I own a Nitro 640LX with a 90hp Yamaha.  I'm currently using a 3 blade prop w/ a dia. of 13" and a 19" pitch.  The boat runs great with this combo except when I carry a passenger with me.  It takes forever to get the boat on plane and when it finally gets there my wot speed is 37mph at 6000 rpms compared to a wot speed of 46mph at 6000 rpms when I'm alone.  Will switching to a 4 blade prop help me get a better holeshot and a decent top end speed when I have a friend fishing with me? Also does anyone know if I'll need to go to a different dia. and pitch? Does anyone have any other suggestions?  Thanx

a four blade prop should help with holeshot,  but i dont think it will help with top end..46 mph seems like alot for a 90 horse  is that speedo or gps?

A 4-blade will help the holeshot, but will be slightly slower top end.

Is it a carbed 2 stroke motor?  Do you notice this more when it is hotter and more humid out?  How do your plugs look?  I've seen this problem many times before with 2 stroke carbed motors that are jetted grossly fat in the summer heat.  Not only do they run doggy and slow but they suck way too much gas.  

Cajun, the speed is from my gps. Yes, Jeff the Yamaha is a carbed 2 stroke.  It doesn't matter if it is hotter or humid out, whenever I have a passenger with me it has a horrible holeshot and low topend.  My plugs look great.  Unfortunately carbed 2 strokes do suck alot of gas and my Yamaha ain't an exception. It maybe gets 4mpg. I'm thinking of replacing my current Yamaha with a 4 stroke 90hp yamaha or a 90hp Mercury Optimax. thanx for everyones help.