Battery cause rough idle?

[jedimaster]

Hi guys,
I have always had a rough idle and rough dead slow performance.
The other day I went to the lake and my starter motor battery was dead(Left the bilge blower by mistake). I hooked up my trolling motor battery instead so I could get out on the lake and do some fishing. The idle was noticably better, I could even run my motor at a slow troll and I have never been able to do that.
I have always checked the charge on the starter motor and it has always been up in the 13 volt area.
Could the battery be causing the rough slow performance issues I have been having?

Its on a 3.0 mercuiser 140hp. 1988.
I have changed the plugs, and wires, seafoam run through, timming, compresion all good. Points, cap and rotor were next on my list to replace, but now I am wondering if its just a matter of the battery?

 

[WillyBWright]

Re: Battery cause rough idle?

I wouldn't think so. A battery can show good voltage but have poor capacity. However if it was bad enough to affect running, it wouldn't turn over the motor and start in the first place. Still, if putting on a different battery solved the problem, take the hint.