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Old 07-01-2003, 08:55 AM   #1 (permalink)
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trucks misses at low RPM's - Chevy 350

I just put on new plugs,wires and also a rebuilt Q-jet. My truck ran great for a short time, but seems to be missing at low RPM's.

I pulled the plugs and they were pretty black, I cleaned them and it did not really help.

I figure it may be the Q-jet needs some adjusting?????possibly running to rich?

I am no mechaninc, any ideas would be great,

I have been building the truck for about 5 months now, I just got it 'driveable' , this is a trail only truck.
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Old 07-01-2003, 11:52 AM   #2 (permalink)
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Could be the carb, black plugs is a sign of a rich mixture but should still fire unless they're wet and your fouling them. You're plugs should be a light tannish grey color. Could be ignition too, do you have points or electronic?
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Old 07-01-2003, 12:28 PM   #3 (permalink)
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There is nothing electronic on the truck. I never did put on a new dist cap or button, maybe I can install those and it may help.


The carb has two adjustmnets, one is the idle, and I assume teh other is the adjument for fuel mixture??? Maybe I can fiddle with the carb adjustments some

I know I sound liek a idiot, but Engine mechanics is not my strong point.
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Old 07-01-2003, 01:28 PM   #4 (permalink)
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The older Q-jets have three adjustments, four if you count the fast idle.
The idle speed is adjusted on the drivers side of the carb on the main body. This is the one that cracks the primaries open when you screw it in.
The idle mixture screws are in the baseplate. Sounds like you found one. Should be one on the other side of the carb too. Ones at the 1:00 and the other is at the 11:00 position. 12:00 being the front. 1 1/2 to 2 turns out is a good starting point. Going in richens the mix and out leans it. These are for idle mixture only. Once your above idle these aren't doing anything for you. They will affect your off idle acceleration though.
The newer carbs have a fifth adjustment for part throttle and above. There is a spring in there to lean the mixture during cruise. If you have one of these you need to buy a book.
Try this and your new ignition parts and let us know.
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Old 07-01-2003, 03:12 PM   #5 (permalink)
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try replacing ther cap and rotor and then check the dwell.(and timing)

always electronics first. it's the easiest and cheapest and most likley to go out.

how many miles are on this motor? are the valve stem seals any good? does it use oil? does it smoke?

how old is the Q jet? does it have the brass float or the foam one?
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Old 07-01-2003, 04:40 PM   #6 (permalink)
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I will try the mixture adjust....you mentioned this will help at idle and coming off idle....coming of idle is where I am getting my hesitation.

the q-jet is a few months old, and the truck has had maybe 10 gallons run through it. I do not know about the miles on motor, it is a cate engine that is several years old, but the truck does have some slight smoke when it is 'reeved' up, but I just assume that is becuase of the fuel running to rich., no leaks

I am not sure about the brass or foam floats? how do I check?
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Old 07-01-2003, 10:06 PM   #7 (permalink)
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When you rebuilt the carb, was the float that you installed Black, or copper in coloring? black = foam, copper = copper(obviously). Try checking the spark plug wires and make sure they arent laying up against the exhaust manifold, and if they are, try to position them so that they wont get hot. I had this problem quite recently, and actually, i ran it till the gas tank was empty, before that it was skipping at low RPMs and smoking black (indicates rich mixture). After i ran out of gas, it didnt smoke black. HAHA, but it did still miss. Also, try replacing the spark plugs, make sure that you find out the proper gapping for the plugs. The store should know. But i hope this helps. Lemme know. Thanks
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