Hi Guys: I have installed my stage 2 scoop and have the carb sealed of from the engine heat. Now i am getting a stumble off idle. At crusing speed it does not feel right. Tip into the throtle and the car feel mushy and has a slight shudder before clearing up to run smooth. At full throttle the motor feel really strong At idle the motor feel as it has increased in rpm. Is all a result of getting good fresh air???? What to do???? My thought is the carb is leaning out and should go up in jet sizes for the primary side. The motor ran smooth and no stumble before the hood scoop install. Please shoot me some ideas so I can get this thing to the track for a test run.Ken
Ken, What carb is it? You may need to tighten up the air valve spring for the secondaries if it is a Qjet. They're on the passenger side of the carb. There's a set screw (hex) and a slotted screw (tension spring). You'll want to take baby steps with this adjustment. Tighten it up about an 1/8th of a turn and see if it helps. Keep going until it is gone. Mark your starting point on the body along with the slot of the screw. Once the set screw is loose, it'll spring back, so keep your slotted head screwdriver holding it in place as you loosen the set screw.
I would look at the timing, and how it advances with increasing speed. What RPM is all the advance in? Off idle stumble can be caused by the primary throttle blades being open too much causing the idle tranfer slot to feed at curb idle. If this is the case, try running more initial advance at idle. This allows the car to idle with the tthrottle blades more closed at idle. Also look at the accelerator pump, and confirm it is working, and adjust that as necessary. Also check for a vacuum leak. Try reving the motor a little to get into the primary circuit. Then choke it and see if the RPMs go up as you do. That would indicate the need for more jet. Knowing what carb you have would help.
I'm running into the same problem after putting a Stage 2 scoop on. I have a holley 950 HP. Ran like a raped ape before. Still runs fine, just a little "burp" right off the line.
I should have told you guys what carb it is. 750 holley worked to flow about 780 cfm. Double pumper and running a stub stack for the first time.T he carb was pro built at a carb shop in Denver and has worked great until the stage 2 scoop install. Primary jets are 66. Secondary jets are 85. After reading my Holley book for the hundredth time I finally found that if you install any type of fresh air system, you must increase fuel. I thought that I would go up 4 sizes on the primary to 70. The holley book calls for 70 from the factory. Leave the secondays alone and see what happens. Also changed to #24 autolite plug which is a medium heat range. Had 23 plugs and felt the plug was too cold accroding to the GSCA text book. I guess the final answer is? keep changing until it runs best. Thanks for the input. Ken:grin: :grin: :grin:
