Ad Radar
Item Posts    Sort Order

1973 Impala Vacuum Reading and RPM Settings

 
bigcoaxum
V-6 Camaros rule!
Posts: 28
Joined: 12/08
Posted: 08/07/12 05:37 AM

I have a 73 impala with a stock 350 engine with an edelbrock performer series intake and 600 cfm carburetor.  My carb is out of tune and i would like to tune it exactly where it needs to be.  I know alot of people tune them by ear but i prefer not to.  I have purchased a vacuum pressure guage and a dwell tachometer to set the carb.  For the vacuum guage, what should the vacuum reading be on a 1973 impala? Also, at what rpm should it run?  I need to know this information in order to set my carb exactly where it should be to get the best possible throttle response.  Does anyone have any videos that could help me with this process.  this is my  first time setting a carburetor.  i know about the 2 idle mixture screws and what they do, i just need a little help with the whole process.  I have a haynes manual for a 69-90 impala but I think that is a wide range.   Confused  

Post Reply
zman123
Everything in my driveway’s a Chevy
Posts: 537
Joined: 06/08
Posted: 08/07/12 08:46 AM

You need to adjust the idle mixture screws to get the maximum vaccuum on each side. Just turn each screw in until the vaccuum drops, then turn them back out 1/8 th turn at a time until you stop getting a gain in vaccuum.  

Post Reply
bigcoaxum
V-6 Camaros rule!
Posts: 28
Joined: 12/08
Posted: 08/07/12 09:11 AM

Ok thanks. I will try this and see what happens.  What about the RPM? At what RPM should my engine run?  

Post Reply
idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 08/07/12 05:01 PM

If you have an Edelbrock 600 CFM carb, look up the manual on their website and follow the instructions. Its easy enough, seriously. Setting the part-throttle mixture is part of the tuning process that involves the idle circuit AND the primary circuit. But those are tuned seperately on any carb.

Most cars with stock or mildly modified carbureted V8s like to idle at 600 RPM in gear, give or take 50-100 RPM. That means usually around 800 in neutral.

The vacuum gauge reading is normally between 16 and 22, but thats a very wide and general range and the number is much lower for high-RPM engines. Here again, your vacuum gauge should have good instructions about this, read them. The thing to look for on that gauge is steadiness. A needle that stays on one number at idle with no shaking is an indicator of a healthy engine.

To set the idle mixture, the special tool needed is a CO monitor, or an oxygen sensor, with a readout that tells how rich/lean the mixture is. But nobody really has those much. So do play with your carb, but study first and read the manufacturer's instructions if possible. So you know what you're doing when you do it.

The reason you want the engine speed below about 800 and the vacuum advance disconnected and plugged while you set initial timing and idle settings is so the distributor won't advance the timing or cause a vacuum leak and mess up your readings. An adjustable timing light is the best tool you could have, and its always a good idea to check your timing marks against a "top dead center finding tool" to make sure nothing is out of whack with the numbers.  
idrivejunk

Post Reply
skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 08/07/12 06:31 PM

Hi Junkman,
 As you stated 800 rpm is a good idle for a  SBC.
 My ZZ4 is easy on the Auto box when cold with that setting.
 All the best from Skyeking in that place down under....  
skyeking

Post Reply
76Skylark
Big Block power for the win
Posts: 868
Joined: 12/11
Posted: 08/09/12 01:34 PM

everyone that answered is right but If I may,If you can put on the E-brake and/or if you have some Help........ set it in Gear and the Max rpm should be from a low 700 to650 even to a high 700's  what your looking for is just under it wanting to Drag you through a red light,that can equel 8-850 or some in netural.got it? then hunt for highest vacuum/idle quality and re set idle speed when done,make sure vacuum advance works but is undone and plugged on carb side when setting.I think 12 deg. is the most for a stock cam SB And 14-18 in.vac is about right but could be a little higher but not lower,that is what you get with Cams and then it ALL starts to change.Old chevy 265's(60's)only used between 5-8 deg. advance,so things change!  

Post Reply
bigcoaxum
V-6 Camaros rule!
Posts: 28
Joined: 12/08
Posted: 08/10/12 08:59 AM

thanks guys, my vacuum reads 19-20, barely moving between the two and my rpm is hovering around 825-850. I have a timing light but I have not experience at all in setting the timing for a small block 350.  where should the timing be and how do i check it.  My cars runs better now but i want to make sure everything is perfect.  Photos and videos would be very helpful.

thanks  

Post Reply
redneckjoe69
I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 08/10/12 09:46 AM

http://www.youtube.com/watch?v=UYGU7mTwsZc  

Post Reply
bigcoaxum
V-6 Camaros rule!
Posts: 28
Joined: 12/08
Posted: 08/11/12 01:48 PM

Thanks guys for all of your help!!!!!!!!!  

Post Reply
TO TOP