"66" Evinrude 40hp problem

[Milford1971]

Bought a used 16 ft. alum. with a 40hp Evirude. Took it to a boat shop to fix it because it seemed to run on only one cyclinder. Took them two months and I still have the same problem. They don't know what could be wrong.<br /> I haven't worked on a motor for thirty some yrs. but figure to give it a try. Compression is good in both cycliders, have a blue spark on each plug but the bottom one doesn't seem to fire and I can't get any high rpm in gear. Any idea's where I should start? Could it be a carb problen, valve, etc? Help, the ole lady say's sell, but this is just what I wanted in a fishing boat.

 

[JB]

Re: "66" Evinrude 40hp problem

Howdy, Milford.<br /><br />Welcome to iboats. <br /><br />Give us a model number, Milford. Without that we don't know what you have.

 

[Milford1971]

Re: "66" Evinrude 40hp problem

Sorry about that, model#40652B

 

[Paul Moir]

Re: "66" Evinrude 40hp problem

Test to see if you can draw a 1/4"-3/8" long spark off each lead. By far the most common problem with these magneto ignition systems is a cracked coil causing an arc-over, and this test will often pick it up. The wide gap simulates firing under compression.<br /><br />If that turns up an obvious problem, repairing it isn't difficult. But you will need a few special tools. You'll need a flywheel holder so you can remove the flywheel nut. You will need a torque wrench (reading 105ft/lbs) to retorque the flywheel nut when done, and you'll need a flywheel puller.<br /><br />A common automotive "harmonic balancer puller" equipped with 1/4"-20tpi high grade (8) bolts works as a flywheel puller. You cannot pull by the rim. You can jam the starter's pinion with a solid piece of plastic, etc, in lieu of a proper flywheel puller.<br /><br />Nice thing about these old Big Twins is they're easy to wrench yourself and parts are cheap. Plus they run so well.

 

[Joe Reeves]

Re: "66" Evinrude 40hp problem

Should you have proper spark on both cylinders but lose one cylinder's spark as the throttle is advanced, the problem could be as follows.<br /><br />(Magneto Armature Plate)<br />(J. Reeves)<br /> <br />If the armature plate has a a loose fitting, wobbling motion (the plate that the points, coils etc are attached to), it is usually caused by a slightly worn support ring. This allows the point setting to change erratically as the armature plate turns.<br /> <br />The cure is to remove the armature plate so that the support which is attached to the powerhead with 4 screws is visible. Then, with a screwdriver and hammer, or some tool of your choosing, and looking straight down at the support ring, make an indentation at what would be called the 12, 3, 6, and 9 O'clock positions. Install the armature plate and check for a smooth turning wobble free movement.<br /><br />You may need to do that procedure a few times to obtain the proper fit (not too tight, not too loose), but it's worth the effort. <br /><br />On the other hand, if the spark is perfect all the way through the throttle range..... if fuel is blown back thru the carburetor throat when the engine is running, the usual cause is a faulty/broken intake leaf valve.<br /><br />Also, on some models (if a fuel problem), one cylinder will run lean if the carburetor is fouled or adjusted improperly even though only one carburetor is involved (it happens).