1972 Johnson 25 HP (25R72R) running like garbage. PLEASE HELP!!!!

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pet575

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I've had a couple of years' worth of trouble with the idle on this motor so I bought a SELOC manual and a carb rebuilt kit. It previously ran like a top at any speed but slow idle so I figured the carb needed to be rebuilt. Did a carb rebuild, following the instructions in the SELOC manual, and reinstalled. The carb has a single needle valve for only the low speed. There is no high-speed needle.

Now the engine will start and run at high idle but it will not continue running at low idle speed. Figured that is a needle adjustment and not a big deal. However, I now have a problem in that this motor runs like absolute garbage when I try to run it at high speeds/planing speeds. It will miss/cut out and have huge power loss. After awhile it will either not produce much power over a high idle and then it will die at slower idle speeds.

When this happens I've also experienced a few hard starts in which the plugs became wet fouled. I replaced the fuel filter screen on the fuel pump along with the carb re-install. I'm sure that it was done correctly and was the correct screen part. While in there I took a look at the fuel pump and thought it might be worth replacing down the road but have not done so yet. I also replaced the external fuel line between the gas tank and the motor but I have now reached the point where I don't want to just start throwing parts at this motor and guessing.

The best I can tell, this engine is getting a ton of fuel dumped onto the plugs. I don't have enough knowledge/experience to know how to tell whether this is because I didn't rebuild the carb correctly (this was my first rebuild but, again, I followed the SELOC instructions very carefully). Alternatively, it could be an insufficient spark that was causing the poor idle all along and now has just become more evident with the rebuilt carb involved.

Anyone have any thoughts, tips, etc. on how I can diagnose this? My first plan at this point is to pull the flywheel and inspect the points/ignition wires to see if I can spot corrosion, etc. in that system.

I guess my big question is how I can tell if I did a crappy job on the carb rebuild?
 
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racerone

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" most carburetor problems " turn out to be something else.----------------------Start with a compression test and report the actual values you get.---------Next you do a proper spark check and test to see if spark will jump an actual gap of 1/4" or more.-----Is the thermostat installed and working properly?-----Did you remove the high speed fuel jet ( orifice ) to make sure it is clean ?----If you answer questions you will get help.
 

steelespike

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We'll assume the compression is good because it ran good before you fiddled with it.
Have you checked the coils. They do fail with age.If they are original they are suspect.
Check the spark. Remove the plugs check gap (.030). With insulated pliers hold one at a time against the power head so you can see the gap.
Crank it over. Spark should be blue and have an audible snap.You could also use a spark checker.
Let us know what you find.
 

pet575

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Thanks guys.

I've wondered to myself if I have the float set correctly. Again, all I have to go by is the SELOC instructions and I thought I followed them pretty well. I'll double check it.

I don't know how to do a compression test. Does that require the motor be running or can you check that on land and just turning the motor over?

I will check the spark and do the test. Forgot to mention the plugs were replaced when the rebuilt carb was reinstalled and I verified the correct gap before installing.

I will also check the high speed orifice. I thoroughly cleaned it during the rebuild but will definitely double check it.

Will also check the coils as well.


I'm afraid I'm ignorant on checking the thermostat so I'll dig back into my SELOC manual to figure out how to do that. I'm walking out on a limb by saying my honest answer to this question is that I didn't think this motor had a thermostat. I'm an I/O guy by nature and this is my first outboard so I'm learning as I go.
 

pet575

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And a HUGE thank you for the responses. At least I have a little plan of attack to work here. Yesterday my mindset was to drive it to a local marine shop and leave it out of surrender. That or throw it in the lake! :laugh:
 

racerone

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Small cover ( 3 screws ) on top of the cylider head hides the thermostat.----I often find no thermostat or if there is one it is stuck open.---Note , a proper spark test does not use plugs at a gap of 0.030", you need to test and see if the ignition will jump a gap of 1/4" or more.-----If it passes that test you have " good spark "
 
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bonz_d

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you can go to any of the auto parts stores and purchase a nice adjustable spark tester for under $20.00, It's a good investment.
 

restornator

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The throttle link needs to be set right since you took the carb off. You know, that little arm with the screw that links the cam follower and throttle. And are you running j4c plugs?
 

pet575

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Thanks guys. So will the spark tester lights show me enough if I'm running the motor with it attached? I guess I'm trying to figure out if I can hook the spark tester up and run the boat under power out on the water and the tester will actually visually show me a weaker spark? I know I have SOME spark or it would never start/run and it would not idle. My understanding is that these tester lights are a "Yes or No" type of light rather than a "how strong is the spark?" type of light. Am I not understanding them correctly?
 

restornator

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get an inline tester with an adjustable gap. It plugs into the spark boot and alligator clips to the engine block
 

pet575

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Guys I finally got around to getting the spark tester over the weekend. Unfortunately I was not able to locate one with an adjustable gap at any of my local parts stores so the one I got just has a little glass-looking window in it where I can view the gap. I'm going to try to get to a meaningful test here in the next few days. I'll report back when I have something.
 

pet575

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Semi-update. Tried to start and got absolutely nothing. No spark on the meter, no attempt to run, nothing. While I was pulling the starting cord I could not see a bit of spark on the the tester. Was pretty sure that I had no spark whatsoever.

Shortly after, I decided I'd hook up the tester to my lawn mower to see what the tester SHOULD look like. I noticed that I pretty much had the same condition while pulling and that the tester window didn't really light up until the motor started to run.

So, I got some fresh gas over the weekend and will try again tonight to see if I can get ANYTHING out of the motor as far as starting, running poorly, etc. so I can see how the spark tester looks compared to when I ran it on the lawn mower.

Will report back ASAP.
 

AlTn

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the tester you have...does it "test" while installed to the spark plug?...or do you remove the spark plug, hook the plug wire to one end of the tester and the other end of the tester clips to a ground on the motor and the spark "jumps" a gap within this "glass window"?
 

pet575

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It is the kind that you hook to the spark plug while installed and hook the other end into the plug wire. It has a window to look through, though.
 

pet575

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My local auto parts store did not have the kind with the tester clips and the adjustable gap. Do I need to move along elsewhere and get the one that can "jump" the gap?
 

pet575

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If so, does anyone have a recommendation from Advance Auto, NAPA, or O'Reilly?
 

racerone

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Can you make one ?----Piece of plywood 4 inches square.----Staple or glue 2 pieces of hefty wire to it with a gap of 5/16".----Stick the end of one wire in the sparkplug boot.---The other end to a ground on the motor.---Pull cord and see / listen for the spark.
 

AlTn

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Lesle tool 50850, spark tester, works...or something like it...the added benefit is that with both plugs removed it's much easier to pull the motor through..you should ground the spark plug lead that isn't being tested...I use a wire with alligator clips on each end as a grounding wire, but anything that accomplishes the grounding will work...just to add, make sure you are on a good ground with the spark checker otherwise it can leave you scratching your head...that's from experience
 

pet575

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OK so I picked up the Lesle 50850 last night and put it on for testing. I set the gap by eyeballing it with the same gap the plugs have and then tried to fire it. I got significant spark from both leads while pulling the cord with the plugs out. The question I have is "Is it enough spark?" I have no idea how to know that. I was able to get some video in the darkness of my garage. I'm not sure how good the video is but here goes:

https://www.youtube.com/watch?v=ApCzQSPjsqQ

Here is what the gap of the tester was set to:


And here is what the plugs look like (nice and dark):


Given the amount of spark that I was seeing, I think it is sufficient and it seems like I have a problem with too much fuel dumping into the cylinders.

Any thoughts on that?
 
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