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I have a 460, Weiand Stealth intake, with an 850 built by Pro-Systems, 4 corner idle and I have a wide band to monitor A/F ratios. Not sure what is ideal ratio, but it idles great at about 13.5-13,9. So I take it for a drive on the street for about 20 minutes, idle quality goes downhill. I notice A/F ratio now up 18-20. I guess I should be looking for vacuum leaks around intake, carb, etc. Any ideas as to why its leaning out idling while hot?
 

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I feel your on the right track, and you have a great way of knowing what the fuel ratio is, do you have one for each side about 9" rearward of where the primary tubes join the collector? 14 to 1 is ideal, and idle is important, but under load engine speed are going to be more important, have you recorded the a/f ratio at 2500 rpm under a hard steady climb?

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Another question, is the exh heat riser ports in the manifold plugged off?

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My guess is the fuel is boiling.
 

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My guess is TommyK is correct. My 502 starts off at 14.0-14.5 at a cool idle and slowly but surely creeps up to 16-18 at hot idle. Iv'e never worried about it, idles fine, plugs look great, doesn't overheat. On a light cruise I can get the afr to 15-16. I'm using a Holley 950 HP that I tweaked a bit.

I guess you try wrapping the fuel line, phenolic spacer and the rest of the tricks to keep the fuel cooler.
 

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Discussion Starter #7
I only have one 02 sensor and its probably about 10-12in on the pipe after the collector. I do have the heat riser ports plugged. I'll see if I have an extra phenolic spacer laying around and wrap the lines and see what happens. You have me thinking about the fuel also, It runs fairly good with pump gas, and lately I've been running some ethanol free pump gas and I have to wonder if it has maybe a lower boiling point. One thing, the rear idle circuit feeds off the rear bowl and if I'm just casually cruising around that rear bowl will get hotter and hotter since fuel isn't used very much.

I have a Innovate LM2 A/F meter and I believe it can log the fuel ratios while I run it under load and I can review later.

Thanks for the help
 

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I have a 460, Weiand Stealth intake, with an 850 built by Pro-Systems, 4 corner idle and I have a wide band to monitor A/F ratios. Not sure what is ideal ratio, but it idles great at about 13.5-13,9. So I take it for a drive on the street for about 20 minutes, idle quality goes downhill. I notice A/F ratio now up 18-20. I guess I should be looking for vacuum leaks around intake, carb, etc. Any ideas as to why its leaning out idling while hot?
I only have one 02 sensor and its probably about 10-12in on the pipe after the collector. I do have the heat riser ports plugged. I'll see if I have an extra phenolic spacer laying around and wrap the lines and see what happens. You have me thinking about the fuel also, It runs fairly good with pump gas, and lately I've been running some ethanol free pump gas and I have to wonder if it has maybe a lower boiling point. One thing, the rear idle circuit feeds off the rear bowl and if I'm just casually cruising around that rear bowl will get hotter and hotter since fuel isn't used very much.

I have a Innovate LM2 A/F meter and I believe it can log the fuel ratios while I run it under load and I can review later.

Thanks for the help
Peak power won't be at 13.9 under load. 12.8 12.9. . You keep running it at 13.9 ,. And pull a head off guaranteed all the exhaust valves are white as a ghost.
 
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