9.9 HP Johnson Powerhead Questions - Advice Needed!

Re: 9.9 HP Johnson Powerhead Questions - Advice Needed!

Did your mechanic do a tune up as well as the T-stat? The compression is Ok at 105however, I would think it should be a little higher,(maybe 120 or so) but, as long as it's close to being equal like you have, I wouldn't worry about it. Having to choke the motor to re-start is quite normal but, a carb cleaning and some new plugs would most likely take care of that. In my opinion, a re-build isn't neccessary.

Re: 9.9 HP Johnson Powerhead Questions - Advice Needed!

my 1st thought is link and sync carb, second is that a seafoam treatment can't hurt and over the last few months has made my engine run smoother and smoother.... (i love the envious looks at the dock when i just tap the start button and she purrs) suggest you become aquainted with the machinists website, incredible info on your engine.
here is the link
http://www.sschapterpsa.com/ramblings/Johnson 9.9_15.htm
I have the 15hp version of your engine (now a short shaft) all I can say is i love it.

if you have the lean rich idle mixture screw i suggest getting engine to full temp setting the adjustment so that it idles the way you like.... then pulling the knob off and setting it to the lean position or a click away from it, then when you want to start your motor and warm it up you can turn it to the rich side and it will idle like a dream til it warms up and you have to lean it. should eliminate alot of choking once she has been run for the day.

Sean

Re: 9.9 HP Johnson Powerhead Questions - Advice Needed!

ONERC -- these later year a motors (after 93) does not have the front idle adjustment, but one off the RH side of the carb & the thread pitch is twice as fine as the earlier motors.

I have a 93 which is the 1st if the new series & they don't idle down nearly as well as the older ones. Fine for regular boating but for a fishermen trolling ??? And it seems to be a little harder to start.

I think if he adjusts this idle screw a little richer, checks or replaces the plugs & if that does not do it then look at rebuilding the carb, it will run fine for his purposes. Another thing to look at is to increase the throttle start speed position. They will start in a faster position, but can get stubborn if to slow.

Re: 9.9 HP Johnson Powerhead Questions - Advice Needed!

Thanks for the feedback guys. Great information....
I got the motor home and am finishing up my paint job on the shaft. Sanded and Primed with Zinc paint and got one coat of Johnson White on it. Goes on my Sailboat tomorrow.

Re: 9.9 HP Johnson Powerhead Questions - Advice Needed!

Your head may need replacing, as mine did. What happens is if the thermostat gets badly corroded, then the sealing area where the thermostat seal goes gets corroded out and the thermostst does not seal, so the engine over cools and due to that it needs a choke even after running. You could try gooping up the thermostats seal with a good sealant like Yamabond, or Threebond 1104, and see if it seals. Use the heat crayons on the engine block to determine if it's really getting up to temperature, ...I suspect it is not getting fully warm.