Lean Idle

[HarleyJack17]

Holley 750 Vacuum Second. List 80508S. I converted it from a meter plate to screw in jets. Stock 72 in front, rear is 77.
445 Stroker, RPM intake, custom Lykins Roller Cam and BBM heads.

I have not ran the truck down the road at speed but I have ran it a lot moving it, letting it run etc. It runs fine as far the how.....however, the emissions are obnoxious! Very very strong which indicates to me it is lean at idle. Again, runs fine, wraps up fine(no load), in temp range, no issues but terrible eye burning smell.
Adjusted with in specs etc.....think I am at 1.75 turns out maybe 2. Secondaries are closed as they should be.

Question: Is there any reason it would be running so lean? Without checking with 02 it is a guess but when I say she will burn your eyes, I mean it. Seems I remember something about these not being the best out of the box and needed some help. Anyway, just want to ask in case others have ran into similar.

[GerryP]

Don't go by turns of the idle mixture screw.  Turn it to where the engine is running properly.  There's nothing really wrong with the idle circuit or the idle, intermediate, or main fuel circuits.  It's not custom built for your engine so you have to tune it to what your engine wants.  This is a case where an A-F meter would do some good.  Not so that you can tune to the meter, but so the meter can tell you what your engine likes.

[cjshaker]

Never heard of anyone using an A-F meter for adjusting idle. Adjust it in to where the engine wants to idle down, then back out about a 1/4 turn. Repeat on other side, go back and forth a couple of times to make sure they're even and both working properly, and it should be good. Add a 1/4 turn if you feel the need, but adding any more fuel will only make it richer than it needs to be.

I agree that eye burning mixture indicates lean, but if the engine seems happy with it, I don't see the issue. I've never ran BBM heads, but maybe the modern chamber design lets the engine get away with less fuel at idle? But again, I don't see the issue if the engine is happy with it.

[e philpott]

I've never installed a AFR gauge just for idle but once installed you check everything and every mode, super rich or super lean will burn eyes from the unburned fuel going out the exhaust , seems like Drew just posted on FB about a carb he received that didn't have the secondary idle feed holes cut in the gasket causing a real lean condition at idle so you might just need to take apart and give the carb a good look over

[My427stang]

Make sure initial timing is right, then make sure you aren't in the transition slots on the primary.  Sometimes you have to open the secondaries a little to get out of the transition circuit on the primaries.  I rarely see my a/f adjustment as far out as yours though, I usually start at 1 1/8 turns out on 2 circuit, and 3/4 on 4 corner idle, but I'd look close at primary throttle plate location

I'd also look close that you have the right metering block and gasket combo, should be easy to see the idle and transition passages

Last, it's very common for the corners to curl on the body where the float bowl screws bolt on. if they had been zonked down a few time, you may have to machine the surfaces to stop cross channeling.

My gut says if secondaries are closed, your primaries are bit too far open, but remember, exhaust can hold some stink for a while, so get it out on the road and put some heat in the mufflers

[1964Fastback]

When adjusting idle, I try to have a vacuum gauge and tach hooked up, and adjust the mixture screws to try to get the highest of both.  If I'm unsure whether it's currently lean or rich, especially if the screws are not doing much, I'll lightly cup my hands over the air horn or pull a vacuum cap to introduce a leak and see what the vacuum gauge and tach tell me for the direction.

Timing plays a big part, too, especially with a large cam, with more timing making it idle better.  Try to nail down the timing first, then lock it down and don't change it any more while adjusting the idle.  Changing the timing will affect the idle but not vice versa.

Keeping a notebook of what you do, at least with my tri-power (six screws), helps me.  When I got the idle close, I shut down the engine, let it cool down so I didn't get burned and could work comfortably, then carefully screwed in each screw one at a time until it seated while counting the turns, then backed it out to the original position and wrote it down.  If there was a significant difference between the screw turns on a given carb, I'd turn one screw in and the other out, to get them close.  This is probably overkill when working on one carb and two mixture screws. 

Pat

[HarleyJack17]

Sorry for the late response. When I stated secondaries were closed, I meant they are in spec on adjustment, just to clarify. The truck idles fine, is fine. Timing is good. All settings dialed right in, were normal, and responsive. Steady 800 RPM, 750 RPM or so in gear. No indications of anything amiss.

I only mentioned the AF meter as a possible way to verify the data vs. smell. The truck has only been idled around the driveway/in and out of the garage.  I am only bringing this up because it is odd to me. One would think if it is acting right then ignore it, but man....it smells. Water temp solid, oil pressure solid, purrs, cranks, throttle response(unloaded) is great.....just a stinker.  Very well could be that all is fine and it is a by product of not being ran. I will take the stuff into consideration. Just making sure there may not be a smoking gun before I take it out on the first shake down run.

[My427stang]

Well, the secondaries don't have to be in a single place to be right (or wrong).

All it takes is a little airflow in the primaries to pull transition fuel.  Opening the secondaries lets you close the primaries.

However, I rarely see carb a/f adjustment out as far as you have it, that makes it richer, depending on float level could pull fuel easier, but I agree, get a run on it.  It's good for it anyway and you can make sure there isn't just stink from the exhaust