Need help jetting a holley
 

I am currently trying to dial in my 830 CFM Holleys which on are on a pair of 509s. The motors are 9:1 Compression, stock rectangular port heads with some bowl blending, Edlebrock Performer RPM intakes, full roller Comp Cams valve trains (587 intake/601 exhaust 226/234duration, and dry exhaust.

The distributors are Mallory which have been convertered to a Petronix Ignitor II system with a Flame Thrower II coil. Initial timing is 14 degrees and total is 32.

The current jetting is 82 primary and 84 secondary. The plugs are AC R42T (one heat range cooler than stock).

At idle the plugs are dark brown in color. After a 3400 RPM run (1 mile), I quickly came to a stop and shut down the motors. I checked plugs on #1 and #8 on both motors and the plugs/insulators were white in color. Same procedure after 4000 RPM run and same results.

From what I have been told, the plugs should be medium to a dark brown in color. Any suggestions on the proper color for a marine application and jet sizes I should try would be greatly apprieciated.

Thank you,
Jack

http://www.empirenet.com/pkelley2/sparkplugreading.html

The "real" way to read plugs

"NOTE> If the base ring has a full turn of color with some spots of heavy dry soot, then jetting is too rich, REGARDLESS, if the porcelain is "BONE-WHITE", jetting is still TOO RICH !!! NOTE> Do not look at the porcelain to read jetting !!!"

Very informative article, thanks.

No problem, got that link from a post long ago... The only trick is actually suddenly shutting down the boat under these conditions is not the safest thing in the world. Do it on a calm day and plenty of space.

try 84 primary and 88 secondary
with 6.5 pv

JMHERBERT,

I found that article on a drag racing website. Do you think their results are applicable (1/4 mile 12 seconds or less) to pushing a 11,000 pound boat at 3500 RPM for an hour or two at a time?

Does anyone else have an engine similar to mine and know what jets they are running in their holley?

BY U BOY,

I have been told the same jets that you recommended. I was told by a friend that he thinks that the jetting on a Merc HP 500 were 84s and 88s.

Thanks

Hp 500's use staggered jetting and no secondary powervalve. 6.5 PV in the primary. A PV in the secondaries would be worth about 6-8 jet sizes.

Primaries port-81/starb-75
Secondaries port 89/starb-93

There are many on this board that know more than me, but I got that webpage from this board some time ago. Maybe it was the same advice on a different webpage, but the info is the same.

To me, it makes sense, as our motors have a lot in common with drag racers, as they are rode hard, with gas and not alky. Those kind of drag racers also want their motors to last more than a few passes. I was also told basically the same advice in tuning HP Harley motors, to check the plugs in the same manner, with the importance of shutting the motors off while under 3/4 to full load.

Griff,

I have 6.5 PV on the primary and secondary side. Do you mean that if the HP 500 had a 6.5 PV in the rear that jets would be 6-8 jet sizes higher or lower?

What jets came in that carb from factory,are you using fuel with 10% methenal.I have been reading plugs using the above method for years and have had no detonation problems.Thr porcelon will only color when idling and remain white under load,if they color under full load way too rich.The fuel we use is alot different then it use to be.The only time i see porcelon turning brown under load is when i put octane boost in my dyno fuel cell.I have egt and afr gauges on my dyno set up but still play close attention to plug.Let me know the above info and i will make you my recomendation.

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.

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.

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.

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

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

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.

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