Idle Adjustment Help
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,414
Likes: 1
From: NC
Idle Adjustment Help
I have a 74 with a stock 350 and a Carter Q-Jet. I am having trouble getting the idle set. I know there are two needle valves and a throttle valve hex screw. I notice that when i close the driver side needle valve the idle becomes very low and almost stalls. When I do the same on the passenger side needle valve I get no noticeable change in rpm’s. Is this an indication of a rebuild needed? If not then how do you set the needle valves and throttle screw?
The engine will not idel a 600 RPM’s let alone in gear (Auto Trans). I have to have it set @ 950 to 1000 RPM’s to sit at a stop sign with a heavy foot on the brakes.
Any Help is Appreciated
Bill
The engine will not idel a 600 RPM’s let alone in gear (Auto Trans). I have to have it set @ 950 to 1000 RPM’s to sit at a stop sign with a heavy foot on the brakes.
Any Help is Appreciated
Bill
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by hayman
I have a 74 with a stock 350 and a Carter Q-Jet. I am having trouble getting the idle set. I know there are two needle valves and a throttle valve hex screw. I notice that when i close the driver side needle valve the idle becomes very low and almost stalls. When I do the same on the passenger side needle valve I get no noticeable change in rpm’s. Is this an indication of a rebuild needed? If not then how do you set the needle valves and throttle screw?
The engine will not idle a 600 RPM’s let alone in gear (Auto Trans). I have to have it set @ 950 to 1000 RPM’s to sit at a stop sign with a heavy foot on the brakes.
Any Help is Appreciated
Bill
The engine will not idle a 600 RPM’s let alone in gear (Auto Trans). I have to have it set @ 950 to 1000 RPM’s to sit at a stop sign with a heavy foot on the brakes.
Any Help is Appreciated
Bill
do you have a vacuum Gauge?
second, you are talking about both the mixture adjustment as well as the idle speed adjustment.
secondly have you set the timing properly?
OK what you are seeing is what is know as the lean roll position. when a vacuum gage is connected you can use this to set the idle mixture based on the leanest point the engine can have before a drop off in manifold pressure occurs.
however this procedure should not be done until you are sure the timing is set, with the right associated idle speed.
Sound like you may be mixing up your procedure.
if you have verified, timing and idle speed, the set the idle mixture using the "lean roll" condition on both mixture screws, and still only see a drop on one side vs the other, then it may be time to investigate a little further.
but before i would say rebuild the carb, i would like to have you tell us a little more about its condition
original? ever been rebuilt at all? aftermarket?
also what sort of vacuum is the engine pulling?
steady needle low?
steady needle normal 12-15 in Hg
fluctuating needle low?
fluctuating needle normal?
steady needle then fluctuating when increased RPM's
you get the idea?
cheers
tim
this it the
Last edited by sweethence; Oct 9, 2006 at 08:20 AM.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
I think his point was that the pass side idle mix screw has no effect when adjusted, which tells me that it is blocked. You can try removing the screw, squirt the hile with carb cleaner and retry to see what happens. You can do this with the carb in place
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Also possible the throttle shaft/bore is toast.... vacuum leak at the shaft.
Standard sign is high idle (won't idle low) and non-effective mixture screw or screws because the throttle disc is too far above the idle ports for the screws to have any effect.
Standard sign is high idle (won't idle low) and non-effective mixture screw or screws because the throttle disc is too far above the idle ports for the screws to have any effect.
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by Tom454
Also possible the throttle shaft/bore is toast.... vacuum leak at the shaft.
Standard sign is high idle (won't idle low) and non-effective mixture screw or screws because the throttle disc is too far above the idle ports for the screws to have any effect.
Standard sign is high idle (won't idle low) and non-effective mixture screw or screws because the throttle disc is too far above the idle ports for the screws to have any effect.
good point
cheers
tim
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Bill -
If the idle mixture screws are not balanced, you can get the car to run with one screw closed and the other out of whack. So just do this:
Run both idle mixture screws in until they lightly seat. Back both out 2 full turns. Start the car and set idle speed to a low, steady idle using the idle speed screw. Once set to a low idle, evenly adjust both mixture screws until best (smoothest) idle is achieved, turning each one 1/2 turn at a time. Use the leanest (furthest in) setting that produces best idle quality. This should be within 1 turn in or out from the 2-turn base setting. Once best idle has been achieved, re-set the idle speed screw to the idle speed of your preference.
If the idle mixture screws are not balanced, you can get the car to run with one screw closed and the other out of whack. So just do this:
Run both idle mixture screws in until they lightly seat. Back both out 2 full turns. Start the car and set idle speed to a low, steady idle using the idle speed screw. Once set to a low idle, evenly adjust both mixture screws until best (smoothest) idle is achieved, turning each one 1/2 turn at a time. Use the leanest (furthest in) setting that produces best idle quality. This should be within 1 turn in or out from the 2-turn base setting. Once best idle has been achieved, re-set the idle speed screw to the idle speed of your preference.
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,414
Likes: 1
From: NC
Well yesterday I bought a rebuild kit for this carb and during disassembly I noticed that most of the screws were un-torqued. Took no effort to unscrew any of the screw. As I reached the innards I discovered rust deposits on couple of spring and this odd looking build up in the bottom of the reservoir area. Very Nasty Looking.
I am surprised it ran at all.
Everything is soaking right now. Any tips or suggestion for the rebuild?
Bill
I am surprised it ran at all.
Everything is soaking right now. Any tips or suggestion for the rebuild?
Bill
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Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by hayman
Well yesterday I bought a rebuild kit for this carb and during disassembly I noticed that most of the screws were un-torqued. Took no effort to unscrew any of the screw. As I reached the innards I discovered rust deposits on couple of spring and this odd looking build up in the bottom of the reservoir area. Very Nasty Looking.
I am surprised it ran at all.
Everything is soaking right now. Any tips or suggestion for the rebuild?
Bill
I am surprised it ran at all.
Everything is soaking right now. Any tips or suggestion for the rebuild?
Bill
take your time, make sure the air horn isnt warped, dont lose the power piston spring
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Originally Posted by hayman
Lars??
Lars is our resident forum qjet & tuning Guru he posted earlier.....
You can rebuilt the Qjet yourself, just make sure everthing is clean and true ( air horn), and inspect and replace wear items ( gaskets, metering rods, float, power psiton spring. also inspect the base plate and butterflies for proper movement and wear/ damage, and the idle mixture screws for damage at the tips, and set the float level according to spec.. this will give you the best possible start point before you get into the tuning phase....
Also search the threads fro lars, you find some good readign there, if he is willing to take you carb and hook it up great, lots of good reviews on his work, but if not then go ahead and giddy up....
nothing like doing it yourself