I build around 25marine engiens a year. and dyno aprox. 10 a year . I have been in this industiry for 22 years and have built ton of engines for custmores on the chesapeake bay. I have crewed , crew chief . and race for more tham 12 years . my personal race boat that I have a partner in runs only 4 numbers higer jet than stock in a 950 making 655.hp 515ci alum head 10.5cr with a fairly large cam. but back to the subject I use a lot of 750 4779. holley carbs and what I 'm telling al is what I have learned over the years acutal boat tuning and dyno tuning experance I would not tell some one to do something that I have no knowlage in . sorry for the bad spelling,

I don't have any EGT, wish I did. Based on your last post, I take it your not concerned with the bluing of the electrodes, the white porcelain or the high vacuum readings? At least if we went to the higher PV (8.5) they would get more fuel on plane in the mid range which is were they seem to be lacking fuel. As for fuel pressure, I have small gages on the feeds to the carbs and they always seem to be bouncing between 6-7 psi, idle or on plane. The fuel lines are 3/8".

Perhaps the 8.5 PV with say #78's (currently #76's) which addresses the mid range plug reading and go up from 86's on the secondaries to #88 since the plug had much more bluing of the electrodes at the 4,000 rpm run, leave the 6.5 PV in the secondary since it should be open anyway at about 3500 RPM. What do you think about that?

By the way, how many hours have you seen on the 454's that you have set- up with Holley DP 750's and the 76/84 jets combination? Have you ever had one apart after say 150 hours and if so what did the heads, valves, guides etc., look like?

That's a good point formulaz583. If the PV is simply to "help out" under load then perhaps we should leave them where they are for now. We've never run these MR43T plugs with the higher jets or the 34 degree total timing. Would the extended tip Champions that I had in there be more likely to run black and tend to foul at idle with the larger jet comb and how would the total time being less than 34 degrees have effected the Champions relative to plug reading back then?

al you said that you had 6 to 7 psi at idle and while running .what kind of fuel pump andwhat kind of fuel filter are you running . what size fuel line from the tank to the filter.you have enough jet in that card to work something is being over looked.as for looking at valve jobs over150hrs. I recently freshend up a pair that was in use for three seasons aprox .200 to 225 hours on them and they look good. I run a silcone bronze liner in the valve guide and am able to run clearnces thight and get good life out of the valve job.

The fuel lines are 3/8 from the tank to the side mounted Tempo fuel filters and then 3/8" up to the fuel manifold feeding the carbs. The fuel pumps are standard (as far as I can tell) mechanical marine fuel pump, I replaced them last year as part of trying to solve a top end pop through the carbs back then. While increasing the secondary jets back then, the pop moved to higher RPM's and disappeared once I got to #88's in the secondaries from the original #80's.

al 3/8 rubber fuel line if so the fittings are like 5/16 ID and the fuel filterneeds to be drilled out to 3/8 ID in the housing . you should change the fuel pump to a holley or a hardin pump that dose'nt req, a regulator. I use a 1/2 pick up tube and a 5/8 line to the filter . I use a perma cool filter that flows 125 gal ph. then -8 line to pump and -8 line to carb . and most casees dont have a problem with fuel dilvery

Thanks for the reminder formulaz583, no I failed/forgot to check the floats, will do that next in the water. I plan on spending extended time at the lake this Saturday playing with the jets. With the new timing and MR43T plugs, I'm going back to #86 and #90's and see what everything looks like there, after the float check. Like everyone has said, if it's to rich all I lose is a time, to lean and I'm back in the shop ($$$$) and possibly single again!!! Between the plugs and the timing change I need to see what that set-up will yield relative to the plug readings. Will let you know how I make out.

Hey Alcor
Your time spent here has been good, ALOT of info huh? My two cebts is this; a basic rule of thumb IS rich is better than lean at least in marine. Good for you asking for help. I had a problem with my fuel supply being restricted, unbeknownst to me. Its always the little things that kill you, and I was wondering why my 575s couldn't spin a 25p three blade cleaver over 5000rpm in a 5700lb boat. Turns out 1/4" fuel shutoffs at the tank were a no no hu? A basic rule to that is 3/8" will feed up to around 425hp and anything above that really should get the 1/2" treatment(at least carb motors). I have had good basic running (before other issues ruined that) with 82pr 90 sec with a 6.5 pv in my 1040 BG 4150s (too big, but I got them to work well) at 13 deg initial at 900rpm and 34 total (sutphen 30 gave me those basics) at 3200rpm. After my fix of the fuel system, I made a consistant 8lbs of fp all through the rpm band, it pulled like a mule through 78 and 5000rpm before I pulled back and that was all in about 3-4secs from half throttle to full, so you can see where 5700+rpm and more mph were the big signs I fixed the issue. Of course, my headers leaking down and loading my motors up when they werent running, and banging like hell on start up ended any more of THAT. I don't pretend to know any more than the next guy, and alot less than most of the excellent replys you've gotten, but my little experience is one that may help you. By the way, investing in a nice MSD set up for each motor will really make things clear and simple.

Thanks for the word of encouragement Darkhorse468, I believe while I'm at this I'll see what it takes to change the 3/8" to 1/2", can't hurt and certainly sounds like it helped you. I presume I scrap the mechanical pumps. What can I use in their place that's reasonably affordable? I know your going to say electric, right? Thanks again.

al the cross is a autolite #145