25hp Evinrude 1973 (aint firing on top cylinder)

[WTDucks]

Howdy Boys... <br /><br />Im stumped on this. Top cylinder aint firing. Start the motor up and pull the top wire off the plug and there is no difference in the way its idling. Pull the bottom plug and it dies right off. Top plug is wet. Heres what I have done to this motor:<br /><br />1)New points and condersers.<br />2)Rebuilt carb. Sprayed the heck outa the carb. Its as clean as a babys backside after a good scrubbin.<br />3)Still messin with the needle valve. Got it around 1 turn out from being seated or there abouts. No more than 1/4 turn from one full turn out.<br />4)Top crankshaft seal was replaced while I was down there working the points. A thank ya to Dane from Denmark for a heads up for this. It was wet when I looked down there.<br /><br />Now here is the strange thing. When I take the top plug out, put it up next to the block and give it a pull it shocks the fire outa me. But, when a take the plug away from the block and give it a pull I dont see a spark. When I do this with the bottom plug, the cylinder thats firing, I can see a spark at the plug gap when I give it a pull away from the block. Am I looking at a bad magnito? Can they check these things or do I need to just get another one?<br /><br />Yall got any ideas? This here Texas boy is scratchin his head and kickin some dry Texas dust on this one!!!<br /><br />WTDucks

 

[Xcusme]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

That is strange! Try swapping plugs. If you get fire to the top plug, the original plug would seem internally shorted. Strange that you see the spark jump the plug gap without the plug base being grounded. Perhaps we should notify the scientific community, you may have re-written the laws of physics! . I'm assuming the top coil is good if you're getting bit. The plug body has to be grounded to the block to complete the high voltage path to ground, across the air gap of the plug of course.<br />You did make sure the arm on the points were aligned on the high side of the cam and gapped at .020 right??

 

[G DANE]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

Hi again WTDucks<br /><br />These point/condenser ignitions can really be tricky !<br /><br />I'd recommend:<br /><br />1: Try to swap the wires from the stator to the coils, 1 to 2 and 2 to 1. Get a nail or some piece of metal that has same diameter as top of sparkplug and put it in the rubber plug at end of sparkplugwire. Hold it 3/8" from block with a dry clouth. Make someone else pull wire. Can both sparks jump the gap with strong blue flame ? Try to increase gap slightly to see if the one spark is weaker than the other. Swap coil wires again. If the weak spark follows the one coil, the coil is bad. My guess would be that one of your conensers or points are bad, causing weak spark. Often weak spark makes plugs foul fast, making us believe we have a plug problem ! I would recommen changing both sets of pionts/condensers with OMC new ones, I have been fooling around with changing plugs half a season once, only to learn ignition was week at one cylinder, causing plugs to foul. New pionts/condensers, set to 0.020 at set mark on cam, clean connectons, and test again.<br /><br />What you experience with differences in ignition points exactly that way. Try that and post back.

 

[WTDucks]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

Thanks for the info Guys. Ill be working on it a little later this evening. I do have new points and condensers on the motor. They are gapped at .020. Im betting that they are not the problem as I went over them pretty good. Had a buddy double check my work and it looked ok to him too.<br /><br />Gonna be checking out the coils first and rule them out before I pop the flywheel and take a look at the points.<br /><br />Thanks again for the info and Ill let ya know.

 

[G DANE]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

If you bought aftermarket condensers, the one I was messing with was a bad new one !!! Try to swap coilwires and rig up some kind of spark gap. Then you will know if you have one weaker spark, and if it is plug, coil or point/condenser. Condenser most likely. Are the breakerpoints parallel when open ?

 

[BF]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

maybe I'm outta whack here, but.... shouldn't the outside of the plug be grounded (in contact with the block) when you've pulled it out and are testing for spark?? If the plug was just hanging in mid air way out there, maybe it'll spark maybe not, but that's not how I'd test it.<br /><br />Have you checked compression on the top cylinder? From the info in this thread, it's not clear to me why you think it's an ignition problem.<br /><br />Brent

 

[BF]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

xcuseme... oops, I missed your point about the plug being grounded.... Oh well, a litte redundancy is good <br /><br />Brent

 

[MadeCoolCom]

Re: 25hp Evinrude 1973 (aint firing on top cylinder)

I don't belive that the sparkplug could spark without being grounded somewhere. when you said that "I can see a spark at the plug gap when I give it a pull away from the block." That plug must be gronded to somehow if you see a spark jumping on that spark plug. If you see a spark jumping with the spark plug not being grounded to something we need to think about some more. I "never knew you check spark plug like that. <br />From what you have posted this is what you should check<br /><br />"You said Im stumped on this. Top cylinder aint firing. Start the motor up and pull the top wire off the plug and there is no difference in the way its idling"<br /><br />Checking the top clyinder problem.<br />Re check the top clyinder spark plug again take it out and place the threads to the block so it will be a good ground do not let the center part that is insulated touch ground and give a pull should see a spark jump to the center termial on the spark plug.<br />If not then you found a problem there. You need to fix.<br /><br />If you have a good spark then maybe you should check something else that might be causing the problem on the top clyinder. Like the timming. And anything that could be affecting the top clyinder.