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1974 Mercury Merc500 Starting Issue

T

Tonino

New member
Hello all. My Merc500 was running like gangbusters when it suddenly died akin to a catastrophic electrical failure. It will not start, but rather just pop occasionally out the exhaust. There is spark at each of the plugs tested individually while cranking - white and fat. Compression is 130psi in all cylinders. The switchbox and energizer ohm values are consistent with the values given in the service manual. The timing marks on the belt pulley and flywheel are dead on where they should be. I see no carbon tracks in the distributor cap nor cracks, rotor looks good. Did separate continuity readings from inside the cap to the spark plug ends and they're fine. The carbon stick and spring in the distributor cap are look ok and there is plenty of stick left and good spring tension. I couldn't get a continuity reading from the carbon stick to the coil end of the center distributor wire. Why is this? Tested individually there is spark at the plugs. I plan to replace the cap, rotor, maybe even the energizer coils if necessary. I just bought a used Factory switch box that also tests ok that has been worked on by CDI (green potting) that I can try. Has anyone else had an enigma such as this? Consensus seems to be something may have failed in the switch box that is corrupting the timing of the energizer pulses to the coil, ergo the late ignition pops. Any help would be most appreciated. Thanks all.
Tonino
 
Have you tested the tilt switch? Is it correctly installed? It was designed to kill the ignition momentarily if you struck an object at high speed to keep the engine from over revving and destroying itself from no load.
 
Checked the flywheel key ?----Possibly sheared ?--So easy and simple to check.-----Costs no beer tokens to check it.
 
fitz73222 said:
Have you tested the tilt switch? Is it correctly installed? It was designed to kill the ignition momentarily if you struck an object at high speed to keep the engine from over revving and destroying itself from no load.
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Thank you for the reply Fitz. Yes, its not the Mercury tilt switch.
racerone said:
Checked the flywheel key ?----Possibly sheared ?--So easy and simple to check.-----Costs no beer tokens to check it.
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Thank you for the reply Racerone. The flywheel is tight as is the belt cog on the distributor. Timing marks line up perfectly. The belt has plenty of tooth depth left and tooth edges are still decent and not rounded off and is relatively new. The nib on the bottom of the cog is right in line as well.
 
Roger that and agree with all. My crank is splined with a hub and stator on it. The flywheel bolts to the hub with 8 bolts. The flywheel hole alignment position with the timing mark on the hub is marked on the flywheel. That said, however, I will do a "sanity check" when we put it back together to ensure everything is where it should be and that the flywheel, hub or something is not "spun" on the crankshaft. From the outside looking in, it is indeed the only thing that makes sense. If thats what happened, that means it spun while I was decelerating. I was running her full bore for short spurts and was coming off one when I started decelerating. Will keep y'all posted and thanks again for the assist. Much appreciated.
 
Indeed it does. Can't argue with that. My flywheel assy. doesn't look like whats in the parts book but rest assured racerone, I will be digging down to see whats what by pulling the hub and stator off for a looksee. Thanks again for your patience and persistance.
 
i looked up the parts on the crankshaft stub and they're showing a key also. I'll dig into it tomorrow if I can. Thanks again.
 
Hi Racerone. The crankshaft is keyed and it it was in the slot of the hub. No signs of shearing or slippage on the contact surfaces of the hub or crank stub. re-installed everything and pulled #1 piston to TDC and the timing mark was right on TDC. So thats that. The new rotor fits into the distributor shaft nice and tight, along with the new cap and carbon stick/spring. We plan on finishing it up tomorrow afternoon. Will let you know what happens. We have two switch boxes. Will try them both. Both are factory but one has been worked on by CDI. Thanks for hanging in there with me. This is my first venture into the "Merc" series with the Thunderbolt lightening energizer/switchbox system. Tough learning curve.
 
Hi again Racerone. We installed the CDI modified switchbox and she fired up nicely. Next will be fine tuning and a water test. Glad its over but I learned a lot about these Lightning Energizer Thunderbolt ignitions. In the end, I guess the normal test results on the switchboxes are meaningless. That is to say while they pass the test readings in the service manual, the switching that goes on in the box can be going haywire like maybe firing two cylinders simultaneously. I've never seen a schematic diagram of one nor will CDI speak with us commoners - preferring now to speak with only certified technicians and account holders. Probably too much phone time with DIY'rs with no financial return. Well suffice it to say they will repair the one I have installed if it fails and thats a good thing. Will be looking for maybe some spares in the meantime LOL. Thanks again for your help. Much appreciated.
 
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