Low RPM, Setup, Prop Recommendation/Other Cougar 21 MTR 2.4L carbed

[trickcraft]

I have a cougar 21 MTR (1985) with a 200hp blackmax on it (also a 1985).
I spent the summer so far getting it running.

New head gaskets
New Carson Marine Reeds
Clean carbs, new gaskets, reset floats.
new popet
new impellar
Link and Sync
Test for BTDC (ensure alignment of .462 on flywheel)
rebuild fuel pump.


Starts and runs now. No bogs but would not spin over 4000. Thought maybe tach (30 years old) but get lots of cavitation getting out of the hole. When cavitation, tach goes beyond 4 K therefore tach seems to work. Also cavitates out of hole unless jackplate is almost all the way down. This seems odd as when jackplate is all the way up, the bullet is nearly aligned. (see pictures below). Propeller was a spinelli cleaver with a 29P. (at least thats what I think.)
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I changed over to a quicksilver 26P.
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RPM was almost bang on to the Spinelli. Had more people in the boat though. Cavitation was pretty much the same as well.

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When i bought the boat, it was not really running. Compression was checked a year or so earlier. I called the mechanic. He said that there was noting out of spec for compression.

Speedo is not working so have know idea what my WOT speed is. Have not disconnected the advance timing box as I could not find anyone with a timing light locally here and the shop needed two weeks to ensure timing is accurate. More pics of relationship of motor to hull in next post.

Need some help here.

[trickcraft]

The pic of the alignment between bullet and bottom of hull in above post follows what i believe to be zero trim. The pics below do not have zero trim but are more for information purposes.
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Tach settings.looks good
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Not perpendicular to transom but shows jack plate height and length of shaft.
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[trickcraft]

I might add that my jackplate is ancient and unreliable (a marine engineering) and I should really replace it which leads to what the set-off should be a a great base line starting point

[Dave Strong]

Motor is to low, need a 6" jack plate. But first run a 21 pitch prop and see if the motor revs past 6000rpm if not might have an issue with the engine such as bad stator. Try a small pitch prop first and see if you get rpm.

Dave