running lean, what do I do?
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
running lean, what do I do?
I have a 74 L-48, and the car is running a bit lean, how far is a reasonable ammount to adjust the needle vlaves? 1/2/ turn? 1/4 turn?
(and I un-screw them to make it run richer, correct?)
Miles
(and I un-screw them to make it run richer, correct?)
Miles
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
What leads you to beleive it's running lean? Popping exhaust on decel? Plugs looking overheated?
If the idle mixture is not adjusted correctly it'll idle like crap- rough. Backing the screws out may not fix it. Get a vacuum gauge and hook it to a full time vacuum port, then adjust for the highest vacuum, the set the idle speed to the correct spot (650 in Drive. maybe?)
If the idle mixture is not adjusted correctly it'll idle like crap- rough. Backing the screws out may not fix it. Get a vacuum gauge and hook it to a full time vacuum port, then adjust for the highest vacuum, the set the idle speed to the correct spot (650 in Drive. maybe?)
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
Ive got the stock Q-jet, and this summer I pulled it off, pulled it appart, and did the routine up-keep on it, (cleaning, float, ect ect) when we installed it, it started running about 20* hotter than its EVER ran, 2 summers ago I would run the AC on high on a 95*+ day and the car would never go above 190*
every one that Ive spoke to has said it could be running lean and that would make it run a bit hotter
I also replaced the thermostat, so I know its not that, and the radiator is full
Thanks!
Miles
every one that Ive spoke to has said it could be running lean and that would make it run a bit hotter
I also replaced the thermostat, so I know its not that, and the radiator is full
Thanks!
Miles
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
What leads you to beleive it's running lean? Popping exhaust on decel? Plugs looking overheated?
If the idle mixture is not adjusted correctly it'll idle like crap- rough. Backing the screws out may not fix it. Get a vacuum gauge and hook it to a full time vacuum port, then adjust for the highest vacuum, the set the idle speed to the correct spot (650 in Drive. maybe?)
If the idle mixture is not adjusted correctly it'll idle like crap- rough. Backing the screws out may not fix it. Get a vacuum gauge and hook it to a full time vacuum port, then adjust for the highest vacuum, the set the idle speed to the correct spot (650 in Drive. maybe?)
Miles
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
follow Tim's advice of using a vacuum gauge to correctly set your idle mixture - adjust idle mixture screws to achieve highest steady vacuum level.
unless you broke something inside the carb while working on it you wouldn't have changed the A/F mixture which is controlled by the jets and rods but you may have inadvently moved the idle mixture adjustment.
Also, when you reinstalled the carb you may have changed the connection for your vacuum advance. If it wasn't running hot before but it is now check to make sure the vacuum advance line is connected to full manifold vacuum, not ported vacuum.
If you followed the service guide when reinstalling the carb it would have directed you to connect the vac adv hose to a ported vacuum source
unless you broke something inside the carb while working on it you wouldn't have changed the A/F mixture which is controlled by the jets and rods but you may have inadvently moved the idle mixture adjustment.
Also, when you reinstalled the carb you may have changed the connection for your vacuum advance. If it wasn't running hot before but it is now check to make sure the vacuum advance line is connected to full manifold vacuum, not ported vacuum.
If you followed the service guide when reinstalling the carb it would have directed you to connect the vac adv hose to a ported vacuum source
Thread Starter
Safety Car
Joined: Nov 2006
Posts: 4,449
Likes: 0
well...a few weeks ago paul67 and I were trying to get my carb/dist/ect vacuum hoses hooked up correct, to which we got a few figured out, but not all of them, so heres a couple pics of what Ive got
(the one Im holding in the top pic goes to the dist)
when dad gets back, Im going to ask if hes got a vacuum gauge, if not Ill buy one, but where is the best location to hook it up to?
Miles
(the one Im holding in the top pic goes to the dist)
when dad gets back, Im going to ask if hes got a vacuum gauge, if not Ill buy one, but where is the best location to hook it up to?
Miles
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Le Mans Master
Joined: Dec 2007
Posts: 6,422
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From: McHenry Illinois
Miles, one of the things you can do is pull your spark plugs and post pics of the tips and get opinions on whether you are running lean or not. Keep track of which cylinder they came out of. Your heating problem may or may not be related.
Last edited by '75; Aug 31, 2008 at 10:08 PM.
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
I run my vacuum guage off the hose that comes from the intake fitting on the pasenger side rear. That is the fitting for the vacuum accessories. In your picture, it is the fitting on the manifold between the carb and dizz.