460 stumble
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New User
Joined: Apr 2006
Posts: 19
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460 stumble
My 79 460 stumbles quite a bit when the timing is set lower than 20* btdc. Put it back to 20* and stumble's gone. Is this normal? Should timing be set that high? I set it with the vaccum line disconected and plugged. No other vaccum leaks anywhere. Should I go with a smaller discharge nozzel in the holley or take some spring pressure off the accelerator pump arm? HOLLEY 750 vaccum secondaries. Maby getting too much of a squirt?
Junior User
Joined: Mar 2007
Posts: 78
Likes: 2
From: Pinedale Wyoming
460 stumble
you need to run 38 deg. total timing to get max power at full throttle. vac advance adds approx. 15 deg. this = 53 wich is too much at part throttle. bare in mind that an engine has no vac. at full throttle. so if you set your timing at 38 with vac hooked up you lose that 15 deg. at full throtle = 23 deg. this is fine if you have alot of compression. kills power on a low compression engine
Elder User
Joined: Dec 2006
Posts: 881
Likes: 1
From: Sudbury, ONT.
If the vacuum advance is supposed to be hooked to a ported vacuum (only has vacuum when throttle is opened) then why do you have to diconnect it to set timing? Shouldn't there be zero vacuum at the ported vacuum if the truck is at idle? Just looking for some clarification.
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New User
Joined: Apr 2006
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Well at an idle and vac. hooked up there is no advance. It stays where I set it. But what's with the stumble and sometimes a backfire when it is set below 20*? Like I said, no Vaccum leaks anywhere. Thinkingb fuel related issue. Might go with an Edelbrock soon.
