Quick Question for Merc Experts

[LaqueRatt]

Do the idle adjustment screws work normally on in line 4s (mine is a 75 HP) or are they backwards? I read somewhere that you tighten them, clockwise to richen the mix instead of turning CCW like most carbs. I'm thinking this is wrong as I watched a vid on adj the carbs and the guy was doing it in the normal manner. So I think I did it wrong and want to take another stab at it. A quick reply would be very helpful since it's getting cold here and I've yet to get my new toy splashed.

 

[Chris1956]

Carb idle mixture screws richen the mixture when turned open (CCW).

 

[LaqueRatt]

Thank you Chris. The amount of misinformation online is amazing! So I'm obviously too lean I think. Could this cause a high idle speed?

 

[Chris1956]

Generally too lean a mixture will cause the motor to bog when trying to accelerate. If she doesn't bog, and idles reasonably well, the idle mixture is fine.

Mercs of your type will idle a bit faster when the idle mixture is too lean, but not a lot faster, mostly just smoother. They usually just will not accelerate, as they do not have accelerator pumps, like automobile carbs.

Remember, the throttle cable must push the throttle closed to slow the idle speed.

 

[LaqueRatt]

Good to know. It's 50 out with a stiff N breeze, not feeling much like getting wet, but it needs to be done. Hopefully it'll warm up.

 

[LaqueRatt]

Got after it yesterday, but all I managed to do was get the idle to drop down, but it many times idles high and then drops down. Weird. All I did was pry around on the cables trying to figure out how to release them to adj. Now I think they are OK, but maybe need lube or something?

Oddly didn't seem like turning the screws on the carbs did much of anything. I tried turning them in until the motor faltered, but it pretty much didn't falter at all. It even ran pretty good with the top carb screw fully seated! It was pretty cool outside. Should that make a difference though?

To cap off my lousy day, the muffs fell off while I was messing with the carbs and now it doesn't want to pee unless I rev it way up and then drop it down. At idle it doesn't pee at all. No idea how long it ran without water, probably not too long, but seems like I likely killed my impeller.

My first time changing one. Are all the Mercs pretty much the same? Should I change the housing too? Is aftermarket OK for these or should I go with OEM?

 

[merc850]

You set the low speed needles (with the motor warmed up), in forward, running in the water at about 900 rpms. Set them 1 1/4 turrns out to start the process. Revving the h**l out of the motor in N with muffs can lead to destruction.

 

[LaqueRatt]

Guess I'm attending the school of hard knocks here. I'm learning, but it's proving to be a steep curve Haven't been revving the hell out of it really, but have been giving it some brief bursts just to see if it is accelerating without bogging. I'm kind of lost now, but guess will not mess with adjustments until can get it out on the lake.

Thanks for mentioning the 1 1/4 turns out starting setting. Suspected as much even though sources I saw said 1 1/2. It actually seems to run best at 1 turn out.

What I really need right now though is help finding the correct impeller. Motor is is an '85 (I think) 75 HP s/n: A168931

 

[merc850]

It won't run right until you set it up in water, the back pressure and prop resistance change the way it performs. Muffs are good for winterizing and pre-season starting.