Performance Parts Require High Idle ? 305 H.O.

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Tynan918

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I have an '84 MCSS with a 305 High Output/L69... Just bought it about 3 weeks ago and the seller wasn't mechanically inclined to tell me of any modifications to the engine, and I'm very new to engine performance and performance parts...

He told me it was a 350 but after I ran the head and block casting numbers, I found out the engine is a 305 High Ouput/L69... Camaro heads and Corvette cam, and a performance racing engine of the 1980's ... or that's at least that's what I'm reading in other forums...

I have a 1405 Edelbrock Carburetor, Ebelbrock Single Plane Intake, and I bought and installed and aftermarket HEI Vacuum Advance Distributor (Manifold), wires, and spark plugs...

On a cold start, I can't adjust the carb and get the idle RPM's at 600 without rough idling and stalling if I hit the throttle pedal... Whether I advance or retard the timing with the distributor, or play with the mixing screws, or play with both idling screws, I still get the same results...

Lowest I can get is maybe 800 RPM at idle, but 1,000 RPM's runs smooth and shows correct with a vacuum gauge. Is 1000 RPM correct considering the engine and performance parts ?

But after the engine warms up, doesn't the RPM drop almost 200 ? Giving me about 800 RPM at idle, and then dropping down another 200-300 again in Drive ?

Also, does high RPM bring high fuel consumption and engine damage with it?

No vacuum leaks, did the cigar smoke test, smoke only comes out the top of the carburetor choke...

Really want better gas mileage...should I run it at the 1,000 RPM's and run 93 octane or....?

Any help and tips is appreciated, this is my only car and daily driver...
 
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ELCAM

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You really need to know what cam is in the engine and how it timed in relation to the crankshaft, there are timing sets that allow to retard or advance the cam.

Running a high idle will not affect the engine negatively. It will wear the torque converter, possibly burn clutches and increase the transmission fluid temperature with an automatic transmission..
 
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Tynan918

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You really need to know what cam is in the engine and how it timed in relation to the crankshaft, there are timing sets that allow to retard or advance the cam.

Running a high idle will not affect the engine negatively. It will wear the torque converter, possibly burn clutches and increase the transmission fluid temperature with an automatic transmission..
Is 1000 RPM normal on a cold start ?
 

ELCAM

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It's going to idle high with the choke closed.

What's the idle once the choke opens fully?
 
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oldsmobile joe

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no, its too low. with the carb set to the fast idle position, the rpms should be around 1600.
 
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oldsmobile joe

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do you still have the emission label on the radiator support, fan shroud area? it will tell you your base timing, base idle and fast idle info.
 
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ELCAM

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do you still have the emission label on the radiator support, fan shroud area? it will tell you your base timing, base idle and fast idle info.

With a non original carburetor, intake and distributor and possibly cam I am not sure these specifications are going to be that accurate.
 
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oldsmobile joe

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it will be more accurate than the guessing your doing now. from there you tweak the numbers as required.
 

Tynan918

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Aug 2, 2021
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It's going to idle high with the choke closed.

What's the idle once the choke opens fully?
Not sure, never knew of a drop in RPM with the choke open (warmed up), but I have let the engine idle 15-20 min before, and never thought to check the RPM after the engine warms up. I'll check that out tomorrow.
 
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