Does this sound normal? (Wierd sound at full throttle)

[bhughes]

I just got my 1958 18hp Johnson running the past weekend after replacing the lower unit. Before that I had only run it in neutral in a bucket.

The motor seems to run fine, the only thing that sounded wierd now is when it his full throttle, it starts making this hollow sounding roar that last for about 10 seconds and then goes away and then comes back in and out. It doesn't sound that bad, but it's different than the regular sound of the engine when the sound goes away. It's almost the same sound the engine is already making, just amplified and hollow sounding. It only happens at full throttle.

I figure its just b/c its an old motor and it's not going to sound perfect but just seeing if that sounds familiar to anyone else. I'm going to replace the spark plugs this weekend with the recommended J4C's. I haven't even checked what type are on there right now, they were already on there, but it seems to run okay.

 

[bhughes]

Re: Does this sound normal? (Wierd sound at full throttle)

.....

 

[bankerjohn]

Re: Does this sound normal? (Wierd sound at full throttle)

This may be a dumb question, but is there adequate lube in your "new" lower unit?

Have you checked it since you ran the motor and heard the "hollow sounding roar"?

 

[bhughes]

Re: Does this sound normal? (Wierd sound at full throttle)

It should be adequate. I changed it when I put the new one on. I filled it up till it came out the top vent whole, then put the screws trying not to lose too much. Some still dripped out the bottom but should be enough. Also, it only does it at top end, so seems like it would make the sound the whole time if it was the lower unit.

 

[bankerjohn]

Re: Does this sound normal? (Wierd sound at full throttle)

Have you checked it since you ran the motor and heard the "hollow sounding roar"?

If not, then it's not beyond impossible that the lube has leaked out and/or been contaminated with water getting into the gearcase.

 

[bhughes]

Re: Does this sound normal? (Wierd sound at full throttle)

how can I check how much oil is in the gear case without just emptying the whole thing?

 

[bankerjohn]

Re: Does this sound normal? (Wierd sound at full throttle)

how can I check how much oil is in the gear case without just emptying the whole thing?

Just take out the TOP plug ... and then you should be able to tell if it's still full or not ... and whether it's "milky" (indicating water has gotten in) or not!