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Is my wideband off, or does my car just like to idle at 12:1?

3K views 12 replies 8 participants last post by  vegascarnut 
#1 ·
This is more a curiosity for me than a concern, because my car runs great. I've just had a lot of people tell me I should be shooting for 13.5-14 with this engine. Combo is in sig.

I have run a couple different carbs on it:

CSU Holley HP 750 with annular boosters (flows about 625)
Edelbrock 1406 with some significant recalibration for my car

I've become very good at tuning both of them over the past couple of years, and I like them both for different reasons. When I set them up properly, with a vacuum gauge, both of them idle well with about 11 inches of vacuum when fully warmed up. My initial timing is set at 18, and I'm only running one light spring on the mechanical advance because from 1,500 RPM and up, the car feels best with all 35 degrees of advance.

When all is said and done with idle tuning, the wide band reads about 12:1. In fact, this car seems to like to be on the rich side everywhere.

Anyone else have a similar experience? Thanks!
 
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#3 ·
very, very light tan
 
#4 ·
Either A stock Autolite carb, or the Holley Street HP series with the adjustible air bleeds, will give you more idle tuning ability.
I used two of the AEM wideband gauges on my Shelbys and HiPo's. The best idle a/f ratio I got

14.4 with a vintage Paxton supercharger
13.7 with a stock Autolite HiPo carb
13.1 with a set of four 48 IDA Weber carbs.

My Initial timing was 22 (modified). Total timing was 40 degrees (stock HiPo).

Your cam will have a great impact on the a/f sweet spot.


Z
 
#5 ·
The cruise AFR seems happiest around 13.5:1, which is still a little rich, but that's what it likes apparently. The idle may just like to be a little richer still. I can get it to about 12.5:1 before the vacuum signal starts to fall.
 
#7 ·
With a Holley you can start leaning out primary jet size to make the reading different, once you find that size then you have to add fuel to the power valve restrictions to add some lost volume of fuel at WOT. As long as everything else is right, the response and efficiency of the engine becomes more dramatic, runs as if it has fuel injection when you find that tune.

This is needed someties with Double Pumpers that usually are assembled to be rich for the track when you buy these carbs new.

The Universal Tune is just that...
 
#8 ·
I have yet to see a brand new Holley carb over the last 45 years that didn't run rich right out of the box. Especially at fault is the stock setting for the float bowl fuel level. It is always too high for the best running. You can very often get a rich running Holley to run perfectly by dialing down the fuel level inthe float bowls and not have to adjust ANYTHING ELSE. Additionally, a set of main jet extensions will do more to eliminate fuel starvation than raising the float level. That's just the way those carbs have to be tuned to get around the way the float bowls and vent system was designed. I ran these carbs on a supercharged 289 numerous times flat out for as long as a tank of gas would last (west Texas endurance runs) and never had fuel starvation issues despite having the float level set much lower than stock.

Z
 
#9 ·
I assume you are running pump gas? A cam with a significant amount of overlap will require the idles to run a bit rich but your cam, if it is still a TFS stage 1 cam, does not have a lot of overlap. It should have a fairly normal idle a/fr. For it to have to be that fat to idle is something strange going on. Maybe it is the idle bleeds? Is your transition off idle to the primary jets smooth? 13.5 for cruise looks pretty good to me.
 
#10 ·
Take it to a shop with a sniffer to verify your readings are right. If they are then don't worry about it. You're plugs aren't drowning and it feels good.
 
#11 ·
As we are talking about wideband sensors, I purchased one that came with a Bosh sensor. I read somewhere that its possible to damage them if you leave them installed, but not powered. Might this be a specific type of sensor, true of all sensors not not true at all? I'd have to dig out my box to see exactly which one I have.
 
#13 ·
I've gone back through, and checked everything. I started by rechecking my timing, which was just a little off from what I thought I had set. It was at 35 all in, but it wasn't coming in as fast as I had written down. I had a lighter spring for the advance that I had not used. Took the distributor apart, and replaced the spring. Now advance is all in by 1,500. I also have vacuum advance hooked up to manifold vacuum.

Reset the idle mixture with the revised timing, and vacuum has improved some, with AFR now about 13.5:1 at idle. I revised the primary jetting, back to a size I had used before, and have now improved the AFR to around 14:1 almost everywhere. I'm going to pull plugs and take a look, but throttle response is better than before. I need to bring the jets down on the secondaries now. Too rich at WOT.

I'm tempted to throw a little more timing at it, but everyone who runs the Twisted Wedge heads says 35 is about all you want to throw at them. Any opinions on that statement?

So thanks everyone for encouraging me to take another look at some things. Takes time, but sometimes it's worth it just to recheck everything. Seems like every time I mess with it, it gets a little better. --Sean
 
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