valve for 1971 25hp Johnson

    Great info thanks. Just still curious if that needle for a 72 would work in a 71. If not I will look to “fix” the old one or try that outboard parts store mentioned.
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    Slow speed needle valve for 1971 25hp Johnson

    The slow speed needle valve on my 71 25hp Johnson is worn and slightly bent although I straightened it the best I could. Im looking to replace it and noticed there are none available on eBay or any of the OMC parts online stores. The part number listed is 314691. I noticed there are slow speed...
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    1970 25hp Johnson lower paint question?

    Will do. It shipped today. I’m interested to see how the paint looks and holds up. Cool to see you also have a 70 25hp Johnson. I also have a 71. They are great motors once they are dialed in. I bought a service manual on eBay for cheap and it’s got good info along with YouTube and this forum
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    1970 25hp Johnson lower paint question?

    Thanks just ordered paint from vintage outboard.
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