Idle speed for Mercruiser 3.0L, out of gear, and on water muffs is what?

[scarbro24k]

The Sea Ray 160BR had a Merc 3.0L with a Mercarb and it had a min. idle, out gear on the water muffs of 1650rpm.
3.0L Mercruiser eng. sn: C460258.
Replaced the Mercarb with a Rochester 2MC and it idled at 2500rpm out of the box and out of gear on water muffs.
I managed to get the idle speed down to 1700rpm with the idle mixture screws.

There doesn't seem to be much left on the idle speed screw adjustment. Maybe 1turn or less.

So, what is the proper idle speed out of water, on water muffs and out of gear?
None of the manuals I've read have the info.
They all refer to a "in gear, in the water idle speed of 650 - 800 rpm."

I definitely do not want to shift into gear this little bugger at 1700 rpm.
I checked the boat tach against my shop tach and they match rpms for 4-cycl setting.
I am waiting on a water impeller/water box rebuild kit before continuing.
I bought the boat used and I think the unit was run a couple of times with no water because there is very little water coming
out of the prop hub and a lot out of the water tube near the universal joint.
The engine water temp stays at about 170F when warm.
I have more experience with a 1977 SeaRay 240WE OMC 235 engine than the Mercruiser. So, I'm learning.
I have the Seloc Mercruiser Sterndrive manual and several downloads from the Adults Only section
and I have watched several of the Youtube videos on the water impeller replacement, carb replacement and the Trim limit switch replacements.
All of which are on my "to-Do" list.
By the way, this is a boat my wife picked out as "Her" boat. So, I am trying to make sure it is a safe as possible.
This boat can be a scary ride when at top throttle. And my wife can be scary if she thinks "Her" boat has a problem.
So, I am plunging ahead with this repair to "Her" boat.

 

[alldodge]

The Sea Ray 160BR had a Merc 3.0L with a Mercarb and it had a min. idle, out gear on the water muffs of 1650rpm.
3.0L Mercruiser eng. sn: C460258.
Replaced the Mercarb with a Rochester 2MC and it idled at 2500rpm out of the box and out of gear on water muffs.
I managed to get the idle speed down to 1700rpm with the idle mixture screws.

There doesn't seem to be much left on the idle speed screw adjustment. Maybe 1turn or less.

So, what is the proper idle speed out of water, on water muffs and out of gear?
None of the manuals I've read have the info.
They all refer to a "in gear, in the water idle speed of 650 - 800 rpm."

I definitely do not want to shift into gear this little bugger at 1700 rpm.
I checked the boat tach against my shop tach and they match rpms for 4-cycl setting.
I am waiting on a water impeller/water box rebuild kit before continuing.
I bought the boat used and I think the unit was run a couple of times with no water because there is very little water coming
out of the prop hub and a lot out of the water tube near the universal joint.
The engine water temp stays at about 170F when warm.
I have more experience with a 1977 SeaRay 240WE OMC 235 engine than the Mercruiser. So, I'm learning.
I have the Seloc Mercruiser Sterndrive manual and several downloads from the Adults Only section
and I have watched several of the Youtube videos on the water impeller replacement, carb replacement and the Trim limit switch replacements.
All of which are on my "to-Do" list.
By the way, this is a boat my wife picked out as "Her" boat. So, I am trying to make sure it is a safe as possible.
This boat can be a scary ride when at top throttle. And my wife can be scary if she thinks "Her" boat has a problem.
So, I am plunging ahead with this repair to "Her" boat.

:welcome: to iboats

The idle is only set correctly in the water and in gear for your engine. Add about a 100 rpm for the muffs, and first time you have it out get in the clear and check it. Or keep it tied to the dock and let it pull as you adjust.

