Start with the first. I had a Holley 4160 vacuum secondary carb on my engine. I had the timing set at approximately 13 BTDC at idle. There was always something that seemed wrong with that carb because no matter what I did, it always ran really rich out the exhaust. I've rebuilt the carb, installed all new components, well at least all but the floats, and still really rich. It didn't seem to have all that much power but the engine sounded like it was running right.

I pulled the 4160 after draining the bowls and found the galley area inside the intake manifold extremely wet with gas.. Hopefully I've not washed my cylinders.

I decided to buy a Summit Racing 600cfm vacuum secondary carb. It's a modified version of the Autolite 4100 or Holley 4010. Before I put the carb on I made sure to check that my idle/air screws were 1.5 turns out and that all the screws were tightened. I put the carb on using the included spacer/gasket they provide, tubed it up with 3/8th stainless, and primed the bowls. Double checked the float levels through the sights in the bowls (nice feature).

When I fired it up, it was extremely high rpm so I stopped it immediately and adjusted the throttle idle screw which brought it down, but even almost all the way backed out it was idling too high. I know the choke was on, but this was definitely too high for normal use even with the throttle. The first thing I thought was the timing. I adjusted the timing by ear to where it sounded like a normal idle.

At this point the engine sounded better than it ever did. I checked the exhaust and absolutely no gas smell. I was so happy! I walked back around to the front of the truck and revved the throttle and it instantly backfired through the carb. Freaked me out and actually made my heart sink. I adjusted the dizzy again to where the idle dropped a bit more and I brought it back up again with the throttle idle screw. Revved it again and POP through the carb again also.

I decided to call it a day since it was raining and getting dark and cold. I'll hit it up again in the morning. I did not hook up the timing light or vacuum gauge yet, but will tomorrow as long as the weather cooperates.

Questions:

1. Could I have had it 180 degrees out and somehow mysteriously the thing ran since it was uber rich?
2. Could an overly rich condition (once you get rid of that overly rich condition) cause you to retard or advance the timing to the extreme somehow?
3. Could I be smoking crack to even ask these questions???

Please help!

 

The reason for your high idle isn't the timing it is the carb adjustment. Most carbs have two idle adjustments, curb idle and fast idle. Without your truck on unscrew the curb idle screw (the one you have been adjusting) out until you feel no tension then screw it back in about 5 full turns, this should give you a base line. Next, still with the engine off open the throttle all of the way. There should be a small screw that stops the throttle from closing. Unscrew this screw a couple of turns. When you adjusted your timing you retarded it so much it is causing it to back fire through the intake which could blow the power valve if you are not carefull. Put the timing back where it was and crank it up. If it still idles higher than you would like, try bringing it back down with the curb idle screw, if it doesnt change shut it off and back the tiny screw out a couple more turns.

 

The choke being on has a lot to do with the idle, you can't adjust it unless the choke is straight up, totally open.

I don't think you can adjust the idle speed screw a certain amount of turns and be close. Each engine is different. 1.5 turns I guess is ok for the idle mixture, but people are starting to think that is written in stone and to never touch them again, and that's not true. 1.5 turns MAY be ok, but probably not and after the engine is warmed up and the choke is fully off, you always need to tweak the idle mixture screws.

You spitting back through the carb is normal if the engine hasn't warmed up, or you have blocked the heat passage underneath the carb. It's the engine leaning out when you blip the throttle. They all do it when they are cold. If you feel the engine was properly warmed up and it still does it, then you may need to adjust the accelerator pump if it's adjustable on that carb. But if someone blocked the heat passage under the carb you probably will never get rid of the pop-back when it's cold outside.

 

Heat passage under the carb? I'm not sure I'm following you.. Engine was fully warmed up and choke was fully open. I don't think the accelerator pump would have anything to do with an extremely high idle which makes me think there is something more than just the blipping of the throttle making it backfire through the carb.

As far as the idle/air screws, I was just trying to set a starting point. I would then adjust to get the maximum vacuum from there. It's just the idle was so high... probably around 3k...

 

Not sure where that small screw is that you are referencing once the throttle is open all the way. The curb idle is what I was adjusting... I'll have to check the manual to see where it is, because it's not obvious..

 

Yeah, an exhaust crossover that directs exhaust gasses across the manifold below the carb to help it heat up faster.

 

I should have probably specified that I have an Edlebrock Performer RPM intake. There's no connection from the exhaust.

 

I'll put the dizzy back and try to adjust the fast Idle, but isn't that pretty much just for the choke?

 

I just looked up that manifold, you are correct, no heat passage. Good luck getting that engine to run well in cold weather. It's aluminum, so it may eventually heat up enough to run without spitting back up through the carb. With a open chrome aircleaner I think it's hopeless.

 

I understand now. I'm fine with that. I guess I should have let it really heat up good first before blipping the throttle. I let it idle long enough for the choke to open fully, but I probably didn't let the engine fully warm up. With the high idle initially, I thought there was something else going on.

I'm going to check my timing and vacuum today and see exactly what is going on.

 

I just set my timing back to 10 BTDC and I've backed out the curb idle screw to where it didn't affect the throttle. It looks like it is the fast idle screw. I still need to adjust it down but I can't seem to find my 1/4" wrench. Gotta love it.

Apparently I moved the dizzy so much that the timing was thrown way out and that was causing the backfire.

Now to find that 1/4" wrench!

 

Good to go!!

Amazing how such a little change of the fast idle screw makes all the difference. She is purring like a kitten and the throttle response is unreal compared to what it was before. I am so glad I bought this carb.

Here's the new carb installed. The wiring looks horrible, but just ignore that for now. It's all being redone when I pull the engine.

Notice the 3/8th stainless steel line for fuel. I got all my fittings and tube from ebay. They are Tylok 316 stainless. I added a 3/8th to 3/8th coupler on the up-tube from the fuel pump to make it easy to remove the fuel line later if I ever need to.

 

Looks good. Just allow for it to be a little temperamental in cold weather. A little bit of hesitation sometimes and hopefully you won't have any carb icing. If you have carb icing you will notice it running rich, and wanting to stall, even though the choke is opening up. You might even experience the throttle sticking when running down the highway on a cold damp morning. My old mustang does this.