HELP, proping a Riot

[johnrude]

Guys , I am haveing problems getting the right prop on a Riot that I bought a few months ago, Its been about 10 years since I was in a tunnel boat, The last one I owned was a Mirage jaguar. I went thru several different props on it , untill I tryed a 28" Spenilli Dr4, Man that prop was awesome, One of the few things I have ever owned that worked like it was supposed to, It would bite so hard it would slosh the gas out of the carbs and shut the engine off. I rigged a easy to get to choke botton to push,at just the right time and that thing would FLY. So the first thing I done when I got the Riot ready,was to buy a 28"Spenilli DR4, Sorry to say it doesn't work worth a crap on this boat, It spins out bad when I nail it, (5000 to 6000) and will blow out very easy with the propshaft below the pad, Am i doing something wrong or just got a bad prop? I took it to a local shop and they said they put some more bite in it but it didn't help,I also have a 31"that stays hooked good on top end,(around 7500 rpms) but it isn't worth a crap on takeoff either. Maybe i am just driving the Boat wrong? I get it up on the pads around 70mph, (same way I always did my mirage or STV) then slowly lower the front back down to level it out, this is when the proip will blow out, Guess I am getting to OLD for this **** , because that is not a good feeling at all, I tryed it today with a 25' 4 blade renagade and it came out of the hole like a banshee, and would stray hooked up no matter how you drove it or how many R's you turned it....
thanks in advance for any help guys,,,
J.R.