78 Johnson 115ETL wont go over 12mph

[To-clearer-water]

ok so please note there's been a lot of work put into this once old powerhead, we built it to go offshore and so she has a lot of time and money in her, so the work already done : started of with new sierra .30 over piston and ring kits and bored to match, polished and milled heads, new gaskets through out motor, checked reed valves and reused(probably the only non new parts), New hp carbs, new stater and rectifier and charging 15 amps at 13.5 V, timing , coils, power packs , wiring harness on boat and motor , new fuse panel and new ignition switch, the foot has new clutch dogs, seals , gears and Bearings, and a new waterpump , the whole pump not just an impeller, so all in all the whole motor is new with the exception of the reeds. Put her on the water and did the break in and she ran like a dream better than any of the new motors i have had, ran great for about 3 trips on the water topping out around 45mph ,THEN we had an issue , Motor has about 50 hrs on it now and was great last time we pulled her out the water then i put her back in the water the other weekend and she would only go about 8-12 mph , i thought i spun the prop bushing and like any good offshore fishing guy i pulled one of the new extra props out from the front storage and put her on, same issue, power head still sounds like shes running good but she has lost all power , ran comp checks again have 140 on all cylinders all coils and plugs and power packs checked and all perform to spec, had a second set of carbs went through reset to spec and still same problem, i have a lot of time in this powerhead and love the 2 stroke CD ignition system for off shore since i can pull start her if battery ever has issue but i cant go fishing up river better yet anything close to offshore like this , all trim adjustments and transom position are right , anyone that can help please do

 

[Chinewalker]

Do I understand that the RPM coming up but you're not moving? Any chance there's an issue with the boat itself? Water in the bilge, etc.?

 

[To-clearer-water]

Good Point but no issue with boat, Actually switched out to older motor i have in short term and she rides great , the boat takes on no water had her in 5-8 ft seas and other than water coming over transom nothing in the hull. I have a brand new 60 hp kicker on her and it goes faster with it lol

 

[racerone]

Check the flywheel key ?

 

[To-clearer-water]

ok so i went ahead and pulled carbs and intakes off and sure as i was the reeds are shot. i will put new reeds on in the am and test drive tomorrow night and follow up with verification of the repair, hope this helps someone else in the future.
As a side note i didn't just tear her down i ran a leak down test this time instead of just compression test and found that i had good compression but it slowly dropped down.PLEASE!!! note i am very familiar with testing and tear down ( i am a machinist / engine builder with an engineering degree) if you are not i would advise anyone else to have your local marine run this test for you as to not damage the reeds when done or done with too high of pressure IE this is why i didn't do this at first. I would advise to pull the intake and carbs and use a light