cooltoys61

I have 454 mags with Rev Marine exh and Dart single plane intakes,otherwise stock. I currently have one power valve and 72/86 jets. Is this in the neighborhood to begin testing? My timing is at 32 and at wide open my power seems to fade (detonation?). I only opened up it for a sec. Of course I will pull the plugs but was wondering if these sound too lean? My transom is black but could be from idleing. I'll do more shut down readings when I get close. Thanks for any educated guesses.

Madmax

Primary sounds 2 lean. I would go to 80's at least. Secondary sounds right if you are running a power valve. My friends 454 mag just came off the dyno and 80's in the primary and 90's in the secondary with no power valves on a 800 dp was perfect.

hope that helps.

blue thunder

I have been working this jetting thing for a couple weeks on 430hp 468cid engines with 800cfm dp. Last weekend I ran 84p, 94s and the plugs were black, sooty. I ended up calling Holley the other day to discuss and they said the factory calibration (out of box) for my carbs was 72p, 87s. They went on to say that an engine that needed to be jetted up or down more than 5 sizes had an issue. If you think about that it makes sense, the airbleeds and other machined in calibrations have limits. I was way outside of their limits. This weekend I am going to rejet to 76p, 91s which is +4 sizes and probably a good start for a marine engine. A guy from speedwake, (cfm tech) has also led me in this direction and he seems very knowledgable so I am feeling this is a good re-start point.

So I would say find out what the out of box calibration was for the 750dp and start from somewhere around there. That assumes the carb is a marine carb out of box.

BT

cooltoys61

more guesses? Please.

cooltoys61

Holley web site shows 70-72 prim and nothing bigger than 80's on the secondaries. I also opened the power valve holes (a little) in anticipation of supercharging which I have put off. Think I'll change the PV and go 82 on the secondaries. Anyone? Anyone?

cooltoys61

my #2 and 7 plugs were wet and black(even the porcelain which I now know is not the best indicator).I can't reduce the PV orifice without replacing the plate. I went down to 80's on the secondaries and 70 on the prims. My other motor still has 71 and 84 with stock PV's and is also rich.
Here's my question,,,The boat runs well up to 4k then around 4500 falls off. Is this likely due to the power valve opening or the secondaries coming in? Guess I will have to mark the throttles while at 4300 but seems a little high for just running on the primaries. I'm thinking it must be the first time the motors are working hard enough to open my huge/altered (ruined) power valve.If I hook up a Vac gauge to the stern side vacuum port(the big one)of the carb will this get me the reading I need???? I have some old Holleys around,are the metering plates diff on all other models,I would guess so.

born2burn

Way to rich!!! Here is a shakedown of a simalir engine.
468 9:1
Solid flat tappet
990 heads ported
Team G
750DP with 76p 77s with 50cc pv !!!NOTICE!!! secondaries a little too lean.but right there.
Lightning headers dry
474hp on the dyno

cooltoys61

ttt

formula31

Well, I run 72 primary, 76 secondary, 6.5 PV front and rear on a pair of 3310's which are early 780 cfm's built for corvettes. They had been heavily modified and I use torker 2 single planes.

82 on the secondarys with out a PV should be OK. Id go 84 to be safe.

cooltoys61

Thanks, I went to 80's on the back and it ran good today. 70mph with 6 adults and gas. I was happy because it still isn't tuned or timed well and I only opened it for about 1 min.