Power problem

[VTP54]

1978 40hp Mercury. Hard to start,sometimes starts and runs fine till you shut it off for 15 or 20 minutes.Have to crank and choke engine several times before restarts and them sometimes its only running on one cylinder then the other cyl. starts firing after a minute or two.(maybe)and runs good again.Confidence starts building then all of a sudden it dies out and quits.Then same procedure as before.It will fast idle enough to get back to boat dock as long as you don't try to give it any more throttle. Checked fuelhoses,clean fuel ,replaced inline fuel filter,and pickup tube seems to be ok in tank.How do i check the fuel pump operation and what are the specs for this engine. Seems like fuel problem.Am i on the right track?<br /> Thanks vtp54

 

[Barnacle_Bill]

Re: Power problem

You can try to pump the primer bulb while giving it gas. If it acts like it wants to go, rebuild the fuel pump. Kits are cheap and easy to install. Also check the primer bulb for cracks and pliability. They are the 1st to go.

 

[ronmold]

Re: Power problem

When engine dies on it's own pull the sparkplugs. If they are wet it is an ignition problem, most likely the switchbox. If they are dry it is a fuel delivery problem - the fuel pump would be a good start. If it is the pump you should be able to squeeze the primer bulb repeatedly to take the place of the fuel pump and keep the motor running. Your symptoms sound like the switchbox though. Check here for one:<br /> http://www.seilermarine.com/rapair/mercury.htm

 

[VTP54]

Re: Power problem

Replaced fuel pump to be sure but problem still exists.Checked plugs (wet)no spark at either plug? Is there a way to test a switch box to see if it is operating properly and also will this engine start on its own with the pull rope and conrol plug disconnected if everything is working properly.Very frustrated, don't understand why sometimes it starts and runs other times it's hard to start and only runs on one cyl and then on both and now its not firing at all?

 

[ronmold]

Re: Power problem

You need a switchbox, stator windings would not be so intermittent, they usually just quit. Switchbox problems will act like they have a mind of their own. Only switchbox test I know is to test everything else that is testable by the manuals and when all of those test good that points to the switchbox. If yours is original stuff from '78 it's well past its age. Outboards must have a diet of fresh greens ($$$) to keep healthy!!!!!!

 

[VTP54]

Re: Power problem

Switch box could very likely be my problem but? Seems to me there has to be some kind of trigger to activate the switch box .Is there any test i can try to see if i am getting a trigger signal? the reason i say this is i looked up a switch box for purchase and it also showed a trigger part # for this engine. With my intermittent spark problem it seems the trigger would be the most likely problem. Am I wrong? Thanks vtp54

 

[ronmold]

Re: Power problem

Triggers handle very small amounts of current and rarely fail.

 

[Winger Ed.]

Re: Power problem

Originally posted by VTP54:<br />it seems the trigger would be the most likely problem. Am I wrong?

Get a shop manuel. It will tell you how to ohm out the trigger.<br /><br />Switchboxes are children of the devil. They have to be changed/swapted out with a known good one to be tested.