One problem solved on to the next idle problem

Mercruiser 5.7 2 barrel Mercarb
The boat starts, warms up & will idle @ 600 rpm with the shifter 1/4 forward. When I place the shifter in neutral it will stall. The lower shift cable is new. All the filters were changed, fuel pump good tried adjusting idle screw sparyed it w. carb cleaner Is this an adjustment to the cable or a carb problem?

Alpha 1 shift cable adjustment procedure

Raise outdrive a count of 2-3 seconds from all the way down.
Remove short cable from shift bracket at engine.
Push plastic cable end of short cable all the way IN, have someone turn by hand the prop c’clockwise until full forward engagement.
Measure distance between the center of the brass trunion to the center of the plastic cable end hole that the mounting stud went thru. This measurement must be 6 inches exactly!!

Now shift the control handle to full forward full throttle position.
Try to install short cable onto shift bracket. If it will not fit perfectly adjust the control shift cable trunion “only” until it does. Once there install short cable back onto shift bracket. Now turn control cable trunion 3-4 turns AWAY from the plastic cable end and install into shift bracket.

Shift control handle to neutral. Prop should spin freely with no clicking sounds.

Now shift back into forward but only to the “detent” aprox, 10:00 oclock . This is when forward gear should be fully engaged. Make sure someone is spinning the prop by hand c’clockwise when doing this.
If you have good forward engagement with no slipping then pull handle back to neutral.

Now shift handle to aprox, 2:00 oclock, have the person spin the prop clockwise. This should give you reverse engagement. If it does then you are done! If it does not and you have a clicking sound / not full engagement then adjust the short shift cable end where it is mounted, there is a slot, loosen the hex nut under the cable end and move cable towards the end of the arm, say ¼ inch and retry. When full reverse is obtained you are done.

the idle screw made no difference when adjusted in or out? Then your idle circuit is clogged, with the throttle 1/4 way down it should be on a warm motor about 1000-1200 rpm.

If the above is accurate in my discription you need a carb rebuild.

When shifting into gear and it keeps stalling then it would need a cable adjustment.

CHIEF..............

The boat starts, warms up & will idle @ 600 rpm with the shifter 1/4 forward. When I place the shifter in neutral it will stall.

when warm and the shifter 1/4 the way down it should be at 1000-1200 rpm. When you pull back the shifter when it's in neutral then it should be at 600 and not die the motor. the cutout switch on the shift convertor on the motor the micro switch thingie should not engage.

Actually it will only engage on the water and when there is pressure from the prop that activates it.

So again the carb needs a rebuild, or there is a bunch of slack in the shift cable.

But you posted it was replaced by a mechanic . Did you ask him what he thinks seeing the problem popped up after he worked on the motor.

I spoke to a mechanic who said it sounded like the Carb. I will try some seafaom in the water serparator & if that doesn't work clean & rebuilt. I will also try w/ the shift interupter disconneted & adjust the cable if that works. Thanks for the pointers.
I ran the seafoam I'll let it sit & try it after work. I also dissconnected the Interurper Switch but no diff.
I'll post the results Thanks for the pointers

Was an aftermarket carb rebuild kit used?
In some of the kits, the carb/manifold gasket is thinner than what is required... and it makes a big difference at idle. Makes it impossible to set the idle mixture right.

When the shift control is in forward or in neutral start up the handle is typically at about 10:00 and that is typically idle speed location.

He may be saying 1/4 throttle and it may be so but if it is idleing at 600 rpms that is to low for that shift handle location. Of course if all the cable are out then all bets are off.

I still think that if the engine idles correct, and one shifts back to neutral and it stalls it indicates the short cable is out of adjustment causing the interupter switch to be activated.

The answer here is to disconnect the long control throttle cable from the carb and if it runs at idle then it is most likely not the carb. If it will not idle down on its own with the throttle (carb) linkage all the way seated for base idle then it may be the carb.

Ya, the more I think about, kghost is closer to the problem...
Will the engine start in neutral?

maybe i'm reading it wrong the op.

why not just disconnect the cable from the carb, start the motor and adjust the idle speed screw to the correct rpm

Problem solved
Dissconneted the throttle cable & adjusted. Idles great in the N position.
I put her in the water last night
Thanks for all the help, love this forum its a great resouce