mercury has spark, fuel, and compression but will not start

[timmmaaay1]

20hp mercury 200. I purchased this boat and motor a few months back. It had been sitting outside uncovered. I cleaned the old gas out the carb and all lines. I got the engine running, and took it out on the river. It ran really good, I did run it all the way open. I shut the motor down so I could do some fishing, when I tried to start it again it wouldn't fire at all. I tried gas and either and the engine wouldn't even sputter, putter or anything. I am not a mechanic but I can read and follow direction. So after research I decided to check compression. I only have a pull start because the starter is messing, so I only got the compression up to 70 on both cylinders. So compression seemed good. the motor has a nice blue spark...one of the ignition coils looked real bad so I replaced it. Still no fire. I pulled the flywheel and the key looked fine. I did have to replace some wires because they were crumbling from age. Its been a few weeks and the engine has never fired once mot even with gas or either, I do spray the cylindes with sea foam lubrication after I use either. I do not believe its a gas issue since it never fired once, compression seems good, and it has spark, so can it be a timing issue? Can I check timing with a pull start? Im at the end of my rope here guys, I'm feeling discouraged because im out of ideas...I really need help here. What Should I do next? The engine is around a 1976 model.

 

[gm280]

:welcome: Timmmmaaay1, Nice to have you aboard.

So you state that you have good compression, great spark, acquit fuel and no sheared keyway in the flywheel. So why doesn't it crank? Well those are the only things needed to support the engine to run. So while you think you have all those things, I'm betting you don't. And that doesn't mean you're lying, but it does mean you only think you have those things. I would start with the spark issue. Seeing a good spark jump across a typical spark plug on the side of the engine is one thing. Actually having a good spark inside is an entirely different issue. My suggestion is to buy a spark tester at the local auto parts store. They are really cheap and will tell you for certain if you do have a spark issue. Set the spark tester for 7/16" inch and see if you get a good blue spark and a loud snap as it fires. Do that to all the cylinders as well. If that does check out good, lets move on to fuel. Disconnect the fuel line to the carb and see if fuel comes out when you crank the engine. If so that covers that fuel issue to the carb. Next you stated that the keyway in the flywheel is in perfect shape so that makes the initial timing correct. So that leads to the carb itself. I say it is time to remove the carb and rebuild it. Buy a carb kit and disassembly the carb and thoroughly clean it and reassembly it with new parts supplied in the kit. Reinstall the carb again. I bet it runs...

This is a typical spark tester...they are really cheap...get one!

 

[timmmaaay1]

Thank you for the reply, I really appreciate the info, ill pick up a spark tester and check tomorrow...if it is a gas issue I just wonder why it has never turned over even a little bit? I guess ill find out the issue tomorrow when I check. Thanks

 

[timmmaaay1]

I did take the advice and purchased a spark tester. I found out I do not have a very strong spark on either cylinder. Now I have to figure out why. I did already replace one of the ignition coils but maybe I should replace them both.

 

[gm280]

I did take the advice and purchased a spark tester. I found out I do not have a very strong spark on either cylinder. Now I have to figure out why. I did already replace one of the ignition coils but maybe I should replace them both.

I would say that would be a good idea. Some times the coils can look good but perform terrible. So after you replace the other coil, try the spark tester again and get bad to us here. Let us know what fixed your engine. That way everybody reading your thread can learn from it... :thumb: