Ok, one more question on the Holley jetting.
Now I'm just guessing. Maybe the secondary was cracking or flopping open enough to expose the secondary transfer slot?
Of course I can't find any of the screen shots I made of three springs.
I'll have to open up the dyno files and do over.
Until then, here's a couple of overlaying wide open throttle with and without the secondaries.
Main thing to notice.
Engine accelerates pretty darn well on just two barrels of the '750'.
View attachment 1715497858
The carb here has a downleg secondaries and annular primaries. I suppose the thinking was the annular booster restrict flow so using downlegs in the secondaries would make up for it. Nice thought but messes up fuel distribution and never would recommend it. Anyway as you can see the primary AFR is pretty flat and the secondary AFR is rich, lean, richer and drifts lean.
Disconnecting the secondary demonstrated that problem was entirely in the secondary side.
Datalogger shows that more clearly.
View attachment 1715497860
Bottom scale is time in seconds.
Blue is vacuum. According to the MAP, vacuum came up to 3.5 "Hg at 5700 rpm using just the primary barrels.
Suppose I should mention a little about the engine:
340 with hughes cam 223/230 at 50.
I wondered about the secondaries possibly opening for some reason, and the only thing I could come up with was possibly just vacuum.
That seems like it shouldn't happen though because of the spring.
Now get this.
After I got the top of the vac can down on the Oring everything came real close into line and the secondaries work now.
Remember the last I said was 72 primary jets.
All the way down to 66's in the secondaries with no change.
10 or so on the AFR at 1,200 rpm.
Now the AFR shows everything right about where it would be expected in relation to what the carb has in it right now.
Now it shows 13.5-14 at idle. ( I did have to richen it up again after the O ring sealed)
about 12 where that rich spot was at 1,200 rpm.
14-15 once into the primary jets.
And 16-17 when the secondaries come in at WOT. (makes sense with 66 jets)
Looks like all I have to do now is get 72-74's or so in the secondaries so it's around 12-12.5 at WOT and trim the idle a little leaner and that should be completely acceptable.
A bit leaner on the idle should all but remove that rich off idle spot.
Who the heck would have thought that Oring not sealed to the vac can would cause all this whacked out crap?
Secondaries not opening sure, but everything whacked through the whole carb?
This is one of the things that could make guys throw a carb in the trash.:D
The car is snappy, strong and is back running really nice again, just faster than it ever has been.
The Edelbrock ran great on it, but it wasn't this great.
Thank you for all your effort on this, and I really do appreciate your consultation.
Now remember.
A non sealing oring that seals the quick change vac spring cover can screw your carb up good.
I know I won't forget it.:D
