F70 stalls when going into neutral

[RoosterTail]

This problem only started the last couple of trips. I can be in forward doing say 1000 or so rpm and suddenly bring the motor into neutral, it stops.
This does not happen all the time, but because I have two motors, it is hard to hear when it stops. The other motor is fine.
The motor will fire up again as soon as I start it.
I think the revs may be dropping too much when going back to neutral and it stalls before it can recover.
The rpm at idle at are around 700 and the motor runs smoothly.

[rejesterd]

700 might be slightly low, but I wouldn't expect it to stall out completely like that. I would take a good look at your shift and throttle cables. When you turn the engine from side-to-side, see if that puts any tension on the cables. And just visually inspect them to see if the plastic covering is peeling and leaving the inner cable exposed. Also check the linkage.

[fairdeal]

I can be in forward doing say 1000 or so rpm and suddenly bring the motor into neutral, it stops.
I think the revs may be dropping too much when going back to neutral and it stalls before it can recover.

Part of the job of the ISC valve is to act as a 'dashpot' to prevent that -
although since it seems to otherwise start and idle correctly,
hard to imagine what the 'failure' could be.

But since you have two engines,
you could swap the ISC valves between them,
see what happens.

[RoosterTail]

700 might be slightly low, but I wouldn't expect it to stall out completely like that. I would take a good look at your shift and throttle cables. When you turn the engine from side-to-side, see if that puts any tension on the cables. And just visually inspect them to see if the plastic covering is peeling and leaving the inner cable exposed. Also check the linkage.

I am pretty sure all cables are good turning side to side. I will check again. I am sure when in neutral/idle the linkages are not preloaded.

[RoosterTail]

Part of the job of the ISC valve is to act as a 'dashpot' to prevent that -
although since it seems to otherwise start and idle correctly,
hard to imagine what the 'failure' could be.

But since you have two engines,
you could swap the ISC valves between them,
see what happens.

I can run the engine at home in the drum / muffs and it does not happen. The motor runs as smooth as.
This seems to happen when on the water. Motor is extra long and sits well above waterline.
I could swap ISC. valves and try again. I need to run YDS on laptop out on the water and monitor rpm.
The standard digital gauges round off to one significant figure and the sampling rate is too slow to see where the revs are dropping to.

[rejesterd]

I am pretty sure all cables are good turning side to side. I will check again. I am sure when in neutral/idle the linkages are not preloaded.

I should have mentioned this in my original reply, but the reason to check the linkage/cables is because of the shift position switch (aka the shift cut switch aka the shift interrupt switch). When you're going from in-gear back to neutral, that switch causes the engine to misfire/stutter for a very brief period (to reduce load on the clutch). So if the linkage isn't right, it can cause the switch to engage for too long, and you stall out completely. If you slowly shift back to neutral, it might stall out more often than when you shift quickly.

It could also be related to fuel delivery, but indirectly. If the injectors or the ISC are stuck/clogged slightly, that could also cause this. So as suggested, you can also try swapping the ISC and the injectors between engines and see if the problem moves to the other engine. But the fact that it only happens in the water and not on the muffs (i.e. only under load), points more toward the linkage imo.

[RoosterTail]

I will check action of linkages. Need to watch the gear shift movement in relation to throttle linkage and when the neutral switch makes or breaks. Is the switch NC in neutral?
I can check the action of the switch while working the linkages, (engine off) with a meter if the switch is a contact style (magnetic). I doubt if it is lever operated or of an inductive type.
I think YDS monitors the switch also
Thanks for your time in replying. ...........

Edit: I see it is a lever type.

[rejesterd]

Yeah, YDIS will report ON or OFF for the switch at key-on, but I don't know if it monitors it in real-time. There is an error code relating to the switch, but I honestly don't know what it means exactly. But since it is motion-activated, you should be able to watch it and see if something is wrong. The lever might just need to be adjusted slightly.

[RoosterTail]

I could set up some remote IO I have which can scan in milli seconds straight into a laptop and plot trend in real time.
I would compare TPS voltage (position) vs neutral switch position. The hardest part would be to get wires into the plugs.
But I might just check the switch operation. I wonder if it is just a glorified micro switch, I wonder if the contacts are a bit shitty.