Need help tuning L20 -running too lean on throttle

[Button]

Hey guys, as you might have seen me posting in a few other threads I just got my 510 on the road after 5 years and I am trying to work out the kinks. I have an AEM wideband sensor installed so I can see the A/F ratio. I seem to have good spark, my timing is set at 12 degrees with choke open and vacuum advance disconnected. I rebuilt the carburetor and the jets that are installed were recommend by Top End performance as a good starting place. I just reset the float to 36 and 51 mm to the bottom of the plastic float. My A/F ratio is bout 12-13 at idle and it idles well. The problem is that as soon as I give it any throttle while driving it goes extremely lean (17-18 A/F range). My plugs are way too clean and tell the same story that I am running way too lean. Tonight I am going to grab a small propane bottle so I can check for Vacuum leaks. Any thoughts on what I can try to richen it up, I am pretty stumped? It's worth noting that I had some gas n the tank (2-3 gallons?) that was pretty old and I added in another 5 gallons of fresh 91 on top of it.

My gut thought would be bigger main jet/s to get more fuel in but they are already pretty big. Perhaps smaller air correctors to let in less air?

Set up:
L20B (rebuilt with new pistons,rings, etc.)
electric Fuel pump
Holley Fuel Pressure regulator at about 3.5
header
A87 Head (Freshly rebuilt by a reputable builder)
EI Dizzy with disconnected vacuum advance
NGK BPR6EY plugs gapped at .36

Weber 32/36 settings:
A/F screw is about 2.5 turns out
F50 Emulssion tubes

Primary:
Idle 65
Main 150
Air Corrector 170

Secondary:
Idle 60
Main 190
Air Corrector 180

Thanks

Chris

[bertvorgon]

I will grab my log book and let you know what I run and one of our naturally aspirated members gave a good account of his jetting, so I will see if I can find that too.

[Button]

Thank you Keith. I also think it's a stock L20 cam so nothing crazy going on there.

[Button]

I dug around here some more and the best I could find was in ProFlex's Stress Relief build he and Keith talk about their settings in the oct-nov 2012 time range. Below is a chart of my settings, the settings that ProFlex landed on, and where Keith was at at the time. In that thread though Keith mentions that he was going to experiment a bit more with his mains and airs. Based on this I think my air correctors are too big especially the secondary. I just ordered some new jets to try but I would still love any other thoughts.

[bertvorgon]

Yes, I agree to drop the air corrector on the primary to maybe a 150 and up the primary fuel to maybe 160 and try that.

I currently run a 160 fuel and a 150 air corrector.

At cruise I see the A/F in the 12's.

It is normal for the thing to lean for a fraction of a second when you jump on the throttle. Don't confuse things by going straight to the secondary, just work on the primary to see what it is like at cruise speeds. It does get harder as you get close to the secondary opening, as that too may cause a lean condition for a second, then go to what ever you will get with both circuits feeding fuel.

Personally I like that primary cruise condition of in the 12's as a compromise of good throttle response, fuel economy and moderate exhaust temp.

JUst a note too, I did drill out my secondary progression jet 20% larger to approx a #.70

[Button]

Thanks again Keith. I will make those changes when the jets show up and see how it goes. When you said "I did drill out my secondary progression jet 20% larger to approx a #.70" are you talking about the secondary idle?

I had a little but of brown debris in the bowl so I pulled out the carb screen and opened up my fuel filter and they both had a fair amount of brown debris in them. I can't tell if it's rust particulates or varnished gas or both. I cleaned those out, then drained the gas from the tank and pulled the gas tank out. There is a little bit of surface rust in spots in the tank so I am figuring out what to do now. I am debating whether to treat the tank with phosphorus acid and call it a day or do the whole POR-15 tank seal kit. I am leery of doing any type of sealer because that seems like it will be a real pain if that ever starts peeling off but I also don't want any rust in there. Anyone have any thoughts on the gas tank situation?

[bertvorgon]

Yes, I did mean the secondary idle progression jet. Don't do that yet, you likely will not need that mod.

