1960 Johnson 40hp...thud?

[AMD_237]

For those of you that responded to my water pump thread, thank you for your input. I believe I finally solved that problem, or at least very close. I bought a new head gasket and it seems like the water is circulating very close to the way it is supposed to. Now, it will run/idle fairly well for a good 20-25 seconds and everything seems great and then I hear a thud and it just kind of shuts down. I'm not sure if this thud is coming from the lower unit or what but I don't like the sounds of it and I'm not sure why the motor shuts down when it happens. Anyone experienced something like this? Any ideas?

 

[5150abf]

Re: 1960 Johnson 40hp...thud?

Has this motor been in the water and you are sure the lower is intacked.

The gears in the lower area always turning when the motor is running so if you have chipped a gear it could be sucking that peice between the gears now and then and causing the engine to stall or it sould just be your timing is off and it is back firing, which sound slike a thud.

Maybe drain your lower and be sure there isn't any filings in the oil.

 

[Evinrude Boater]

Re: 1960 Johnson 40hp...thud?

In neutral I would think only the driveshaft is turning with the pinion gear, not the prop shaft gears. The gears should not be meshed until you put it into gear.

 

[AMD_237]

Re: 1960 Johnson 40hp...thud?

The motor shakes pretty violently when the thud occurs. This is what made me think lower unit and not so much a backfire. I probably should just take the lower unit apart and look at everything and make sure. This motor has only been run a few times in my barrel the past 6-7 years because the guy I got it from just let it sit in his garage. I finally got it running pretty well and this seems like it may be the last step before it is boat ready. I hoped maybe it wasn't the lower unit because I'm not real familiar with taking it apart but it sounds like this maybe my only option.

 

[tx1961whaler]

Re: 1960 Johnson 40hp...thud?

The "thud" is probably just a so-called "lean sneeze" that is very common on these twins. I personally wouldn't do anything until you get it on the boat and on the water warmed up in order to adjust the carbs properly.

 

[freddyray21]

Re: 1960 Johnson 40hp...thud?

The "thud" is probably just a so-called "lean sneeze" that is very common on these twins. I personally wouldn't do anything until you get it on the boat and on the water warmed up in order to adjust the carbs properly.

I don't know that I would tear down the lower, but I would be certain that is has the proper gear lube in it before running it on a lake. They will sound like a thud and die suddenly from a lean sneeze. If when it does it the motor does not appear locked up that is probably all it is.

 

[AMD_237]

Re: 1960 Johnson 40hp...thud?

What is this "lean sneeze"? I've never heard of it...can I adjust something to make it go away? It does it sometimes twice or three times before it shuts down but mostly just thuds once and then either dies or almost dies. The motor shakes and it just sounds really bad, like something is going to break or something. If the lower unit didn't have enough oil or very old oil like this one might, could this make this thud occur?

 

[tx1961whaler]

Re: 1960 Johnson 40hp...thud?

A lean sneeze happens when the fuel mixture is too lean. You really can't adjust the carb properly in a barrel. My 40 "sneezes" in the barrel, but doesn't do it when on the water. I don't think it hurts anything.

 

[freddyray21]

Re: 1960 Johnson 40hp...thud?

What is this "lean squeeze"? I've never heard of it...can I adjust something to make it go away? It does it sometimes twice or three times before it shuts down but mostly just thuds once and then either dies or almost dies. The motor shakes and it just sounds really bad, like something is going to break or something. If the lower unit didn't have enough oil or very old oil like this one might, could this make this thud occur?

a lean sneeze is the carb running lean. It will shake and hiccup then die. Turn your low speed needle out about a quarter of a turn and start it. You need to turn the low speed needle in or out until the motor idles smooth without hiccuping or sneezing.

 

[AMD_237]

Re: 1960 Johnson 40hp...thud?

When you say my fuel mixture is too lean does that mean it has too much oil added to the gas or not enough? Sorry I know that's a dumb question but I am running the motor on the gas that I mixed for my 1992 Johnson 6hp motor. Maybe this isn't the correct mixture for the older motors? And if it's not would this cause a "lean sneeze"?

 

[tx1961whaler]

Re: 1960 Johnson 40hp...thud?

No, it's not the oil to gas ratio that is incorrect; it is the fuel air mixture that is not adjusted properly. The fuel air ratio is controlled by the needle valve adjustment on the carb.
And....I typed the word "ration" twice instead of ratio! Maybe it's depression era thinking creeping back.......

 

[freddyray21]

Re: 1960 Johnson 40hp...thud?

a lean sneeze will hurt it. If the motor is running too lean then it is not getting enough gas. If it's not getting enough gas it's not getting enough oil. The mixture on your 1992 is 50:1 the 1960 is made to run on 24:1 or twice as much oil. The low speed needle mixture adjust the amount of air and gas at idle. turning it out lets more gas in and thus less air. and vice versa. They will run different in a barrel than on the water as the carb generally sucks in a bit of exhaust. Put a fan on it when running and it will blow the exhaust away from the carb and you can get it real close in a barrel that way.

 

[asdasc]

Re: 1960 Johnson 40hp...thud?

OK, now that I know what it is being described, I had the same thing for a while when running cold especially. I opened up the low speed carb adjust by unscrewing left about 1/8 to 1/4 turn and it now runs wonderfully. I hadn't had that problem in the summer, but I figured it was due to the colder temps. Or, maybe someone twisted something while I wasn't looking!

Easy fix.