'80 80hp, Misses then runs great???

dctucker

Seaman Apprentice
Joined
Oct 6, 2004
Messages
36
1980 4-cyl 80hp. <br /><br />Tough to start when cold, eventually runs, though seems to be missing on at least 1 cylinder, down on power, lousy throttle response, smokey (rich exhaust, as at least 1 cyl not firing). After initial startup, it starts fine, just touch the key and it's running.<br /> <br />After running a while (~1 hour), something fires, and it runs like a champ with full power, snappy throttle response, etc. Joy to run at this point.<br /><br />Next morning, same thing... Just cleaned/rebuilt carbs (though it was happening last season too, was hoping, but not really expecting that the carb rebuilt would do the trick), fresh plugs, new impeller.<br /><br />I'm thinking switchbox is the most likely culprit or maybe trigger? Possibly a sticky ring, but I Seafoamed last season, no effect on this problem, is leading me to think electronics. Though I've never done a compression check on this motor, cold or warm...<br /><br />How can I diagnose, other than just throwing expensive parts at it?
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: '80 80hp, Misses then runs great???

Sounds like you need to test the ign system, if is missing 1 cyl. it could be a plug, coil or switch box. If missing on 2 cyls. 1 and 3 or 2 and 4 it's a trigger, if it's 1 and 2 or 3 and 4 it's probably a stator
 

dctucker

Seaman Apprentice
Joined
Oct 6, 2004
Messages
36
Re: '80 80hp, Misses then runs great???

Thanks Laddies. Hadn't really thought of coils or stator... I think I can rule out plugs, as I just installed fresh ones. Plug wires, possibly??<br /><br />I'll review the Seloc manual, but any advice on how to actually test for each of the possibilities?
 
Joined
Nov 29, 2006
Messages
20
Re: '80 80hp, Misses then runs great???

I have a Merc 80hp (800) 4 cyl and had a bad miss on number 4 cyl. I replaced the plug wire and the hot leads from the coils to the switch box as they were old. Now it runs great.
5600 rpm with a aluminum 19 pitch prop on a 18' aluminum boat.
Engineoff1.jpg

Good luck...
 

dctucker

Seaman Apprentice
Joined
Oct 6, 2004
Messages
36
Re: '80 80hp, Misses then runs great???

Cpt_Quint said:
I have a Merc 80hp (800) 4 cyl and had a bad miss on number 4 cyl. I replaced the plug wire and the hot leads from the coils to the switch box as they were old. Now it runs great.
5600 rpm with a aluminum 19 pitch prop on a 18' aluminum boat.
Good luck...
Wow, haven't poked around here for a while, surprised to see this back near the top! Funny timing, as I just today started de-rigging the old Merc. I'm about ready to take it off the hull.

I'm throwing in the towel, repowering with a shiny new E-TEC. I love the way this motor runs, I just don't have the time, patience and experience to sort out the electrical issues to make it the absolutely reliable runner I need it to be.

If anyone wants it, PM me.
 
Top