Jetting question. Primaries larger than secondaries
#51
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Yes, look up the Holley 4781 here - http://documents.holley.com/techlibr...al_listing.pdf
Front and rear 6.5 PV. 80 jets all in both in it's stock form.
Front and rear 6.5 PV. 80 jets all in both in it's stock form.
#52
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Put O2 bungs in over the winter. Finally close to getting the carburetors dialed in. NA 515 cu.in. 850 holley's (4150), just under 600hp on the dyno. 6.5 PV front and back, Jets 88 front, 87 rear. I pull about 8" of vacuum at cruise.
In my cruise range, AFR is bouncing around 13 and my WOT is in the upper 10s.
I need to jump to probably 90 in the front (to get closer to 12) and possibly drop to 86 or 85 in the rear (to try and end up around 11.5).
Seems odd to me that according to the O2 sensors, I need this much more jetting in the primaries.
Is this something I should be concerned about? Possibly the wrong carburetors for the application?
In my cruise range, AFR is bouncing around 13 and my WOT is in the upper 10s.
I need to jump to probably 90 in the front (to get closer to 12) and possibly drop to 86 or 85 in the rear (to try and end up around 11.5).
Seems odd to me that according to the O2 sensors, I need this much more jetting in the primaries.
Is this something I should be concerned about? Possibly the wrong carburetors for the application?
Try 6.5 PV in Primary, block the Secondary. Jet 80 Primary and 88 Secondary and see where you are then. I think it will be real close, maybe a bit on the rich side.
Mark
#53
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I'm still learning here, but I don't see how removing the rear PV and dropping jet sizes would make me rich? My biggest concern right now is my lean cruise.
#55
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Mark
#56
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Joe has a lot of great carb info, however I feel 1:1 will be horrible . Throttles will be too sensitive (oops, didn't want that much power - think docking at etc) and air speed will be down when starting to accelerate....will take a bit for the boosters to get going.
And if I'm wrong, which is very possible, what do you do about the accelerator pumps ? Every touch of the throttle will be a ton of fuel.
IMHO - let's get this thing to work as a normal carb before trying other more unconventional things.
And if I'm wrong, which is very possible, what do you do about the accelerator pumps ? Every touch of the throttle will be a ton of fuel.
IMHO - let's get this thing to work as a normal carb before trying other more unconventional things.
I was concerned that this would result in the boat using a lot more fuel, but I really haven't seen that.
#58
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Update.....
I am up to 90 jets with 6.5 PV primary and 98 jets no PV secondary. I'm getting pretty close, under 13 afr at cruise.
Regarding power valves... I understand what makes them open (a vacuum lower than the PV number), but when should they be open? For instance when I am at the top of my primary (just before secondary starts to open), should the PV be open? Is it only for lower vacuum situations like accelerating or WOT? My vacuum is rarely below my PV value until closer to WOT.
I am up to 90 jets with 6.5 PV primary and 98 jets no PV secondary. I'm getting pretty close, under 13 afr at cruise.
Regarding power valves... I understand what makes them open (a vacuum lower than the PV number), but when should they be open? For instance when I am at the top of my primary (just before secondary starts to open), should the PV be open? Is it only for lower vacuum situations like accelerating or WOT? My vacuum is rarely below my PV value until closer to WOT.
#59
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I`m tired of the powervalves. My carbs are boost referenced so pretty much anytime I`m on plane it`s open and there`s unmetered extra fuel dumping down the carb.
Too rich at 3000 , too lean at 4000.
I`m going to eliminate the power valve and jet up 10 sizes and see what happens. I`d rather pull metered fuel out of the jets than just dump it in.
After that it`s time for EFI and get out of this 1960 technology.
Too rich at 3000 , too lean at 4000.
I`m going to eliminate the power valve and jet up 10 sizes and see what happens. I`d rather pull metered fuel out of the jets than just dump it in.
After that it`s time for EFI and get out of this 1960 technology.