Hey guys, while changing these jets this evening, I decided to turn those air mixture screws that the carb rebuilder told me not to F_ _K with, that's what he said. Anyway, the primaries were an even 1 turn off the seats; the secondaries were 1/4 of a turn off the seats, that doesn't seem right to me. These are just idle settings right? No effect after idle right? I read how to adjust them, sweet spot between the points were they begin to decrease rpm's at idle, right? Does a 1/4 of a turn sound "light" to you guys, the book says start a one full turn off the seat. Why would the front ones be 1 turn and the secondary side be only a 1/4 of a turn?

al not to get off the subject . but what brand of needle a seats did your rebuilder put in your cards. some of the reduilders use a small needle a seat and the wont flow the right amount fuel . holley or barry grantare the only ones I use. as for fuel pumps a holley street pump with 3/8 pipe threads flows 110 per hour and dosent req. a regulator

Not sure on the brand of needles or seats. What do one of these stock marine pumps flow, any idea? The 110 per hour would do it? What about the diaphragm rupture tube on these pumps, would the street pumps have those? I changed the pumps last year as part of the rebuild because they were standard automotive ones and didn't have the rupture fittings tube to accommodate the hose to the air cleaners as well as I simply wanted to eliminate them as potential reason (fuel flow or lack thereof) for popping problem I was having then.

holley makes a marine version with the tube in the top case . or install one on the street pump . needle a seats how many pices are comming out of the fuel bowl. a large screw and under that a large nut or a large nut with a medium screw comming thruught the nut.stock pump flows about 90 gph. but the only have 1/4 pipe fittings which restrict them.

to get the right jet size just hook up a wide band data logger and it will tell you your a/f ratio make sure to weld the bose befor the water line so no water gets on the wideband o2 sensor

Al,i see you said you have 6-7 psi fuel pressure at idle and "while running". If your "while running" means w.o.t then don't waste your money upgrading fuel lines or pumps. 6-7 psi at carb wide open is still 6-7 psi wide open weather you have stock pumps or aftermarket.

Alcor,
Holley marine 130gph internally regulated mechanicals work very well, and are even coated to resist rotting out.(their aluminum). Summit has them for cheap. Call them and get the pt#s or if you need, I'll dig them up. They also sell large port regulators(1/2") if your like me and like to know for sure. Also helps setting the correct press. all the time. And no problem for the encouragement...we ALL need it in this "hobby" of ours.

What a difference!!!! Here's something to thing about:

8/21/04: Total time: believed to be 34 degrees at 3000 rpm, set at no load, both engines Jets: #76 in primaries & #86 in secondaries

Vacuum Vacuum
RPM’s Port Eng. Starboard Eng.
Idle in gear, 900 rpm 18 - 19
2000 (load, nose way up) 10 - 9
3000 (load, on plane) 6 - 5
4000 (load, on plane) 4 - 3


9/4/04: Checked total time again, closer this time. port eng. was actually 33-34 degrees, starboard was beyond 34 degrees, perhaps about 36. Reset total time, both set at 33-34 degrees now with #84 primaries, #86 secondaries. Also check float levels, found ok. reset idle with vacuum gauge.

Vacuum Vacuum
RPM’s Port Eng. Starboard Eng.
Idle in gear, 900 rpm 16 - 16
2000 (load, nose way up) 9 - 9
3000 (load, on plane) 10 - 10
3500 (load, on plane) 7 - 7

To rough to take reading at higher rpm's, will check those later.

First, obviously the vacuum reading are way down and are now the same on both engines at the same rpm, must have been difference in timing. Notice how on the 9/21 vacuum readings continues to reduce as rpm's go up. On 9/4, the vacuum drops from 9 hg at 2000 rpm to 10 hg at 3000 (got richer?) and then goes to 7 at 3500 rpm. Remember, the secondaries at kicking in at about 3200 rpm or so. I think this indicates that they get a bit richer when the secondaries begin kicking in. Ran for about 20 minutes, pulled same #7 plugs, not stark white any longer, dull white.

Both engines are as strong or stronger than they've ever been. Comes out of the hole great and great throttle response all the way up. Believe we're very close. Pulled a plug after idling back to the dock for about 3 -5 minutes, they weren't back, almost gray. Plan on changing to #86 on primary and #88's on secondaries and I believe I'm going to run them there awhile.

Guys, it's been a long thread and I really, really appreciate all the input/ideas/opinions and help all of you have contributed. If any of you guys ever make it New Orleans way, please look me up. Drinks are on me! I'll let you know if there's anything note worthy in the weeks ahead. Love to chad, put I feel the need, the need for speed. See ya on the water!!!!!!!

Went to #86 primaries and #88 in secondaries. Based on the slight drop in vacuum reading at various rpm's previously checked, believe these are the right jets.

According to Holly's website, "Manifold vacuum will increase the closer you get to ideal jetting; it will fall off once you past this point." That's exactly what happened when we went form 84/86's to 86/88's. May be a little rich but like most of you have said, better a little rich than lean. It's never run or performed better. Thanks again for all the help on this one.

Sorry guys, back again. Ran the boat yesterday with the Holley 750 DP with #86/88's jets in primaries and secondaries. After a good long run, nice and warm engines, hooked up vacuum gauge and took readings, vacuum increased (not decreased as previously reported) over those taken with #84/86 jets, indicating still moving towards proper mixture. Will go to #88/90's and run it later today.

Who's running Holley 750's on a 500 hp 454 and who's running the Holley 850. The reason I ask is that Holley's website says if you have to change jets (up or down) 8-10 jets sizes, you either have fuel delivery problem or the wrong carb. for the application. With the 88/90's, I'm up 17 sizes on the primaries and 10 sizes on the secondaries. http://www.holley.com/HiOctn/TechSer...fo/TI-220.html. Since fuel pressure is above 5 psi at WOT, as bad as I hate to, $$$$$$, I'm leaning towards wrong carbs.

Also they have a chart that shows 450 cid engines that are modified "Mild" or "Wild" would require Holley 800 or Holley 850 respectively. http://www.holley.com/HiOctn/TechSer.../FMCTech3.html