Maybe too much dependancy on the IAC's and need to adjust min air spec ?

This happened out of the blue on my donzi blackhawk and I adjusted the throttle blade just a touch to raise the idle rpm about 50. I know you're not supposed to do that, but 5 years later it was still running and shifting great.

Exactly what I'm saying. IAC's can't move real fast, so if timing is correct and IAC is working correctly, many times adjusting 'minimum air' (throttle blade setting) can be all that's needed. I run into this with mildly hopped up cars with tight torque converters. Takes some of the dependancy off the IAC's job.

In these situations, we add a second IAC. Then you have twice as much IAC, they work twice as fast and only have to open half the amount to do the same thing. We use them a lot on bigger power engines that are in larger boats with big props and gear. It's a tremendous load on the engines when you put them in gear. 1 IAC would never get the job done on a big cat with 1.24 gears and 41" props. The same principal applies here. You have an engine that is under a tremendous amount of load with the dual props when the drive is put into gear. A second IAC will help a bunch. We've actually done them on another P29.
Eddie

In my post # 19 again I could have sworn Merc somewhere in a SB or something change the idle speed to 650 or 700 for smallblock MPI Blackhawk apps.

When I get a chance I will try to find any related info on this

if all possible can you give me your engine serial numbers and did your boat originally come with Blackhawk drives from day one from Merc / builder build ?

Yes, the P-29 is an original Blackhawk boat.

Going off memory, I think my Donzi Blackhawk(502 mag) idled at 650 in nuetral.

Can the P29 owner post your engine serial numbers and outdrive serial numbers ?

Listed at that timeframe was 600 rpm from Mercruiser but as I said from the start I think that changed with Blackhawk drive apps as the rpm was changed to higher rpm setting. Not many Blackhawk out currently running around. I have not seen one in years to work on. Just saying.

After rereading it says Idol should be 600rpm "in gear". I'll have to take it back out and confirm that. I'm going to run it in the Shoot Out PR next week. I'll make adjustments if needed on idle then and see if that makes a difference.

Any updates?