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bh2002
06-17-2010, 10:10 AM
I have run into some electrical problems that I can't guite figure out. I am not extremely mechanical, but usually have learned how to combat problems with the help of mechanical friends. I haven't ran into a problem like this before so I might not explain everything in the correct terms, but I need some help. I've had some guys help me that are real handy with car engines; however, I know that it is much different with marine electrical work. If somebody can lead me down the right path I would appreciate it so I don't start throwing money away into areas that aren't the problems.

To start out I have a 1978 MC SS 351W Prestolite distributor

I started out with what I thought was a bad ballast resistor. I wired around the old worn out resistor by wiring the low voltage wire to the coil to the 12v wire to the resistor. I started the boat and ran it on the trailer trying to see if she ran smooth because last some she missed a little at about 25 mph. She ran fine as far as i could tell. I let it run for about 15 minutes. I shut her down and restarted just to make sure she would still start. I then went out and got a new resistor from the local part store. I don't think it is marine specific because the resistor wire is in a ceramic housing with the back open (not completely sealed off); however, it looked the same as the one I took off with the exception of the mounting bracket. I put the resistor on and I haven't been able to get any fire to my plugs since. I was aware that i could have burned up my points from running without a resistor; however, the wire from the coil to distributor cap was jumping a pretty good spark. Which made me think my points were OK. I took the old points and condenser off and sure enough the points were pitted in one area. I replaced them with marine specific points that looked just like the old ones. The condenser I got looked a little different with a wire from the canister instead of a metal band like the old one. I thought that would surely work and I'm still not getting fire. In fact the points look a little toasted after I cranked on it a few times. I had a friend bring a volt meter over last night and we checked a few spots. It looks like the wire from the resistor to the positive terminal is getting 12v when the key is in the run position and about 6v when it is in the start position. I feel like i'm not getting enough power to my coil... Is this right? There is one wire to the positive terminal on the coil from the resistor and two wires to the negative terminal on the coil (one to the points and another I'm assuming is a ground wire).

I feel like my small resistor problem has turned into many problems. I'm very confused at this point. Any help will be greatly appreciated.

hkallestad
06-17-2010, 10:17 AM
I can't help you much, but if I had problems with the points I would convert to electronic ignition right away, people never look back after doing that. This one might be what you need for that: http://skidim.com/prodinfo.asp?number=RP173071 .

bh2002
06-17-2010, 10:58 AM
Thanks for the suggestion. I thought about that, but at this point I want to figure out what the problem is with the current setup... it should be firing now. It might be a problem that an electronic ignition won't fix. I'm also trying to get it out on the water some this weekend. I will probably go to an EI as soon as I have my big problem figured out and have a little more time.

oldairboater
06-17-2010, 11:22 AM
Seems backwards. Been a long time since I messed with points, coils, and voltage resisters. If I remember right voltage was higher starting and dropped when running to help keep from burning points. I still have a dwell meter somewhere in the garage.

Luv2Ski
06-17-2010, 11:24 AM
It looks like the wire from the resistor to the positive terminal is getting 12v when the key is in the run position and about 6v when it is in the start position. I feel like i'm not getting enough power to my coil... Is this right? There is one wire to the positive terminal on the coil from the resistor and two wires to the negative terminal on the coil (one to the points and another I'm assuming is a ground wire).


Voltage will drop while starting the engine and to the best of my knowledge 6v is not unreasonable. This is the reason the ballast resistor is often bypassed when the ignition is in the start position. You could hook up a batter charger while starting if you wanted, would think that would confirm that this is not the issue.

That second wire on the coil drives the tachometer. Not sure it will help much, but here is a wiring schematic for a 79 (http://www.mastercraftboats.com/teamtalk/showthread.php?p=581436)

With your statement about a good strong spark at the coil wire I tend to think you are looking in the wrong places. Have you tested to be sure there is good spark at the plugs? If you ground a plug and see a nice bright spark, then the coil and ballast are probably not your problem. Did you adjust ignition timing or anything else at the same time? Could your cap be rotated? All plug wires are tight? Are you sure your points are adjusted correctly?

oxberger
06-17-2010, 11:32 AM
bh2002, congrats on your first post, sorry it had to be for something frustrating like an electrical problem. I've had similar problems with mine in the past and it's a huge PIA. I'm not sure what the voltage should be going to the coil when the ignition is on, but I would check all cables and wires for cracks or corrosion. That was part of my problem. I corrected that and was still having issues that I couldn't correct. I took the advice of several guys on here and upgraded to the EI. I haven't had a problem since. My thought process is like yours. I would rather track down the problem and be sure what it was, but after all the time spent hunting and trying different things I gave up and went electronic. Best thing I ever did. Good luck. Hopefully some of the other guys will be around to help with better suggestions.

bh2002
06-17-2010, 11:43 AM
I have checked spark to my plugs and it is very weak and intermittent. I don't know anything about timing and don't have the tools to mess with it. Nothing has been adjust at this point. I gapped my points .018. Is this right? My cap looks good no cracks or corosion, rotor looks good, plug wires look good. I'm not getting much spark to any plug so i wouldn't think that it would be my plug wires because I wouldn't think they would all go bad at one time. I have also tried jumping a spark on a brand new plug and it is very weak.

Luv2Ski
06-17-2010, 12:47 PM
Yes, I believe the spec for that distributor is 0.016 to 0.018 when the points are in the full-open position. Set the dwell to 31 degrees once you get it running

I think the next thing to do is to verify that your coil is okay. I suppose there is a chance you overheated it when you had the ballast resistor removed, best to eliminate that has a potential problem. This is easy to do if you have not done it before. You simply need to compare the resistance of the primary and secondary coils to their specifications. Unfortunately I don't have those specs handy, a search of teamtalk should find them for you but let me know if you can't locate and I can help.

To help search for a voltage leak, turn the engine over in the dark and look for sparks. Had a cracked cap once and it was a light show!