HelpwifeMercury Ibll try this again

" Wifey says, get it fixed, do

" Wifey says, get it fixed, don't spend anything, or sell the ______ thing.

I've been playing with my '70 80hp Merc ser#2881497 with Thunderbolt Ign. for 3 years.

Ran fine, pulled into a spot for lunch, wouldn't start. Took it to marina that specialized in old boats. They had it for a year (literally, beginning of one summer to the middle of the next) Changed switch box and put the crappiest used external wire harness ( bare wires showing, green with corrosion) charged me $300.00. and sent me on my way with the 2 lower cylinders not firing. I thought it was the carb on the bottom two, while fiddling with it for 10 minutes, engine quit, no spark, no refunds, no fishing.

Tried I boats web page, advice.... buy a new one! I really want to keep this one, and if I sell, probably won't get a new one. I replaced internal wires with new wire of same guage. Tested and found rectifier is bad ( read on this site that it can't be the problem) have the manuals... original merc and the other one... can't find anything else wrong.

What do I do next?
Thanks... and sorry for the long post, just trying to give detail.
Bob "

" Bob,
Have you taken the

" Bob,
Have you taken the distributer cap off and thoroughly cleaned it paying close attention to the coil wire spring and carbon bushing.Then go over those plug wires ,make sure you have continuity.If you had spark in # 1&2 and nothing in 3&4 it should't be trigger,switchbox,or coil.Get this spark problem fixed first ,then if it doesn't perform ,rebuild carbs & fuel pump(piece of cake).Don't sell it.I have 1975 850 ,it's been through alot ,but won't quit.Wouln't hurt to check compression.Keep us posted. "

" A thirty year old motor. You

" A thirty year old motor. You need to establish the mechanical condition of the motor.Do a compression test. Remove the bypass covers and inspect for condition of pistons and rings. Look for end play in the rods and bearings.Many motors "look" in good shape , but only testing and good trouble shooting will confirm this. "

" Compression is good on all 4

" Compression is good on all 4 cyl. It only started with 1&2 not running ( when I was told it was the carb) but now no spark on any cylinder.
I was wondering what the logical path of a spark might be, so I can see where the breakdown is. Kind of like
Key to battery, battery to X X to Y Y to Z Z to sparkplug. If that makes any sense.
I have the Mercury Manual, and the Clymer's manual. Neither one works this way, they just have a bunch of different tests.
Since I suspect more than one problem, I figured if I could track the whole system in order, I could replace all bad parts, instead of doing what the marina did, and fix one part, but not the cause of what made it go bad.

Thanks "