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  1. #1

    Default 1973 Johnson 25 hp starts but won't stay running

    First of all, thanks to racerone and others who assisted me a few months ago with my OMC 40 hp military motor starter. Racerone went above and beyond to identify what my motor really is and filling is some very interesting facts.

    Now to the problem at hand. I am assisting a friend who purchased a 1973 Johnson 25 hp Model 25RL73A. He purchased it "as is" and it was not running when he brought it to me. I checked for spark and it had a good strong spark from both plugs. Compression was 92 in both cylinders. I think that is a little low but thought it should run. I then pulled the carb and found several issues. The screw plug at the bottom of the bowl was missing and the hole was filled with caulk! After disassembling, the gasket inside the bowl was missing as was the gasket around the idle jet. The needle valve was not connected to the float with the wire mechanism. I replaced the missing gaskets, screw plug, and a new needle valve and seat. I cleaned up the caulking and soaked the carb in cleaner for two nights. I can run a wire through the passage ways including the three small holes in the throat. I installed new gas lines and gas pump. The motor will start if I spray (mixed) gas down the carb throat but will not stay running. My next thought was the leave valves. I took the intake off and cleaned the crud off the intake plate. The leaf valves looked good. One casked looked almost new but the other was trash so I replaced it. I also replaced the head gasket. Still no changed. It will start with a little squirt of gas but will not stay running. If I pull the screw plug and pump the gas bulb, gas flows freely.

    What am I missing?

    Sorry this got so long but I am wanted you all to know what I have done so far. Any and all suggestions are greatly appreciated.

    wf all, I would like


  2. #2
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Welcome back. The main metering jet is located behind that screw plug....sometimes they are not opened to the correct size, or opened at all. This is removable with just the right size screwdriver. If you have a decent screwdriver you can grind it to fit perfectly, rounding the edges and shortening the end to make a little bit bigger size to fit the larger slot in the jet which is of course threaded in. Careful not to be hasty and mess it up in there. Once you remove the jet, you can carefully clean it to it's normal opening size. I think the 25 horse (22 cu in.) takes a 72D. Make sure that the little donut gasket is making a good seal there in the base of the float bowl.
    Last edited by timguy; 10-26-2021 at 01:35 AM.

  3. #3

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Thanks Timguy for your response. I ordered a new metering jet. When I tried to take the old one out, the PO had messed it up. I measured the ID of the new jet and made sure the old jet was open to that size. The donut gasket at the base of the bowl is also new. Marineengine sent two gaskets with my order. Would it hurt to put both in? Something is causing the air/gas mixture not to get sucked into the combustion chamber. In your opinion, is the compression too low for that? When I had the head off, the cylinder walls were in very good condition. When it runs, it sounds very solid. Still puzzled. Thanks again!

  4. #4
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    The compression is adequate. A real healthy....as brand new 22 cu in will show 120 to 130. I sell them right down to 90 psi. Buyers love em. This is perhaps the most powerful production outboard as power/weight ratio goes. A short shaft non electric start weighs barely 70 pounds, yet produces a strong 25 horsepower. The problem you have is likely not compression related. When you shot carb cleaner into the low speed needle chamber, with the needle removed - of course, did it come out nicely from the little holes on top inside the carb throat?Click image for larger version. 

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    If that little donut gasket part number 40 is not making a good seal then it will not be able to suck the fuel.
    Last edited by timguy; 10-27-2021 at 10:55 AM. Reason: Add photo

  5. #5
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    The term---" strong spark " ----Means nothing to me and others.------The magneto in good condition can jump a gap of up to 5/16" on a test device.----Do that test.----The crud on the reed valves may indicate moisture was inside this engine.-----Possibly stuck rings.------A few hrs of running may free them up.

  6. #6
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Hi, Racer. Glad your here to help. Bruce.....make sure that this port I've marked for you, is open and flowing uninterrupted to the float needle valve.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #7

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Tim and Racer: Thanks for your reply. Tim - We are now in CO but lived in Faribault for 10 years. I really miss MN, especially ice fishing. I have read all the threads on this site about motors that start and won't stay running. There was a 2 screen exchange that you were engaged with in 2019 with Apexmaster34 that I could have written. The thread suddenly ended so I am assuming the person posting gave up? I do not give up, especially on something like this and will respectfully follow all your suggestions and appreciate the time you take with people like me.

    I have a gallon of carb cleaner that I have soaked this carb in. I have run a small wire through all the passage ways as much as possible and blown them compressed air. I will check on your idea of gas coming through the three little holes in the throat later today and get back with you. I mentioned in my first reply that marineengine sent me two of those donut seals. Would it hurt to put both in just to be sure there is a good seal?

    Racer - I have read your description of the spark test several times on this site and will complete it later today as well and report back. Thank you for chiming in on my current problem.

