Engine misfire

[noah4009]

Hi
I have a 1971 Chrysler 55HP. Model is 557HC Serial 3188. The motor was running fine by the previous owner until his son did a supposily tune up. He knew nothing about boat motors. The plug port was stripped. I had that repaired. The plug wires were also cut. That too I replaced. I tried to start it and after about 5-10 seconds it backfired very very loud. I stopped at that point being I know as much. Nothing. On this motor are the plug wires connected top to top and bottom to bottom or are they crossed. I had them top to top. Also what else should I check.
Thanks
Noah

 

[Frank Acampora]

Re: Engine misfire

It's been so long since I worked on my 55 that I forgot which wire is top (#1).

However, you still need to check the points. If it is not electronic ignition, then there are two sets under the flywheel. They must be set to .020 at the top of the cam lobe. You also need to check the flywheel key; if the son did not torque the flywheel nut to 95 ft. pounds, then the flywheel may have spun on the shaft and broken the key. This is a common cause of backfiring. If the key is broken, you can still get one over at The Chrysler Crew---franzmarine.com.

Matter of fact, why not stop in to the chat room tonight at 9PM Eastern Standard Time.

What kind of tune-up has a procedure for cutting the plug wires? Sounds fishy to me but I have seen stranger things done to Chryslers.

QL77J4C is an OMC plug. It will probably work in the 55 but I would not trust it. It could be a bit too hot and might melt a hole in the piston crown. They probably used those plugs because they could not get the L4J (remember I said they are no longer made?) and were too lazy or lacked the knowledge to find the correct plug--NGK B8S

 

[eurolarva]

Re: Engine misfire

Another good plug that cross references to the L4J is a champion L82C. These plugs I believe only work when the plug wire is permanant to the coil. If it has a detachable plug wire seems to me you need a gapless plug like a UL 18V plug. You should not be using automotive wires either instead you should have actual marine wires. If the re wire job was done by cutting wires and then using electrical tape to apply the new wires this could be your problem.