Help: Z-box with carbureted boat and mapping river course?

VermontSkierVermontSkier Posts: 57 Baller
edited May 22 in Boat Talk
Hi Ballers,

I am wanting to install z-box on my 2002 Malibu sportster which has an Indmar 5.7 that is carbureted. I have Perfect Pass 9.2 and would like to dabble in tournaments this year and try to get a closer pull to zero-off. So, I have two questions:

1. How does z-box work with a carbureted engine? Will it be difficult to tune it so it has quick response time? If z-box wouldn't be a big improvement, does bumping up the Kx values help with the pull?

2. Do folks have experience with mapping a course on a river? We generally have pretty calm conditions but there is sometimes flow when the dam south of our course needs to produce power. Would I be needing to re-map every time I ski (assuming there is some shifting from river current?) I know mapping is pretty easy, and is probably a good idea to go through the course slowly every time we ski to check for any debris/missing balls.

Thanks for any ideas/input!


  • WindsurfnutWindsurfnut Posts: 237 Baller
    If your prefect pass is working on your carb boat now, adding zbox will be simple. Most tuning will be in the ball settings, which is determined by mapping and not the zbox.

    I don't have experience mapping with a river, but I think you would have to have a major shift in the course for the gates to be that far off. Seems the tolerance of the mapping trigger is fairly wide.
  • 503Kento503Kento Posts: 164 Baller
    I had a PP/zbox in a carbed boat. You will never get the response of throttle by wire injected boat but PP gives you all the information to get as close as possible with the technology you have. Make sure you have good throttle return spring. There is a big thread here about the ball timing @Windsurfnut is talking about.

    As far as mapping goes, if the course shifts significantly when current changes you could just map it as a second course. This would assume that the current is consistent when it is present. But really, I doubt that the balls move very far unless it’s a pretty strong current.
    Get high, get fast, and do some good work
  • DanoDano Posts: 220 Baller
    edited May 23
    I have pp stargazer zbox on a 351w carbed. In my experience the issue is not PP or the carbureted motor. It was difficult to get a solid pull with my original prop. I installed an 0J 310 cnc prop. The prop was such a huge improvement and now PP gets solid ball times and behaves about as good as can be expected. Very very close to to a DBW setup. I’ve been playing around with Kx+ And ++. You can certainly tell the difference between the two, I think kx++ is closest to DBW but I don’t have a lot of time behind a DBW to reference. I’m very happy with the set up, Perfect Pass and OJ props had the best customer service I could imagine, and they delivered on their promises with a product that has performed as advertised. I have not messed with the background settings at all. The only change I’ve made was I lowered all my baseline rpm’s a little so that PP would lock onto and settle into set speed a little faster without overshooting the desired speed.
  • skiboynyskiboyny Posts: 302 Baller
    Z-box works fine on cabutrated boats. It's not exactly the same as Zero off but it's much closer than say Stargazer or hand driving. I too ski on a river that makes power. I map a couple of times a year really don't need to. The map is virtual, so it really only looks at the position of the gates. They don't move much it's just me being fussy. lol
  • VermontSkierVermontSkier Posts: 57 Baller
    Thank you all for the feedback on both z-box with the carb and mapping a river course, super helpful and appreciated!

    I know I won't be able to get the same pull as zero-off but it will be nice to get something a bit tighter.

    @503Kento what do you mean by good throttle return spring? I think mine seems okay, speed locks in without big adjustments when pulling a skier but is it worth buying a different spring?

    Thanks again everyone!
  • BraceMakerBraceMaker Posts: 5,129 Mega Baller
    @VermontSkier -the basic set up of the carb perfect for smoothly adding and removing speed. Think of like driving your car down the street you just smoothly control your speed.

    But if you want to approximate ZO you need to make the whole system just a bit more "digital". Since PP just lets out slack on a cable which slows the boat down the only thing that takes up that slack is the throttle return spring. And the factory one is sluggish.

