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Discussion Starter · #1 ·
A couple of months ago I decided to take the plung and buy a wide band oxygen sensor. Motorhead influenced me alot and I bought the LM-1.
I wanted a very accurage instrument, one that could store data for later analzing and one that could be calibrated accurately and quickly at home.
It was costly, about $500 canadian.
I always thought my car ran great with it's #80 jets in the 2 850 double pumpers. It even pulled down 14 or 15 mpg
After unstalling the LM-1 I found I had a miss at low rpm and I was running extremely rich.
For maximum power to want 13.2, good cruising economy 14-15 or even 16 or 17 if the motor will take it.
The word lean ONLY refers to WOT. At WOT you need 12.5 naturally aspirated or 11 or 10 blown.
I also learned that IDLE mixture controls cruising mixture. If you idle rich you cruise rich.
I also learned that a simple 1/8th of a turn on the idle screws can send you from 12 into the 14 range. Yes a simple 1/8th turn so how can you tune strickly by ear??
Anyway I ended up dropping 8 jet sizes. From the stock holley 80's down to 72's. My fuel mixtures went from the 10-11 to the high 13's low 14 and even with playing with the idle mixture screw into the 16's and 17's.
The motor runs better, I have experienced at least a 25% increase in fuel range and my plugs look like new.
Doing plug checks doesn't work for street driving. Sure you get an overall rough indication.
Also since I joined the LM-1 club and there is a Tuners forum I have learned that our holley carbs have at least 10 or 12 different jets PER metering block that can be changed to fine tune to get a consistant fuel curve threwout the operating range.
Seat of your pants might work for drag racing but not for a good running street machine.
You can spend up to $300 in a jetting kit for a single holley but if you work at it our carbs can be made to run as lean as fuel injection, very economical and very clean from a carbon point of view.
In every case where I have installed the LM-1 I found EVERYONE runs too rich.
In every case jet size was wayway too rich.

This is copy of an email I got this morning from another LM-1 new owner.
I got his fuel curves at the start and he has a good running 383 stroker and he was solid in the 12's and even dropping into the 11's.
This is not his quarter mile times but his air to fuel ratio:laughing: :laughing:

this is his email this morning
Hey... I went down 4 jets sizes. Nothing changed below 3200 RPM which confirms what you were runs on the idle curcuit below that. But over 3200 my AFR went up one full point, from low 12's to low 13's. So... I am getting closer. Tomorrow I am going to go down another 3 jet sizes....boy was I running rich!

Everyone who is serious about tuning their car needs the wide band oxygen sensor. When you have you car dyno tuned it is the carb that receives the most work. Sure the ignition curve needs to be right but that is far easier to check with a cheap timing light then the carb..

A well tuned car needs
1 A wide band oxygen sensor
2 A proper ignition curve

With vacuum advance you can burn these lean mixtures. If you are NOT running a vacuum advance you have a RETARTED igniton for a street car.
NO exceptions.

If you want further information follow this link on carb tuning. IT is one of many that I have memorized over the past few months

424 Posts
I got one about a month ago, but only had a chance to use it twice, just watching it no recording. Now I am up on jack stands in the middle of about 6 projects.

But on those two occasions I was supprised how rich I was. At idle I am around 14 at cruise 13 to 13.5 and wot it can drop down into the high 10's and 11's. I can't wait till I am back on the ground and can record some driving and finially tune my car right.
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