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Old 02-04-2011, 03:57 PM
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305 Quadrajet Rough Idle

Hey guys I am having trouble with my car idling rough. It is a 305 with a very mild 274H06 Cam in it. I have to have it idle at around 1000 rpm and when I put it in gear it slams down to about 600 and the car will literally shudder and shake. I have adjusted timing and idle fuel mix to no avail. You guys have any idea on how to smooth this thing out?

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Old 02-04-2011, 03:58 PM
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Check around the base for a vaccum leak. JMO


Cole
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Old 02-04-2011, 03:59 PM
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I couldn't find an exhaust leak anywhere I even plugged all the ports up.
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Old 02-04-2011, 04:06 PM
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Take some carb cleaner and spray around the base of the carb and anywhere around it that it could have a vacuum leak, And see if the idle changes when spraying these places. if it changes you have found a problem spot.JMO
It should smooth out if you hit a leak with the spray.

Cole
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Old 02-04-2011, 05:14 PM
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Yep I tried that and squirted everywhere its a no go no change at all.
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Old 02-04-2011, 06:09 PM
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If you are not real good with a q-jet you probably need to find someone that is IMHO especially if you been tweaking on it. They are great carbs when they are good but if they need work you need to know what you are doing when it comes to a q-jet carb. JMO

Cole
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Old 02-04-2011, 06:38 PM
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Quote:
Originally Posted by jmabrao
Hey guys I am having trouble with my car idling rough. It is a 305 with a very mild 274H06 Cam in it. I have to have it idle at around 1000 rpm and when I put it in gear it slams down to about 600 and the car will literally shudder and shake. I have adjusted timing and idle fuel mix to no avail. You guys have any idea on how to smooth this thing out?
It will take a looser torque converter. That may be a mild cam in a 350 but in a 305, it isn't.
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Old 02-04-2011, 06:39 PM
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Quote:
Originally Posted by cobalt327
It will take a looser torque converter. That may be a mild cam in a 350 but in a 305, it isn't.
Good call Cobalt. I didn't think about that.

Cole
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Old 02-04-2011, 06:52 PM
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The Q-jet IS a good carb, and Cole has it right- first the basics, THEN go looking deeper. More times than I care to recount, a busted vacuum hose has been the main problem.

But you won't be able to just bolt ANY carb up to a modded engine w/the stock settings and expect it to be perfect. Maybe one out of 20 times the carb will need nothing. The other 19 times, the carb will need opened up at least once- and possibly a dozen times- before it is dialed in 'perfectly'.

Besides the TC stall speed, some carb-related things that may need attention (by no means is this all-inclusive):

Rejetted
softer power piston spring
Different secondary rods and air valve spring setting
Enlarged idle port orifices


Good luck in any event.
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Old 02-04-2011, 07:57 PM
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here is a great place if you need Q-Jet parts or tech info....he wrote the book on them!
http://www.cliffshighperformance.com/parts.html
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Old 02-04-2011, 08:00 PM
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Did this just start doing it all of a sudden? Has it ran good in the past or have you just put it together?
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Old 02-04-2011, 08:09 PM
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It's been like this ever since I had it. it did the same thing wth the edelbrock Carb I had on it beforehand

Last edited by jmabrao; 02-04-2011 at 08:17 PM.
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Old 02-04-2011, 09:44 PM
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Quote:
Originally Posted by jmabrao
It's been like this ever since I had it. it did the same thing wth the edelbrock Carb I had on it beforehand
I don't doubt it. The carb is not the root issue here- it's the torque converter.
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Old 02-04-2011, 09:55 PM
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Quote:
Originally Posted by jmabrao
Hey guys I am having trouble with my car idling rough. It is a 305 with a very mild 274H06 Cam in it. I have to have it idle at around 1000 rpm and when I put it in gear it slams down to about 600 and the car will literally shudder and shake. I have adjusted timing and idle fuel mix to no avail. You guys have any idea on how to smooth this thing out?
Shutter and shake, sounds like converter to me
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Old 02-04-2011, 10:00 PM
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You can try to crutch it up by using more timing. I would hook the vacuum advance up to manifold vacuum to begin with.

Dial in around 18 degrees or so of initial, be sure the total stays below 36 degrees or so. You may need to modify the distributor to make this happen.

Lower the idle speed back down after using manifold vacuum, also readjust the idle mixture screws to give the highest vacuum/idle speed. This will help the idle to stabilize some.
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