I'm not giving much thought to the surging, many (not all) motors have this issue at a given RPM, it's the backfire issue
Check that the distributor is in correct position
While the compression variation between 7 and 6 is 13.5% don't see this as the issue either, probably a gauge or test...
Might use a drill bit just a slight bit larger then the bolt, turning in reverse to give a ever so slight taper in the Gel. Put the bolt half way in or so and apply 5200
Doing it at low tide wouldn't a caddy be easier? Figure gravity lets it out, and not having to carry is a big plus. Did find a 32 Gal caddy with electric pump but could also use a hand pump
I'm on an inland lake and it's totally illegal here
Found it, only thing missing is after this was done I decided to remove all bottom paint and epoxy it white. In doing this I had to go from the Hill Marine 4x4 props to the Merc 3x3 24 pitch because of reducing the drag...
Found the one on OSO and there is one here somewhere
https://www.offshoreonly.com/forums/do-yourself-boating-budget/318849-complete-repowering-brick-25.html
This is a Bravo 3 prop set. Both got me close to 5K RPM. I have a thread which went into detail and will see if I can find
Off hand I don't remember which pitch set I used with each leg but wound up using 24 pitch on the 2.0 at the end.
Biggest issue with the motors is you really need a scanner to check codes. I might be something like a loose connection or bad crank position sensor but without one it's playing a game of darts
A lower ratio leg with higher pitch prop is better than the reverse
Another example same Formula 27PC
530HP motor using a 1.82 ratio drive would get up but not very well. Switch to 2.00 drive and came up much faster. The lower ratio let the motor spin up into it's max torque area sooner
If the crane scale was accurate then the only thing left is you need more motor. The boat most often came with twin 225 of 260hp motors. Your setup sounds like the Formula 27PC I had with a single 454. The single motor didn't have enough power for the hull. I swapped out the motor a few times...
Back firing through intake is caused by spark happening at wrong time, intake valve not fully closed.
It's suggested to keep a spare cap in the boat and wait for issues to start that are unexplained easy. Swap out and if it's fixed all good, if not dig further
The caps on these motors may last a long time and others have a very short life. You can't look at one and see that it's bad. Search the net and you'll find they go out without warning. Yours may be fine but only one way to find out
If cap is good I would do a compression test
I would suggest taking boat and having it weighted
Boat spec says it's around 6K lb, so with gear and trailer its up around 10K. Wonder if hull is water logged
