1972 Johnson 25HP Won't Rev Up and Sputters

[cgwoods]

I recently purchased a 1972 Johnson 25HP and have been trying to get it running better. The issue is that it will start to rev up and then sputters and cuts out. Sometimes it will rev up well and stay revved for 10 seconds but then always sputters and cuts out. It idles really well and will rev to about 1/2 throttle but anything above 1/2 throttle and will sputter. I have cleaned the carb 4 times with carb cleaner and compressed air and installed a carb kit. I put a new fuel pump and gasket on, new condensers, one new coil, new plugs and wires, new head gasket, and new exhaust gasket. The points are clean and set to 020. It seems as though my problem has gotten worse since I decarbed the cylinders with sea foam but i'm not totally sure that it's related. The reason that I replaced the coil was that I thought I was getting intermittent spark to one cylinder as it was sometimes only firing on one cylinder. Since then I have checked again and both cylinders are firing as it will stay running if I pull either plug. I thought I was getting water in the lower cylinder because the spark plug immediately fouls and has a black soot on it. The lower cylinder/piston also gets this black soot on it and it's pushing out a nasty black/oily substance in the water tank after running it. I replaced the head gasket but it was still sputtering and cutting out when I tried to rev it, and the lower cylinder still had black soot on it. So I then made a new gasket out of copper gasket maker for the inner and outer exhaust covers and it still has the same result. I also checked to make sure the reeds weren't stuck or damaged and they appear to be in very good shape. I also looked over the cylinders and they don't appear to have any cracks. The compression is roughly 85psi in both cylinders. If anyone has any ideas or insight please let me know.

 

[nwcove]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

i would clean the carb for the 6th time, but soak it overnight and make sure the hs jet is spotless clean. also replace all the fuel lines as they can deteriorate and put crud into the carb. it will accumulate at the bottom of the bowl, which happens to be where the hs jet is.

 

[jayboonze]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

If i may....But before I do let me say this is all under the assumption that your motor is equipped with "slow mode".

I had the very same symptoms you are describing, just a week ago on my 1997 50HP Johnson. Turns out the temperature sensor was faulty and sending the engin into Slow Mode. If you are not familiar with this (and i was not either untill i did some research online), Slow Mode is a safety mechanism that limits your RPM's and allows you to limp home in the event your engine overheats.

On my engine there is a brown wire coming from the temperature sensor and goes to the power pack.(I think) regardless of where it goes, i disconnected the brown wire at a convenient rubber boot disconnect, pullled the key out of the ignition, reinserted the key and and fired her up. She ran like a top. I plugged the brown wire back in and the problem came back.

I hope this helps.

 

[Howard Sterndrive]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

The compression is roughly 85psi in both cylinders. If anyone has any ideas or insight please let me know.

100 psi is minimum for that motor.

 

[popsmazz1]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

my motor does the same thing, bad fuel pump, check the output of pump.

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Thanks for all the input. I soaked the carb overnight and used compressed air today before I put it back together. I also realized that the gasket in the center of the bowl that connects the high speed jet to the throat of the carb was missing so I bought a new one. I also replaced the fuel line and then put it back together and it is still running the same. I really don't know where to go from here. I also noticed that there was a creamy oil oozing out from the seal under the power head where the pan and the exhaust housing meet. But I couldn't tell if it was just had and oil leaking from inside the pan.

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Is it possible that I have a vaccum leak or is there any other way for water to enter the cylinder besides the exhaust cover gasket or head gasket? I checked the cylinder walls for cracks and couldn't find any. I pulled the intake manifold and fuel pump vaccum cover off and I can see a really black/oily liquid coating the airway from the intake manifold to the intake ports only on the lower cylinder. As you can see in the pictures I posted, the lower cylinder keeps getting fouled and the upper cylinder looks normal. I am 90% sure that it is not an ignition issue because I have very good spark on both cylinders and have even replaced a coil that looked questionable, which changed nothing. I just don't understand why only the bottom cylinder is so oily and fouled, unless it is just left over carbon from me decarbonizing the cylinders and is totally unrelated to the issue I am having. I have also checked the fuel pump and it seems to be working just fine. I replaced the vaccum gasket and even put the pump on from my 15hp and nothing has changed. The primer bulb stays firm and doesn't seem to be losing any pressure while the engine is running. Any further help/ideas is much appreciated.

