Mercruiser RPM at idle

[acdc96]

I just changed the oil, sparkplugs, and sparkplugs wires. Going to replace the distributor cap and rotor when the parts come in.
I was wondering what's the idle rpm for my 1986 Mercsuiser 260hp V8 5.7L?
Right now it's between 1200rpm and 1400 rpm. that seems a little high but I could be wrong. It sounds the same as always. Any ideas?

 

[Silly Seville]

Re: Mercruiser RPM at idle

I was wondering what's the idle rpm for my 1986 Mercsuiser 260hp V8 5.7L?
Right now it's between 1200rpm and 1400 rpm

That is WAY too high! Do you have the choke on and engine cold when getting this reading? Man, if you try shifting at those rpm's, you're gonna start breaking expensive stuff.

Should be 700-750 max while idling in the water. 650 is ideal, and if the engine is tuned properly, will do so.

I would check your tachometer for possible malfunction, or buy a quality tach and wire it directly to the coil to see what you're getting.

 

[bilge rat jim]

Re: Mercruiser RPM at idle

Mercruiser 5.7L Marine Engine Specifications | Performance Product Technologies

 

[acdc96]

Re: Mercruiser RPM at idle

Silly Seville... I believe your right about the tach. I think I have a bad ground or bad wiring. It did give some trouble earlier in the year but it stopped last month. It would be at 500 rpm when the key was turned but engine not running.
So 1200 - 500 = 700RPM

Thanks for the help. I will post what the problem is at a later date.

 

[acdc96]

Re: Mercruiser RPM at idle

Update:
I took the tach out of the boat and cleaned the whole thing inside out. Now it looks like a brand new gauge. I also "Rented" a tach from west marine to verify the tach I have was accurate. Turned out it was. I returned the new tach and started the motor and it was now idling at 1000 rpm. Little high so I adjusted the idle screw and got it Down as low as I could with the motor running. Amazingly I got it down to 400 rpm. It ran for 5 min like that and I shut the engine off and tried restarting it. It would sputter out as soon as it would start. Increased the idle screw and got it fine tuned between 600-700rpm. Now it runs like a champ!
4 barrel Rochester carbs are the best! I never adjusted or rebuilt that thing and it sat for 5 years and runs like new! I believe running SeaFoam through it helped a lot as well.

Just a few more thing before I put it in the water.
Thanks all