Motor left me stranded

Boatin_in_KY

Cadet
Joined
Jun 13, 2011
Messages
9
Hey guys, I just bought a '77 Cobia with a Mercury 700 with Thunderbolt ignition. Took it out on the lake Saturday and it was running pretty well. The first thing it did was drop in RPM while running steady, which I attributed to the throttle linkage needing adjustment (have to go pretty far forward for it to engage, and farther for it to rev up). Rode around for about 10 minutes and then brought it down to neutral and it died, but started back up. Riding around a few minutes later we hit a wave and it sputtered down and died. After some coaxing it restarted for about 5 seconds, kind of rough, then died again. Will crank over all day long, just won't start. Had to get towed in ::facepalm: Tried some started fluid when I got home, didn't help. Battery has plenty of power. Going to try to test the fuel pump later, but am open to anything else to look at. Thanks!
 

joed

Lieutenant Junior Grade
Joined
Sep 28, 2002
Messages
1,132
Re: Motor left me stranded

Check the compression on each cylinder.
 

Boatin_in_KY

Cadet
Joined
Jun 13, 2011
Messages
9
Re: Motor left me stranded

Planning on checking the compression, need to get a gauge. Not sure I follow the oil in the gas? Yes I had it mixed 50:1.
 

Wingedwheel

Lieutenant Junior Grade
Joined
Jun 16, 2009
Messages
1,071
Re: Motor left me stranded

Yep, I agree with joed, check the compression.
 
Joined
Jun 13, 2011
Messages
1
Re: Motor left me stranded

If you go to Autozone you can rent a compression tester tool, you put down like a 40 dollar deposit and when your turn it in you get your deposit back:) It's what I used on my 1974 85hp merc.
 

daveswaves

Ensign
Joined
Mar 22, 2002
Messages
901
Re: Motor left me stranded

Hey guys, I just bought a '77 Cobia with a Mercury 700 with Thunderbolt ignition. Took it out on the lake Saturday and it was running pretty well. The first thing it did was drop in RPM while running steady, which I attributed to the throttle linkage needing adjustment (have to go pretty far forward for it to engage, and farther for it to rev up). Rode around for about 10 minutes and then brought it down to neutral and it died, but started back up. Riding around a few minutes later we hit a wave and it sputtered down and died. After some coaxing it restarted for about 5 seconds, kind of rough, then died again. Will crank over all day long, just won't start. Had to get towed in ::facepalm: Tried some started fluid when I got home, didn't help. Battery has plenty of power. Going to try to test the fuel pump later, but am open to anything else to look at. Thanks!

The good news is that if it will crank over all day it is not seized. If it did not fire with starting fluid it sounds like you are not getting spark, double check spark before you go any further. By all means check the compression, just dont forget the spark.
 

Boatin_in_KY

Cadet
Joined
Jun 13, 2011
Messages
9
Re: Motor left me stranded

Thanks for all the help guys, I am going to try and get over tonight to do some testing.
 

PHE

Seaman
Joined
May 17, 2011
Messages
58
Re: Motor left me stranded

If it was running good then stopped running good, had good water for cooling (does it have a good impeller, was it pissing?) and there was oil in the gas, and it wouldn't fire on starter fluid (which you shouldn't use on a outboard), it sounds like you don't have spark. Since it didn't hit on any cylinders, I would guess stator, trigger, switchbox, or wiring. Check for spark at the plugs and work your way back.

Good luck Boatin_in_KY. I'm planning on boating in Kentucky tomorrow. Driving down to Lake Cumberland.
 
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