Thinking of an air-fuel meter to tune carb - any experience?

[Luce]

I have one of the LM's hooked to my megasquirt(don't recall which one) and the gauge on the dash. It'll respond quicker than your eye can read it.

works great telling me all is well with the EFI, and I've heard they're great for tuning carbs too.

[Wbulk]

If you go to the tech area of Innovates site you can read about their various products. They gave a program CD with the gauge I bought and among other things you can set the speed of the display. The cool thing about the data logging is the play back feature; you can play it back in real time or speed it up. If using a laptop where ever you point on the graph it tells the exact reading at that point. Another real advantage of data logging is you can see spikes in specific circuits that you may not see on the gauge because they happen so fast. The reason I bought the gauge was the ability to hook up a laptop. I figured why buy the LM2 for a lot more money when I can hook up a laptop to the gauge and do about the same thing and print out the graph.

Also consider when tuning your carb circuits have overlapping areas. I am doing idle, then main metering, then power valve and accelerator pump. I will disconnect the secondary rod until I get these where I want them and then work of the secondary jets. We will see how that goes.

I wish I could post a pictures of the data log graphs but I have not been able to post pictures for a few weeks.

[Karl Bebout]

PaulProe: I got all interested in reading the Ford Muscle article you listed and darn if they didn't want money to read the second page, with the results. Crapola!

[Tom Howland]

Yes it does. It reads so quickly it bounces around about 5 tenths. You need to average yourself. I'm running webers so maybe that's why mine bounces.

[lippy]

I called Ole, and he only works for another guy (John Bishop). So I essentially have to pay both of them. And Ole mentioned John isn't always reliable getting back to people. This is the sort of thing I have no patience for, and I can't find another carb tuner in the area. I just ordered an LM-2 and I'll learn to do it myself after I get a bung welded on.

[Mohuska]

I use an AEM. It mounts in the dash and reads vacuum and AF ratio. It data logs 3 hours of data and plugs into your computer so you can down load and evaluate the data. I have dual quada and it has helped a lot getting things dialed in.

Cheers,

Mike

[Randy Rosenberg]

Originally Posted by lippy

I called Ole, and he only works for another guy (John Bishop). So I essentially have to pay both of them. And Ole mentioned John isn't always reliable getting back to people. This is the sort of thing I have no patience for, and I can't find another carb tuner in the area. I just ordered an LM-2 and I'll learn to do it myself after I get a bung welded on.

I've referred a few friends to Ole and John, and never once did I hear that they were charged for "both of them" as a standard statement. Yes, John does the scheduling (they work on only 4 cars on a Saturday), and I've heard that John may re-curve the distributor, based solely on Ole's instruction, but that's all I recall John doing. Ole looks at the entire Fuel/Ignition setup, not just fuel mixtures.

[lippy]

Originally Posted by Randy Rosenberg

I've referred a few friends to Ole and John, and never once did I hear that they were charged for "both of them" as a standard statement. Yes, John does the scheduling (they work on only 4 cars on a Saturday), and I've heard that John may re-curve the distributor, based solely on Ole's instruction, but that's all I recall John doing. Ole looks at the entire Fuel/Ignition setup, not just fuel mixtures.

Thanks. I'll see what they say. I called John a couple days ago but haven't yet heard back.

[patrickt]

Lippy, what is that makes you think your carb is not set right?

[lippy]

Originally Posted by patrickt

Lippy, what is that makes you think your carb is not set right?

(1) Runs on after stopping sometimes. Not that bad, but it does go for 1s or so. Could just be bad gas or ignition, but I retarded the timing from 36 to 34 (full). Problem still present. (2) It was stumbling when I gave it throttle. I changed the acceleration pump nozzles to 37s and I think that did the trick. (3) Plugs fouled. My first coil was out of spec and I replaced it, and hope that did the trick.

This is a pricey engine and I want to make sure it's operating within range for a carb'd car. With a sideband, I can verify and optimize.

Also, the fuel was percolating when I stopped. I added a 0.25" phenolic spacer and I *think* that fixed the percolation.

[patrickt]

Fair enough. I'm sure Brent picked a nice carb for your set up, and it is tuneable so that the engine will run perfectly. Here's a tip though, a brand new build will have the potential for more crap to get in to the carb than a build with a few years and a few thousand miles under its belt. Little flecks from the hoses, the lines, goo from here and there, it all makes its way in to the carb and filters don't always stop it. I don't know how many holes the emulsion tubes coming down for the main circuit has in your carb, but it doesn't take much to hamper one of them. A little dried varnish, a little fleck of hose/dirt/whathaveyou in and around the holes/tubes/passageways and it will throw off the performance. Then you find yourself trying to compensate for that shortcoming by tweaking other parts of the circuits. So, just make sure the insides of your metering blocks are clean enough to eat off of. Seriously, it really is a BFD with a fresh build, today's ethanol fuels, and you should try and get a chlorinated carb cleaner. They're outlawed in your state (California), I believe, so the best you're going to get is going to be something acetone based, which is better than nothing. But if you find yourself in a cheap, crappy dollar store, look for a no-name carb cleaner that has dichloromethane (methylene chloride) or another VOC that has chlorine as a component -- maybe you'll get lucky. Dang, you would think that in a state where you can just buy Panama Red at the corner dime store you'd be able to buy a chlorinated carb cleaner as well. I use a separate little miniature polyimide tubing, that is thin enough to fit through the high speed (main) bleeds, to blast everything out. The tube that comes with your cleaner is usually too fat to fit in there and will just blast it back in to your eyes -- but that's better than nothing. If your AF meter gives you wacky readings, the first thing to suspect is crap in the carb.

