Am I running lean?

[advinnie]

Just some advance needed.
I have a 1600 draw through turbo bug and have been doing some A/F ratio work and I’m a little concerned I’m running lean. Any way at idle I’m getting a reading of 21:1 but as soon as I start driving that drops to to 13.5:1.
Cruising I’m getting 13.9:1 but in all over driving conditions I’m between 13.1 to 13.7:1 at all rpm’s and engine load conditions up to 5psi of boost. Now I’ve tried lager idles and although that drop the A/F ratio in the lower rpms to 12.8:1 she run rough with black smoke coming out the exhaust and when I tried bigger mains she would accelerate great in the lower rpm’s then loose power in the upoer. Now someone on here once gave me some advice on chancing the emulsion tubes but I have forgot what they said.
Thanks for your help

[buguy]

I can't help with what to do with it, but yes your lean. I'd try to keep it 16:1 Max at idle. And I would shoot for 12:1 under boost. At cruise your not crazy lean but your on the edge. At 5 psi it's probably not quite as critical, but still not good practice. When you start boosting more, your going to want to drop it down to 11.5:1 or maybe even a bit lower to be safe.
Are you sure your getting accurate readings? Any reason to believe they might not be?

[advinnie]

I’m getting another sensor today cause I to can not believe how lean it’s saying at idle and even with a pair of 70 idles with the mixture screws all the way out it’s still only reading 19.8:1. I’m wanting to set back to 10 psi of boost but until I get this mixture right I’m staying with the 5 max, I’ve all ready destroyed one piston and ring due to a lean condition I don’t want to do it again

[madmike]

Adam, if you quit making new 'Post' instead of keeping all your questions in one post we can help you better
Yes sounds like the sensor took a $hit did you try a mix up the jets? you know you can ,cuz the air&Fuel all go to the same place

[buguy]

I don't know. I think the sensors work or they dont. Could it be the placement?

[advinnie]

Sorry I will from now on keep all my questions under my largest post
Yes tried mixing up the jets but was getting the same readings

[buguy]

I'd also check the placement. Seems like you might be getting free air and its jacking up your readings. But I guess getting a sensor isn't the worst thing you can do.

[Chip Birks]

Let it idle where its happy, and not getting hot while doing it, leaner won't load up or foul plugs.

Under boost with a draw through carb and distributor I'd say 12:1 or lower. I cruise mine as lean as it'll go without cutting out, between 16:1 and 18:1. I run lots of ignition advance and watch head temps. But it doesn't seem to mind sipping fuel when I'm not spanking it.

[buguy]

I would just be a little concerned about the jump from lean at idle to the transition when you mash it. Once you get it close you will be able to tell where its happy. The joys of a carb is taking it apart a million times to fine tune it!
I've spent A LOT of time with mine trying to get the idle AFR where I want it but I should have just let it go where it wants and focused on the rest of the tune. I have the opposite problem. I can't get mine lean enough at idle. Not without filling and re-drilling passages anyway

[advinnie]

This is the reason I’m not trusting the readings I’m getting, it’s saying I’m very lean at idle so upped the idle jets to the 70’s unscrewed the mixtures all the way after a few minutes at idle she starts to cough black smoke out the exhaust and starts to run lumpy and at this point if i blip the throttle loads of black smoke leaves the exhaust and I have to hold the rpm at 2000 rpm to clear the engine out.
Now the way I was setting the idle mixture screws was to lean them out to gain the highest rpm possible then a quarter turn more rich so the rpm drops just a little (30 rpm) the engine is very happy with this setting but I was getting a A/F reading of 20 ish to 1
Anyway the new sensor didn’t turn up today so can’t play with it hopefully it will be here tomorrow. I believe it must be the sensor cause with the laptop plugged in the A/F gauge on the screen keeps turning of with a low volt warning message in the middle of it.

[advinnie]

New sensor turned up and here’s the results
Idle now at 15.8:1 and no black smoke and that’s where the engine is happiest so left it there any richer and she started to puff smoke
Cruising i now get 16.2:1 ( old sensor read 13.9:1)
Gentle acceleration I’m getting 12.6:1 from 1500 rpm to max rpm
Now let’s say I’m cruising at 40 mph in third with a reading of 16.2:1 then floor it for a split second and i mean a split second I get a lean spike of 18.5:1 ish and a little hasitation and then she goes and the A/F ratio drops down to 10.9:1 for a second then goes up to 12.3:1 and stays at this figure till I hit max rpm or till I let of the go pedal
The other thing I’ve have noticed is that when at idle I’m reading 15.8:1 but if I blip the throttle and then take my foot off the engine falls back to idle and I get a reading of 14:1 and slowly that figure leans out back to 15.8:1 is this normal?
Plus the idle speed is at 1000 rpm but if I up that to 1200 rpm I get a constant reading of 14.5:1

[Clonebug]

My engine has always preferred 12.8:1 at idle.....that is with a carb or EFI turbo.

You have to set yours where your engine likes to idle........"Best Lean Idle" like every carb or FI engine is set at.

Just make sure you are cheating it with too little or too much advance.

Try setting it with about 10-12 degrees advance at idle once....maybe up to 14 degrees.

The idea is to keep the throttle plate as close to fully closed as possible so you don't expose the transition ports and use that fuel circuit for idle.

[advinnie]

Idle timing is set to 15 degrees BTDC at the moment

[madmike]

Adam, My Wideband Does the same thing as yours , Normal split second reading

[buguy]

Mine too. Same with blipping at idle. I think it's a draw through thing. Your always going to have residual fuel in the intake that will burn off as it idles.
But I had the same problem. Slight hesitation when mashing it. That's why I went richer at idle and cruise so I didn't get the spike as much. I also increased the size of my accel pump shooter.