Tuning an Autolite 1100 w/ wideband O2

[jamyers]

'68 200 with stock internals, DS/HEI ignition, Autolite 1100 carb and a diy-ported exhaust manifold. 3-speed manual tranny, manual choke.

Just got my JAW wideband together and in the Ranchero, (see this thread), and here are my AF ratios at various points:

Idle: 13.7-14.3 (this is the only one I've adjusted yet)
WOT: 12.0-12.5
Part-throttle cruising under 50mph (just loafing along): 16-18
Cruising on the highway at 60+: 16-20, and the faster I go the leaner it gets and the wider the swings - which are pretty fast, it gets pretty hard to catch the numbers changing on the display.

From what I've read, the idle and wot are ok, but the cruise AFR's are pretty lean (even though it's been like this for about a year and the plugs look good.)

One thing that concerns me is the speed at which the AFR's spike/dip, at 70mph or better the digital display is jumping between 16.something and 20.something so fast it's hard to tell what's what. I'm working on borrowing a laptop so I can datalog then average, but surely it's not normal to change so much so fast, is it?

Comments anybody?

 

[BIGREDRASA]

Could be a defective power valve. It looks like and accelerator pump without a lever. Inside it has a diaphragm that enriches the mixture at low vacuum. If it is defective, it will do spooky things.

 

[Bort62]

Well, The 1100 doesnt have a lot of options when it comes to tuning...

But, overall that looks ok. Certainly, it's a little lean @ cruise... but IMO that is not necessarily a bad thing (especially if you don't notice any driveability problems)

 

[jamyers]

I think the power valve is ok, since when I stick my foot in it I can see when the mixture goes richer on the way to wot. Then again, the Autolite power valve isn't the easiest one in the world to get at...

I noted that when I was playing with the idle mixture settings, as I went leaner it got more erratic, and as I went richer it didn't jump around nearly as much (by 12.0:1 it was pretty solid). I'm thinking that with the oh-so-wonderfully designed log intake and the just-as-terrific stock exhaust manifold, it's "normal" for the AFR's to start jumping around as it goes leaner and one or two cylinders are on the border of lean misfire.

The wideband controller takes something like 2000 samples per second and is currently giving me a running average of 100 samples that's refreshed on the display 8 times a second, so it's showing me EVERY little dip and spike in the exhaust stream.

Does that make sense to anybody else?

Next step is to swap the ol' HW5200 back on.

 

[MustangSix]

Makes sense to me. There is always the possibility of unvaporized fuel droplets in the log, especially at idle, even with a warmed up engine. When it finally gets sucked into one of the cylinders, the mixture changes and it registers on your wideband as a fluctuation.

 

[jamyers]

I think that's my story and I'm gonna stick to it for now.

 

[Harte3]

A lean burn at cruise = good mpg. As long as you are not getting a lean misfire be happy

If you want to see a real dancing light show on an AFR guage use a narrow band set up

 

[jamyers]

Well, I got motivated and swapped the old HW5200 back on, then went for a drive.

WAY less jumping around - the leaping AFR's were due to the Autolite. With the 5200 on, the AFR will stay pretty well put, for example at cruise it varies from 13.5 to 13.7, mostly solid on 13.6 (rich, I know). I got the 1100 from a board member who got it from Pony Carbs, and it's in good shape, so that shows me the difference between carb designs is night and day.

Now I'm going to have to go back and re-read that honking long thread on jetting a HW5200, and dig my books and notes back out.
Idle is way lean at 16+, cruise is rich at 13.6, and wot is just about right at 13.0

I'm having fun! 8)

 

[ASMART]

Keep us upto date. Should be interesting tosee what kind of results you get including milage.

 

[BIGREDRASA]

The thing with the power valve is at what vacuum it opens. It is not about engine speed, but load as it affects vacuum. I'm curious if you documented vaccum and corresponding AFRs?

 

[james singleton]

I am not trying to hijack the thread here, but this is a question concerning the 1100 carb that I am sure someone can answer for me. I just bought a 1100 carb off of Ebay and (if memory serves me here) would like to know if there is a plastic insert that goes over the top of the carb throat that allows the stock air cleaner to seat properly on top of the carb. I currently have a 200engine (with a 1940carb), but I orginally had a 170engine with a stock 1100 carb and I seem to recall a plastic insert that sits on top of the carb!?????? Am I correct on this??? If indeed it does take this plastic insert, does anyone know where I can obtain one??? Thanks, Jim

 

[jamyers]

@ BIGREDRASA: I didn't document the vacuum/AFR, but you could sure see it as you opened the throttle.

On the HW5200, the power valve operation is not nearly as noticeable, but you know exactly when the accellerator pump starts and stops - the dip in AFR is huge (which makes me think I can reduce it quite a bit and save some gas.)

@ james singleton: If I recall, some did and some didn't - most earlier cars with the flat air cleaner housing bottoms didn't. If you want one of that type base, let me know - I've got several laying around.

 

[james singleton]

James/Jamyers, I really appreciate your offer, and yes I could use one of those carb/air cleaner insert/adapters (whatever they are called). I have a stock oil-bath type air cleaner that I believe needs the insert for the air cleaner to sit properly on the 1100 carb throat. Let me know what would be the best way to contact you, and I will mail you some postage/delivery money (and a cost for the insert) and I will get it in the mail to you! Thanks so much, Jim

 

[jamyers]

James/Jamyers, I really appreciate your offer, and yes I could use one of those carb/air cleaner insert/adapters (whatever they are called). I have a stock oil-bath type air cleaner that I believe needs the insert for the air cleaner to sit properly on the 1100 carb throat. Let me know what would be the best way to contact you, and I will mail you some postage/delivery money (and a cost for the insert) and I will get it in the mail to you! Thanks so much, Jim

Sorry for the confusion, but mine don't have adapters, they're just the old-style flat aircleaner bases that sit directly on the carb. They do fit 1100 carbs though, if you wanted to convert from the oil-bath to a paper filter you're welcome to a base or a complete aircleaner for the postage.