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Old 02-04-2008, 02:27 PM
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305 ignition timing issues

Hey everyone.. im new here, ive been checking out the site for a few days and I really like it here. Was wondering if you all could give me some much needed input on the problem im having...

I have a stock 305sbc with an intake and 4bbl Q-jet from an old 350. I took the carb apart and its clean and in tact. When the engine is not in gear it free revs without a problem. My issue is that i am getting a backfire up through the carb while i go down the road and mash the throttle. Now i seen a few threads on here that say its a lean side effect. Not sure if thats possible since the carb is off of a 350.. but i could be wrong... anyway, as of right now my timing is set at 4 degrees btdc and i have tried all the way up to 12 degrees btdc. My spark plugs (from my opinion) dont look too bad. I have also adjusted the valves in the engine and still the same problem. Only other things i can think of is a. a rounded cam lobe (but i didnt notice anything out of the ordinary while adjusting the valves), b. something is up with the distributor (maybe the mechanical weights .. not sure what to check for there though) or c. i screwed up the valve timing when i replaced the timing chain and gears.

Sorry this is so long. If anyone could give some feedback it would be greatly appreciated. Thanks

Jason

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Old 02-05-2008, 09:14 PM
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305

Timing: Hook up your timing light, slowly open the throttle while watching your timing marks. Your timing should advance when rpm goes up. If nothing moves by 3500, then your advance is stuck (not uncommon on HEI distributors.

Carb:
It might be clean but your accelerator pump might be hard as a rock and not sealing tight enough, or the orifices may be gummed up, not giving you any pump shot when you open the throttle. With the engine off and air cleaner off, look down the primaries of the carb, while opening and closing the throttle. You should see 2 equal streams (like an old fashion squirt gun) of "pump shot" when you rapidly open the throttle.

Good luck
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Old 02-06-2008, 08:59 AM
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If its only happening under load, My first suspect would be a bad plug wire.
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Old 02-08-2008, 05:05 PM
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Thanks for the support!

I bought a rebuild kit for the carb, cleaned it up and put it back together. The engine ran better but still was sluggish. So I hooked up the timing light, disconnected the vacuum advance and reved up the engine to see if there was any change in the timing... and there wasnt. That tells me the mechanical advance is not working properly. So tomorrow Im going to take out the distributor and see if I can get it to work right.. Wish me luck and thanks again for the help!!
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