1973 18 HP Evinrude 2 sets of points or 1

[w2much]

Picked up another project motor to play with for a bit. It starts and runs but. Backfires , pops, runs on one cylinder then 2 then one. The bottom cylinder has a nice spark the top not so good. I switched the coils top to bottom and still the top cylinder spark is weak. I am guessing that one set of points is out of set or bad.There are two sets of points in this motor correct? Any suggestions appreciated.

 

[alldodge]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Picked up another project motor to play with for a bit. It starts and runs but. Backfires , pops, runs on one cylinder then 2 then one. The bottom cylinder has a nice spark the top not so good. I switched the coils top to bottom and still the top cylinder spark is weak. I am guessing that one set of points is out of set or bad.There are two sets of points in this motor correct? Any suggestions appreciated.

Yep, two sets of points
Boatinfo - 1971-1989 Evinrude Service manual

 

[Crosbyman]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Evinrude Magneto Parts for 1973 18hp 18304A Outboard Motor

see part 10

 

[F_R]

Re: 1973 18 HP Evinrude 2 sets of points or 1

That is the infamous OMC Lo-Tension Magneto. BOTH sets of points have to be good in order for it to run properly, unlike the old Universal Magneto which would chug along just fine on one cylinder with one bad set of points.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Having switched the coils, the constant being weak spark in the upper cylinder would bad points or incorrectly gapped points be a likely culprit of the weak spark?

 

[HighTrim]

Re: 1973 18 HP Evinrude 2 sets of points or 1

hard to say without inspection. Try dressing them with a points file or wet/dry wrapped around a hacksaw blade, blowing off with compressed air, regapping then cleaning with business card stock dipped in acetone, or any other paper that wont leave fibres.

 

[twocyclemania]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Have you replaced or swapped out the condensers? Also, I had an 18 years ago that started missing on the return trip. Long story short. I found the ignition wire in the spark plug boot to be corroded. Cut a chunk out of it and returned home firing on both cylinders. Check condensers and ignition wires.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Great suggestions . Thank You. I do get a light shock while removing the weak spark plug wire, not the strong jolt but a berarble shock while holding the spark plug boot.

 

[F_R]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Great suggestions . Thank You. I do get a light shock while removing the weak spark plug wire, not the strong jolt but a berarble shock while holding the spark plug boot.

You'll never catch me testing spark that way!!! I HATE getting shocked.

Your spark plug wires are integral with the coils, so they followed the coil when you swapped them.

Yes, the points are the #1 offender in that motor. BOTH sets must be making very good connection to ground for the driver coil to generate electricity. Then ONE set opens to send that juice to a coil to make it fire. (Over-simplified explanation).

 

[tomhath]

Re: 1973 18 HP Evinrude 2 sets of points or 1

When you clean the points make sure the side that's grounded has a good connection. Often it's just a friction fit against a post, and bad ground there will cause a weak spark.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Thanks again gentlemen.Looking forward to pulling the flywheel to see what I find.

 

[F_R]

Re: 1973 18 HP Evinrude 2 sets of points or 1

In case you don't already know, you need a flywheel puller to get it off and a torque wrench to put it back on. Shaft and flywheel tapers must be shiny clean and dry, and you must torque the nut to 40-45 ft/lbs. No guessing.

Ignore this advice at risk of destroying a crankshaft or flywheel or both.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Still in limbo. Removed the flywheel , cleaned and adjusted the points and put it back together. The one set of points needed adjustment as it was less than .018" 'Started right up , ran on two cylinders and idled smoothly for about 20 minutes. I was feeling like one smart fellow. It then began to exhibit the same symptoms as before, running only on the bottom cylinder with backfiring and coughing one then both cylinders firing, bottom cylinder runs constant . I can pull the plug wire off the top cylinder and it runs good on the bottom cylinder.When I place the top plug wire back on it starts to cough, backfire and fire the top cylinder intermittently. Both cylinders have 90 lbs compression. I do not have a spark gap tester but I used a spark tester on the top cylinder while the motor was running, it fires constantly but there is no fire in the hole.I started it a few hours later and it runs the same as before I adjusted the points(coughing, backfiring, bottom cylinder firing , top cylinder firing but not running on two cylinders.) The plugs do not appear to be washed by water intrusion. Suggestions??

 

[tjhamms]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Sounds like your top ignition coil may be bad. It will start to fail as it heats up. Also just to be sure test the driver coil, spark plug lead and boot connection as already mentioned.

 

[Vintage Boat Guy]

Re: 1973 18 HP Evinrude 2 sets of points or 1

You say one cylinder has good spark? Try swapping plugs. Then readjust the points on the bad cylinder to match the good one. If all else fails, replace the points.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

Question regarding reply from tjhamms: There is only one top ignition coil the one under the flywheel
. Are there two seperate cicuits within this coil. I thought that if it fired one cylinder it should fire both. Can this top coil be bad and only fire one cylinder?There are however two coils at the plugs, these I have already switched top to bottom with the result being still problematic to the top cylinder only.

 

[F_R]

Re: 1973 18 HP Evinrude 2 sets of points or 1

I'm sure he was speaking of "top" and "bottom" as applied to the spark coils. The one under the flywheel Is called a "driver" coil. It generates the electricity for both cylinders. The timing of the points opening is what decides which one gets the juice.

 

[tjhamms]

Re: 1973 18 HP Evinrude 2 sets of points or 1

As F_R stated. You have two ignition coils, one for each cylinder. (Top and Bottom). Driver coil is under the flywheel.If you break it down. Driver coil juices points,then you will see the wire from points goes to ignition coil, witch "increases" the juice for ignition (spark plug). The ignition coils will fail when they get hot.If your confident the ignition coil is ok. Check the wire from ignition coil, back to the points.(make sure insulation is ok. Recheck points after running.(they may be moving). Its cheap enough to just replace the points and condensers. I assumed you already replaced the spark plugs.

 

[w2much]

Re: 1973 18 HP Evinrude 2 sets of points or 1

How do I test the driver coil. I have an Ohm meter. Thanks

 

[TN-25]

Re: 1973 18 HP Evinrude 2 sets of points or 1

I would also suspect the coil since they exhibit intermittent failures once they heat up. It needs to be hot in order to fail. Handling and testing it when hot can be tricky.

A twin cylinder with only a single point set would have to be an old opposed twin circa 1930s, the type that fires both cylinders simultaneously.