    Bruce

  8. #8
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Okay....l remember that. There is no need to run two gaskets in there.If there is too much clearance for the standard donut gasket to work, then something is wrong with the float bowl....it is warped from being overtightened. You can check if it's sealing by applying a little of your wife's least favorite lipstick. Then tighten normally....not too tight, then remove and look to see the action of the lipstick.
    P.S. Be sure to get permission from your wife first. If she finds your playing around with her lipstick, it could lead to suspicions.

  9. #9

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Racer - Spark jumped very strong the on tester I made. I spread it out to a half inch and it jumped that gap.

    Tim - it is hard to tell with the carb on the motor if carb cleaner is getting from the low speed needle chamber to those three little holes but I did get carb cleaner in the carb throat when I sprayed into the chamber. When I had the carb off the last time, I can get my wire started into those hole but it was difficult to work the wire into the hole very far.

    I bought an inline clear fuel filter today just so I can watch the gas go from the pump to the carb. We have bad weather outside today so it will be a few days before I can try another test run with water. I bought a new fuel pump but the possibility exists that it is not functioning properly. I thought the visual the clear fuel filter offered would help. I will post when I attempt another start.

  10. #10
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Okay, have you had it running without giving it a direct shot of fuel into the carb? Or will it only fire with a prime? Your quote: "It will start with a little squirt of gas but will not stay running. If I pull the screw plug and pump the gas bulb, gas flows freely." So fuel is in the float bowl but not getting into the upper part of the carb in order to be administered. There has to be a blockage or that donut gasket is not sealing.

  11. #11

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Partial Success! I took the carb apart for the umpteenth time for the lipstick test. The carb passed that test with a dark red impression. Reassembled everything and installed the clear bowl fuel filter I purchased yesterday. Without priming the carb throat it started and ran on its own without dying in the first 10 seconds. But I noticed right away that there was no gas coming in from the pump and it died when the bowl was empty. I squeezed the bulb tight again and it fired right up. Everyone once in a while a little squirt would come out from the pump but not enough to keep it running without squeezing the bulb. So I bought a bad fuel pump. The marineengine.com pump is $147.00. They are on EBay and Amazon for as low as $9.95. I think I paid around $20.00 for the one I bought. What pump do you recommend?

    Also, I am missing the linkage between the choke lever and the carb. It must be a rare bird. It is unavailable on marine engine.com. There was one on Ebay for $55.00. Do you have any sources for that piece? It is Part No. 0315236.

    Thanks again to you and racer for you efforts on the behalf of people like me who like to keep old things going. This motor sits besides my 1949 Willys Jeep (that I have had for 32 years) and my 1998 F150 with 317000+ miles on it that pulls my 1971 Starcraft powered by my 1982 OMC Military outboard.

  12. #12

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    A second thought would be that the fuel pump is ok and there is something wrong (obstructing) the port on the side of the motor where the pump attaches that would restrict the pulse coming from inside the motor. Is this possible?

  13. #13
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Rarely is that pulse port plugged. You can check it by loosening the pump and cranking it over. You will see/note/hear some action there. Could you have a leak on your suction side between the motor and the tank? Have you tried a known GOOD tank and hose?
    Yes I may have that linkage....will take a look today while I'm trying to figure out this stupid 3hp that some fool had messed up.
    I embrace older technology and equipment. This new stuff is really not for me. Yes, I have a 1997 F150 with just under 300 thou on it. It is never driven in the winter. It is a fantastic truck.... 4.6 and plenty of power, even towing a boat with the box loaded with heavy gear and the boat loaded with 60 gallon of fuel tanks, twin 25's and 2 100 pound propane tanks weighing in at 170 pounds each. This NEW stuff is not only ugly, it's highly expensive....I don't envy owners/drivers of this newer gear, I feel pity for them. Why does my 74 Chevy 3/4 ton get so much attention...?? I'm just trying to do my job with equipment I can trust.
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    Last edited by timguy; 11-02-2021 at 12:57 PM. Reason: Add photo

  14. #14

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    I replaced the connection on the hose from the tank at the motor as the other one was leaking. I do not see any gas leakage when I pump the bulb. I will get my tank from my motor and give it a try per your suggestion.

    Should there be a squirt of gas from every rotation of the motor? What I am seeing now is a very erratic squirt, not real consistent. I will loosen the pump and see if I can detect action at the port. The motor does not have an electric start so it is a little hard to pull the rope and check for things like that at the same time.

    I know YouTube videos can be suspect, but I have watched a bunch of them covering old Johnsons and have yet to see anyone with this type of issue. It has to be something so simple. Thanks again on your reply and I will get back to you when I learn more.

  15. #15
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    How long does the motor run after it starts ?-----And does it keep running when an assistant operates the manual pump ?

