Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

[ewpvic]

Can anyone tell me why my idle screw looks NOTHING like the picture that is shown in the manual? Did someone jack the dang thing doing a rebuild...????

 

[alldodge]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

What's your engine serial number

 

[ewpvic]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

B732203

 

[alldodge]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

Looks right to me other then the rusty nut. Probably changed it out with one that was not stainless steel.

Don't know if this pic will come out large enough


If it doesn't work out go to
Parts Catalog | Mercury Marine
and enter your serial number

Go hear for the service manual and start on page 201
Boatinfo - Mercruiser Service Manual nr. 8 - 1985-1989 - Mercury Marine 4 Cylinder Engines

 

[ewpvic]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

So my idle screw is SUPPOSE to contact the radius part of the throttle lever? Because, that's where mine makes contact. NOT on the flat tang?

Doesn't seem like that's right. How can it keep pressure on that piece with just 2 turns after contact? The black paint has been rubbed off (see my picture).

 

[alldodge]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

Yes your idle screw should rest against the radius part. The radius is a bit of a cam lobe so to speak. When the engine is cold and you pump the throttle the choke closes and the radius turns which sets the idle up a bit. As the engine warms up the choke starts closing and the idle is decreased until it comes to rest in the spot where the choke plate is fully open. This is why the paint is wore off the radius. If your carb and throttle linkage is adjusted correctly and in good order it should remain in contact.

 

[ewpvic]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

OK. I see now....so, when I back the screw off of that cam, what position should the cam return to? Or, will it?

 

[achris]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

OK. I see now....so, when I back the screw off of that cam, what position should the cam return to? Or, will it?

If the engine is cold the cam will more to the 'cold' position. Same if the engine is warm, it will move to the warm position.....

That radius is a hang-over from the automotive fast idle cam. Just in a marine engine it's no longer stepped...

 

[ewpvic]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

But how do it know? Errr, uh....How would I know?

I just trust that it is still mechanically working properly, and then use the static idle procedure in the manual? It performs and responds as designed, but I think it is idling low.

 

[achris]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

That radius plate (as you're calling it) is linked (mechanically) to the choke plate. When the choke heater coil is cold it pulls the choke plate shut. That pulls the link and moves the radius plate.... HTH....

If your engine is idling slow, wind the idle speed screw in a little more.

 

[ewpvic]

Re: Mercruiser 3.7 Carb Idle Screw vs Sevice Manual Picture

10-4.

Just didn't want to booger anything up if I gave the screw a bit of a turn. I think I "bumped" it while I was screwing with the engine. I'm gonna check it with an external tach and make sure I am spot on what spec idle should be.

Running great in gear all the way up the rpm range. Timing stays within spec.

Thanks guys.