1980 115 Inline6 - lower RPM

[hempfarmer]

My engine has been running well but this weekend I noticed that full throttle I am only able to get to 4900 RPM vs the usual 5200 RPM. I have owned this engine for 2 years and this is the first time anything has changed. Should I be concerned? I am using the same prop and haven't adjusted the tilt.

The only other thing of concern is I think my battery is on it's last legs. It's hard to say what year it is but there is a copyright year of 2000 on it so it could be 10 years old... I had one issue recentely where I was barely able to start my engine after listening to the stereo for 45 minutes. The starter would only crank for 2 or 3 seconds. Is there a chance a battery in poor condition could impact my RPM at WOT because the altenator is working extra hard?

 

[nathanhooper]

Re: 1980 115 Inline6 - lower RPM

I would consult a manual, or wait till someone chimes in here before I ran it again. I remember reading just yesterday about my 1979 inline6, and there were strong warnings against using a battery with too low of a voltage or one with too high of a voltage. It talked about it damaging the switchboxes, which in turn can effect rpm's. Just food for thought, I am far from knowing much of anything about these motors.

 

[hempfarmer]

Re: 1980 115 Inline6 - lower RPM

Appreciate the advice. My friend had a similar engine and said he always had an issue with his batter not fully charging up.

In my case I run a CD deck with four 6X9's for an hour at a time with the engine not running. Not worried about the price, can anyone recommened a good battery that will exceed my requirements and work properly with my outboard?

 

[Chris1956]

Re: 1980 115 Inline6 - lower RPM

Hemp, Your motor has an ADI ignition, which is not dependent on the battery for power. You do need to replace your battery, however. You might look up the wattage of the stereo and make a calculation on how long you use it with the engine off. This will give you a data point on choosing a battery.

I would think a single 27 series battery would serve you well. Remember that motor can only charge 6A/hour. Running the stereo too long, means that you can never catch up on recharging the battery.

 

[Puddy905]

Re: 1980 115 Inline6 - lower RPM

I would be more concerned about the 300 RPM drop than the battery. Batteries are generally only good for 5 years, so it is probably best to replace it. If you are losing 300 RPM's at WOT, that could be another issue. Was this your first time out this year? It may not be getting enough fuel, due to dirty gas, clogged filter, dirty jets, etc.

 

[Mercury60]

Re: 1980 115 Inline6 - lower RPM

Any chance your tach could be lying to you? How does it feel? Does it have all the get up and go it had last year? Do the throttle cables need adjustment on these motors? With the engine off put the throttle all the way forward, then go to the motor and see if there is any room left on the throttle.