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Also, could this issue be caused by bad crank seals? And does the carb float need to be adjusted, if so how is this done?

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

I also forgot to mention that when I pulled the cover off the thermostat I found that the previous owner must have removed it and didn't replace it. Could a missing thermostat affect performance?

 

[AlTn]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

surprised it ran that well w/o the boss gasket in place..to the float, with the bowl off and the carb inverted the float should be parallel with the carb body..slightly higher on the free end is called for, but w/o a gauge one person's slightly might vary from another persons..the float should be installed with the small tab on the hinge arm pointing towards the carb body, not towards the bowl and I adjust the float by bending the arm..doesn't usually take much

Yes, w/o the thermostat the motor can run too cool and produce more carbon to gum up the rings, etc. BTW, what type plugs are you using?...J6..J4 ?

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Thanks for the info. It had J6's in it when I got it but couldn't find a J6 at the parts store I was at so I bough J4's and J8's. What do you suggest?

 

[AlTn]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

I'd think J8's would be too hot long term, but any of'em would do till you get it running better..how have you been cleaning the main jet < orfice plug > in the carb?

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

I have soaked the carb overnight aft removing the orfice and other pieces of the carb. Then blew all passage ways out with compressed air, then used a can of carb cleaner spraying all passageways. Then compressed air and put it back together

 

[AlTn]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

are the 2 hoses..1. from the bottom of the crank case to the upper crank bearing and 1 from the upper bypass cover to the intake cover..in place?...since your motor idles well I don't think the crank seals will be a factor. Post back when you've had a chance to run it ater you've adjusted the float level.

 

[pn]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

my guess.

no gas to bottom cyl. sooty dry spark plug i'd say crank seal, how does one check the crank seal? i'm thinking that oil goo coming out of it is a dead give away

or too much gas no fire, coil, possible dirty ground.

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Ok so I got replaced the lower crank seal and the 2 hoses you had fore mentioned, blew some more compressed air through the carb, adjusted the float (not much as it looked pretty close to what you had said was good) and then put it all back together. And then ran it for 20-30 mins in the tank and it seems to be idling ok but if I let it idle for 4-5 mins it will start to bog down, so I rev it a little and it smokes like crazy and any mid to upper rpm's. You can also see in the pics I have posted that there is a TON of oily residue coming from the exhaust. It also seeps out of the spark plug threads while running and the spark plugs are both fouled. Thanks again for the help

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

Could my issue be related to the decarbing I did?

 

[AlTn]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

yeah, that barrel situation looks pretty extreme. The only thoughts I can offer at this point is the needle valve isn't shutting off the flow as it should, as pn notes maybe one cylinder isn't firing as it should.

At idle...how much of an effect does leaning and richening the idle mixture have?...will the engine die or start to backfire if you screw it in too far?...will it stumble,cough and overload if you screw it out too far?

 

[cgwoods]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

It seems to respond normally to the idle screw and I think I found the sweet spot as it is idling well. I switched to the j8's and they aren't fouling like the j6's were. But it still is extremely smoky and oily and bogs before revving up.

I also decided to check compression and noticed that it has dropped from 90 in both cylinders to about 65-70. But my compression tester isn't the greatest so I don't know how accurate this is.

 

[oldcatamount]

Re: 1972 Johnson 25HP Won't Rev Up and Sputters

I've got another suggestion for ya. Have you done a "link and synch" adjustment to the carb linkage? I had a similar issue with an '83 Johnson 25hp. It turns out that the carb linkage was way off and causing it to run like yours is.