    You can go further and modify the secondary circuit on the carb, or you can go to a different power valve, or adjust the accelerator pump to give it more "go juice" but the first thing is to make sure it shuts down when the slack is released.
  • Ski_DadSki_Dad Posts: 507 Baller
    i have 9.3 and ZBox in my 2003 Sunsetter LXI - i can't imagine it makes much difference if you have fuel injected or carb for the servo version of perfect pass.
  • 503Kento503Kento Posts: 164 Baller
    @VermontSkier Your standard spring is probably ok if it’s not worn out. My PP shipped with and extra spring to help the servo work better as it can only pull the throttle and release tension so a heavier return spring help with throttle response when the servo backs off on the throttle. I ran the spring from the throttle arm to a bolt on my intake manifold. I don’t have that boat anymore otherwise I’d post a picture.
    Get high, get fast, and do some good work
  • BraceMakerBraceMaker Posts: 5,129 Mega Baller
    @Ski_Dad the difference between them is essentially that a carb has to do a series of things to change fueling, efi not so much. Carb shaft gets opened which squeezes fuel out of the accelerator pump and gives the engine more juice, simultaneously the primaries open up and then a mechanical linkage pushes on the secondaries, the manifold vacuum drops which opens the power valve providing the fuel the engine requires to accelerate.

    But on coming off throttle the linkage has to push shut the secondary and then the manifold vacuum comes up and closes the power valve which cuts off fueling so making sure the carb is actually shutting right away adds "off throttle" response.
  • VermontSkierVermontSkier Posts: 57 Baller
    @503Kento I actually never installed the extra spring that PP sent with mine, until I found it in my boat last night. It is pretty long so I am guessing I have it set up somewhat similarly to you from the throttle arm to the manifold.

    @BraceMaker thanks for the great insight. I need to learn bit more about tuning my carb. I still don't have a great understanding of how to get it properly running. Most of my attention to the carb is adjusting the idle speed so its not taking off too hot when tightening up the rope for a skier.
  • BraceMakerBraceMaker Posts: 5,129 Mega Baller
    @VermontSkier - if you're having idle issues like you turn down the idle screw and that works when the engine is hot, but then you have trouble with cold starting or idle when cold - that's usually either an ignition issue such as a sticky advance or it could be a vacuum leak as well.

    Don't run to tweaking the carb first.
  • DWDW Posts: 2,516 Mega Baller
    @VermontSkier - As noted and others have also posted in other threads, PP works better with a strong throttle return spring. When engaged, the PP servo motor works against the throttle return spring to control the throttle. The firmer resistance of a strong spring results in faster throttle adjustments particularly when releasing the throttle so to maintain correct speed, the reapplication of throttle is now quicker/firmer as the system wants to stay at the correct speed (or more accurately position for GPS systems).
    As for carbs, there is a lot of good info available on how to tune them. Your boat probably has a Holley carb so information on tuning is readily available. To your comment on idle speed, you might want to go to the first step basics to correct any issues you have. Your boat should not have any problem idling at 650 RPM.
  • VermontSkierVermontSkier Posts: 57 Baller
    @BraceMaker and @DW thank you for the advice. Putting a strong return spring on (I didn't have one on before) has helped immensely with PP and the boat is idling pretty well now since it is actually going fully back to idle thanks to the spring. Now I feel dumb I didn't have that on sooner!

    And the boat is indeed a Holley carb. I do need to learn a bit more about it. One of the pains is starting. Sometimes it is hard to start both cold and warm, almost always requiring a pump or two of the throttle. Is that more carb or would an electrical tune-up help this? I.E. plugs, cap, rotor, and wires?
  • BraceMakerBraceMaker Posts: 5,129 Mega Baller
    The two would be electrical tune and check the electric choke for cold.

    But try this first. To start your boat pull out the silver knob so the shifter is in neutral. Then go full throttle in reverse twice. This will squirt some fuel out of the accelerator pump. Squirt squirt. Then move the throttle back to neutral amd crank the engine going forwards with throttle.

    Going full throttle will set the choke and pump the accelerator pump. But the silver knob blocks full forwards throttle doesnt block full in reverse.

  • DWDW Posts: 2,516 Mega Baller
    It is very common to have to pump the throttle a couple of times on a cold start. On a hot start the tendency is a need for more air so knob pulled and a slight crack of the throttle to allow a nice start. If that cures the start issue, it is carb related and usually is. A weak electrical spark will exacerbate the problem so yes a tune up might help. How old is the coil, that can be part of a weak electrical system.
  • DFWskierDFWskier Posts: 21 Baller
    My thoughts:

    1. map and calibrate on a calm day
    2. the 9.3 software w zbox gives you a very close to ZO pull, and no overshooting the gates

    With SG 9.3 and zbox, my buoy count is the same between my 93 prostar and a 22 prostar w ZO. And I have no boat payment :)
Sign In or Register to comment.