Home › Forum › Ask A Member › 1979 Johnson 140 Carb sync
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fleetwin.
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September 12, 2017 at 8:52 pm #8212
Hello,
I don’t usually work on motors this "new". My Neighbor has a 1979 Johnson 140hp V4. It runs well, but seems to lack power out of the hole. What should I look for on these to see if the carbs are opening at the correct point? Is the timing on these fixed based of the timer base under the flywheel?
Any advice would be helpful.Thanks
AdamSeptember 12, 2017 at 8:56 pm #64789I think Mumbles did a post about that a while back….in Dockside I think
http://www.richardsoutboardtools.com
classicomctools@gmail.comSeptember 12, 2017 at 9:14 pm #64790I did see his post about extending the linkage shafts to exaggerate the movement. I was thinking more along the lines of making sure the carbs are opening at the correct time with respect to spark advance…..do these motors not need to be synchronized the way the older OMCs do???
September 13, 2017 at 3:49 pm #64830Adam-
How familiar are you with these engines? Do you have a manual? Is all the linkage and throttles moving freely? Is the timer base hitting its full advance stop? Are the throttle plates opening fully?
Most of these synchronization adjustments won’t really affect WOT acceleration that much, they are meant more for smooth running at lower speeds and off idle.
The 140s develop a little more top end power, but sometimes at the expense of midrange performance. Tell us more about the rig, prop style and pitch, along with WOT RPM. These engines need to wind up at WOT or they will perform poorly, especially at midrange. Does the engine have power trim? Does the bow tend to pop up excessively during acceleration? This engine needs to turn up at least 5500 RPM at WOT when properly trimmed.
This is an old engine, that had a lot of compression, not really designed to run on today’s fuels. I would definitely do a compression test. Some of these engines had low octane kits installed, which was mainly thicker head gaskets that lowered compression and performance. The thicker head gaskets are pretty easy to spot.September 14, 2017 at 11:31 am #64866I am not at all familiar with these engines.
The 140 is on a 1979 Sidewinder that it was sold as a package when new. It does have power trim and the stock prop. I don’t know the pitch off hand.
I will take a closer look at it next time that I see my neighbor at the cottage. He just recently mentioned that he felt that it lacked low end power. WOT seems OK.
Is there a specific point when the carb butterflies should open?Adam
September 14, 2017 at 4:30 pm #64876Yes, there is a specific point where the throttles should begin to open. The carbs must be synchronized, and the pick up timing must be set as well. Again, these specific adjustments won’t affect idle to full acceleration performance much, but you do need to make sure the throttles are opening fully and the timer base is hitting its full advance stop.
The sidewinder is a short performance hull that does tend to "squat" when accelerated, popping the bow up severely before getting on plane, which makes finding the right prop difficult. The prop that provides best WOT throttle performance will probably be the worst for acceleration. This rig will probably have to be under propped a bit to provide satisfactory acceleration, especially for water skiing.
The place to start here is knowing the prop style and pitch, along with WOT RPM when properly trimmed out. I will look to see if I have a manual for this engine, perhaps I can post a few of the synchronization pages…. -
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