'83 2001 losing power at 35mph

I have a 1983 Ski Nautique, 351W.  Installed a new carb, Protonix EI, new plugs.  Cranks up with one turn, runs very smooth.  After start up, I can run it up to full throttle with no problem, smooth and strong, hits about 42- 45 mph.  After about 30 minutes, it starts to bog down when I push it past 35 mph, back off and runs great again.  It's not missing, just struggling, like it's not getting enough fuel.  If I let it cool for 10 minutes or so, it runs great, then same issue.  Temp gauge at 180, oil pressure great, amps great.  Any help is appreciated.....

Also could be clogged fuel vent.  Try leaving the cap a little loose & see if that fixes it.

Thanks for the suggestions.  Everything is brand new, fuel dip tube, lines, vent, etc.  Only 35 hours on new motor.  Installed the new carb at about 32 hours and basically never ran better, ......now this!  KENO, your suggestion might be the first step to narrow it down.  Yes, I have a Moeller fuel filter under there, you just can't see it. (Another) new filter added in March.  I think the PCV is within the left valve cover cap? with the hose running to the carb.  The right one is just a breather.  

Good idea Pete.

I thought about putting the points back, but I don't have the parts I removed to install the PerTronix.  I think there was a bottom plate, which was replaced by the PerTronix plate where the points and condenser were attached. Maybe I could find one. The springs are good, new.  The engine was a Crate 351W reverse rotation.  The only reason I didn't replace the Prestolite was I couldn't find a new one. Turned out to be fine, gear, bearings all tight. Old engine had about 300 hours.   Just thought it would better to have EI.  Pic is of the oil pump. Water definitely in the oil.  Thoughts on getting another points mounting plate somewhere? 

If this thing doesn't start appreciating my efforts, I might have to sell it......  except I'd lose my butt.  This was my wife's family's boat.  Her gave it to us when they moved from their lake house in Texas.  We made a lap around the lake in it as a "get-away-boat" after we were married.  Very sentimental and I couldn't wait to rebuild it.  Here's a before and after......

Capt'n Dave wrote:   I think the PVC is within the left valve cover cap? with the hose running to the carb.  The right one is just a breather.

KENO, I didn't really give a PCV much consideration.  After reading what the PCV does, I'm a bit more concerned.  One of the breather's has a clip in it holding (what I think/thought is) a PCV.  If it is in the cap, the cap is not tight and is often on leaning askew on the breather when I open the engine compartment.  I'll use a hose clamp and get it tight.  So, my question is if one valve cover is just a "breather", how does the pressure build in the other valve cover to operate the PCV?

oh and the fuel problem. 

everything can be new. but still have an obstruction. i would test the portable tank solution. it is easy to test. 

my vw had a piece of rubber, that came of when mounting new hoses, and was stuck in the carberatur. (ok you still would find that with the portable tank...) 

also check your sparkplugs. what color are they. can you see if thjey have to much fuel or not. that can also help your diagnoses