MSD ignition conversion to '69 Johnson 55hp

[1980SeaNymph]

Just completed the conversion of my old Johnny to the MSD Street Fire CD box, and she runs like a top. However, the one thing that I have heard is that because of the higher voltage output of this sys, (45KV) it can eventually burn up the cap and rotor that were only designed to handle 30KV. I've heard guys getting around this by running a second coil with its secondary output directly grounded to the block, to cut primary voltage in half. Question is this... should the second coil be wired in series or parallel? Seems to me it should be in series (two loads in series = half voltage to each load). Any thoughts? At $300 for a new cap, and an NLA rotor, I don't want to scrap either one. Pretty much removes the advantage of going with the MSD setup.

 

[1980SeaNymph]

Re: MSD ignition conversion to '69 Johnson 55hp

Anybody home?

 

[BonairII]

Re: MSD ignition conversion to '69 Johnson 55hp

I know very little about electrical systems.....but what about using a resistor wire or something that limits the current going to the distributor?

 

[Daviet]

Re: MSD ignition conversion to '69 Johnson 55hp

MSD don't have any suggestions? They made the conversion, maybe they have encountered the problem, check with them and see what they say.

 

[Sprky]

Re: MSD ignition conversion to '69 Johnson 55hp

SN You are way over the heads of the folks around this site with what you are doing.

The burned cap and rotor is heresay or you have seen it?

Asking MSD any questions about one of their systems that has been adapted for use other than specified, is like talking to a wall...........

I ran 2, 3cyl pwc boxes and mag pick-ups on a v4 OMC that we raced. Anytime I would try and talk to the Tech guys they would tell me that the boxes were not designed for what I was doing.

I loved the msd. You could light water with it.

Have you turned your motor over with the plugs out, the ignition on and listened to it sing?

Kinda kule

 

[1980SeaNymph]

Re: MSD ignition conversion to '69 Johnson 55hp

Well... MSD didn't really make the conversion... I did, after losing all spark and not being able to find an amplifier box while on vacation I think I'm still gonna give them a call tomorrow and see what they have to say about reducing the output of their system.

I thought about running a ballast resistor on the feed to the coil, but the coil feed from the box is running at 450V, rather than the 12V a ballast resistor is designed to handle...right??? Maybe I'm totally wrong on that.. I dunno.

Aside from the technical issues- man, what a difference that made! Used to have to crank the hell out of it to get it to fire after it was even a little warm (I was getting concerned about starter wear!) Now, I swear I could walk up to it and bump the flywheel by hand and it would fire! NO... I'm not gonna try

 

[1980SeaNymph]

Re: MSD ignition conversion to '69 Johnson 55hp

Sprky-
Haven't actually seen the burned cap & rotor happen w/my own eyes, but it seems to be a common concern. So... I guess you're right, it is just heresay. Still just want to be reasonably sure I'm not gonna fry an overpriced vintage OMC part. (I've already done that...lol)

I don't feel I'm over the heads of anyone on this site- everyone has their own area of expertise. That is one of the benefits of having a site like this where so many minds can come together. Some have good ideas, some do not, and everyone is learning something along the way. Just have to take things for what they are worth.

 

[1980SeaNymph]

Re: MSD ignition conversion to '69 Johnson 55hp

Anybody else have any input on the original coil question?

 

[seahorse5]

Re: MSD ignition conversion to '69 Johnson 55hp

Sprky-
Haven't actually seen the burned cap & rotor happen w/my own eyes, but it seems to be a common concern. So... I guess you're right, it is just heresay. .

Keep in mind that electricity is lazy. It only uses enough to jump the spark plug gap at that particular moment. The ignition system may be able to put out 45,000 volts, but that is at open circuit. Normal running may only need 8000 volts at idle and 20,000 during acceleration or full speed. Each engine, plug type, and gap will have different requirements at different throttle settings. I wouldn't worry about the distributor or rotor.

 

[1980SeaNymph]

Re: MSD ignition conversion to '69 Johnson 55hp

Keep in mind that electricity is lazy. It only uses enough to jump the spark plug gap at that particular moment. The ignition system may be able to put out 45,000 volts, but that is at open circuit. Normal running may only need 8000 volts at idle and 20,000 during acceleration or full speed. Each engine, plug type, and gap will have different requirements at different throttle settings. I wouldn't worry about the distributor or rotor.

Sorry, haven't been able to respond in awhile, been busy.

So... basically what you're saying is that as long as I don't increase the resistance in the secondary circuit (ie- keep the solid core wires and standard plug gap), spark voltage will be about the same as stock? Kinda makes sense, just hadn't thought of it that way.

We romped on her pretty hard the other day at the lake (WOT for abt 1/2hr straight, plus many "hole shots") I've been gonna pop the flywheel back off just to check cap & rotor condition after this, but haven't had a chance to yet. I'll update when I do... hopefully this weekend. Never missed a lick the whole day, all seems to be well.

 

[charger_1]

Re: MSD ignition conversion to '69 Johnson 55hp

Well... MSD didn't really make the conversion... I did, after losing all spark and not being able to find an amplifier box while on vacation I think I'm still gonna give them a call tomorrow and see what they have to say about reducing the output of their system.

I was thinking about doing the exact same conversion for the same exact reason actually! Could you save a fellow some time and let me know what you ended up having to do for the convert? It should be pretty simple, as it's just a mag pickup, but your experience would be appreciated if shared

thanks

 

[keithnra]

Inknow this is really old i just wanted to save it