1978 Johnson 25hp HELP!!

[jdkirby83]

I just picked up a '78 Johnson 25hp tiller with pull start only. I am having an issue starting the motor. I got it to turn over twice, each time it would throttle up then "pop". After it would pop I would throttle down all the way where it then dies out. I only had it running for a few seconds, but kinda freaked out when I heard it pop. Is it possibly too rich. Im new to boat motors, so please be nice. I was also wondering what the idle position should be set at (i.e. turn the screw all the way in then 1 1/2 turns out??). I have a basic knowledge of air cooled motors but mostly just motorcycles. Thank you for your time.

 

[Lyle29464]

Re: 1978 Johnson 25hp HELP!!

I think your best bet is a house call by someone that knows your motor.

 

[Haffiman]

Re: 1978 Johnson 25hp HELP!!

Might have been a lean sneeze, might be an ignition issue.
Pull out the plugs and attach a spark tester. Slowly pull the starter and notice that the plugs sparks strong BLUE, 1-2-1-2- and never spark at the same time!!!
If sparking at the same time, pull apart the plugs from/to powerpack and carefully clean out all pins and sleeves and check for burn marks between the pins at the bottom of the plugs. If still a problem, change powerpack.
As engine is new to you, pull down the carb and clean and change gaskets. Use carb cleaner in a spray can and check that all channels are open.
Start with the mix screw about 3 turns out.
At lowes possible idle, turn the mix 1/4 at a time until engine 'pops', then back off 1/2.

 

[jdkirby83]

Re: 1978 Johnson 25hp HELP!!

Thank you for the advise. I leave for vacation tomorrow so I will work on the motor when I get back. I will update on the progress. Thank you again.