  16. #16

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    As mentioned in #11, I can get it to stay running if I give the bulb a squeeze. Gas is squirting out of the pump at a very inconsistent rate and not keep the bowl on the fuel filter with enough gas to keep it running. Giving the bulb a squeeze forces enough gas into the fuel filter bowl to keep the motor running. That is why I was questioning if I purchased a bad fuel pump. I don't know if I should see a squirt from the fuel pump on a regular basis as the motor turns. I was also at a slow idle (I have read your posts about not over-revving) with the idle adjustment at slightly under two turns. In post #12, my second thought was the fuel pump is good and was wondering if there could be something obstructing at the port where the fuel pump attaches to the motor. Thanks racer for your assistance.

  17. #17
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    I have never seen an obstruction at the pulse port.---------Fuel pump pulses out fuel when pulling the motor over.------Fuel pump is operated by PRESSURE pulses from the crankcase.----Maybe there is an issue there.

  18. #18
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Then it sounds like a cheepo fuel pump.
    Couldn't find a spare linkage, but I didn't look in the semi trailers yet. If I can't find one, I know where to go. Tim's Outboard in Hackensack MN. 218 682 2331, Mike, Dan, Theresa, or Calley
    Some of the pressure produced when the fuel pump's cylinder fires down is trapped in the crankcase chamber by the reed valve. This produces a good amount of force to be directed to the back side of the pump diaphragm through that port. Pretty simple. "Brilliant engineering". Worked in 1973....still works today. Only problem is, we are expected to keep this old equipment running with modern aftermarket trash. I have original water pump impellers and fuel pumps still operating perfectly from the 50's and 60's. They say "if you don't use it in 7 years you don't need it"....They couldn't be MORE WRONG!
    Last edited by timguy; 11-03-2021 at 01:23 AM. Reason: Typo

  19. #19

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Did the new fuel pump come with a gasket? If there is not a good seal between crank and fuel pump you'll get nowhere fast. As an experiment, you could try to run the engine with gravity fed fuel. Just connect a funnel directly to the hose that goes to carb, pour some fuel in funnel and keep it raised above carb. If engine runs fine then, well, the pump is crap.

  20. #20

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Thanks bigtime and Tim for your suggestions. Tom - I hooked up my tank and the gas flowed much more freely. I took the owner's fuel line apart and found more plumber's putty. (see #1 ) I cleaned it up and gas flows freely now. Bigtime - the issue is the fuel pump. Tim - I called Tim's in Hackensack and they are checking on the pump and the choke connector. I will let you know what I hear from them. I used to fish around Hackensack quite a bit. Had a pretty close encounter with a bear one night when we were tenting north of town on a fishing trip with a buddy. Step by step will solve this mystery. Thanks again for the responses.

  21. #21

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Tim - Tim's Outboard is shipping a fuel pump. They also had the choke piece I need. I will update when the new parts are installed.

  22. #22

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Just wanted to say, what a cracking thread Guys. This is definitely what it’s all about.

  23. #23

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Good news! Tim - I ordered a fuel pump from Tim's Outboard, installed it and it solved the problem.We took the motor to the lake this morning and it ran great! The lesson for me (and for anyone else listening in) - buy parts from known suppliers. I bought a fuel pump on Ama*** not knowing the manufacturer or anything about it. I just assumed since it was new it would work. WRONG! Tim's sold me a reconditioned pump for a few dollars more than I paid for the new one and it works like it should. The key to discovering that the gas was not being pumped into the carb was installing a clear-bowl fuel filter where I could see nothing was coming from the pump. Tim's also had the choke connecting arm that I was missing. There was one on eBay for $54.00. Tim's price was $5.00.

    Thanks again to Tim and Racer for the time you take to help people like me keep the vintage motors running!

  24. #24
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Your very welcome, my friend. That's how we progress, passing our knowledge along to help others. When you work on this stuff for 40, 50, or even 65 years....like Racer, Joe, and our other senior techs....you learn alot. This is the finest marine forum....especially covering outboards, on the web. There are thousands of years of experience right at your finger tips. I applaud folks like you who show appreciation for those of us who try to help. Take care and come see us again. Tim

  25. #25

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Bruce, do you have a part number that you ordered from Tim's for the fuel pump? I'm in need of one and am finding the same issues with OEM prices and poor reviews of Ama*** cheapos. On a recommendation from Timguy, I recently purchased a used flywheel to help my brother get his 2002 Mercury going. Excellent price and quality.

  26. #26
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    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Just started refurbishing a 1975 model 20 HP Johnson , Canadian marketed.-----The little square fuel pump will get a new diaphragm to make it work like new.-----About the only thing that can go wrong with these simple PRESSURE operated pumps.

  27. #27

    Default Re: 1973 Johnson 25 hp starts but won't stay running

    Give Tims Outboard a call. Have your model number ready and they will know which pump is for you. In my case they offered a new or good used. Because of TimGuy's response (#18), I chose to go with the good used as it was $40.00 less. Racer's comment about replacing the diaphragm is also a good option as it is the only moving part in the pump. Just be sure to disassemble the pump carefully and put it back together the same way.

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