[DeTomaso] Carburetor Tuning question
Will Kooiman
will.kooiman at gmail.com
Wed Feb 19 14:38:50 EST 2014
Here's a good site that explains Holleys: http://www.bob2000.com/carb.htm
The concepts are the same between Holleys and Carters (The Edelbrock is essentially a reissue Carter AFB).
Good advice from Dave.
On Jan 29, 2014, at 1:10 PM, Peter Cajthaml <pcajthaml at gmail.com> wrote:
> I recently installed an Edelbrock Performer RPM manifold and Performer 1406 carburetor on #2761, and asked Dave Londry for some tuning advice. With his permission, I am posting his advice as many can benefit from it. Thanks for the wealth of information Dave!
> Peter
> #2761
>
> Here is Dave's reply:
> ------------------------------------------------------
> Beg, borrow or steal an A/F meter such as Innovate. You don't have to be very far off to feel A/F error.
> http://www.ebay.com/itm/Innovate-MTX-L-Digital-Wideband-Air-Fuel-Gauge-Kit-Wide-Band-WideBand-o2-Sensor-/191051619330?pt=Motors_Automotive_Tools&hash=item2c7b905c02&vxp=mtr
> If you do get a meter, don't run the engine without power to the O2 sensor.
> I wrecked one that way to learn.
>
> Having 2 is even better, and having bungs is way better than the clamp on the tailpipe.
> We can't all have 2 meters, but I'd stop and put a bung below the collector.
> I can scarcely get a reading below 2000 rpm on my car with the clamp.
> The exhaust reversions are pretty fierce.
>
> All the carb tuning you'll do will be about A/F.
> Work up from idle, because the idle setting affects operation well into primary opening.
>
> I'm assuming you have zero-ethanol gasoline,
> if not the A/F ratios need adjusting but I can give you the adjusted numbers
>
> 1. Make sure you're happy with your timing.
> 2. Get the idle A/F set (maybe 14.5).
> The edelbrock max rpm method is OK, if you can't read the A/F at idle.
> 3. Then I'd do the ease-into-WOT runs from low (maybe 2500 to 3500) RPM
> and keep at it across 3500 to 4500 and 4500 to 5500 until I had it close to 12.5:1 for power.
> 3rd gear is nice for visibility, but 2nd works if you don't have the space. (1st just goes by waay too fast)
> 4. Next I'd do the "boot-it" checks to set the accelerator-pump stroke (nozzle also if you have to, but I doubt it)
> Don't worry about the meter until you get rid of any detonation.
> Then you can see if the meter response if fast enough to show you if you're getting too much
> (down toward 10:1) or too little (over 13:1) fuel during throttle opening.
> ** Now you're power tuned. **
> 5. You can go back and check the A/F at constant speed.
> (15.5:1 is nice, but unless you really care about fuel economy, anything down to 14 is OK)
> The higher the gear you use, the more meaningful the throttle opening is for a given rpm.
> (I don't look at anything under 2500 rpm - the idle screws are still dominant there anyway.)
> -----------------------------------------------------
> The Edelbrock manual is pretty good about showing you how to track the metering rod/jet/spring
> combinations to change the A/F. Just remember that the difference between the jet and the
> skinny part of the metering rod is what gives you the A/F at high throttle openings.
> So when you get the WOT runs done, then you can adjust the constant-speed A/F by
> changing the fat part of the rod. Of course you won't have the rod you want.
> unless you bought a kit with a bunch of rods; but you can go to another rod/jet
> combination. Just keep the annular area of the little-end opening the same when going to the next pair.
> The spring just controls the the transition from big end to little end (higher/lower vacuum).
> It's way quick to change rods and springs, but changing jets requires taking the linkage down and the top off the body.
>
> The float levels on that carb were fine, so I'd leave them unless you see something suspicious.
>
> I've attached a chart I made of all the jet / rod openings and relative annular areas
> PerformerJet_Rod_Map.pdf
> (HiVacArea = big end, LoVacArea = little end.)
> -------------------------------------------------------------------
> I've also attached a chart I pieced together for all the Performer and Thunder rods and jets.
> Performer & Thunder Rod_Jet Chart
> They all fit in a Performer anyway.
> --------------------------------------------------------
> And for good measure - here's an A/F chart for real gasoline
> AirFuel_chart.jpg
> and a list of all the metering rod kits that Edelbrock sells.
> JetRod&Spring kits.pdf
>
> _______________________________________________
>
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>
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-------------- next part --------------
Here's a good site that explains Holleys:
[1]http://www.bob2000.com/carb.htm
The concepts are the same between Holleys and Carters (The Edelbrock is
essentially a reissue Carter AFB).
