4.3L OMC Cobra

th08tu

Cadet
Joined
Jul 22, 2019
Messages
18
Hello All,
Recently I purchased a 1991 OMC Cobra 4.3L. The motor, upper and lower unit, and boat for that matter, are all in excellent condition, but I am now having a problem.
When I purchased the boat I made sure it started and ran fine before I pulled it away. The only thing that was of concern was the battery, as we used a separate battery to start the boat.
When I got it back to my place the next day, I put the muffs on and started it a few times in my driveway. I did put jumper cables from the battery in the boat to my car, thinking that this would help get it going. Once it was started I let it run until it warmed up (ten minutes or so) just at idle while I poked around checking out a few other things.

Fast forward a few days, I tried to start the boat again. This time I just used the original battery in the boat. It cranked very slowly at first, and then it sped up. After cranking for between 5-10 seconds it sounded like it was cranking normally, but would not start. I picked a battery charger and charged the battery overnight. It charged all night and when I checked the charger in the morning it showed an 80% charge. When I got home from work there was an error code "The battery does not go into Maintenance mode after being charged for 24 hours on the charger."
Thinking that the battery may still have an 80% charge, I turned on the water and tried to start the motor. It started cranking very slow again but then sped up after 2-3 seconds. It cranked at what sounded like a good speed for a few more seconds but would not start the engine. I tried the jumper cables to my truck again, but still could not get the engine to start. Same cranking scenario where it start slow for a chug or two and then speeds up. The reading on the dash voltage shows the battery voltage between 11-12v when the key is the on position, and then it drops below 10v when cranking. I'm not sure if I trust the dash 100% however. I don't have a multimeter that is working so I can't check at the batter right now until I get a new one.

What would be your next steps to determine what the problem is on why it won't start? I'm not 100% convinced it is a battery problem, but I am thinking that I take the battery in to get tested at least. I am thinking it is not a battery problem because after the first few turns of the engine it does crank at what sounds like a proper speed.

When I take the flame arrestor off the carb I can look into it and smell gas in the carb. This is after pumping the throttle a few times before I crank it.

Thank you for your help!
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,241
Ayuh,.... The battery, dirty connections, possibly both ends of both cables, or a dyin' starter are my 1st guesses,.....
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,236
According to what the charger is telling you...the battery needs to be replaced...if it only comes up to 80% its probably sulfated and not going to come back up to charge...also...my experience with boats is that they come with the cheapest junk for battery cables. First thing I'd do...is replace those junk auto quality cables...with marine tinned cables (Ancor brand) with the crimped on terminal lugs. Then...buy a set of Ancor tinned brass clamps....and bolt em on to the terminal lugs.....if you replace your positive and negative cables with these products...and replace the battery....make sure all connections are good...and clean...you will put an end to starting system problems...as long as you have a good starter...There are places that will make up cables to your spec...I used 2 gauge for my shorter run of batt cables and 1/0 for the longer run...the gauge of the cables...has to be sized for the load (starting) and return path distance (from the batt to the starter and then from the batt to the ground on the engine bell housing stud). There are charts where you can look up what size to use (Blue Seas Systems website) but for a battery right next to the engine/starter, 2 gauge will be fine.

I did this about 15 years ago when I put in my dual battery system and have not had chronic problems with batteries. I will say that the conductivity of the tinned brass battery clamps is superior to the plain lead ones. Pay once and get rid of the chronic nuisances...

oh and do NOT use wingnuts, they get loose and can leave you stranded, use the terminal lugs and bolt on the battery cables.



http://www.ancorproducts.com/en/prod.../battery-cable
http://www.ancorproducts.com/en/prod...eavy-duty-lugs
http://www.ancorproducts.com/en/prod...nals/terminals
 

th08tu

Cadet
Joined
Jul 22, 2019
Messages
18
thank you both for the response. I will pick up a battery on my way home from work today as well as the cables you recommend.

What size battery would you recommend? These are the two that I found:

Group 24 Deep Cycle and Starting Battery:
  • 675 marine cranking amps, 65 amp hours, 120 minutes reserve capacity
Group 24 Starting Battery:
  • 1000 marine cranking amps, 130 minutes reserve capacity
Group 31 Deep Cycle Battery:
  • 800 marine cranking amps, 105 amp hours, 185 minute reserve capacity
The Group 31 battery is about $80 more than the group 24. All are above what the manual recommends, but I'll get what you guys recommend.
 
Last edited:

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,241
Ayuh,.... Either of the group 24s is fine, though I usually buy the group 27 combo batteries from Napa,....

Group 31 is waayyy overkill in a runabout,....
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,236
Agreed...I've been using the gp 27 Deka dual purpose batteries for years...I get at least 6 years out of em...rated at 650 cca which is fine...anything beyond this....is too dang heavy to be hoisting out of the boat for my old back lol....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
50,752
for a 4.3, a group 24 is more than enough, however I would go Group 27 myself

make sure to clean every battery cable connection too
 

th08tu

Cadet
Joined
Jul 22, 2019
Messages
18
Ok guys. New battery in and I cleaned all the wiring all the way to the starter. It now cranks like a champ. And that’s all it does. I’m thinking I may just need to take it in to a mechanic, but do you guys have any other ideas? Here is what I have tried:

- sprayed a little starting fluid in the carb
- pumped the throttle several times
- fearing I flooded it I let it sit for 30 minutes and started over with no starting fluid

im totally stuck now, I don’t understand how it would start one day and then after sitting for two days nothing.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
13,236
Did you check for spark? These engines have a points distributor that requires maintenance (ie changing points condenser cap n rotor).....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,752
Maintenance of points type ignition covered in stickies
 
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