Originally Posted by Budman II

Well, I had the chance to buy an 800 that probably had the factory Holley jetting, but it was not a marine carb. According to Holley's documentation, in addition to j-tubes and sealed throttle bushings their marine carbs have different metering blocks for marine use.

Originally Posted by cubicinches

Either way, you'd probably be changing jets anyway. Now you've got the right carb and some good info on a starting point.

Originally Posted by getrdunn

I ran very simular set up. Almost identacle years ago and ended up with simular jetting boating out of MI. I had to dig a little however found the old dyno sheets. Bone stock 800 cfm 9022 with the choke horns and chokes. The prim and sec in seq as you stated 79,74 & 86,89. Worked well and ran great. Plug readings were always great. The staggered jetting you have is just a tad more than stock. I recall spending some time to even out the egt's the best I could. As you know and as mentioned every application will vary. The stock jetting was just a little much for my app. When I got the carbs they were very fresh take offs but I don't remember the jetting being exactly as stated although it may have been. Merc may have changed up the jetting a little back then also.

Just noticed my comp was 9.6/1 and had lightenings for exhaust. Your probably boderline or could go either way with intake. What max rpm you plan on running? I was 5,600 - 5,700. On the water I actually liked the single plane the best. I definately pulled harder mid range.

Originally Posted by Budman II

And keep the stock PV in the primary side? I guess the only true way to select the PV would be to measure manifold vacuum.

Originally Posted by Griff

The HP500 carb does not have a secondary PV.

I would start with 78 primary and 88 secondary jets.

Originally Posted by Budman II

Just looking through the stuff I have laying around in the shop, I have an old 850 Holley with 80's on all four corners, and my Demon has 88's on the primary side. Is 80 primary and 88 secondary a close enough starting point?

Originally Posted by Budman II

getrdunn, were you running a 496 with dual plane intake, or single plane? Looks like you were set up a little leaner than my carb is out of the box - which would follow logic as the HP500 has a little bit more cam than I have. I have a set of Lightnings that I considered running, but with my exhaust port mismatch (see other thread), I don't think I could run them without some custom collectors. I am not planning to spin this one up past 5200 - 5400. It has forged Mahle flat top pistons and good I-beam rods, but it has the Eagle cast steel crank, so I am going to err on the side of caution. I spend most of my time cruising between 3000 - 4000 RPM anyway, with the very occasional full throttle blast.