questions... please help

[lwb97]

I have a 78 Glastron Carlson cvx20 with a 429. It has a mild cam and aluminum intake. I just installed a place diverter and loader scoop and took her to the water. The max rpm I can get is around 4200 (up from a previous of 4000). I can play with the diverter and gain speed at that rpm but it never really goes above 4200. I am getting ready to swap the 650 vacuum secondary carb for a 750 dp. My questions are 1) what is the typical engine rpm a boat of this size carrying a 200lb driver should be able to achieve... the tank is a 25gallon i believe and usually ran at full to half tank range 2) will a swap in carb along with a bump in timing translate into more rpm and 3) are there any suggestions to combat porposing... the diverter takes care of it completely when i trim it down but as it comes up to the top (rooster tail from hell) it begins to bounce uncontrollably... are trim tabs the cure? i am wanting to find a happy medium with performance and usablity... the boat currently runs perfectly (no missing or sputtering) but i would like to utilize every bit of performance i could get out of it when the time comes

any and all suggestions and comments will be appreciated

some more info:
the jet is a berkeley 12je
impeller is either and a or b
cam specs are uncertain.... i bought this boat complete and running

[2slow4u]

dont no if its jet related but if the advance in the distributor is stuck or not opening all the way it can cause lower rpm's. secondary's not opening all the way can hold back rpm's as well. maybe this helps??

[BIGA]

the rpm of the engine is directly related to the power absorbed by the impellor size. IF you have a aa in it you are probably not off far on the rpm. the impellor can be cut down in size to raise your rpm. also remember an article in the now defunct hot boat mag where some of the fords had the cam retarded in it from the factory recall a 4-6 degree bushing. if i remember the article correctly when they degreed the cam i.e a new timing chain set it made something like 50-75 more horsepower which would bring up your rpm if this is your case. on the bouncing , the cav plates will usually help this problem.

[2slow4u]

question. i no nothing about jet boats. i will be the first to admit that!! but by advancing the cam does that not move the peak torque to a lower rpm and retarding raises the horsepower peak rpm? or something like that? i always though that moving the center line around just moved the curves around but really did not make a signicant gain in torque or horsepower? just thinking of my drag cars. im VERY new to the boating world!

[boatnut62]

If you have a berkeley there are some options on ride plates that go directly beneath the pump. and they are adjustable to an extent. but triming the bow down will result in more boat in the water thus creating more drag and slower speeds. trim tabs would in my opinion be a mistake. but thats just me. the ride plate below the pump is the key. depending on the way you have your motor built is the deciding factor on the best cut for your impeller. you should be able to turn 4400 rpm with an a cut. your hp and tourqe curves meet somewhere along the line. cutting down will increase you rpm but if you have already met you max tourque it isnt needed. remember a motor hooked to a jet is very similar to hooking it to a dyno. you can refer to cahrts at many berkeley or dominator sites and see just how much hp your producing. another thing to think about is engine temp. a pump will make about 150 psi to the motor and this is way too much and even if you run through logs first the water doesnt have time to get warm. if yoou are not getting your power plant to a good operating temp you are not making the the most efficent combustion. a bypass regulator right off the pump alowing about 15 pounds of pressure will get you about 140 degrees at the manifold. doing this years back gave me 400 rpm and i have made this mod to every jet i have owned and the result has always been a more eficient running motor. also you are less likely to blow out a manifold gasket. a problem for ols 455's. good luck.