1976 70HP Johnson Power Loss

[midnightscape]

After my boat sitting for almost 2 summers not running, it just doesn't seem to have the power at full throttle that it did before. I have changed the gear oil, fresh gas, new plugs, but am wondering if there is something further (dirty carb?) I'm new at working on these so I ordered an original service manual to guide me if I need to work on it but wondering if any one has some ideas on what to look for first.

Thanks,
Jason

 

[jim_in_day]

Re: 1976 70HP Johnson Power Loss

I would seriously look at your spark, my guess is you only have 2 plugs firing. I have the exact same motor, and when it drops a cylinder like that your power goes way down. You may also have a clogged carb, but usually we see the low speed jets clog on them, as the high speed jets are much larger (to flow more gas) and therefore harder to plug. The other thing to be aware of is that your impellor in your water pump may have dried out and not pump water. That puts your motor in danger of overheating and possibly seizing. Please read the "Awakening a sleeping motor" thread to keep your motor happy and let us know what happens so others can benefit from how your problem gets solved

 

[midnightscape]

Re: 1976 70HP Johnson Power Loss

How does one check for spark safely? I did have all the plugs out and on the wires while someone turned it over, but I couldnt tell holding the wires with the needlenose (I could however when I grabbed the end of the plug!). I read (in the FAQ I think) about holding it to the block?
Would the impellor drying out be from sitting those 2 years? And this wouldn't have anything to do with the power correct?
Also, I'd be interested to hear what your "maintenance schedule" is on the motor, I'll be the first to admit I haven't done much besides the new plugs, fresh gear lube and Sea Foam before parking for the season. I want to make sure and start doing it right to get the most out of this motor.

Thanks,
Jason