Hello
I finally got a bigger carb to try on my engine.
The engine is a 427 CI .030 over with L71 square heads, 2.19/1.88 valves,
solid lifter cam .520/.520 lift, 242/242 duration at .050 , 114 degrees lobe centerline angle.
Until now, I was running a 650 CFM HOLLEY 4150 double pumper carb, no choke.
I now received a 4010 HOLLEY double pumper 750 CFM carb, no choke.
What size power valves, primary & 2nd needles should I run ?
The carb came off a small block stroker engine and I presently have no idea whats inside.
Will check it up this W/E.
Location: At my Bar drinking and wrenching in Lafayette Colorado
Re: paging Lars and all other carb gurus. (WESCH)
WESCH -
On unknown carbs, I always like to put them back to their stock, baseline configuration forst, and then tune from there. If you post up the list number, I can give you the stock specs for it. Give it a rebuild with an original Holley kit & parts, set your primary AND secondary idle speeds up correctly, level out the floats, and crack the idle mix screws to 1 turn out from seated. A 6.5 power valve works pretty good for most applications. Once set up and running, pull a couple of plugs and do a plug reading to determine if you need to bump the jet size up or down a notch or two.
Thanks for your answer.
This carb just received a HOLLEY kit.
I got the old parts with it. Both float vlv, both powervalves , both inline filters.
It doesn't look like if the prim and 2nd needles got repl.
The old power valves are 65th , so I suspect the new once being the same.
The 4010 carb is a R84013-1 , dated 2392.
I guess, I can just install it and try it out.
Lars, which book can you recommend for HOLLEY overhaul/tuning that also explains the function of the components ?
And thanks for your previous help on my ignition adjustment. Man, this engine never worked so good ! When it reaches 3500 RPM, it's like a afterburner.
I hope to get even more out of it with this carb.
Ok, just got the confirmation from the previous owner of this carb.
It's been overhauled with a standard HOLLEY rebuild kit.
Thanks for all info.
Just an other question.
Will my Vette consume much more fuel with the 750 CFM carb ?
Re: paging Lars and all other carb gurus. (Boofers)
Hi Boofer
Quote:
Who is Gunther?
Gunther is me , the proud owner of a 68 Convertible with a beautifull big block, manual 4 gear M21 close ratio and crazy 3,70 rear end.
I still can't believe that driving something like this is allowed. :flag
Location: At my Bar drinking and wrenching in Lafayette Colorado
Re: paging Lars and all other carb gurus. (Lasse)
Lasse -
Holley carbs with 2-corner idle systems (no secondary needles) still discharge idle fuel through the secondary throttles: there are idle fuel transfer passages in the top surface of the throttle plate that transfer idle fuel from the primary side to the secondary side (they're curved passages that run down the right and left side of the throttle plate). Adjusting the idle mixture on the primary side affects the primary and secondary idle fuel equally. For this reason, the secondary idle should be set up even on 2-corner idle carbs in order to achieve best idle and best off-idle throttle response. Cracking the secondaries open equal with the primaries will assure that you will get the proper transition slot exposure for best carb performance.
Nice info Lars! I have read all kinds of Holley material, but hasn't found that sort of information :thumbs:
I have read that the transfer slot shall be exposed by 0.04" and sec trottels screw 'touch' plus 1/4 turn.
How do you measure when the pri/sec trootlles are equal?
Can I count turns on primary stop screw until it slightly touch (when the idle is set) and add sec stop screw turns (1/4 turn), divided it by two and set them equal to that amount?
Location: At my Bar drinking and wrenching in Lafayette Colorado
Re: paging Lars and all other carb gurus. (Lasse)
Lasse -
Set the primary throttle to expose .020" of the transfer slot as viewed from the bottom of the carb. At .020", the transfer slot will appear as a square hole (the slot is about .020" wide). Then, hold the carb up to a light and look up through the bottom of the carb: You will be able to see the "light gap" around the primary throttle blades. Adjust the secondary throttles to match the same "light gap." This will give you a nice, balanced setting with very good idle and throttle response.
paging Lars and all other carb gurus.
