100 % CORRECT - All Blackhawk's and Bravo's outdrives do not use or have a shift interrupt switch nor an adjustment for one.

Is these engines TBI or MPI being a 1996 vintage ?

In the water or on the water hose throttle only NOT in gear can you rev these engines up - Just asking if you have silent choice or just straight thru transom exhaust. how does engines run and shift into gear on the water hose - unloaded ?

I would scan the engines and what is your idle RPM's showing on the tachs and on the scan ? Blackhawks needed to be set at a bit higher idle,

My bad. I thought they were utilized in the Blackhawk application due to the dual prop load and higher in gear idle speed. That being said, slightly off topic, but due to same, would adding them be a good idea?

P-29s all came with MPI

Both idle at 600rpms in neutral.

Whenever engines are pulled, bilges cleaned/painted, and there are running problems afterwards I always think "bad ground". Not sure a ground problem makes sense in this situation, though. IAC's were also my first thought. Get the ECU's scanned and see what comes up.

When the bilge was cleaned is it possible moisture caused some corrosion under the distributor caps? I have heard they can be a problem sometimes. Seems to be a timing or ignitition issue to me from what you are describing.

Engines were pulled then bilge was cleaned up. We'll find out soon I'm dropping it off Thursday:D

adding if a digital tach and or the scan can verify your engine idle is really 600 rpms before you shift into gear - that is too low. Not saying this is your exact 100 % problem but 600 rpms is not helping either. You have to find out (the problem) why your rpms are only 600 if in fact your tachs are showing the correct readings.

Possible fuel restriction first thing comes to mind.

BUP - I have twin 2006 6.2 MPI's and SC5000 vessel view. Ran both engines the other weekend on the hose to dewinterize. After warmed up I bring them to idle and they both are right at 600 rpm according to the SC5000. That is where they normally idle for me. Just telling my experience.

Yes sir that is correct. I have not seen or touched a Blackhawk drive app in years. For some reason I thought a fully warmed up MPI with a BLACKHAWK app was idle min at 650 to 700 RPM's.

I went to look back in my service notes and it was listed for bravo and Blackhawk apps a 350 MPI should have an idle of 600 rpms. SO MY BAD. I POSTED INCORRECT INFO.

With that said somehow I could of sworn that idle with MPI engine and Blackhawk app was 700 rpms / 650 rpms bare min.. If I ever find that info and what app w/ Blackhawk that applies to, I will post it. But again I still might be totally wrong.

Have you verified the factory Idle RPM spec, 600 sounds low, there is a limited amount of rotating inertia at that RPM. You state none of the rotating parts were changed, but it is common to replace with a lighter flywheel, such as aluminum. You mention the props are 31", but have they or the gear ratio been changed.

Personally, I believe in heavier, not lighter flywheels, and would raise the RPM in 100 RPM increments until the shift can be made without stalling. Testing in such a manner may help with the solution.