Intolerant1

The engine is a stock OMC454 oval port with a Weiand Stealth intake and straight thru 4" exhaust, stock exhaust manifolds. The motor had a very restrictive intake with an adapter and had developed an exhaust leak at the crossover tube so I changed it to the Weiand when I pulled it apart. I also removed the stock "corkscrew" mufflers which were aparently also very restrictive. The stock carb is a 750cfm 4150 style marine.

Stock jetting was at 73 primary, 56 secondary. Thats not a typo. The secondary jets were that much smaller. I guess the exhaust just wouldnt let it breath. I have a complete Holley jet assortment so I threw in 85 primary and 86 secondary just to get it running and be safe. Power valves were 2.5 both sides stock. This is a pretty common carb and motor so I'm hoping someone can tell me where I should be on jets and power valves.

Im also having a strange thing happen when the secondarys open. I get a whistle noise ( almost sounds like a turbo spooling up) as they open. I threw a four hole spacer under the carb and it goes away. Wasnt there before I changed from stock. Checked over and over for vacume leaks and none found.

Ps...I started this tuning 2 years ago but the boat has been in storage due to a couple injuries (to me) so Im kind of starting over

Intolerant1

formula31

Ill pop my 3310 780's open when I get home tonight but Im pretty sure they have 78's in the primarys and 82's in the secondary with 6.5 power valves in both. I run a torker 2 intake and gil exhaust. Is your 750 mechnaical secondarys or vacuum? I had Wieand stealths on my formula and one engine did the whistle thing and the other one didnt. Never did figure it out and they both ran strong.

Intolerant1

Vacume secondaries. I put the four hole spacer back under the carb and the whistle is gone. Had to go up two sizes on the secondary spring with the spacer or it bogged when they opened too soon. That spacer must significantly increase the vacume signal. Any help on the jetting would be appreciated.

formula31

74 primary, 81 secondarys. 6.5 power valves both. .31 squirters with large accelerator pump. couldnt tell what spring I had in the vacuum diaphram. I also have my primary plates drilled for idle quality. Not sure what drill size but I could measure if you need it.

Intolerant1

I just went through Holleys listing for all there carbs and picked out the marine units. All the 750's are set up about as you describe so Ill try that and see how she goes. Thanx.

Heres a link...good source for initial setup.

http://www.mortec.com/carbs.htm