MPH issue

[77Hawaiian]

Hey All!! Im new at this Jet Boat thing so be patient with me I have a 21ft Hawaiian Jet it has a bbc 454, I replaced the plugs and wires and timed it...rebuilt the carb and reinstalled.. I GPS'd the boat and WOT I only got 32 mph out of her ??? when I hit the diverter I was at 28mph... I did make a mistake of not putting 91 0ctane in it I put 87... I was told that is a no-no but I find it hard to believe that could be the issue...I checked the go pedal ( pushed it all the way down to the floor ) to check WOT and it was all the way open..nothing in the intake either! any thoughts ??

[samari]

Welcome to the board!

87 octane should be fine you won't get any more speed from 91 unless you have a bunch of work done to the motor.

I don't deal with jet boats much but others will ad to this.
First what rpm was it running at wot?
The brand of pump might be helpfull as well.
What is the timing set at?

[delawarerick]

Im not a jet boater but my friends problem for speed was in his pump. He sent it to Ca and had it reworked and claimed it woke his up. Rick

[John Hice]

Welcome aboard 77.
Yes, the first thing is what RPM's are you turning at full throttle. You should be around 4000 to 4500 for most marine 454's. if you are not getting full RPM's check to make sure the secondarys are opening up if it is a vacumme secondary carb.
If the RPM's are up there and it sounds like you are just "spinning your wheels" the problem is in the pump. I suggest you go to the "Berkeley" web site http://www.berkeleyjet.com/default.htm and study there trouble shooting guidlines. That is if it is a Berkeley pump. There are a number of good web sites for other model pumps as well. http://www.americanturbine.com/ , http://hi-techperformance.com/ , http://cpperformance.com/products_jet_drives.aspx ,
Good luck and have fun.

[77Hawaiian]

Sorry guys been away on business...Im right at 3600 RPMs and 34 MHP I raised my trim tabs to see if that helped but it didnt only caused porposing !! Motor sounds strong isnt cutting out at the 3600 just wont go any higher is all ... Im not sure what the timing is set at I had it done by someone else ...any thoughts ??

[150aintenuff]

varify your secondarys are opening.....other option is your secondarys are flooding the engine..... seen that happen before 2....

[77Hawaiian]

Im thinking I may just replace the whole carb..its a 600 Holley I may go with an 850 w/ #80 jets ??

[Jetboat Jared]

welcome we need pics of this boat plezz

[77Hawaiian]

These are some pics of my " Pain in the Arse "

[150aintenuff]

what is a600 doing on a bbc.......way to small of carb...

[77Hawaiian]

Not sure why its on there!! I just bought the boat in December what size carb "Should" be on this motor ??

[150aintenuff]

@ 6000 RPM redline a 454 will use 788 CFM if figured at 100% Volumetreic effecency

that 600 is really only good to 4500 RPM at its best.. not accounting for losses in effency...

[77Hawaiian]

So if I stick a 850 on there it should be good to go ?!? I may go with #90 jets also... any thoughts ?

[150aintenuff]

850 is more than plenty... as for jetting i dont think you will be that fat... closer to 80's

my buddies 565 only runs 94's...

[TX-19onSaUcE]

put on one of these on your engine and be done with it. The polished $269 version ran my 454 in my old taylor 66mph @ 4600 rpm if i remember correctly. unless your makin big hp dont waste your time with an 800 850 cfm carbs. you wont ever need the cfm at the rpm youll ever turn to need that much. 750cfm carb will be fine. Run a smaller carb and the fuel economy will get better and throttle response will be better on your engine.
this holley is a single metering block holley (not a true double pumper) but id put money on it that you bolt it on and might not even have to re-jet it.
http://www.jegs.com/p/Holley/743613/10002/-1
I have a Proform 950 cfm on my 496 and it only made 3 hp less peak hp than a 1050 dominator but made 15 more ft lbs of torque and had better throttle responce.