Crusader 305 w/ Delco EST Not Achieving High RPMs

So I have a 1978 Silverton 26 Express with the original Crusader 305 which I installed a new Delco Voyager EST distributor kit in at the end of last season. I had timing/advance setup on it and it was getting up to 4300 RPMs while at idle. Probably the mistake I made was not taking her out on the water after it was installed because now this past weekend I took her out for the first time and she doesn't want to get above 2500 RPMs while in gear at WOT. She will still start up and idle fine and will get up to 4300 RPMs at WOT in neutral. I'm thinking to go back and recheck the timing/advance but was wondering if there's anything else I should be looking out for that could cause this issue? Thanks!

WOT is really meaningless in neutral...

timing advance, however, can be measured at the dock...usually easier than while underway...

what is the max timing advance and at what RPM does it occur?

if the timing is ok, what's the condition of the fuel in the tank?? fuel filters checked? then fuel pressure should be checked.

Thanks for the advice. I had replaced all of my fuel filters at the end of last season as well but probably worthwhile to check them to make sure there isn't a clog, as well as the fuel pressure. I had added fuel stabilizer to my tanks last year before she was pulled out of the water and topped them off with fresh gas on Sunday as well so I would hope the fuel is fine. I will need to double check the timing, I believe it was at 8* at 750 RPM and 27* at full advance when I installed it at the end of last season, but like I said I'll need to double check those.

Another thought I had was when installing the Delco Voyager EST, I had plugged the vacuum advance tube that ran from the carb to the original distributor since the Delco doesn't use that. Should I leave that unplugged? It's a Rochester Quadrajet carb.

full advance @ 27 degrees doesn't tell the whole story...need to know @ what rpm it occurs.

Vacuum advance on the distributor????? Are you serious???? there shouldn't have been any vacuum advance on the distributors....you don't want to leave any vacuum fitting on the carb uncapped....and there should only be one "vacuum port" and it should be connected to the choke pulloff....

Yeah I assumed that the silver nipple on the left hand side of my original distributor that I replaced (above) was for the vacuum advance. There was a hose connected to it that ran from the carb which I now have plugged.

I'll get you official timing values this weekend when I'm able to get back down to my boat. Thanks again for your assistance.