HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

[58sealine]

Just resurected a 64 evinrude 40 hp. Rebuilt carb and set throttle linkage close as I can get it to therepair manual's recomendation. Set the points at .020 and adjusted coils as close to manual recomendation as posible without special tool. Fires up fine and will idel down but wants to backfire and wont stay running at low idle. Will accelerate fine with intermittent backfire. Also it gives you a mild shock while running and a pretty good shock when backfiring
I would appreciate as much help as posible with this.
Thanks in advance.

 

[geoffwga1]

Re: HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

Sounds as if your high tension lead or leads is arcing to ground somewhere.It will involve pulling the flywheel again but I would check under the magplate to make sure your plug leads are not being pinched somehow.Someone else may come up with a better idea.
Good luck,you have a great motor there once it's ironed out.

 

[HighTrim]

Re: HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

What did you torque the flywheel nut to?

Did you replace the plug leads when adjusting ignition? Coils were not cracked or damaged were they?

If its not a mild backfire due to running lean, you have a short in the ignition somewhere. Running at night may help locate it. Likely the plug leads where they exit the mag plate.

 

[58sealine]

Re: HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

Thanks everyone. Just the information I am looking for!
Just some background on the engine - I salvaged old coils, condensers and spark plug leads from a 1959 35 hp donor motor that had many other issues (but did run though poorly). The donor motor was also giving me mild shocks during running but I just figured it was a pinched wire or shorting lead that would be corrected with the transfer of ignition parts from the 1959 to the 1964.
I opened the slow idle adjustment needle 1 1/2 turns and worked my way closed from there. This had no effect on the backfiring.
I do appreciate the question regarding the torquing of the flywheel (105 lbs). I realize there are many things that can go wrong with an improperly torqued FW.
I will order new coils, wires, condenser and points and go through the ignition system this time with new parts.
Please keep sending suggestions and opinions.
Thanks,
58Sealine

 

[HighTrim]

Re: HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

You used the original coils? Werent they cracked/damaged? If they were, get them out of there. They are never still good. That, along with plug wires and you should be good to go.

 

[1946Zephyr]

Re: HELP! Old Big Twinn causes shocks when running, idles but backfires and cuts out

Yea, once you totally clean the magplate and put new components on, you'll notice a difference.