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new 4434 SBC carb/ idle issues

2K views 19 replies 8 participants last post by  JJLT1 
#1 · (Edited)
434 cu in SBC installed a 950cfm Holley ultra XP carb at first obtained the highest vacuum reading of between 9" and 10". ( this after exposing some secondary transfer slot otherwise idle mixture screws had no effect at idle except when nearly closed idle improved primary was cranked up exposing too much transfer slot and found that Idle bypass fully closed gave the best idle ) installed a 4.5 power valve in this carb . Fuel bowls level set to 1/2 sight gage. everything runs ok (some unburnt fuel smell from exhaust) when I come back an hour or two and have to readjust all over again?
I got timing set at 34 degrees@ 3400 rpm as per engine makers specs.
Ok So I tried a new Holley HP Carb (950) CFM use same number power valve, bowls set to 1/2 I get occasional backfire through carb when blipping throttle, adjusted pump shot, only get 4" to 5" of vacuum with this carb and adjusting idle miture has no effect.rpms seem to rise after throttle opening and closing on second carb. I do notice that my vacuum pump is constantly on all the time though and it should turn off after engine start up and it senses engine vacuum? maybe got a vacuum leak im thinkin?
this is my Cam specs:
vid of engine running, seems good https://www.youtube.com/watch?v=yUnMTZMRZCU
then restart a few hours later runs like crap?

Part Type: Camshaft
Application: Chevrolet Small Block V8 305-350, '87-'98 (Carbureted)
Cam Style: Hydraulic Roller for OE Roller Applications
Basic RPM Range: 2600-6400 2800-6600
Manufacturers Description: Rough idle, needs good heads. Good upper mid-range. Needs 3500+ stall.
Intake Duration @ .050": 247
Exhaust Duration @ .050": 253
Advertised Intake Duration (@ .006"): 300
Advertised Exhaust Duration (@ .006"): 306
Intake Valve Lift with 1.60 Rocker Ratio: .603"
Exhaust Valve Lift with 1.60 Rocker Ratio: .619"
Lobe Separation Angle: 110 Degrees
Intake Centerline: 106 Degrees
Small Base Circle: No
Cam Gear Attachment: 3-Bolt (step-nose)
Valve Adjustment: Zero Lash Plus ½ Turn
Manufacturer: Howards Cams & Racing Components
Manufacturer's Part Number: 180345-10
Weight: 10.0 lbs.

Note: Oil with ZDDP or ZDDP Additive Required
Note: Stock (O.E) valve springs cannot be used.
Pulling my hair out on this one!
 
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#15 ·
Now you just need a belly pan for the carb to seal it to the cowl induction, easy HP there after 60 mph from the high pressure air near the windshield.

On that engine probably worth 30-50 HP at 100mph.

I like the SS headlights better myself but I know the RS is better looking to most, some serious beans invested...not to mention lots of wrench time.

Nice car!:cool:
 
#16 ·
This Engine Provides Both The Power And The Sound That Screams "Hot Rod". Utilizing A Mild "Street Roller" Cam Profile And A 10.5 Compression Ratio, It Delivers The Tire Melting Power You Want And The Crusing Reliability You Need In A Pump Gas Friendly Package.

Horsepower
Torque
Bore & Stroke
Compression Ratio
Fuel Requirement
715 @ 6200 RPM
665 @ 4500 RPM
4.500 x 4.250
10.5 to 1
92 Octane
This I copied from an add from someone selling racing/street engines.Almost identical to your claim? except 540 cubes
 
#19 ·
It's not the nature of the beast. With modern day parts and the correct camshaft a carb engine should start like an EFI engine. A 750cfm carb will feed that thing to 5000 rpm, after that if you plan on doing some spirited driving your going to need 850 to 950 depending on RPM range. These Morphed SB have the same demands of a BBC in the same CID.

Air need area to turn. You get air moving to fast and then try to change its direction, well the air will look like a Cup Car New Hampshire speedway at full speed in turn 3.

By the way, Thank you for your service to this country.
 
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