1989 mercury classic 50 wont run above 2500 rpms and will not plane out

hello, i bought this boat a few months ago knowing that it did not run. performed compression test and had 120 psi on all 4. purchased carb kits and installed, installed new fuel pump. removed lower unit and replaced waterpump. put boat in water and it would not run over 2500 rpms. if i choke engine it dies instantly. i tried removing fuel cap in case the tank wasnt venting with no change in performance. checked physical condition of electrical components and insulation was coming off most of the wiring so i decided to replace the stator, trigger, rectifier, all four coils and wires, spark plugs and the switchbox. put boat back into water and still will not run over 2500 rpms. removed powerhead and replaced crank seals, checked exhaust tube for plugging, installed new exhaust gaskets and plate. reinstalled powerhead. boat still will not run over 2500 rpms in gear. i am running out of ideas. please help!

Mark flywheel for TDC # 1 , #2, #3 ,#4 for each cylinder.-----Run with timing light and check if each lead is firing at the correct time.----Checked the reed valves ?

i could see 1 set of reed valves through the bottom of the bearing seal carrier but i could not see all of them. The one set that i saw looked brand new which i guess would be normal for what i assume is stainless steel. i will check the timing on each cylinder tonight and let you know. i really appreciate the help. thank you Sir

Marked top dead center on all 4 and ther are firing as they should the marks i made on the flywheel are about a half inch from the pointer but can clearly see the marks i made for 1 thru four when i switch the wire lead to each plug

Are the boost venturis in place ?-----A blockage in one carburetor can be the issue.----Need an assistant to drive the boat.---Try this , run at full throttle on the lake / river.--------Shine a strong / strong flashlight into carburetor bores and observe / compare fuel coming up the main nozzles.----Serial # of the motor ?

Venturis are in place with the flared ends looking at me when i look into the carburetor the serial# is Ob258277. I wouldnt be able to try the other suggestion until this weekend. I will ask you this though. I was looking at the carb breakdown on this website where i ordered the repair kits. There is a slotted brass screw close to the top of the carbs that the breakdown does not show. The kit comes with a new plug. They were torn up pretty bad and wouldnt come out where someone destroyed the slot in the screw at one time or another. I was looking at a manual from boat info .com and they showed a carb that was indentical to mine exept it had actual diaphragm pumps on the side covers. On that diagram it show what they were calling an idle tube under the slotted screw. If they are there on my carbs i did not remove and clean them because based on the diagram on this site there didnt appear to be anything there. Thank you for the help

I went ahead and removed carbs again so that i could address the plugs that i mentioned. I reved plugs and found some debri blocking the holes under the plugs. Cleaned and blew through everything again. Reinstalled carbs and put back in water yesterday. I was finally able to get on plane eventually achieving about 5500 rpms. I belive i need to lean out the adjustments a quarter turn or so to get on plane faster but it appears my rpm issue is resolved. Thanks for your help

Good work getting her lined out.

If you lean her out too much, it will bog when you open the throttle. The trick is to get JUST enough richness to compensate for the lack of accelerator pumps in the carbs.

Jeff