Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Setting Up and Adjusting Idle
defiant1:
--- Quote from: Cliff Ruggles on June 15, 2011, 07:23:09 PM ---Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air. That's a "hefty" cam in a 350 engine at that compression ratio. Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff
--- End quote ---
Not sure, let me ask the vendor. All the data sheet says is 106 ICL @ .050 tappet rise. LSA: 108+2
Shaun
omaha:
yeah, I agree with the PCV issue. the pcv should not drop that much. THat cam is bigger than I expected and yeah, if it has tight lobes like 106 for example, it will idle somewhat rough and need more idle fuel. LSA means lobe separation angle, and is how "tight" the intake lobe is in comparison to the exhaust lobe. You must find out how tight the cam is. The installed centerline refers to where the cam is installed by using the lobe center of the intake as a reference. Tight lobe seperation cam will idle a bit rough due to the increased overlap however, it will retain more cylinder pressure (just comparitivley speaking of course) because of the earlier closing intake valve so it could actually be a good coice for a 350 cube engine where comprerssion is a bit harder to make than a large cube engine.
defiant1:
--- Quote from: Cliff Ruggles on June 15, 2011, 07:23:09 PM ---Looking at the engine combination, it's going to need more idle fuel to the mixtures screws, and more idle bypass air. That's a "hefty" cam in a 350 engine at that compression ratio. Is the cam ground on a 108 LSA (Lobe Separation Angle), or is ground on a 112LSA and installed at 108 ICL (Intake Center Line)?......Cliff
--- End quote ---
Back from vacation (visited Mt. Rushmore, I highly recommend the Black Hills if you have not been). At any rate, Cliff, the vendor said the cam was ground based off the 108 LSA and it is installed at 106 ICL. What other adjustments do I need to make to the carb to get it to idle right. I got a parade on July 4th and need to have the car up and running before then.
d1
Cliff Ruggles:
108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
defiant1:
--- Quote from: Cliff Ruggles on June 21, 2011, 04:08:11 AM ---108LSA is not helping the situation. I'd go bigger on the idle tubes, .038 or even .039", .058" down channel restrictions, and .110" idle bypass air. It needs more idle fuel and some help getting back on the idle curcuit.
Don't rule out timing either, it may need more initial timing to be happy. I just cured idle troubles with a Buick 350 yesterday, by adding idle fuel, and recurving the distrbutor for more timing at idle speed.....Cliff
--- End quote ---
Thanks Cliff, I will order the parts from you tomorrow.
Shaun
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