4 bbl carb question
 

looks like my vacuum secondaries not opening summit : SUM-M08600VS on a 383 . 4 spd. Should I be able see them spitting gas when I'm cranking throttle under hood. this is fairly new carb and car runs smooth but I think no secondary power also stalls when launching - I see floats are little low.. any tips appreciated
thnx

1. No.... Its not a Double Pumper Carb...
2. Adjust Secondary Spring with a lighter one if you want it to open sooner... Use a tighter spring if it is opening to quickly.
3. May Need to Adjust the Accelerator Pump...
4. Float Adjustment should be in the middle of the site glass... OR if the carb has Site Screws, Should just Dribble out of the hole..

uh...,this is doubpe pumper oh maybe you mean no accelerator pump on secondaries ?. confused I guess . I saw a guy use a paper clip on vacuum rod then drive and see if it moved - otherwise I guess you can't se the gas flowing unless under load?

Uh.. Yes... Thats a Vacuum Secondary and has no Accelerator Pump on the back half.
( confused I guess ) Maybe so?
( I saw a guy use a paper clip on vacuum rod then drive and see if it moved - otherwise I guess you can't se the gas flowing unless under load?[/QUOTE]) You could use a "GoPro" maybe?

My recommendations would be to go look in at the Holley Web site and read some of the how too's and view a few videos for adjustments....

Thanks for reply. Summit had a number or helpful videos. I adjusted floats and it launches incredibly better. Yikes. I was looking for something I’m not going to see basically. Fuelbentering secondsries is out of view. Anyway will do psperclip thing and feel better about vacuum working.

Sounds like your making great forward progress!!! Keep chipping at it... Cheers

ok so I need estimate of what rpms this motor is.. 68' 383hp. mild cam, Summit 600 cfm 4 bbl., dual ex., edelbrock dual plane performer intake. Are they talking about rpm limits or what it? I got a tack but I've never redlined it. Is this rpm number something based on chart I found below? Maybe the 5200 for 335 HP number?any help appreciated.
Year
Carburetion Horsepower Torque (lbs/ft) Compression
1966-1967 4-bb 325@4800 rpm 425@2800 rpm 10:1
1968-1969 sc 4-bbl 330@5000 rpm 425@3200 rpm 10:1
1968-1969 hp 4-bbl (Carter AVS)335@5200 rpm 425@3400 rpm 10:1
1970 2-bbl 290@4400 rpm n/a 8.7:1
1970 4-bbl 330@5000 rpm 425@3200 rpm 9.5:1
1970 4-bbl (Holley) 335@5200 rpm 425@3400 rpm 9.5:1

ok ignore my post - collective wisdom on another thread tells me max for this motor is like 5500 to maybe low 6000s. answers my basic question anyway. this is a great website.

The thing that deturmans the up RPM limit besides the cam and lifters is the heavy OEM pistons. The crank and rods when prepared are good to 7k but with the heavy cast pistons 5500 to 6000 is pushing it.

ok thanks - new cam and lifters..1010 crank, new cam, cam bearings, lifters, high volume oil pump. Summit Mild Racing Cam: Hydraulic flat tappet, Valve Lift with Factory Rocker Arm Ratio: 0.466 int./0.488 exh.
Crane Cams Anti-Pump Up Hydraulic Lifters, COMP Cam valve springs

Duration is what determines the RPM range of a cam but you still need to respect the piston RPM limits. Do you have the duration or the operating rate of the cam? Did you replace the pistons?

info on last rebuild did not indicate any piston replacement
some specs for cam:
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,000-5,500
Intake Duration at 050 inch Lift: 224
Exhaust Duration at 050 inch Lift: 234
Duration at 050 inch Lift: 224 int./234 exh.
Advertised Intake Duration: 298
Advertised Exhaust Duration: 303
Advertised Duration: 298 int./303 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.466 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.488 in.
Valve Lift with Factory Rocker Arm Ratio: 0.466 int./0.488 exh.
Lobe Separation (degrees): 114

Crane Anti-Pump Up Hydraulic Lifters
1010 crank, new cam and cam bearings

That will work nice with stock pistons

Great thanks. ! So maybe max rpm range I should keep in mind is like 6000 ?

I would say 5,000 to 5,200 Max... Just My opinion ... :)

I'd go 5500 with it if, it was a 440 I'd go about 5200.

so with cam data I posted which numbers describe cam duration? The 234/235 numbers or the higher ‘advertised ‘ duration. Confused on that one I guess thnx