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Discussion Starter #1
I have a 68 Z 28 and put about 50 miles on it today. It ran great all day and all of a sudden, it started to run rough on low idle, and seems like it has lost some pick up and power as well (mostly on the low end). I pulled the air cleaner off and checked the plug wires on the distributor and they seemed fine.

In addition I was starting it while it was running rough and it will not start as easy either.

Any ideas would help alot.

Tks.

TR
 

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May need to remove the mixture screws and blow in a little carb cleaner through the holes. Then use the vacuum gauge to readjust the screws once they are back installed.
 

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Is there a real gas smell at idle? You might have blown your power valves. When they blow, the car starts running poorly and there is a pretty good gas smell to it.

alan
 

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Discussion Starter #6
points.

holley 453 carb.

odometer reads 52 K

I looked at all the plugs today and they all look good. also checked for spark and it's fine. I did change 1 plug because the ceramic part was cracked and adjusted the timing a little. It seems to run a little better at the moment, pick up and power seem better.

I now have a backfire while the engine is warmed up. I hit the gas and it backfires 1 time.

any idea?
 

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Put a timing light on it to make sure the timing is steady when it's acting up.
 

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Backfired thru the carb or tail pipe? Good catch on the bad plug. A fouled plug will make a 302 run real poor.

alan
 

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about 50 miles on it today. It ran great all day and all of a sudden, it started to run rough on low idle, and seems like it has lost some pick up and power as well
This a new projext on the road??
if so crap in the carb bowel valve/bowel fuel height and/or crap in the fuel filters

I looked at all the plugs today and they all look good. also checked for spark and it's fine. I did change 1 plug because the ceramic part was cracked and adjusted the timing a little. It seems to run a little better at the moment, pick up and power seem better.

I now have a backfire while the engine is warmed up. I hit the gas and it backfires 1 time.
Check the HT line order.
 

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You can also put the timing light on each plug wire to see if one cyl. is still misfiring, if popping thru carb than it sounds too lean. Sounds like trash in carb., floats too low, or bad floats (full of fuel), acc. pump not working.

Dan E.
69 SS396 4spd. 4.10 posi. x66 coupe
 

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Discussion Starter #11
ok I reset timing and retard a few degrees. seems like it starts and idles better now. but ....on idle if you hit the gas pedal I still have backfire, but not as bad. still sound like a carb. problem? if so what step shold I take first?

Tks.

TR
 

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Is it possible that its not running on all 8-cylinders, if you have headers check each tub to see how warm it is compared to each other... If you have stock exhaust manifold check the old School way and see if each wire has spark...

Also check the dwell on the points and the vacuum advance can.
 

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ok I reset timing and retard a few degrees. seems like it starts and idles better now. but ....on idle if you hit the gas pedal I still have backfire, but not as bad. still sound like a carb. problem? if so what step shold I take first?

Tks.

TR
Do you have vacuum advance on this engine? When you set the timing, did you disconnect the vacuum advance line? What is the base timing number you settled on? If you do have vacuum advance, 20* BTDC isn't uncommon for idle, but base idle will be more like 8* - 12* depending on the engine. If the timing is too far retarded, you can get some backfire, but don't blindly give it a tweak to see if it fixes the issue. Give us your timing numbers so we'll know where you are.
 

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I had the exact same problem. I put the timing light on each plug wire and found a few plugs were not firing every time. New plugs solved the problem.
 
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