need help with my combo

[swampdog]

Hey guys, I'm new on ***boat.com. I have been reading the posts and enjoying your comments. It seems that most everyone here knows jet boats really well. I have a 96 Starbuck 17' with a ZZ502 and a berkley JB pump with an A3 impeller and a SS loader. I am turning 5000 RPM but according to the speedo I'm only doing 62 MPH. I have a place divertor, but no ride plate. Is there something I can do to get at least 70 MPH out of her. thanks Wayne

[Keithb87]

Is it a GPS Speedo or the kind that trails in the water?
The later is not all that accurate.

[FASTRAT]

u need to ck it with a hand held GPS...the most accurate way!...there not that expensive to buy ($100) & they work great
fastrat

[502 JET]

Hey guys, I'm new on ***boat.com. I have been reading the posts and enjoying your comments. It seems that most everyone here knows jet boats really well. I have a 96 Starbuck 17' with a ZZ502 and a berkley JB pump with an A3 impeller and a SS loader. I am turning 5000 RPM but according to the speedo I'm only doing 62 MPH. I have a place divertor, but no ride plate. Is there something I can do to get at least 70 MPH out of her. thanks Wayne
What is the condition of your pump?If you are running an A3 impeller it seems like alot of rpm.That is of course your engine is 502HP.Is your tach accurate?Gps it and see what your speed is.You would be better off with a single A impeller and you would see alot more speed.I ran 75 mph gps 450 hp 502 Dominator B impeller 5500rpm 21' Eliminator Scorpion.

[DUCKY]

Yeah, something about your combo or numbers isn't right. A 500hp motor will only turn an A3 impeller about 4000rpm if the pump is tight. Get your real speed, find out if your tach is accurate, and find out what impeller is really in your pump. Also take a good look at the bottom of the boat for hook. I don't know how long you have owned the boat, but alot of new jetters like to crank the place diverter to the moon for a nice "tail" and that alone will kill top end.
Good Luck!

[swampdog]

Thanks guys, I will check with handheld GPS. It is definatly an A3 impeller, I put it in myself. The pump looked in great shape and it had a B impeller but I wanted a better cruise RPM so I put the A3 in. In return I fiqured I would have a better top end. I was turning the B impeller 5700 RPM. I just got the boat w/o engine and had the 502. It is definately a ZZ502 with an 850 mighty demon carburetor.

[502 JET]

Turning the B at 5700 rpm sounds correct.Did you shim the new impeller correctly?

[swampdog]

I had .028 clearance