I just picked myself up an AEM Wide band to replace my Innovate, looking forward to see how that goes. I hope the mounting of the gauge is the same, that way I can use my existing mount.

[Button]

So after a bit of an ordeal I cleaned the gas tank out really well and cleaned or replaced all of the fuel lines. After that I swapped out some jets to what is listed below and overall it is much better and not running nearly as lean. I am however still running lean (14.5 -16.5) when I am getting on the throttle pretty good. I am thinking of dropping the Primary air corrector down to a 160 from a 170, does that seem like the right move? I'm still no sure if when I am on the throttle above 2500 rpm if that is more primary or Secondary circuit. It's also worth noting that it really dieseled when I turned the car off. I had to put it in second and dump the clutch to kill it.

Current set up.
timed at 13 with out vacuum attached
F50 emulsion tubes in both
Primary:
Idle 65
Main 160
Air Corrector 170

Secondary:
Idle 60
Main 190
Air Corrector 140

[bertvorgon]

For sure drop to a 160..or...drop to a 150...and just see what it does...some times a BIG jump is warranted so you can see a major change, then tune back up from there.

Just to be clear...it will lean for a bit when you jump on the throttle but what is your "steady state" A/F reading?

You will know if you are on the secondary as it should really pickup in acceleration.

Some times a good hill helps with tuning, as it loads the car more than on a straight, so you do not end up going ballisticly fast, specially for the secondary, where you do not want it lean as you approach whatever top speed it will reach.

[Button]

Thanks Keith I dropped the Primary Air Corrector down to 150 and things are much better. It idles good at about 13.1 at 2.5 turns out. On the primary circuit while cruising I am at about ~12.7 which is maybe a little rich but seems good. When I am giving it throttle, especially while under load it will jump to abut 14.6 on the Primary. When the Secondary kicks in it drops to 12.7 which seems good. So overall much better just goes a little lean while on the throttle on the Primary. I am thinking of maybe bumping the Main Jet from a 160 to 165 to perhaps richen it up while getting on it. What do you guys think?

[bertvorgon]

Your in the zone now IMHO.

I cruise in the 12's and if you are in the 12'a with the secondary open, that is a good number to me...IT IS SAFE!

Sure, try the 165, but, keep an eye on the plugs too...ON THE PRIMARY...don't want it too rich when you are not asking for full power.

How does the motor react when you just JUMP on the throttle and go for full throttle? Crisp or does it stumble still?

[bertvorgon]

You know...a plane ticket and I'm there..as long as it is warm and sunny.

Cold, colder and wet here, with a chance of huge wind and more cold and rain......

[bertvorgon]

In my opinion too, maybe decrease that plug gap a hair... .032"

[Button]

I'll try decreasing the gap a bit. For my own knowledge why do you recommend that? what does the smaller gap do? I need a bit more seat time but it does seem pretty crisp when I get on the gas and it doesn't stumble. It does run like crap (A/F ratio around 10) until the choke opens all the way up and it diesels pretty bad when I shut it off. The gas is fresh and there is ~45 miles on the engine so i don't think it's carbon build up causing the dieseling. I'm not sure what's going on there. I will lower the idle speed a bit to see if that helps with the dieseling.

[bertvorgon]

Basically, because of my experience, I have seen people chase some issues and it turns out the plug gap has been too large.

Have the gap in this zone potentially eliminates the plug/spark as an issue.

Then.. if and when all seems good, sure, maybe open the gap up a bit more...

Not that you are close to my motor but I run .028", works like a dream to 8,000 RPM

Quote from a hot rod article:



What dictates the width of a spark plug gap is both the amount of voltage and amperage of your ignition system as well as cylinder pressure and air / fuel mixture density. The rule of thumb is that the more power an engine makes, the smaller the gap needs to be. Race engines (contrary to popular belief) use smaller gaps than most "stock" engines do because of higher cylinder pressures and denser air/fuel mixtures. This is because a small, intense spark is better for lighting a highly dense, very wet fuel mixture like you'll find in high powered race or performance engines, kind of like these new lighters you see these days with a small, intense blue flame. They light cigars, fires, etc better in the rain or wind where a weak yellow flame that you get from a match or a typical Bic type lighter isn't as hot and easily blows out.

