1983 Mercruiser 470, No Spark

[JohnWatt]

We have an old Grady White 205 with a rebuilt 1983 470 engine and new outdrive. Ran great last year after rebuild. This Spring - no spark. Now has new plugs, new coil, and new condenser. Points have 2 hours and look clean. With ignition on we can measure 12v to coil and to condenser and points. All ignition wires show 9 - 10ohms. Neutral interrupt switch seems to work, but we have not removed its 12v supply yet to attempt start as we measured 12v at coil, etc. Still no spark at plugs. Suggestions?

 

[Don S]

Re: 1983 Mercruiser 470, No Spark

Try some new points. You might run a points file over the old points and see if it gets spark, but you will still have to replace them.

Points can get burned and glazed over just by leaving the ignition switch on with the points closed. Looks means nothing. They need to make electrical contact to work.

 

[Eric 3.7LX Alpha 1]

Re: 1983 Mercruiser 470, No Spark

Agree with Don, the points are 95% the issue in these cases. You can save your old coil as a spare, unless you tested resistance across the primary and secondary and it's outta spec.

You shouldn't have 12-volts to the coil with the ignition on, it should be wired thru a purple resistance wire off the choke and be lower more like 9'sh volts. The coil only gets full 12-volts when the starter is cranking the engine thru the purple/yellow wire off the starter solenoid.

 

[JohnWatt]

Re: 1983 Mercruiser 470, No Spark

Agree with Don, the points are 95% the issue in these cases. You can save your old coil as a spare, unless you tested resistance across the primary and secondary and it's outta spec.

You shouldn't have 12-volts to the coil with the ignition on, it should be wired thru a purple resistance wire off the choke and be lower more like 9'sh volts. The coil only gets full 12-volts when the starter is cranking the engine thru the purple/yellow wire off the starter solenoid.

View attachment 195553

Thanks to both suggestions. We will recheck the wiring and look for the resistance wire and get a new set of points.