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Hello everybody first time here but I need help. I have a 71 olds 350 with a mild cam, headers, aluminum intake, and holly 650 carb. The vehicle runs great and starts right up. The problem is as I drive the farther I drive and longer I drive I loose a lot of rpm at idle. It starts out on the choke at around 900 rpm. It drops to about 700 to 750 when it warms up. If I keep driving and stop it will be all the way down to around 600 and barley running. When I give it gas it will go very well. Any suggestions would be greatly appreciated. Auto trans by the way.
You need to set the fast idle and curb idle speed screws independently. You also need to verify that the choke opens at the right time. I'm not a Holley expert but every carb has separate adjusting screws for fast idle and curb idle.
As said, check the curb idle when fully warm, bump it up 50 to 100 RPM. Also what is your base timing set at? Ported or manifold vacuum advance? Points ignition?
As said, check the curb idle when fully warm, bump it up 50 to 100 RPM. Also what is your base timing set at? Ported or manifold vacuum advance? Points ignition?
base trmming is about 10 to 12 BTDC.i set everything with a vacuum gauge. Manifold vacuum advance and points. It runs real strong on top end. The idle circut seems to be my only problem. Thanks for your help.
Timing sounds right. What cam is it and how much vacuum on the gauge? Can you exchange the idle air bleeds? Have you adjusted the mixture screws? Adjust the mixture screws for the highest idle and set the curb idle screw up and down as necessary. I personally like about 900 to 1000 RPM in park and it usually ends up about 750 or 800 RPM in drive.
Timing sounds right. What cam is it and how much vacuum on the gauge? Can you exchange the idle air bleeds? Have you adjusted the mixture screws? Adjust the mixture screws for the highest idle and set the curb idle screw up and down as necessary. I personally like about 900 to 1000 RPM in park and it usually ends up about 750 or 800 RPM in drive.
I am not sure about the cam specs. I am running about 18 to 20 on vacuum. I set the mixture screws with a vacuum gauge to the highest vacuum. I think the idle is set right. The thing I notice is when I run the motor in my garage it seems to be running rich because it burns your eyes and smells very strong. If I try to screw the mixture screws in to lean it out a bit it starts running rough. Thanks again for the reply and the help. I might could lean out with the mixture screws and try to advance trmming a little to smooth out the engine.
The rich idle may be necessary to cover a small air leak at one port. Adust the idle leaner for a test and use WD or propane to investigate--see if it smooths out.
Don't forget to test on the valley side of the manifold with propane.
Timing sounds right. What cam is it and how much vacuum on the gauge? Can you exchange the idle air bleeds? Have you adjusted the mixture screws? Adjust the mixture screws for the highest idle and set the curb idle screw up and down as necessary. I personally like about 900 to 1000 RPM in park and it usually ends up about 750 or 800 RPM in drive.
Originally Posted by oldcutlass
We still don't know what distributor he's running?
I am sorry I am running stock gm distributor that came on the engine. I am kinda old school. This motor is in a 1951 Chevy truck.
No problem. I'm assuming your dwell was set to 30? Did you connect your vacuum advance to manifold vacuum? Also be careful on advancing your timing too far as your total advance with vacuum will cause pinging under light acceleration.
No problem. I'm assuming your dwell was set to 30? Did you connect your vacuum advance to manifold vacuum? Also be careful on advancing your timing too far as your total advance with vacuum will cause pinging under light acceleration.
I might have found part of the problem. I put the vacuum advance on the Holley carb where it said it went but at idle there is no vacuum on that port. I am getting a fitting for the intake so it will be fulltime vacuum.
I'm confused. The OP's car starts out with a high idle. As the engine warms up, idle speed drops. How does the distributor have anything to do with that?
Joe, as said, just making sure the timing an dwell were in spec before addressing the carb. That cam is probably the 204/214 "Performer" cam, mine had similar vacuum readings. That cam with 8 to 1 compression will like a couple more degrees of timing. Set the mixture screws to the highest vacuum/RPM and bump your curb idle up a good 50 RPM and see if the problem still occurs.
Joe, as said, just making sure the timing an dwell were in spec before addressing the carb. That cam is probably the 204/214 "Performer" cam, mine had similar vacuum readings. That cam with 8 to 1 compression will like a couple more degrees of timing. Set the mixture screws to the highest vacuum/RPM and bump your curb idle up a good 50 RPM and see if the problem still occurs.
thanks guys for all the help. I am going to start fresh this morning an check everything starting with dwell and trimming. I will then adjust air mixture screws using my vacuum gauge. I will let you know how that goes.
thanks guys for all the help. I am going to start fresh this morning an check everything starting with dwell and trimming. I will then adjust air mixture screws using my vacuum gauge. I will let you know how that goes.
problem solved. Don' know exactly why but moved the vacuum advance to manifold,bumped the trmming up 2 degrees, checked dwell, and then adjusted mixture screws with vacuum gauge. Runs great and idle stays at about 750 at idle. I want to thank all who helped. This is a great forum. I really appreciate it guys.
February 15th, 2018, 01:12 PM
