best rpm for a late 70's/early 80's merc v6

[James Townsend]

I have an older merc v6 and am trying to find out the "best" operating rpm. I have heard that running one of these older mercs at too low rpm over time on a regular basis can cause carbon build-up and eventualy lest to powerhead failure. Is this right?<br />Thanks.

 

[James Townsend]

Re: best rpm for a late 70's/early 80's merc v6

thats "lead", not "lest"

 

[graddy]

Re: best rpm for a late 70's/early 80's merc v6

You need to prop that engine out to as close as you can to 5500 RPM's. That is with your boat fully loaded. Over proping a outboard engine can cause detonation.

 

[James Townsend]

Re: best rpm for a late 70's/early 80's merc v6

So is my merc v6 "happier" running at around 5k on a regular basis as opposed to say 3k?

 

[Spidybot]

Re: best rpm for a late 70's/early 80's merc v6

No.<br /><br />You should prop your motor so, that full flat out (WOT) rpm is within the specified range.<br /><br />Once that is in order, you can run the motor at any rpm - you will soon know that your mgp is better when on clear plane so giving full throttle until the boat planes and then drawing back to 1/2 or 3/4 gives you good cruising speed and fair fuel consumption.<br /><br />If you go at a speed with the bow raised high, you will spend much power (and fuel) just to lift the bow. Bad idea - slow further down or add more to get on plane, then adjust the speed.<br /><br />At planing hull simply performs better when on plane.