120 Merc I/O Only 4.8v @coil/missing mid RPM

[Colorado Boat Nut]

120 Merc I/O Only 4.8v @coil/missing mid RPM <br />it also wont go above say half throttle it starts to fall off/missing, until you get out of it a little it smells rich if you don’t –it’s missing bad I guess it’s going to smell rich <br /> is 4.8volts at the pos side of the coil normal ? point’s cap and rotor are good and set –new plug’s<br />I did the screw driver trick with the plug wires and at best got a ¼ inch spark<br />I tested the resistance on the (like new 4 yr old maybe 40 hrs on them + or -) plug wires<br />And got a wide range of results including a dead wire, how ever the cylinders are firing , but the spark seems a little weak on all cyl<br />Can I run a High performance auto coil like an “Accel” super stock or does it have to be marine?<br /><br />Ive done a lot of work on it this summer to correct it please See:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=003009 <br />any ideas<br />thanx<br />CBN

 

[Trent]

Re: 120 Merc I/O Only 4.8v @coil/missing mid RPM

First find out why the voltage at the coil is low. You need 9.5 at the + side of the coil to run correctly. Disconnect the tach wire and see if the voltage goes up? Disconnect the shift interrupt switch and see if the voltage goes up? These are the other wires that are connected to the + side of the coil. You need a good blue spark at the coil and sparkplug wires.....

 

[McKenzie]

Re: 120 Merc I/O Only 4.8v @coil/missing mid RPM

I would guess this boat has a resistance wire (as opposed to a ballast resistor) and it has gone bad. I believe to replace it, you need to pull apart your whole engine wiring harness. I would instead get a new coil with an ceramic block ballast resistor and run a 12v wire to it from the ignition circuit. I run a hipo auto coil too, all i did was put a heavy coat of rust/corrosion inhibitor on it. I got a 60,000v coil because i was having a rough time starting without giving it some throttle, with the new coil, starts right up. Got mine at jcwhitney.com for about $30

 

[Colorado Boat Nut]

Re: 120 Merc I/O Only 4.8v @coil/missing mid RPM

Right on, that was what I was hoping I would hear.<br /> I thought it should have more than 4.8v ,<br />Now to find out why<br />Thanx a lot guy’s <br />Im sure glad I found this place.<br />C.B.N.

 

[Colorado Boat Nut]

Re: 120 Merc I/O Only 4.8v @coil/missing mid RPM

Well let’s hope this work’s! <br />I changed my point’s for the heck of it <br />I changed the plug wire’s because of the resistance questions and because I ripped the plug connector off of the number one wire the last time I worked on the boat. So it got new wires <br />I had bought a new coil resistor but then I rechecked the voltage at the coil and it was on the high side of 10V so I will continue to watch that .<br />Well now my spark is considerably stronger and the boat seems like it’s running even smoother (at idle on the muffs ) <br />I was also able to set the timing to spec from advanced<br />Hopefully I can launch it next weekend and try it out<br /><br />Wish me luck<br />CBN