[Wbulk]

This subject of tuning a carb with a wideband gauge deserves an in depth thread of it's own. So not to get too far off track I will mention a few things to think about. Before I got mine I read everything I could find on the subject and realized it gave you the ability to do fine tuning beyond in the ballpark tuning, as in the the past from reading plugs. Fuel has changed and varies between areas of the country and is not as easy as it was years ago to read plugs. What I found was that you can fine tune circuits that were very difficult in the past. If the car is moved from one area of the country to another it is unlikely the tune is the same, and no way it will be the same if the altitude is 1,500 or more different.
I live at 5,000 feet and I believe the vast majority of cars that are running an aftermarket carb as this altitude are off. I believe the Youtube video I posted is representative of perhaps the majority of modified carbed cars on the road, except perhaps those run at sea level that most manufacturers tune for.

Be aware that temperature, humidity, and type of fuel all effect AF ratio. If your car is tuned on a dyno at 90 deg. it will not likely be the same as 60 deg.. The same goes for fuel. In various parts of the country there is summer fuel and winter fuel. This can change the AF ratio burn results. The same goes for humidity.

When I shut down my car last October I had summer fuel in the tank and the temp was about 70 deg in the middle of the day. My main metering circuit was averaging just about 14.8. at about 4K rpms. I recently put in winter fuel with the temp in the 50s and ran the car. This time it was averaging 14.2 I know that I will have to check this again when it gets a little warmer and when summer fuel comes out.

Carbs are primitive, but what we can do with a wide band gauge is make the ball park smaller and kind of move it into the infield. Then we are averaging with temp, fuel, and humidity within a smaller area.

[lippy]

Wbulk and Patrick - thanks, that's all good information. I suspect my carb is close. But for starters I just want to verify at different operating conditions whether something is far enough off in either direction to lessen the engine's longevity or diminish its performance significantly. Over time I'd use the tool more for optimization.

[patrickt]

On second thought, don't clean your carb. Play with the new meter, learn to use it, and get some good, repeatable, base line readings. Then thoroughly clean out your carb and do it again. See if the readings change any.

[DanEC]

Originally Posted by lippy

(1) Runs on after stopping sometimes.

Sometimes run on can simply be brought on by a high idle. What are you idling at?

Also, since I understand this engine to be pretty stout - are you familiar with the issue of where the throttle blade should sit at idle with respect to the idle slots in the bore? If the trottle blade rests at the upper part or above the idle fuel slots at idle, you lose tuning control of your idle fuel mixture and consequently tend to open the throttle up more with the idle screw to keep it running. If your idle is not responsive to adjustments in the idle screws this could be a part of the problem. When shutting the engine off, fuel can continue to be pulled from the idle slots and promote run on until the engine comes to a complete stop. On most Holley's it's pretty easy to compensate for because there is a set screw on the secondary throttle blades. The secondary throttle blades can be opened slightly to allow more air through them at idle - allowing the main idle adjustment to be backed off and the primary throttle blade to rest in the center of the idle slots where it needs to be. Actually I would anticipate Brent would check this when breaking in and dynoing the engine but if you have set the idle up a little higher in the car, it may have gotten outside where it needs to be.

Sorry if I'm telling you a bunch of stuff you have already looked at or considered.

[bingo2]

All good suggestions thus far but, as most of the carburetor tuning threads go, hardly anyone ever mentions the most important component of the process.

Ignition first and foremost. You'll never get the carburetor tuned correctly without ensuring your ignition system is in tiptop operating condition with the proper spark plugs gapped correctly and the initial and total advance set to specification along with the correct advance curve.

My suggestion is to call Brent and go over the specification for your engine.

[bingo2]

I'd like to add to my previous post.

It appears you've made at least one change to the carburetor to allieviate an off idle stumble; you changed the nozzle size.

Hopefully, before doing so, you went through the basic setup for your carburetor.

An off idle stumble can manifest itself in many ways; for instance, improper initial timing, incorrect setting of the idle mixture screws or improperly sized idle feed restrictions, a vacuum leak, float height, just to name a few. Changing the nozzle size may have masked the real cause of the stumble.

[lippy]

bingo2 - All true, and all good points. I worked with Brent and am as sure as I can be that the ignition is ok. I did check float height - it's easy with this carb because it has Pyrex sight glasses on both sides of each bowl. My first coil was out of spec, so I replaced that as well. The stumble wasn't only off idle, but also at speed when I hit it relatively hard. I spoke with Brent and his carb guy and they were the ones that suggested I go to a bigger nozzle. Since the problem is both off idle and at speed, our conclusion was that the nozzle should be upsized. I hope to get more time on the road tomorrow, but based on a short drive the larger nozzle seems to have helpled. Thanks!

[bingo2]

Great...sounds like you're on the right track. Good Luck!

[lippy]

A follow up on this topic. Wideband meters can be great, but they also can drive you pretty far off course if you don't use them in context. After a ton of fiddling with main jets, air bleeds, restrictors, etc, I still couldn't get this carb dialed in. As it turns out, AFR readings for engines with big cams with a lot overlap are useless and inaccurate at low load/RPM because a lot of unburnt fuel and air pass through the engine, and the Wideband meter reads lean. Because I used the meter to adjust the idle screws, my idle mixture was rich and this was affecting my tune at all conditions. Once I learned this and used the wideband only for WOT and cruise under load, and tuned idle using idle speed and vacuum, the carb tune fell into place and I think I'm very close now. To be fair, Brent and one of the tech guys at Holley warned me that the best way to tune is to read plugs, and not to use a wideband. Brent also added that this is one of the reasons he specs racing plugs, as they are easier to read with unleaded gas.