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Old 07-18-2010, 04:51 PM
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too much fuel + fouled plugs

I have a 750 cfm q-jet on a chevy 350 and when i had it running it was dumping so much fuel in the motor that there was white smoke coming up out of the carb and now i have 2 cylinders not firing because the plugs are fouled. How can i fix this?

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Old 07-18-2010, 05:25 PM
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Could be several things. First of all check the float level and make sure its the correct height and also that your float is still good. Also check the needle and seat and make sure its not sticking and there is no debris keeping it from closing all the way. Also check fuel pressure if you can and make sure its not too much. Normal for a carburetor is 5-7 psi.
Check for any debris in the carb air bleeds but that would not cause flooding though but check to make sure anyways.

If its coming out of the vent on the top of the carb one of the above is most likely the culprit. I have that issue sometime with my holley and just a tap of the screwdriver handle and it makes it unstuck but my carb is only half a year old though. Maybe yours might need rebuilt.
Eric
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Old 07-18-2010, 05:29 PM
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I was also thinking about getting a rebuilt holley or edelbrock instead of messing with the q-jet. Do you think it's worth it?
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Old 07-18-2010, 06:12 PM
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Well I myself am a holley man but if you wanted to swap out to a holley or edelbrock with your current qjet intake then you will have to use an adapter plate to do so.

Qudrajet will give you the best fuel mileage wise. Edelbrock's which I had a couple before are easy to tune and somewhat better then a holley on fuel mileage wise on a mild build.

Holley's have more fine tuning options then what an edelbrock does. I did a holley swap on my brothers 305 chevy and it runs just fine that way but we plan on doing an intake swap sometime soon in order for him to have a regular square bore intake. His fuel mileage really did not change much.

Anyways what is your setup anyways and how old is your carb and what kind of shape is it in? If your carb is still in good overall condition then a rebuild might be all you need. But if its worn out then you could go the route I did and get the holley carb you want and my recommendation is a holley 600 1850 vacuum secondary model.

I have one that I got direct from holley off of ebay for around $200 shipped and am running one on my 350 and my brother is running a rebuilt one on his 305 and they are a easy carb to tune for a mild build.
Eric
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Old 07-18-2010, 06:45 PM
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here's my setup:
Stock 350 block, crank, rods
Flat top pistons
Sealed power rings
Stock iron 350 heads. (They're 1969, thats all i know)
Cam specs: Advertised Duration 262 272
Duration @ .050" 204 214
Valve Lift w/ 1.5 Rocker Arms 0.420 0.442
Valve Lift @ Cam 0.280 0.295
Max Lift Angle 107 117
Lobe Separation 112
Cam Timing @ .050" - Opens -5 ATDC 44 BBDC
Cam Timing @ .050" - Closes 29 ABDC -10 BTDC
Hydraulic lifters
Holley contender intake
q-jet 750cfm carb


The q-jet has definitely seen better days. The choke and the choke plates are gone and someone before me put screws in some of the unused vacuum ports that i can't seem to get out. It seems like too big of a carb for my setup also.
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Old 07-18-2010, 07:08 PM
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Quote:
Originally Posted by bigdog7373
here's my setup:
Stock 350 block, crank, rods
Flat top pistons
Sealed power rings
Stock iron 350 heads. (They're 1969, thats all i know)
Cam specs: Advertised Duration 262 272
Duration @ .050" 204 214
Valve Lift w/ 1.5 Rocker Arms 0.420 0.442
Valve Lift @ Cam 0.280 0.295
Max Lift Angle 107 117
Lobe Separation 112
Cam Timing @ .050" - Opens -5 ATDC 44 BBDC
Cam Timing @ .050" - Closes 29 ABDC -10 BTDC
Hydraulic lifters
Holley contender intake
q-jet 750cfm carb


The q-jet has definitely seen better days. The choke and the choke plates are gone and someone before me put screws in some of the unused vacuum ports that i can't seem to get out. It seems like too big of a carb for my setup also.
Couple of thoughts here. 1969 heads did not have hard seats. If nobody has added hard exhaust seats to them, you could be in trouble after a while if you are using unleaded gas. The valve will eat the seat out of the head.

A Quadrajet is the perfect carburetor for any size motor. The tiny little primary bores will give good throttle response even on a smaller cubic inch motor and the huge vacuum-operated secondaries will feed the motor well at higher rpm's.
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Old 07-18-2010, 08:57 PM
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If I were you, I would look far another Q-jet just like the one you have. The one you have is not too big. The biggest reason would be less of a pain than having to re-configure your accelerator linkage, kick down cable and vacuum hose routing plus, you won't need another intake manifold.
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Old 07-18-2010, 10:15 PM
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well i already have the holley manifold and i havent set up the throttle cables yet so that wouldnt be a problem. btw it has mechanical secodaries. still think i should keep it?
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Old 07-18-2010, 10:29 PM
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A Quad. with maual secondary's
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Old 07-19-2010, 09:57 AM
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aren't they all mechanical secondaries?
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Old 07-22-2010, 03:08 PM
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Yeah, but when they open, the air door controls the air flow and metering rods control the fuel flow on engine demand. It's sort of like vacuum secondary's without a vacuum diaphragm. On older models, the rate at which the secondary's kicked wide open was controlled by spring tension on the air door.

I think I got it right, as I haven't messed with one for a loooooong time!
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