Need help getting the RPMs down

Ok, this is my first jet boat. Having had outboards for years, jets seem a little more complacated. I have a 1976 18ft Taylor SJ. I bought it a couple years ago in really rough shape. I since did a complete resto on everything. It has an Olds 455 thats is estimated to have around 425 hp. A Berkeley 12je pump with an A impeller. At about half to 3/4 throttle its GPSed at 50 mph and 5500 rpm. The impeller charts that I have seen shows that it should be the right impeller. Would a loader help and or a AA impeller? I would really appreciate any advice.

Harley1 said:

Ok, this is my first jet boat. Having had outboards for years, jets seem a little more complacated. I have a 1976 18ft Taylor SJ. I bought it a couple years ago in really rough shape. I since did a complete resto on everything. It has an Olds 455 thats is estimated to have around 425 hp. A Berkeley 12je pump with an A impeller. At about half to 3/4 throttle its GPSed at 50 mph and 5500 rpm. The impeller charts that I have seen shows that it should be the right impeller. Would a loader help and or a AA impeller? I would really appreciate any advice.

Click to expand...

Time to go thru the pump.

My 19'er GPS'd at 45-4600 rpm was 55 mph (A Impeller)

Dan'l

Harley1 said:

Ok, this is my first jet boat. Having had outboards for years, jets seem a little more complacated. I have a 1976 18ft Taylor SJ. I bought it a couple years ago in really rough shape. I since did a complete resto on everything. It has an Olds 455 thats is estimated to have around 425 hp. A Berkeley 12je pump with an A impeller. At about half to 3/4 throttle its GPSed at 50 mph and 5500 rpm. The impeller charts that I have seen shows that it should be the right impeller. Would a loader help and or a AA impeller? I would really appreciate any advice.

Click to expand...

These Mixed flow Jets under nearly any circumstances are very consistent and predictable , A good running Gas Big block "anything" with 425 HP @ WOT will turn a Mixed flow jet 4600 to 4900 depending on who's "A" impeller its running Assuming the jet is in good condition , assuming your Tach is correct , that 5500 tells Me you have an internal Jet issue that needs to be addressed neither a loader or a larger impeller are likely going to correct your current issue (high RPMS versus low speed) Please feel free to call if We can help Tom 804 466 4719

Understanding your Jet Boat... http://www.jetboatperformance.biz/pages/FAQ.html

http://www.jetboatperformance.biz/pages/Jetdrive_Impeller_calculator.html

Hay, thanks for the info. Having just rebuilt the pump {but that doesn't mean I didn't screw something up} I think in going to start with verifying that the tach is working right. Thanks again.

I took it out on the water yesterday. Hooked up a engine tester with a tach on it, and my tach was reading wrong. At full throttle it was only turning 4500 rpm's not 7000 rpm's that my new Sun tach was showing. So thanks for all your help. You guys saved me a lot of time and money.