650 on 355 questions
I have lots of info and questions so hopefully you enjoy the read and can give me some pointers!!!
First off, here's the motor:
350 4 bolt block decked/line-honed and bored to .030 = 355cu in
Forged crank .010/.010, Forged 1 piece oil pump drive, Melling HV pump and pick-up, ARP rods, ARP bolts, Forged Pistons, .125 pop tops
Cloyes Tru Roller Timing Set
COMP CAMS EX286C Cam .284/.480,
Vortec Heads pocket ported and bowl hawged, Dual springs: 1.94 intake valve/1.50 exhaust valve, Lift at both valves .484in, Lobe Center 109.0, Overlap 64
SpeedPro Hydraulic Lifters
Edelbrock Performer Intake
It previously had an Edelbrock 600cfm 1406 performer carb which I ousted in favor of a freshly rebuilt Holley 4777 650 Double pumper. After much screwing around I finally got it running as I had issues with floats/needles and squirters.
Now that it is on and running I've got the idle mixtures/speeds set/etc. However, I'm thinking that the builder put in jets that are too large........at least for the secondaries based on the description I'm about to give!
I took it out and it seem to cruise fine and slowly accelerate fine as well. However, a short burst of W.O.T causes it to nearly stall, hesitate, and then pick-up only AFTER I start backing off the pedal. I can't see outside to tell if its blasting black smoke under a load but it does if you floor it quick in park....... but from this description I think the second shot is choking the motor.
At idle I have around 12-13" of vacuum pressure, going up to around 20-22 if you bring it up and hold @ 2000rpm (or close, I couldn't see the tach) from the engine bay.
It was initially tuned/timed/etc to the edelbrock carb so should I advance the timing slightly to incorporate the added size of the new carb?
***Also, I do not know the size of jets or power valve that are currently in the carb either. I've emailed the builder to save myself a little time before pulling everything apart and actually checking the numbers but does anyone have any GUESS on what sizes would likely work best in this set-up???
It does have an automatic which I know are not ideal for Mech secondaries but it is geared @ 3.73 and has a 2400 stall converter.
*****THANKS IN ADVANCE for any info or direction! It'll save me having to call my mechanic friend over to mock me......and if you need more info just ask and I"ll try my best to accomodate
From the description you gave, it sounds more like you need to go bigger on the shooters(pump shot), and possibly the pump cams. That hesitation and near stall is a lean hole in the fuel curve due to no airspeed through the carb yet when you immediately floor it, so not enough fuel is being pulled from the boosters. The fact that backing off the throttle helps the engine also points to this.
the engine could use a 750 carb, and go with a 4.5-3.5 power valve, 65-67 main jets and use 6-8 spread to the rear, for the stall, a 3000 would be good....
and id try running 36 degrees of timing that would b a good start there, with race gas like 108-110
The 4777 comes jetted 67/73 w/a 65 power valve. Primary and secondary pump nozzle is a 0.028”.
Check the operation and adjustment of the secondary accelerator pump. Like ericnova72 has said- the hole is likely an inadequate secondary pump shot.
Going by your vacuum reading, it does not need anything less than a 55 power valve.
Thanks guys for the direction.......I'm definitly not going to go up to a 750, at least not right now until I do some monkey-work with the current set up.
So......just to check with what you guys have suggested......
I'm going to pull the secondary bowl off and see what size jets he put in. #2 ---- is there a size stamped on the squirter to verify the size so I can go up on???? If so I'll----
1.) Increase my jet sizes in the secondary by 2
2.) Increase my squirter size in the secondary by at least 1-2 sizes
****From what info you guys have given me (which is appreciated!!!) that should be a good start to see if I can correct my hesitation/lean out condition at W.O.T.???
--- And I should be O.K with my primary set-up (For now) as it seems to run excellent until the secondaries come into play on heavy pedal.
Yes, the squirters are stamped with the size. They generally go up in size 2-3 #'s at a time. Next size bigger than 28 is 31, then there is 32, 35, 37, 40, 45. You can also make custom sizes using a hobbyist pin vise and small drill assortment(Drill #'s 61-80, 61 is something like .059", 80 is like .013"). I've taken many years accumulation of 25's and made a bunch of custom sizes, marked with an ingraver.
You may need to change to a different pump cam also, the Holley cam assortment kit is inexpensive and good to have. You'll just have to experiment with it.
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