One of my Df250’s will not reach full rpm

[Follybob]

I have a twin 2008DF 250s. Both have good compression and run well. I recently went from 20 pitch props to 21.5 pitch. The port motor will now reach 6000 rpm while the starboard will only turn around 4800. With the 20 pitch both would reach 6000+. Any insight in to what would cause this rpm difference? The motors were recently installed on my boat if that might be a clue. Thanks for your help!

[Murray]

Strange, have you checked both prop’s numbers to verify that they are the same prop? You weren’t really specific if the props where changed the same time the engines were swapped out or did you change engines run the newer ones for at 6000RPM then change props? Basically I’m trying to determine if it’s the props or is the engine swap that is causing/started the low RPM issue? If you still have the the old 20” props put them back on and see if you can get back to 6000RPM.

With the remote control handle in neutral go back to the engines and look for two small alignment triangles, one stamped on the throttle control arm and the other stamped on the throttle lever holder. They should be aligned in neutral. Back to the remote control and open up the throttle to WOT, did the alignment triangles move the same? Check that the throttle lever is open all the way. The details provided are from a PDF “Set Up Manual” for a 2009 DF90A, If you have the triangles on your engines then our set up procedure would be the same or similar.

[Follybob]

The motors were installed with 20 pitch props. No rpm difference BUT they were redlining so maybe the lack of power wasn’t noticeable until the 21.5 were installed. Also the 21.5 have been reworked so maybe there was a mess up at the prop shop. They are all Suzuki props and all stamped and the sets match each other. So it’s the prop swap that started the issue imo