1973 Evinrude 18hp backfires but wont start

[NotAClue92]

I bought a 16' Jon Boat with a 1973 Evinrude 18hp motor and it will not even try to start even with spraying a little starting fluid into the carb.. I was told its been about 4 years since it was last ran but it ran great before it sat. It just backfires through the exhaust. Ive cleaned the carb, swapped the plug wires(I read that might be the problem on another post I read) tested the compression( it has 115psi at top cylinder and 113 at bottom cylinder), pulled the flywheel and checked the woodruff key, Ive also checked the reed valves (they're also called a stop leaf according to the parts breakdown) and they seem to be okay as far as I can tell. I cannot figure out why it wont start. This is my first outboard 2 stroke Ive worked on and I'm stumped. Any clue what the problem might be?

 

[oldboat1]

Close the needle valve lightly, then open approx. 1 1/2 turns. See if it starts with normal procedures (priming with hand pump, choking).

 

[racerone]

Does spark jump a gap of 1/4" or more, yes or no ?

 

[tomhath]

Are the spark plug wires switched?

 

[hardwater fisherman]

If it is a 1973 then it should have a lo-tension magneto. With external coils. I dont think the plug wires are long enough to switch. Unless someone has made them longer. The top coil goes to the top plug. I would first check for good spark as racer said. If you find no or weak spark. Pull the flywheel and clean and gap the points.

 

[NotAClue92]

It has great spark, great compression, I've checked the flywheel key and it is good. I've tried swapping the plug wires and it didn't change anything. I heard it might be the reed valves and I got down to the stop plate and tore a gasket so all new gaskets are on the way. I will replace the spark plugs since they are cheap and I am not sure when they were last changed. I do have to check the points and probably gap them. I was also told if you mark the magneto with a #2 pencil it makes it spark a lot better. I am wondering if it isn't the kill switch that has gone bad as well. Trial and error is where I am at now and I am assuming it is something small I have missed since I've check almost all major things and they all check out ok. For now I am just waiting on gaskets.

 

[racerone]

Can you send me information about that #2 pencil.----I think I want a bunch of them !!

 

[oldboat1]

Use an adjustable spark tester to check spark, and post results -- also compression test results. Assuming you have good spark and compression as you state, adjust the mixture needle clockwise from it's initial setting (leaner). Mix for the '73 should be 50:1 (about 2 1/2 oz oil for each gallon of fresh gas). I've been working on my '57 18, and find the best idle needle setting is less than one turn open. The high speed orifice at the bottom needs to be squeaky clean. If you haven't done it, pull off the screw plug and at least spray out the orifice with carb spray. (Use that number 2 pencil to create memory joggers for the tests and adjustments.)