 

[Fastatv]

The Sea Ray 160BR had a Merc 3.0L with a Mercarb and it had a min. idle, out gear on the water muffs of 1650rpm.
3.0L Mercruiser eng. sn: C460258.
Replaced the Mercarb with a Rochester 2MC and it idled at 2500rpm out of the box and out of gear on water muffs.
I managed to get the idle speed down to 1700rpm with the idle mixture screws.

There doesn't seem to be much left on the idle speed screw adjustment. Maybe 1turn or less.

So, what is the proper idle speed out of water, on water muffs and out of gear?
None of the manuals I've read have the info.
They all refer to a "in gear, in the water idle speed of 650 - 800 rpm."

I definitely do not want to shift into gear this little bugger at 1700 rpm.
I checked the boat tach against my shop tach and they match rpms for 4-cycl setting.
I am waiting on a water impeller/water box rebuild kit before continuing.
I bought the boat used and I think the unit was run a couple of times with no water because there is very little water coming
out of the prop hub and a lot out of the water tube near the universal joint.
The engine water temp stays at about 170F when warm.
I have more experience with a 1977 SeaRay 240WE OMC 235 engine than the Mercruiser. So, I'm learning.
I have the Seloc Mercruiser Sterndrive manual and several downloads from the Adults Only section
and I have watched several of the Youtube videos on the water impeller replacement, carb replacement and the Trim limit switch replacements.
All of which are on my "to-Do" list.
By the way, this is a boat my wife picked out as "Her" boat. So, I am trying to make sure it is a safe as possible.
This boat can be a scary ride when at top throttle. And my wife can be scary if she thinks "Her" boat has a problem.
So, I am plunging ahead with this repair to "Her" boat.

That's a really high idle speed. You may have some throttle cable adjustment issues. Have you disconnected the throttle cable and then tried to adjust the idle speed? Something is amiss for sure since the engine idled so high with the old carb and the new carb. Except for a possible throttle cable issue, the only other thing that comes to mind would be excessively advanced timing....but that's not likely because if it were that far advanced, engine would be very difficult to even turn over. Or maybe an extremely bad vacuum leak. Let us know what you find.

 

[thumpar]

Do as Fastatv states with the throttle cable. If that doesn't work I would check the tach. Does it sound like it is reved that high?

 

[Rick Stephens]

Running on muffs will usually put most water and exhaust output through the bypasses up next to the bellows. This is so at idle it doesn't build up exhaust back pressure when the boat is in the water. When in the water the entire lower exhaust system is completely full of water.. Only when you are at higher exhaust output and with an open thermostat does more exhaust and water come out the hub. Even then on muffs up to temp and at a high idle most will still come out the bypasses.

Rick

 

[scarbro24k]

The throttle cable is disconnected when testing on both carbs. I replaced the Mercarb because the casting that the bottom carb
butterflys went through was bent and seem to stick. So, I got another carb (Rochester 2MC). I haven't checked the engine timing
yet. The dwell meter says the dwell is set okay. I haven't put a timing light on yet. Not much use until the rpms are in range.

Thanks for the info on the water muff water flow Rick!
I just read a Mercruiser Tech Note that mentioned 1000rpms for a water muff setup.
Then the in-gear idle setup goes to 650 - 800 rpm in the water.
A gear shift at 1000rpms is still pretty hard on the unit. A little less severe
than one at 1700rpms

How can the rpms drop to below 1000rpms just by being in the water and out of gear?
I can see in-gear dropping the rpms. But, out of gear?

In any case I will be back at it in a few days after I replace the water impeller and check the water box.
I don't mind used boats if I am willing to put in the time and money to fix the things the previous owners
just didn't want to do or could not afford. And since this is my wife's purchase, I will do what it takes to make her happy!
A Happy Wife is a Happy Boating Wife!

 

[fishrdan]

Fastatv's suggestions sound appropriate...

1000RPM on the muffs is still high, shoot for 800RPM on the muffs as this should drop to around 700RPM; in the water, warmed up, idling, in gear.

Oh yeah, ditch the Seloc and use the downloaded Merc manuals.