Carb Question

[64drtGt]

I am asking this mostly because I want to learn and progress my ability to properly tune and set up my engines.

On my magnum 318 has a pro comp dual plain air gap intake, flowtech headers, and a 4160 vaccum seccondary 600 CFM holley.

It has always been a little slugish from idle if I just blipped the throttle or romped on it a little. I added more timing and it got a little better but has always had that slight delay. I could bring the rpm some then it would rev fine. The other day it acted weird and we re adjusted the carb some it runs great now will rev great from idle and all but if it sits at an idle for any thing of time 30-45 seconds minimum it starts to fuel smoke and is running very rich. takes gas great but smokes. When its not smoking and running rich at idle its sluggish.

 

[fishy68]

Sounds like the pump shot may me a little less than it should be and when you adjusted the idle mixture screws you have the idle adjusted a little too rich which is compensating for the lack of pump shot but causing another issue. What size pump squirter does it have on it and what color pump cam? Adjust the idle mixture screws in a little at a time until you get the best idle. For the sake of not fouling plugs and using more fuel than necessary I always run the idle mixture as lean as possible and the engine still run right.

If that carb has adjustable floats (if it has a brass screw head plug on each passenger side fuel bowl it's adjustable, no brass plug=non adjustable) check the fuel level before you adjust anything. Fuel level can affect the fuel mixture throughout the entire throttle range.

 

[OldmanRick]

Sounds like the pump shot may me a little less than it should be and when you adjusted the idle mixture screws you have the idle adjusted a little too rich which is compensating for the lack of pump shot but causing another issue.

If the float adjustment is good, meaning just a trickle out of the site holes, I agree with what fishy said above. I'm not a "vacuum reading" A/F adjustment guy when it comes to Holley's. You run in the screws slowly until it just stumble's, then back them out a 1/8th turn. Do it several times back & forth to get you equaled out...and your done.

If you still have a stumbling issue after that, it could very well be your pump shot or it's adjustment? Many 600's over the years come with a #25 nozzle. It may or may not be quite enough for that intake if that's what it has? If so, a #28 may be the remedy? I personally do everything I can first to make it work before playing with accelerator pump cams, especially on a mild engine like you have.

 

[64drtGt]

This carb doesnt have sight holes for the float check also doesnt have adjustable floats its basic 4160 carb. I'm not sure what squirter it has in it. I asked more just because I wanted to learn about them I am planning on a carb swap here in the very near future anyway so this carb doesnt really mean much to me other than a learning experience. I may tune it in just to learn what i am doing and change it anyway. I want small 600-650 mechanical secondary carb.