Good advice from Dave.
On Jan 29, 2014, at 1:10 PM, Peter Cajthaml <[2]pcajthaml at gmail.com>
wrote:
I recently installed an Edelbrock Performer RPM manifold and Performer
1406 carburetor on #2761, and asked Dave Londry for some tuning
advice. With his permission, I am posting his advice as many can
benefit from it. Thanks for the wealth of information Dave!
Peter
#2761
Here is Dave's reply:
------------------------------------------------------
Beg, borrow or steal an A/F meter such as Innovate. You don't have to
be very far off to feel A/F error.
[3]http://www.ebay.com/itm/Innovate-MTX-L-Digital-Wideband-Air-Fuel-Gau
ge-Kit-Wide-Band-WideBand-o2-Sensor-/191051619330?pt=Motors_Automotive_
Tools&hash=item2c7b905c02&vxp=mtr
If you do get a meter, don't run the engine without power to the O2
sensor.
I wrecked one that way to learn.
Having 2 is even better, and having bungs is way better than the clamp
on the tailpipe.
We can't all have 2 meters, but I'd stop and put a bung below the
collector.
I can scarcely get a reading below 2000 rpm on my car with the clamp.
The exhaust reversions are pretty fierce.
All the carb tuning you'll do will be about A/F.
Work up from idle, because the idle setting affects operation well into
primary opening.
I'm assuming you have zero-ethanol gasoline,
if not the A/F ratios need adjusting but I can give you the adjusted
numbers
1. Make sure you're happy with your timing.
2. Get the idle A/F set (maybe 14.5).
The edelbrock max rpm method is OK, if you can't read the A/F at
idle.
3. Then I'd do the ease-into-WOT runs from low (maybe 2500 to 3500) RPM
and keep at it across 3500 to 4500 and 4500 to 5500 until I had it
close to 12.5:1 for power.
3rd gear is nice for visibility, but 2nd works if you don't have
the space. (1st just goes by waay too fast)
4. Next I'd do the "boot-it" checks to set the accelerator-pump stroke
(nozzle also if you have to, but I doubt it)
Don't worry about the meter until you get rid of any detonation.
Then you can see if the meter response if fast enough to show you
if you're getting too much
(down toward 10:1) or too little (over 13:1) fuel during throttle
opening.
** Now you're power tuned. **
5. You can go back and check the A/F at constant speed.
(15.5:1 is nice, but unless you really care about fuel economy,
anything down to 14 is OK)
The higher the gear you use, the more meaningful the throttle
opening is for a given rpm.
(I don't look at anything under 2500 rpm - the idle screws are
still dominant there anyway.)
-----------------------------------------------------
The Edelbrock manual is pretty good about showing you how to track the
metering rod/jet/spring
combinations to change the A/F. Just remember that the difference
between the jet and the
skinny part of the metering rod is what gives you the A/F at high
throttle openings.
So when you get the WOT runs done, then you can adjust the
constant-speed A/F by
changing the fat part of the rod. Of course you won't have the rod you
want.
unless you bought a kit with a bunch of rods; but you can go to
another rod/jet
combination. Just keep the annular area of the little-end opening the
same when going to the next pair.
The spring just controls the the transition from big end to little end
(higher/lower vacuum).
It's way quick to change rods and springs, but changing jets requires
taking the linkage down and the top off the body.
The float levels on that carb were fine, so I'd leave them unless you
see something suspicious.
I've attached a chart I made of all the jet / rod openings and relative
annular areas
PerformerJet_Rod_Map.pdf
(HiVacArea = big end, LoVacArea = little end.)
-------------------------------------------------------------------
I've also attached a chart I pieced together for all the Performer and
Thunder rods and jets.
Performer & Thunder Rod_Jet Chart
They all fit in a Performer anyway.
--------------------------------------------------------
And for good measure - here's an A/F chart for real gasoline
AirFuel_chart.jpg
and a list of all the metering rod kits that Edelbrock sells.
JetRod&Spring kits.pdf
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References
1. http://www.bob2000.com/carb.htm
2. mailto:pcajthaml at gmail.com
3. http://www.ebay.com/itm/Innovate-MTX-L-Digital-Wideband-Air-Fuel-Gauge-Kit-Wide-Band-WideBand-o2-Sensor-/191051619330?pt=Motors_Automotive_Tools&hash=item2c7b905c02&vxp=mtr
4. mailto:DeTomaso at poca.com
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