Won’t plane

My father and I purchased an old fiberglass airboat with a 292 Chevy inline 6. After replacing the wooden prop with the Whirlwind dad was running on his 350 at the same pitch, and adjusting the angle of the 292, the boat refuses to come on plane. We even installed a trim tab to try to help, but it still looks like a river barge. We have adjusted timing, cleaned the carb, replaced cap/rotor/coil/plugs/wires and still nothing. Plus the damn thing keeps eating tachs. Can you help? Right now it hits only 2400rpm.
You are asking a lot from a 292 - is it stock? How big & heavy is the fiberglass hull?

The Chevy 292 inline, six-cylinder engine has a bore and stroke of 3.875 inches by 4.125 inches and a compression ratio of 8.0-to-1. It achieved a maximum 165 gross-horsepower at 3,800 rpm and netted 147 horsepower at 3,600 rpm.
There is a lot of needed, but not supplied information that weighs into this equation.
First, the Hull size (length, beam, and weight), and secondly the prop model and length. Hence, the prior question.

Basically, that 292 isn't going to turn the same prop at the same setting, as did a properly setup 350.
How do those two boat sizes compare (original vs current)?

Without more info, the only recommendation would be to take out pitch until it will turn 3000 rpm and then CROSS YOUR FINGERS.
That may make a big difference, maybe it will not.
In either case, that is your next step other than supplying more info (which may or may not ultimately make any difference).
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my boat is smaller than my dad's and used to run good once we could cross some grass and get it popped up. Just not acting like it used to and our "improvements" have had a very detrimental effect on her. I'll have to get the measurements once I get home. Would you suggest lessening the bite by 2 degrees or so?
Start at taking at least 2-3 degrees out and continue taking out pitch until you have RPM's between 2,800 - 3,000. You should find maximum performance somewhere between 2,800-3,000 RPM. If it ran better with the wooden prop it is probably because it was pitched less and ran around 3,000 RPM.

The 292 can be built to be a torque monster that will outperform any 350 V8 in a direct drive application (off idle to 3000 RPM). They were built to power trucks. Take a look at Clifford Performance for professional upgrade options. I would talk with them about the specific application (airboat, limited to 3,000 RPM) before purchasing anything, particularly a cam.

But do keep in mind you are working on an antique, parts for this engine are roughly double vs. the small block 350.

6=8 Clifford Performance Intakes & Headers
We have adjusted timing, cleaned the carb, replaced cap/rotor/coil/plugs/wires and still nothing. Plus the damn thing keeps eating tachs.
Regarding the distributor, as this is a new to you engine (I believe) I would pull the distributor and give it a full tune up. What you describe as replaced is a good start, but I'm willing to bet the distributor itself has too much end play and needs to be shimmed. Pull the distributor and try pushing and pulling on the drive gear. It should not move much at all. If it does move it means your timing is jumping around by a few degrees making it impossible to time correctly. Remove the gear (push out spring pin) and add shims until just before binding, still turning free.

Also check function of your advance system. If the EGR is defeated and the vacuum advance is not either defeated or setup with an adjustable vacuum can, you will never get a decent idle and max power out of the same setup. Many folks defeat the vacuum advance but it will improve fuel economy if you frog a lot. Mechanical advance should have the lightest weight springs possible so all advance comes in by 2,000 RPM. That or defeat the mechanical advance too.

If you will stick to running 89 or better 93 octane fuel you can add a few extra degrees of advance to add power.

As for eating tachs, my first suggestion is to check and clean all your grounds back to the battery. In particular the ground path for your tach.
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