1975 Johnson 15HP decarb advice needed

[ffountain]

I need advice on decarbing my 15HP. It runs well but not like it did for the first 20 years. It has never been decarbed. Other than a prop and water pump it's all original. I've read alot of threads on decarbing and the use of seafoam and deepcreep. I would like to try this in a 55gal drum in my back yard. Is this safe for my motor or should I just mix a gallon and go to the lake? Is it necessary to use the deepcreep or will the mix give the same results? All advice is appreciated.

 

[rjezuit]

Re: 1975 Johnson 15HP decarb advice needed

Deepcreap is seafoam in a pressurized spray can. Someone has a very detailed instruction set on how to do the decarb, search, you shall find. In a barrel you will get LOTS of smoke, so out on the water is better. Rick

 

[tashasdaddy]

Re: 1975 Johnson 15HP decarb advice needed

you can do it in a barrel, if you keep the hose running, but do not rev over 1500 rpms. i don't suggest it, as there will be black goo to deal with when you empty the barrel.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

 

[ffountain]

Re: 1975 Johnson 15HP decarb advice needed

you can do it in a barrel, if you keep the hose running, but do not rev over 1500 rpms. i don't suggest it, as there will be black goo to deal with when you empty the barrel.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

Took your advice and went to the lake for the decarb. LOTS of smoke. The only thing I did not do was put in new plugs (I read in one of the post on decarbing that while cleaning the cylinders it's also cleaning the plugs). When I finished the decarb I had a hard time getting my engine to start and run on my regular fuel mix. Checked my plugs and I'm getting good fire. Any thoughts on what may have happened?

 

[67Johnson6HP]

Re: 1975 Johnson 15HP decarb advice needed

Maybe new plugs as suggested????

 

[codertimt]

Re: 1975 Johnson 15HP decarb advice needed

Took your advice and went to the lake for the decarb. LOTS of smoke. The only thing I did not do was put in new plugs (I read in one of the post on decarbing that while cleaning the cylinders it's also cleaning the plugs). When I finished the decarb I had a hard time getting my engine to start and run on my regular fuel mix. Checked my plugs and I'm getting good fire. Any thoughts on what may have happened?

By, "When I finished", do you mean the first start after almost stalling the motor with the seafoam or do you mean all subsequent starting attempts after the WOT run around the lake?

A hard start at first is perfectly normal. But after the WOT run, it shouldn't be... Unfortunately, I don't have any further advice in that case, but I just wanted to to clarify the point to make sure everyone is one the same page...

Hope you get it sorted quickly...

 

[Boatist]

Re: 1975 Johnson 15HP decarb advice needed

I also have a 1975 15 HP. It got where it was hard to start when cold and trolling would foul the plugs twice a day. I used the OMC engine turner and it brought up the compression and it started eaiser and no longer fouls the plugs. I change to a old set of plugs before decarbing. When complete and it run several hours then I put back the newer set. With OMC engine turner the plugs will be the color of Carbon after cleaning. Also will get a lot of carbon, gas gue draining from the prop. This is the first time I ever saw that spraying something into the carb made a big difference.

One problem I did notice after cleaning was compression difference of about 5 pounds between cylinders. Also my motor lean rich mixture had to be changed quite a ways to get to run right and one cylinder runs better on the lean side and one better on the rich side. Only a very narrow range where both will fire.

I belive this is likely because I did it with it on the boat and one cylinder may have cleaned better than the outer. This year I am also going to redo but will take it off and lay where the whole piston can be covered. OMC engine turner say leave it in from 3 to 16 hours. A couple of more trys should help. Anyway My 1975 15 HP is much better after cleaning. It made a big improvement but do not be supprised if you have to change the lean rich mixture. Mine was over a half turn difference. I had to turn it as far as it would go then pull the mixture knob and put back on centered then could tune to the sweet spot and center again.

I know OMC engine tuner works good but about $8 a can. I have not used Deep creep yet but want to try.

I not sure what works better or faster, Deep Creap or OMC engine turner and also do not know which is cheaper.

Good luck and report on any findings.

 

[ffountain]

Re: 1975 Johnson 15HP decarb advice needed

By, "When I finished", do you mean the first start after almost stalling the motor with the seafoam or do you mean all subsequent starting attempts after the WOT run around the lake?

A hard start at first is perfectly normal. But after the WOT run, it shouldn't be... Unfortunately, I don't have any further advice in that case, but I just wanted to to clarify the point to make sure everyone is one the same page...

Hope you get it sorted quickly...

By, "When I finished", I mean all subsequent starting attempts after the WOT run around the lake.