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Old 11-25-2009, 08:28 PM
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Chevy Big Block tuning help

I'm working on a 3 yr build. 1949 Chevy truck street rod. I have mechanical skills but this hase me stumped! Chevy 454, edelbrock carb, cam, lifters, 5.5psi fuel, headers, new dist, good spark. I get popping from the exhaust on normal aceleration! Starts fine. I think i have 30deg advance -have timing tape on it. Please advise.

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Old 11-25-2009, 08:44 PM
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I hope you mean 30 degrees total advance, 30 initial is way too high. If you mean 30 total that sounds low.
Pop the valve covers, start the engine, at idle watch each rocker arm, if you see one or two barely moving compared to the rest the cam is shot.
If you meant the engine sat 3 years and you just recently started it and it wasn`t cycled as if it were a new engine this would explain why the cams flat, anytime a engine sits it must be cycled as if it were new upon start up.
If the cam is okay I would check over the ignition system very carefull from timing advance to making sure all the plug wires are in the correct firing order. I would also check it for vacuum leaks.
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Old 11-25-2009, 08:50 PM
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If it's popping out the exhaust it is firing on the wrong cylinder (cross firing , not wired right as in firing order, 4-7 swap cam?)or you have an exhaust valve not seating for some purpose ( valve too tight , not seating , bent etc)

30 degrees total????




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Originally Posted by oldschool49
I'm working on a 3 yr build. 1949 Chevy truck street rod. I have mechanical skills but this hase me stumped! Chevy 454, edelbrock carb, cam, lifters, 5.5psi fuel, headers, new dist, good spark. I get popping from the exhaust on normal aceleration! Starts fine. I think i have 30deg advance -have timing tape on it. Please advise.
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Old 11-25-2009, 09:05 PM
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I did start it during the three years about once a month after the engine was installed, let it idle and warm up. Didn't notice it then. I'm leaning to a valve problem? or vacuum leak? My vac gauge reads a steady 10" at idle and goes lower as RPM increase. Plug wires correct. everything is new, well 3-yrs old now. Two more notes..the A/F on the Elelbrock Carb makes little to no differance in the engine RPM, if the valve adjustment is too tight would it also cause the carb prob and the popping? And... can you explaing or send me a link on the "total" advance? I have a timing tape installed and i have set it to 30 on the timing mark putting the 30 on the TDC mark. Starts great and idle sounds ok.

Last edited by oldschool49; 11-25-2009 at 09:22 PM.
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Old 11-25-2009, 09:12 PM
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When the engine was first installed three years ago was it broken in correctly?? e.g. was it fired up and immediately run above 2200-2500 rpm for a sustained 20 minutes, or has it just been fired and let idle a number of times in these three years??
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Old 11-25-2009, 09:26 PM
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unfortunatally I cant answer that. The build an hopefully break in was done out of my sight and with thte engine just sitting between the frame rails. If it helps, I did drive it several times with just a cab on frame and seamed ok. Didn't get down on it much.
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Old 11-26-2009, 05:10 PM
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Turkey day.. Retimed, checked plug wire order, pulled all plugs and WOW #2 plug was black! Cleaned all plugs cranked it up and popping was gone. Timing is now at 32 degres @ 4000 rpm per cam spec sheet. Test drive was good. New plugs will be put in this weekend! Thanks for the advice. Note to self--- check the basics First!
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Old 11-27-2009, 07:00 AM
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BBC's need lot of timing. 20 initial, 40 total, plus another 10 from the vacuum advance works on my bbc's. you need to get an adjustable vacuum advance canister to limit the vacuum advance.

run the vacuum advance on the manifold vacuum. so you should get 30 degrees at idle. (20 + 10)
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