1974 70hp johnson trouble

Hi all, I recently bought a 1974 70 hp johnson. Compresion was 128 104 and 128. I think the rings may be stuck on the one cylinder so I believe all is fine there.
I put a new water pump in and it pumps water like crazy.
The motor fires right up first try everytime, But doesnt want to run on all 3 cylinders when under power. As far as I can tell number 1 cylinder fires intermitantly.and same for number 3.

I'm looking for any suggestions or help you all could offer,I have not worked on outboard motors alot and im sure there are some patterns to these old motors.

My first guess would be high speed jets right? I am taking carbs off now to clean but please offer your 2 cents as to what my prob may be.
Should I run a tank of gas through this thing before I start to work on it.I have no clue when the last time it was actually used.

Thanks guys

Re: 1974 70hp johnson trouble

I'd just jump in and rebuild the carbs up front, especially since you don't know how long since it's been on the water -- kits are cheap, she always seems happier with fresh carbs, and there's way worse ways to spend a Saturday afternoon.

For your spark test, set your inline tester at 7/16".

I admire your confidence in the one bad cylinder........check out the "decarb" thread in the "engine FAQ" section of iboats -- might help with the sticky rings.

Re: 1974 70hp johnson trouble

I'll go check it out right now, thanks J

Do these things have issues with crank venting? was another thought that ran through my mind.

I guess ill do these carbs up this weekend and get the timing right first.
In my couple hours reading here it seems the carbs and timming are the most likely culprits so i'll start there first. Any other opinions are more then welcome though.
Thanks again

Re: 1974 70hp johnson trouble

you are on the right track. decarb http://forums.iboats.com/showthread.php?t=302825

timing: http://forums.iboats.com/showthread.php?t=228183