canyonman

I am wondering if anyone can help me tune for dual purpose.

I have 5000 pound boat equiped with a 502 with a 950cfm 4150 Holly built locally. Somewhat agressive midrange cam (the specs are my builders secret?). I love the way the motor performs at speed. It pulls nicely from midrange. However, when I pull a skier the motor eventually gets too rich after a few pulls "smokes" (black) and diesels at shut off, more serious dieseling the more times I pull skiers. The only cure is to stop skiing after three or so runs, run the boat around at speed, and go skiing again.

My transom is always grey at the the end of the day if we ski or not.

Jet sizes are currently 77 secondary and 76 primary (came with 78 both). I recently replaced the power valves on the primary and secondary on the possibility they were leaking - no change.

I boat at 1700 or so feet altitude. (the problem is similar but, of course, worse when we boat at higher altitude).

Can any one give me an idea of specs, a method to tune, or a general idea of what is going on?

Griff

First thing I would do is get a smaller carb. An 800 or hp830 would be plenty. It would also give you a lot better throttle response at lower rpms.

paradigm shift

Have you done a plug check at crusing or ski speed with no skier? Do you know what vacuum you are running when pulling skiers. You may be right at or below the vacumm setting of power valve you are running. I do agree the carb is a little big but it should work better than you describe if set up correctly. Really need more info. What heads you are running / Compression ratio and specs on that top secret cam would help.

I forgot to ask what RPM are you running pulling skiers.

fstboater

Need more info rpm compression prop boat size sounds like the power valve is open when at ski speeds.

canyonman

Compression is under 10 about 9.5. The heads are GM cast iron reworked and designed to give a little more squish than stock. The motor is designed to work on 91 octane.

I can't give an exact correlation on RPMs at ski speeds, but 2000-2200 seems about right.

Here is another symptom which may help on cam profile - the motor feels "cammed out" at 5000+. I spin 5200 max all aired out pulling duoprop 28's on a bravo three drive (2 to 1 ratio).

Thanks for your input so far. When does the power valve (stock) come in play?

canyonman

Plug Check..

Checked plugs idling on the hose 1/2 hour. Tan

Checked plugs just running around all speed mostly - no skier. Tan

Checked plugs on 2nd summer trip to Lake Powell 3500 feet after letting the boat sit for four weeks after a previous "rich" experince at Powell where plug was looking dark. It was a 100+ degree day - I was smoking at idle and backfiring when I tried to get on plane. Plugs were wet with gas. I think the plugs were done - I put in new plugs after going to 1500 feet and it ran "better" again (same as what now passes for normal) altough after spending 1/2 hour in a no wake canyon at 1100 rpm it bogged and "backfired" once on first on-plane attempt.

Griff

Sounds like the primaries are too rich. Also, check the float levels with the boat IN the water. They could be set too high or the level in bowls could be creeping up if you pull a skier for a while with the bow up higher than normal cruise. This would cause some raw fuel to drip down the carb.