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Old 08-25-2009, 07:28 PM   #1 (permalink)
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74 chevy 350 flood smoke

Okay I have tried a bunch of different things to try and get a truck I'm building to idle right. Truck is a 83 model with 74 model 350, stock other than being bored .030 over, stock cam. I'm using the older style q-jet carb and older hei distributor and the problem I'm having is light flood smoke while idling and smutting up plugs. I have rebuilt this carb by the recommendations on florida 4x4 with measuring and setting float, metering rods, checking all vacuums to make sure all held vacuum, such as modulator, new brake booster, choke pull off, etc.Built another q-jet and tried it today and it did same. Bought an adapter plate today and put 2bbl on it and did same. Thought maybe a weak ingition coil so I installed new accel brute coil, no change.Timing is set at 8 btdc with vacuum unhooked, running platium tip plugs, new wires.Has a little miss while idiling but think it is because it is getting too much gas. Anybody know what else it could be?
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Old 08-25-2009, 07:59 PM   #2 (permalink)
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you have to make damn sure the mettering rods make it into the jets wher ethey are placed back ing the carb.

the only times i have had that issue was when shit gets caught between the needle and seat or when one of the vacume pots fubared and would over fuel the system. i ripped all the smog shit off of it and havent had that issue again.
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Old 08-25-2009, 08:08 PM   #3 (permalink)
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With it idling look down the primary bores-if you see any raw gas dropping down-yer float may have become porous (weighs more with gas in it) and not as bouyant as a new float. If yer using a brass float rather than the stock one-you can ignore this.
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Old 08-25-2009, 08:28 PM   #4 (permalink)
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haven't thought about a brass float but seems a little odd 3 carbs do same thing, but I guess anything is possible since all are around same year models
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Old 08-25-2009, 08:41 PM   #5 (permalink)
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Three carbs doing the same thing? Nope it's something else. A vacuum leak will richen the mixture. How can you be sure the smoke you see isn't from consumption of oil? If the valve guides and valve stem seals are beyond spec you will definately eat oil at idle when the vacuum signal is high. Black smoke=too rich, blue smoke=oil smoke. If it smokes like Hell after sitting all night on start up-I would suspect shot or no oil seals. On Chevys I always use the OEM seal AND a tulip (Ford type seal)-dries them right up. Also would be a goodidea to hang a vacuum guage on that beast and see what you are pulling and if the needle is stabile. I wouldn't stop there-a compression test would be a good idea. All that and how competant was the engine rebuilt?
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Old 08-25-2009, 08:49 PM   #6 (permalink)
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the 3 carbs you tried did you adjust them all yourself? borrow a known good carb and bolt it on with out adjusting it. that will let you know if it is a carb issue. you said you put a new coil on but still running the old hei dizzy? maybe the dizzy is worn?

compression check all the cylinders since you have a slight miss just to be sure?

just throwing out ideas.
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