Why is my junk so slow????

[Wasted Income]

Here's my setup:
1975 18' Avenger Jet
454 Chevy "recently rebuilt" according to previous owner
Berkley 12JB-A pump with aluminum impeller (has a few nicks on it, nothing major IMO)
Place Diverter, no other mods to pump.
Owner claims it has a brand new wear ring in it.
Two people in the boat, and all I can get is 47 mph out of it. Does that seem right? At the time, I was spinning ~4500 rpm.
Any ideas on what may be wrong? I just replaced the HEI distributor module with an MSD unit, MSD cap and rotor, MSD wires, and set the timing to ~8 initial at 700 rpm, and 36-38* at 3000 rpm
Also just pulled the carb off (750 cfm Carter AFB) and cleaned it out good, and blew everything out with compressed air.
Finally got it running right (so it's not popping) but it's SLOOOOOW....
Going to run the valves tonight, seem to have some valvetrain clatter.
Any ideas??

[VAMI]

Do you have any idea of cam spec and comp ratio of motor or hp estimate?I would think you could run 60 with a mild powered bbc.

[bp]

pump is worn out. an avenger isn't light, but should be able to run quite a bit closer to 60 at 4500...

[TIMINATOR]

It is most likely a car engine rebuilt. Most end up with an "RV" cam, and those are allways smaller than a stock jet-boat cam. Call me during business hrs. and we can get you figured out. TIMINATOR

[Wasted Income]

pump is worn out. an avenger isn't light, but should be able to run quite a bit closer to 60 at 4500...
Hrm....
Where do you think my best place to start with the pump is?
What is "worn out" and what needs to be done to get the efficiency back??
I'm a No0b to jets.
any other pump mods I should do while in there? I don't want to get crazy (setbacks and such...I don't want to touch the fiberglass)

[sstjet]

I would try calling George at arsmarine.com , he is in Morris Illinois and could help point you in the right direction. He put together my cheyenne which runs mid 70's with a b.s. 454. The pump is the key to making a jetboat run fast(efficient):D

[bp]

all clearances need to be within (at or less) specification. my 23' lake tanker, that i bought late last summer, would run 47 at 4300 - shoulder to wear ring clearance was over 0.045 (double what it should be).. if your engine is really turning 4500, something is not right with the pump. you can get a seloc jet repair manual from rex marine that will show you what to do, or you can pull it out and send it to someone else.

[Wasted Income]

Ok, so I took it out for a couple hours last night. Was able to get it to 50 mph with 3 good sized guys in it.
Tweaked the timing a bit, and kicked it up to 53.X mph. Didn't go any further with the timing, because it has 10 month old gas in it. Maybe I'll bump it up a notch again next time to see what it does.
Sooooo, I'm getting closer...but man was this thing a clusterfck. Every time I take it out, I find something that the previous owner screwed up, and every time it gets faster :idea: ;)
Clogged ANOTHER fuel filter last night, too. Looks almost like sand, but black.
Anybody know of a good way to clean the tank without removing it??

[bzking]

First off, stop hammering your boat in your quest to achieve top speed until you address your fuel issues or else you will be dealing with issue's of greater consern $$$, use an electronic fuel pump, jack the front of the boat up on the trailer, add enough hose to the pump and push it back to the fuel outlets on the tank (at the rear of the tanks) provide 12v and suck the fuel out, leave the tank caps off for a couple of days any remaining fuel should evaporate, make sure you empty the fuel/water seperator (if you have one), replace your filters before the carburetor, then have at it...good luck..BzkingQUOTE=Wasted Income;2958374]Ok, so I took it out for a couple hours last night. Was able to get it to 50 mph with 3 good sized guys in it.
Tweaked the timing a bit, and kicked it up to 53.X mph. Didn't go any further with the timing, because it has 10 month old gas in it. Maybe I'll bump it up a notch again next time to see what it does.
Sooooo, I'm getting closer...but man was this thing a clusterfck. Every time I take it out, I find something that the previous owner screwed up, and every time it gets faster :idea: ;)
Clogged ANOTHER fuel filter last night, too. Looks almost like sand, but black.
Anybody know of a good way to clean the tank without removing it??[/QUOTE]

[Wasted Income]

I think I found the culprit. Would running on only 7 cylinders make it slow.... :idea:
http://i235.photobucket.com/albums/ee198/jwjost/1975%20Avenger%20Jet%20Boat/IMG_0728.jpg
http://i235.photobucket.com/albums/ee198/jwjost/1975%20Avenger%20Jet%20Boat/IMG_0727.jpg

[jetboat]

running on 7 is not good! da!.however for the bad news, had a 79 avenger and with minor goodies never ran over 52mph! theres a lot of plywood and glass.ole it two years ago,makes a great stable lake boat, but not for speed.

[VAMI]

When you get your new set make sure they are the one piece style.