jiffy292

6.5 primary. after work gona put the powervalve back in the sec put the jets back it came with and run it. Thanks for the help as i do not know much about this stuff except setting float heights. What is the diffrence when you have a powervalve in the sec vs. no pv?

MILD THUNDER

Even if he had a 10.5 PV in there, fuel shouldnt dribble at idle. Alot of guys think that if a powervalve opens at idle, it makes it dump fuel in the engine at idle. Not so. The powervalve simply add's fuel to the main well, which is then fed to the boosters. If the PV were opening at idle, its no different than how it would idle if he installed 6 size larger jets and plugged the PV.

If a powervalve is BLOWN, then yes, fuel will be sucked past the torn diaphragm, and sucked into the engine, below the throttle blades.

MILD THUNDER

The sole purpose the idea of plugging the rear powervalve, came from drag racing. Under hard acceleration, the fuel in the bowl would go to the back of the rear bowl, uncovering the powervalve, rendering it useless. Really not an issue with boats.

fbc25el

Great info!

airjunky

I would revisit float settings & make sure your not running '80s pre ethanol specs ,some boats can get pretty angular planing out and will benefit from bowl vent baffles rear pv delete and sometimes even rear bowl jet extensions .see if you can tell if surge starts when secondaties open or not 3500 rpm may be still all in primary side

MILD THUNDER

Thanks. The power valve is a very simple concept, but confuses so many people. From things like a 10.5 PV will flood the engine at idle, to confused about how they open/close, and the fact that the size of the restrictions in the metering block, determine how much fuel they add. For example, when the PV opens on a Dominator, it will add much more jet size worth of fuel, than a stock 750 holley. So the idea of generally saying "plug your PV and go up 6 sizes" may not always be the same case from carb to carb.

Example. ICDEDPPL has some Nickerson 850's. They drilled the powervalve restrictions out, to around .093 if I recall. Which is dominator territory. Just by plugging his rear PV, his AFR leaned out a full point. On my stock 850's, by adding a rear powervalve, my AFR richened up about .4-.5. Which makes sense because my power valve restrictions are about 1/2 the diameter of his.

I dont agree with what Nickerson does in that area. So far I've seen a few of his carbs, where they are very lean at cruise, and go pig rich at full throttle. It took alot of work to get ICDEDPPL's AFR's to be within reason. IMO, nearly 14 AFR at 3200 RPM cruise, and low 10's at WOT, is not a very good fuel curve. My fuel curve on my engines, simply goes from about 12.5 at light cruise, to 12.0 at fast cruise, and 11.3 at full throttle. Theres no reason to have a 4 point difference from 3000RPM to WOT on a blown marine engine. What I really love about the modern technology of being able to install a wideband on your engine, is it really starts to show who can, and who cannot, setup a carburetor. For years we all thought "Im gonna have Dean Nickerson, Pat from Prosystems, Chuck Nuyyten, or whoever, build me a carb that will be perfect for my application". IMO, nobody can build a carb to be perfect out of the box for the application. There simply are too many variables. Can it run, sure it can. A 600HP 540 in a 23FT cat, is not gonna need the same setup, as a 600HP 540, in a 38 Top Gun.

Too many times guys set up a carb on the dyno, then put the engine in the boat and it wont idle worth a dam. They forget that the boat might be swinging 18x34P cleaver props, and it actually may need some air/fuel from the idle circuits when shifted. Or, they forget that even though the fuel mixture at 3400RPM looks great on the dyno when all 4 barrels are wide open, that it may not be in the boat when the secondaries arent even open yet.

IMO, in 2014, the best deal going, is a quickfuel carb. The hardware you get is great. They look great. The price is great. The metering blocks are billet, along with the baseplates. The carbs are infinitley adjustable, from air bleeds, to emulsion bleeds, to idle feed restrictors and PV restrictors. Get a wideband, a case of beer, and go do some carb tuning. You'll end up being much further ahead of the game, and have an engine tune that will be safe, and pay for itself in fuel savings after its tuned properly.

payuppsucker

What effect do the air bleeds have on the way the fuel is metered and how? And at what phase of operation are they effective? I have pro sys dominators and would like to do some fine tuning.

rmbuilder

Jiffy,

The Holley OEM specifications are typically very close (and safe) in stock or mildly modified NA engines. Creating modifications that are not supported by data will not only destroy your baseline but often result in significant damage. I would suggest you return to spec to establish a proper baseline, working outward from that point after you accurately determine what fuel delivery adjustments the base requires.
Holley No. 80443 - 850 CFM Mechanical Secondary

Primary - Port 88, Stbd 88
Secondary - Port 96, Stbd 96

Power valve –
Front 122-65
Rear -122-35

Accelerator pump - Primary - 30cc, Secondary - 50cc

Accelerator nozzle - Front - .031. Rear - .031

If you will be attempting to tune based in part by plug reading, you will find the following attachment (Credit; Larry Meaux) instrumental in your success. obtain a quality plug light (10x) and be aware, reading unleaded, ethanol fuels, requires updated skills.

Bob

Budman II

To build on what MT is saying about dyno runs not translating to real world conditions on a boat, when I had my engine dyno'ed, I asked them to run a steady state test at a typical fast cruise RPM under load, just to make sure I wasn't going to go lean or have any issues with oil drainback. (I am running screens in my lifter valley with a HV pump and 8-qt pan - a whole 'nother thread is devoted to this, so not going there. ) When we ran it this way, we found that it was running much leaner than it had been under the quick full throttle power pulls earlier. Header primaries actually got hot enough to start glowing! Needless to say, if I had just dropped it in the boat without running this test and making the necessary adjustments, I would have burned it down. As MT has said, running on the dyno is great for breaking an engine in under controlled conditions and getting a baseline tune, but there is no substitute for actually running it in the boat with something to tell you what is actually happening in the engine in regards to fuel mixture. This is where the advent of wideband O2 sensors has been so helpful.

payuppsucker

Great info Bob, thanks.