View Full Version : A little more '67 Ski-Sporter video

Just Say N20
09-21-2011, 11:46 AM
Shot using the GoPro HD with the "open" back on the housing. Someone was sitting in the middle of the back seat, and I think this helped minimize the wind noise, so you can hear the engine.

The engine is running great, with the exception of the "hole" when you open the secondaries. Right up to 5,000 rpms.


09-21-2011, 12:14 PM
Very nice!!!!

09-21-2011, 12:29 PM
Runs and sounds good, except for hesitation when cracking the secondaries. Post on tech. Someone has a remedy.

09-21-2011, 04:52 PM
Great video Bill. These will help get you through the winter!

My boat has the same carb issue at around 1500 RPMs. Just a second or so of hesitation. I've been told that my Holley carb has a vacuum secondary and if I were to change to a carb w/ a mechanical secondary it would improve performance.

My Ski Sporter doesn't really pull skiers anymore and I generally ease the boat out of the hole, but I'm considering a different carb.

B.O.A.T. = Break Out Another Thousand (actually about $800).

Motor heads - please chime in........

Just Say N20
09-21-2011, 07:45 PM

The issue with mine is the secondaries opening, which happens around 4,200 rpms. I believe the spring that controls vacuum secondaries on my carb is too strong. 715 cfm is a lot of carb for a 350 ci engine, and I don't believe it creates enough vacuum for the spring. A smaller carb = more vacuum (like sucking the same volume of air through a shop vac hose, or a garden hose. There is going to be a lot more vacuum through the smaller hose). I can adjust by putting in a weaker spring. 4,200 always seemed high for them to be opening anyway.

Thanks for the kind words.

09-21-2011, 08:52 PM
I prefer mechanical secondaries for that instant hit.

Moving to a smaller carb, isn't going to change the amount of air that you're motor is pumping.

Ten years ago, when dirt bikes were changing from two strokes to four strokes, the "bog" at the bottom end was a problem with nearly every big "one lung." The fix was to throw an edelbrock qwiksilver pumper carb on.

My carb on the boat has mechanical secondaries and "double pumpers" and it's very responsive at all RPM.

There are a couple guys that do great job on custom marine carbs, send them your specs and they'll send you a carb that will 99% chance be spot on.

Just Say N20
09-21-2011, 11:27 PM
I wasn't suggesting that a smaller carb would change the volume of air the engine used. Rather that carbs works off a vacuum, and are designed to work with certain tolerances. A smaller carb (like a 600 cfm) on my engine will have a higher vacuum than the 715 does on the same engine because you are pulling the same amount of air through a narrower space, creating more vacuum. If it was just a matter of carb size, why wouldn't I put a 1050 on the engine and make HUGE power? Because a 350 can't use enough air to make that big a carb work at the rpms we run in boats.

09-22-2011, 03:08 AM
very nice sunset ride, Bill. I have the same problem, when I push the throttle to hard the engine is almost dying, if I take it easy no problem. I live with that, season is too short to fool around with this issue...

09-22-2011, 05:50 PM
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I gotchya. Yes I agree that the Venturi effect is going to be greater on a smaller bore carb. I don't think the stumble is because of lack of Vaccum (actually depression) it probably has more to do with jetting and not having overlap in some of the carb circuitry.
I'm running an 830 cfm mechanical double pumper and it's downright nasty.

Awesome video btw, awesome boat too! Maybe some time next summer we can meet up on the big water.