Bad compression on Johnson 6 hp 1973

[Hoosmatroos]

Hello,

I have a Johnson 6hp 2 stroke and it will not devellop full power. On idle it runs oke. When i hit the throttle in neutral the revs goes up fine. Under load it builds up revs but slowly and not to full power. I tested the compression and one cylinder has about 60psi and the other 50. I think the motor is worn but perhaps you have a not that expensive solution?

Carb is clean and adjustment is fine.

Martin

 

[liz873]

Re: Bad compression on Johnson 6 hp 1973

I believe compress should be around 85 for that engine if all done correctly. Add a drop of two stoke oil to the cylinders then check if it goes up significantly probably rings.

 

[JB]

Re: Bad compression on Johnson 6 hp 1973

It is not unusual for a rope start engine to compress in that range, Martin. I think if you do a decarbon procedure and test again (exactly as described in the Top Secret file) your concern will be relieved.

In 60+ years of messing with outboards I have never seen one wear out, but I have seen many destroyed by neglect, abuse and misdiagnosis. Your engine is not even 40 years old!

I think your problem has to do with the linkage involved in throttle position and ignition timing. A careful "link 'n' synch" procedure, by the book, is in order. Failing that, investigate carburetor clogging.



Good luck.

 

[kfa4303]

Re: Bad compression on Johnson 6 hp 1973

Hi Hoosmatroos. Welcome to iboats. I agree that all your motor really needs is a little tune up and TLC. I would also suggest decarbing the motor to improve the compression. There are many products you can use to do this. By far the most popular method here in the states is to use a product called SEAFOAM. It usually comes in a white 12-16oz cans for about $10 US in either aerosol or liquid form. Either form is fine. However, you can use other products such as DEEP CREEP, WD-40 or Johnson/Evinrude brand decarbing solution. They all do essentially the same thing. The best part is that they are super easy to use. For starters, tilt the motor all the way up such that the spark plugs are pointing to the sky, now remove the spark plugs and spray in a generous amount of SEAFOAM into the cylinders, reinstall the plugs lightly and let the motor sit overnight (several nights is even better). Once the motor has had a chance to sit with the SEAFOAM in the cylinders, remove the plugs again, lower the motor to the normal operating position and slowly pull the starter rope. You should feel a much smoother action and may even see black goo come out of the cylinders and/or exhaust as you pull the starter rope. After you've pulled it a few times, reinstall the sparkplugs and reattach the spark plug wires. Try starting the motor now. It may take a couple pulls. When the motor starts it WILL smoke like crazy!!!! This is good. That's all of the carbon being burned away. Take the motor out on the water and try to get it up to WOT. This will help burn off the carbon even more efficiently. Once the smoking dies down, you should notice that the motor is running/idling much more smoothly. You may want/need to replace the spark plugs after wards as they can sometimes get very dirty.
Another method involves simply spraying the SEAFOAM dierecly into the engine as it is running. Fire up the motor and let idle for a moment. Now raise the rpms to a high idle and spray the SEAFOAM in to the throttle body of the carb for 2-3 seconds. The rmps will drop, but that's normal. Just rev the motor a bit to compensate. Let the motor come back up to normal idle, then repeat 4-5 times, with 2-3 second squirts of SEAFOAM. Again, the motor will smoke like crazy!!!, but that's what we want. Again, try to get it up to high rpms to burn off all of the carbon. Again, you want to replace the spark plugs. Here's a video of a guy doing a decarb on his 18hp, but it will give you the idea. Hope this helps.
Add the leftover SEAFOAM to your gas tank and you'll help the motor even more. You can also decarb your car, or any other motor in the same way. Here are a couple vids.

http://www.youtube.com/watch?v=sLOuUWV4GrQ&feature=related
http://www.youtube.com/watch?v=pRrHvySchy8&feature=related
http://www.youtube.com/watch?v=ol1Q3zO5j6s

 

[cajuncook1]

Re: Bad compression on Johnson 6 hp 1973

It is not unusual for a rope start engine to compress in that range, Martin. I think if you do a decarbon procedure and test again (exactly as described in the Top Secret file) your concern will be relieved.

In 60+ years of messing with outboards I have never seen one wear out, but I have seen many destroyed by neglect, abuse and misdiagnosis. Your engine is not even 40 years old!

I think your problem has to do with the linkage involved in throttle position and ignition timing. A careful "link 'n' synch" procedure, by the book, is in order. Failing that, investigate carburetor clogging.



Good luck.

I agree with JB. The only thing that I could suggest in addition to JB suggestions is to check that you have good spark on both cylinders. You maybe dropping a cylinder and running on one. Running on one cylinder the motor will idle ok, but will have diminished power.

Went fishing with father-n-law one time and I told that his 6hp Evinrude was running kind weak, but he states it was getting old and worn. It idle ok. So, he had been fishing for months in that present state. He said it got him to the fishing hole and back reliably, but just a little slower.

So, I checked his ignition and the top bottom cylinder was out. So I check under the flywheel and he had a cracked coil, so I changed both coils. The points and condenser were fine and I replaced the oil wicker.

She cranked up beautifully and that little motor now planes his little boat and zooms all over and run like she should. 1968 6hp Evinrude....great little motors.

Another suggestion is to make sure the motor is getting cooled and the water pump is working. If it over heated at one point, it could have compromised your cylinder head gasket or slightly warped your cylinder head. Easy fix.

If every thing else check out and decarbing does not help your compression. Remove your cylinder head. Clean the mating surfaces and apply a new head gasket and re-torque the screws to 60 to 80 inch pounds. Notice I stated inch pounds.

Make sure the cylinder head is flat. Here is a diagram that explains it. Wet the surface lightly and use a figure 8 pattern until the all the surface is shiny. click on the thumb pic.





The torque pattern is an attachment to this post. First past of the torque pattern is 50% torque value, the second pass is 100% torque value, and after you run the motor and it is good and warm up, stop it let cool some and re-torque again for the final time at 100% torque value.


Hope this helps. Take care.

 

[Hoosmatroos]

Re: Bad compression on Johnson 6 hp 1973

Thanks for al your suggestions. I'll post the results in a few days.

 

[Hoosmatroos]

Re: Bad compression on Johnson 6 hp 1973

Sorry but very late response. Forgot to update this post. When I tested the engine again (almost 1,5 years ago now ) I discovered a damaged lead. After repairing that the engine was running fine again. Just needed some TLC. Engine back to the very happy owner.

 

[kfa4303]

Re: Bad compression on Johnson 6 hp 1973

Great news Hoosmatroos! Better late than never.

 

[raczekp1]

Re: Bad compression on Johnson 6 hp 1973

i got one from 72', compresion is 90psi for both holes