A smaller gap will yield a short, intense spark and will usually make the engine real responsive. A wide gap creates a longer spark arc but without sufficient "juice" from your ignition system, (including amps), it can be weak and yellow in color. So a small intense spark is much better than a big, weak spark, especially when dealing with richer fuel mixtures and more volumes of fuel being burned.

A good starting point and pretty much the all around best gap is .035". If you want to experiment to see what works best for your particular engine, ignition system, etc, then try going up to .040" and then .045", noting each time how the engine idles, responds, and pulls to your max RPM. Once you've gone bigger on the gaps, now try going smaller to .032", .030" and .025", and again, note how the engine runs. Whatever the gap was when the engine ran it's best overall, is where you should gap your plugs at.

Just an FYI; most very high powered blown gas, blown alcohol, and even blown fuelers run gaps as small as .026" (give or take) and use ignition systems that use 50,000 - 80,000 volts, but more importantly, up to 40 Amps! Amps are what kill you when you get shocked. Stun guns have up to 1 million volts, but no amps so they aren't lethal. Hell, static electricity you get when you shock yourself against a door knob or your car door can be upwards of 100,000 Volts or more, but does it kill you? Nope. Your house electrical current can kill you too, but it's only 110 Volts, BUT it has 15 - 20 Amps pushing that Voltage behind it. Get hit by your house's 220 Volt system are you will most likely die. Not because of the 220 Volts. Again, it isn't Volts that kill you (think of a stun gun), it's Amps. Most 220 Volt outlets are for running heavier equipment such as your dryer, a welder, etc, and have between 20 - 50 Amps behind them. That kind of current will light your ass up and fry you, but a 50,000 Volt jolt from a spark plug won't, unless you are screwing around with a serious ignition system like what a Top Alcohol or Fueler engine runs with 40 Amps behind them. They even have decals on the tops of the dual magnetos saying "Caution! Lethal Current".

Your ignition system may have lots of Voltage, but no Amperage. This is why even on high energy ignition systems, (CONTRARY to what their lame instructions say to gap your plugs at), you CLOSE the gap on engines making more power. Usually .035" is around the best gap, even though many instruction manuals say to open your gap to .045". Go ahead and try that, but when it doesn't run as good, or it drops cylinders at high RPM because that wider / weaker spark can't light the cylinders consistently, you'll know why. This gets even more true when you are running too rich and have too wet of a mixture. It's harder to light a fire in the rain than it is on a dry summer day. Inside your cylinder isn't much different.

On mild engines, (even you guys who have 400 - 550 HP), that isn't enough power to be concerned with on the gaps, and a gap of .045" will "probably" run just fine because you aren't burning enough fuel (a wet enough mixture) to cause cylinders to drop with a decent ignition system, but start getting over 600, 800, 1,000 horsepower and that .045" or so gap isn't going to work out too well. Either way, your milder engine WILL run better with .035" gaps instead of the .045" gaps that they tell you to run.

spark plug gaps
Now, while we're on the subject of gaps, a little extra trick you can do to your plugs is to do what's commonly called "side gapping" them. This is when you take a small file or a fine grinder to the ground strap and cut it back so it only covers about half of the center electrode. This exposes the spark to the open cylinder and combustion area more and prevents the shrouding that the full length ground strap tends to do on regular plugs. This can be worth a few extra horsepower, just as indexing a set of plugs is worth a few extra ponies. I have another tech tip on how to index spark plugs which can gain you a few extra "free" HP.

As you can see in the image, the plug on the left is a typical plug with a full length ground strap, where the plug on the right is side gapped. You can clearly see how doing this exposes the spark to the open cylinder more and will promote better flame travel and combustion. It's free horsepower for only a few minutes worth of effort.