Air fuel ratios

[Stewart]

I'm playing with a new toy an innovate LM-1 air fuel meter and hopefully the guru's on the board can help me decypher the results

I'm thinking right now I'm rich at idle with it being at 11afr +-.1 about right in the midrange cruise at 14.1 @3500 rpm 3th but lean at highspeed cruise at 17+-.2 4200 WOT was running in the 14's to 16's

 

[MGBGT_noob]

For a better idea of where your intake system needs improvement, you should hook up a few additional sensors to the auxiliary inputs on the LM1.

Fuel consumption should act as a function of RPM and engine load. If your engine runs rich, then the fuel delivery system has given it too much fuel for the current conditions. If it runs lean, the gets too little.

If you are electronically inclined, you can make an RPM sensor using a frequency to voltage converter, such as the LM2907.

You can also hook up a MAP sensor, such as the MPX4250, to measure your engine load.

By mapping the AFR to the MAP and RPM, you should see where your engine gets too much fuel, and where it gets too little.

Someone more familiar with your particular carb setup should then be able to tell you what changes you need to make. For SUs this could include different needle profiles, harder or softer piston springs, or different damper oil viscosity. For Webers, this usually means jet changes (lots of jet changes).

 

[martx-5]

I've got an O2 sensor hooked up to my TR3 with an analog AFR gauge. None of those nice readouts like you're getting. You're readings have two concerns...

1. The high speed cruise is too lean. It should be more like your midrange cruise. 15-14..

2. WOT Should go RICH. In the 13-12 range. Inital tip in might be lean, but it should climb after that.

Those are the kind of readings I see on the TR3.

My engine also runs pig rich at idle, but I'd rather have correct readings while cruising and at WOT. I may mess with differennt needles to fix the idle richness, but not now as I just finished the restoration and want to drive it.

Edit: After looking over your readings on the chart, I'm having a a little trouble distinguishing which group falls into which category. I gave my thoughts based on what you said.

Anyway, there's a nice little program out there that will help determine what needles for the SU carb you can try to change the characteristics of the AFR over the rpm range.

You can download from here.

There's a free download along with an expanded version that costs 10 pounds.

 

[Stewart]

Installed AAA needles in the hif4's and ran it again. Power is up on the high end and it pulls like a freight train to about 90mph at which point I wuss out. Graph is from a standing start to about 75mph. Highspeed cruize at 75mph and 4200 rpm is sitting at 16.2
First run with abd's

Second run with aaa's

 

[Deleted member 3577]

I have a LM-1 also and really like it...

Did you get the RPM sensor with it?
(If not...I recommend it)

Looks like you are still a bit lean.
Mine likes it around 10.5-11 for hard acceleration and about 12.5-13 for cruse.

I assume the spikes are your shift points.