1975 Merc 50hp NO SPARK! Had to take front apart and now doesn't work....HELP!

[eriksamu]

I have a 1975 Mercury 50hp, serial# 4280698. The engine ran perfect, and I mean perfect it didn't even need the throttle advanced to start cold. Anyway, there was a gas line that leaked and to be replaced so front of the motor was taken apart for accessibility. After we put everything back together there is no spark now. We did a resistance check on the kill switch on the MerControl, was good. I checked all the in-line fuses and they are also good. Do you have any suggestions or troubleshooting tips, I keep reading about the switch box (which I'm not familiar with). Also, this motor has a belt driven distributor.

Where does one start........what is the box mounted on the front support that has a red, gree/blue, and yellow on the side which the wires are connected to? Is that the switch box?

 

[sdeck]

Re: 1975 Merc 50hp NO SPARK! Had to take front apart and now doesn't work....HELP!

I have the 1973 version and have had mine apart several times recently fighting with carbs. How extensively did you dismantle? Are all plugs dead? Did you pull the main HT line of the distributor when moving stuff? Also, on mine, many of the circuitry wires had cracked and missing insulation. Check and make sure you are shorting something to ground. Did you get all the wires reconnected?

 

[eriksamu]

Re: 1975 Merc 50hp NO SPARK! Had to take front apart and now doesn't work....HELP!

SSo I did some more checking and found out we have spark. Apparently it doesn't jump as far a gap as I thought because when you the plug and have wire connected there is spark. BUT the motor will still not start, turns over and doesn't fire at all, I'm not professional mechanic but isn't all you need is spark, fuel, intake/exhaust. Any ideas on what could cause this? If you pump the primer we get gas dripping out of crabs so I know we're getting gas I thought of removing the pressure side of fuel pump to check for flow while it turns over.....I'm running out of ideas!

 

[CharlieB]

Re: 1975 Merc 50hp NO SPARK! Had to take front apart and now doesn't work....HELP!

How much spark do you have?

If unable to throw a hot blue arc across a 7/16 gap in free air, it will have problems starting and running reliably.

Test the ignition module following the directions in the service manual or the CDI Ignition Troubleshooting Guide, and repost your findings.

 

[eriksamu]

Re: 1975 Merc 50hp NO SPARK! Had to take front apart and now doesn't work....HELP!

So the spark probably can't jump any gap from what I've saw. I did test the IM and most if not all readings could be considered open (Mohms range). I bought a used IM from a salvage yard but I would love to test it before I install. Does anybody know what the resistance reading is supposed (or the range, ohms, Kohms, Mohms?) to be for the diode direction per cdi's troubleshooting guide? Any input would be appreciated, thanks in advance!

Erik