Mercruiser 3.7 470 wont start

[jmccollum]

So I have a 1985 mercruiser 470, and I can not get it to start. I have a manual on it and done every check I can find. Coil checks out points and gap are good condenser in distributor good. Spark plugs are good wires good, new cap. It will turn over but can not get it to fire. Pulled a plug and watched for spark on a good ground and didn't see anything. What am I missing?

 

[MikDee]

Is the kill switch on by any chance, it should be in the off position?

 

[stonyloam]

How do you know the points are good? They may look good, but not actually BE good. OK back to the beginning. Take off the distributor cap take a piece of insulating material and put between the points, pull the center wire from the cap and place about 1/8 inch from bare engine metal. Turn on the key and with a piece of INSULATED wire briefly jumper across the points. You should get a strong (blue) spark out of the center wire every time you REMOVE the wire. If you do, change your points, they have glazed over. You can use a points file (not sandpaper) to clean them up if you like. If you do not get a spark, look at the distributor ground to make sure it is making good contact.

 

[jmccollum]

I have already done the points test, first time came back hence why I changed them in first post. I set the gap per the manual specs .54mm. Tried to start and nothing. Did the points test again and the test showed good. I'm not sure what kill switch you are referring to, tested the neutral safety switch it is fine, the breaker on the side of the motor is good. Is there another kill our shut off switch I am missing? I am really lost on this one. like in earlier post I have the mercruiser manual and did every test suggested in the trouble shooting portion of the manual can not seem to find something not working.

 

[Eric 3.7LX Alpha 1]

Did you try removing the grey wire off the (-) terminal on the coil? ( the tachometer sender) could have a short and ground out your spark.

The coil gets power off the starter solenoid during cranking... thru the purple/yellow wire... but only during cranking. When the key is released to the run position, that wire is dead and the coil gets powered thru the purple (resistance wire) which gets power from the choke terminal.

If your not getting power from the purple/yellow wire during cranking may not start up, hence the jumper to see.

Run a jumper wire from the (+) terminal of the coil, the other end of jumper to the (+) on the battery... and try.

 

[jmccollum]

I have not tried that, I work night shift tonight will try as soon as I get up tomorrow and post back.

 

[stonyloam]

Aside from what Eric said, not much left. Points OK, providing voltage to coil, coil firing when points open. Only two places to lose the "spark". The spark travels through the wire to the center terminal, down through the carbon button into the rotor, and jumps from the rotor end to the distributor plug terminal out the plug wires to the plugs. Since it is unlikely all 4 plug wires are bad it is logical the problem is in the distributor. The rotor could be making poor contact with the center carbon button, there could be a crack or dirt on the cap that allows the spark to be shorted to ground or the timing could be so far out that the spark can not jump the gap to the plug wire terminal. If jumping to the battery does not work, check and clean the cap and rotor and check the timing.