Old Ride

Before you spend too much time with your carbs you should install a real amplified ignition system such as the Merc thunderbolt system, a nice clean spark. The pertronix conversions belong in a lawnmower.

the duke

PV takes the place of richer jets, so less jet needed WITH a PV.

I set my PV's based on the vaccum reading going on plane, which is when your engine is working under load. If vaccum is 5 while going onto plane, then you need a PV rated at 5 or less so that it is opening and giving you extra fuel then. You need that extra fuel when ever you put the engine under lots of load. Going on plane, running WOT, going from one speed to another by jamming the sticks forward, etc.

US MUSL

MDGperformance:

I believe the carb model is a 9381. The Holley tech book indicates that stock jetting for the carb calls for 78 primary and 78 secondary.

After discovering my detonation problem, I bumped up octane to 93, went to a colder plug, retarded the ignition 3 degrees, rejetted the carb to 82/84. The jets that were changed out were 79/80.

If you swear by reading the rim of the plug which is in the combustion chamber and not the porcelin, I will pay attention to that the next time I run the boat.

I purchase fuel from a Murphy gas station which part of the Super Walmart. I'm not sure about the methenal content.

Should I not be using Petronix ignition? My machinist swears by it. While assemblying the motors, I had the entire ignition system bench tested and was told that it would work fine with my application.

Thank you for your suggestions.

Griff

You would use smaller jets with a PV. Think of the PV as another jet that opens with a reduction in vacuum.

MDGperformance

If i were running that combo i would use right about 82-83 all the way around,34 total advance and run the motor with crossover no stat.I would install vacuum gauge under carb shift boat into gear under load and take reading,vacuum will drop and then stabilze,you want to install powervalve that will just stay closed .if gauge goes to6.5 install 5.5.with that cam you might less vacuum.also check the main drop legs in carb i have seen them get loose and suck air causing lean out condition.i have been using holley 950-1000hp carbs on my 509 and have never had any issues.usually end up with acouple of jets up from factory,always run on dyno and check afr,bcfs and any signs of lean condition.final powervalve choice is set up after testing in boat with vacuum gauge

mrhorsepower1

Get me the list number off the carb and e-mail me. We have 50 years experience in the business with Holley carbs. I will get you dialed in with the correct information.

US MUSL

MDG Performance:

Thank you very much for you suggestions. Sounds like I'm definitely in the ball park with 82 prim and 84 sec. I'll get a vaccum gauge for the in gear reading and adjust my PV accordingly.

Jack