Bill 3

Trying to understand this and make sure I am thinking properly. Sometimes ignorance is bliss and then you install O2 sensors...

Engines/carbs dyno'd and have the correct AFR at WOT. 11 to 11.5 All is well.

Put O2 sensors in and find out that my cruise (even into the secondaries) AFR is 14 (I ask myself why nothing has melted....) In trying to understand better how the circuitry in the Holley 4150 (850 DP) works, I have removed the secondary PV and increased the jet size by 10 at this point but still lean. Increased the primary by 4 and still have a 6.5 PV. The cruise is way better (under 13), but WOT is rich at least as far as I can tell (too much boat traffic when I have been out lately to really open it up). I draw quite a bit of vacuum even at higher RPM's until I get close to WOT, probably 7-8". I am thinking I want or need to change power valves to where it is open by the time the secondaries open.

Questions

Boats, expecially a 38' boat never coast. Why has there not been any issues with melt down with a cruise AFR of 14? (I will mention that it is a full crossover no thermostat system but I will see 140 degrees sometimes).

Can it be assumed that the sum of the jets plus power valves at the proper WOT AFR should more or less always equal the same number? For example If I started with 84's primary, 88's secondary and PV's in both, the total (assuming a PV to be 8 jet sizes) to be 188 (or should it be 376) . So if I go up 4 sizes in the front, I can go down 4 sizes in the rear, or take a PV out and up size jets accordingly but basically I want the total to be close to the 188? Changing the jetting or power valves all has to do with the timing on when the engine gets fed a certain amount of fuel???

I think I am trying to over think things..... I know -Test, test, test.

fbc25el

If your pulling 7-8" of vacuum with a 6.5 power valve it's going to be closed. It does not matter where the RPM is. Maybe try a 8.5 power valve. Do you have a 4 window power valve? What size are the holes behind the power valve?

getrdunn

iTrader: (7)

Where did you mount o2 sensors.

ICDEDPPL

iTrader: (1)

Sounds like you need more jet in the primary and so as not too be too fat overall (wot) pull same amount of jet in the back.
For cruise I change up either jets or play with PV restriction sizes.
How you did not burn that ***** up is beyond me. 14 AFR , thats scary

mike tkach

iTrader: (3)

^^^^i agree,i change only one thing at a time,that way their is no doubt to what caused afr change.

Bill 3

I understand how the power valve works, just haven't figured out at what point I want it open. Are there applications where a different power valve is used in the front vs back?. I have the standard power valve not 4 window. I don't know the size holes, whatever is standard for a typical 4150 (not changeable).

Sensors are mounted in the 10:00 position at the very beginning of the tailpipe after the header.

fbc25el

If you increased the jet size by 10 and still lean I would check size of the boosters size of the angle channels if they are too small they become the main jet. Did you change anything in the engine to cause this?

Bill 3

I increased rear jets by 10 because I removed the PV. I was still lean, but not as bad. If I can't get it close without doing some drilling on the carb, I will probably seek professional help.
I have not changed anything on the engines but this boat is new to me and I don't believe the carbs were ever setup properly.

I understand what Mike was saying about about changing one thing at a time.

My main question above which I think the answer is yes. If I have found a combination of jets/PVs that yields the proper WOT AFR, then the challenge is to make the carb feed the engine the proper amount through the rest of the fuel curve without increasing total fueling.

ezstriper

as stated before, if power valve is closed, then ALL fuel delivered thru jets, tuning with newer carbs using the power valve restriction changes and making sure it opens when it needs to, sounds like WOT valve open AFR are good, valve closed leaning out, also air bleeds can change the AFR at cruise as well

Bill 3

I've been thinking about this.... Don't shoot me

Am I correct to think that when tuning EFI, a MAP sensor is measuring the load on the engine? MAP - Baro = Vac

If this is correct, then (in my case) if idle vacuum is 10-12" and 3500 rpm is 8-10" then even though I am pushing a heavy boat, the engine isn't under an extreme load and could possibly handle 14 AFR???

I have seen EFI AFR tables on here (relative to MAP and RPM) that command 14 in a mid-range (around 3500 rpm) and low MAP (high vacuum) situation. I have also seen where guys are carb tuning a NA engine to the low 12s at WOT and mid 13s in the mid-range. Don't get me wrong, I don't want to run lean. I am just thinking that maybe the carburetor is doing it's job properly and I am trying to force extra fuel down it's throat that isn't necessary (and possibly losing some performance).

Maybe I should also bring this up in this thread http://www.offshoreonly.com/forums/g...n-engines.html