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[Right hand drive]

[rgalajda]

Interesting how the Build Sheet does not mention venturi size under "Primary and Secondary Venturi Specs" nor throttle plate size.

[Robban 54]

Hello
Yes it is fun to drive attracts attention wherever you go people come up and talk and want to take pictures.
The most fun are young guys in their AUDI and BMW at the red lights.
It goes very well as it is but it is always fun to try something new.
I have an AFR meter that usually shows 13 to 14 on the main circuit and it wants around 12 at idle.
It has more horsepower than I can and dare to use but a little better running and a little less fuel consumption would not hurt, it does 0-100 km / h in about 3.7sec so you do not have time to look at the instruments so much.
I have had the carburetor for a few years so not much is original due to 1 to 1 linkage primary and secondary are exactly the same.
MJ 74
Hi air 36
IFR 33
Idel air 60
axpump 30cc red cam
squirters 31 (intending to try 28)
No power valve
emulsion top to bottom
plugged, hole, hole, hole, plugged. do not know the size drilled in the nozzle plate
Ignition locked at 32 degrees with another 20 degrees with vacuum no starting problems and good throttle response.

What kind of car do you drive, is it just a hobby?
Robert

[Right hand drive]

[Right hand drive]

[Robban 54]

Looks like a nice car, how much does it weigh?
I'm also not so worried about fuel consumption without it going as well as possible.
If you think of the throttle when you are idling and at transfer slot, it is only at the front edge that fuel is added at the rear edge, it is clean air and it may not mix so well.
And the front cylinders are quite close to the front edge where the fuel mixture is, the rear cylinders are further away and perhaps only get air.
After the change, the engine feels stronger and responds better.
It was important that it really was 1 to 1 primary / secondary if you look at the photo of the carburetor, I have made a plate so that the curve starts immediately.
Robert

[rgalajda]

Nice looking cars. Are you in the picture Right hand drive ? I would guess your car to be in the 3600 lb range.
Regarding AFR. I tend to tune on the lean side cruise conditions , steady throttle level road . And appropiate vacuum advance.

454 BBC 500 HP : 227@.050” 107 LSA Camshaft

Holley 780 cfm ( original )
Idle AFR 12.6:1 Cruise AFR 13.5:1

After Tuning
Idle AFR 13:1 Cruise AFR 15.5:1

With a Quadrajet it is not unusual to see AFRs in the 16:1 at cruise

Quadrajet 800 cfm tested
Cruise 15.5:1 and light acceleration 16.5:1

Results will vary but these AFR ratios produced no hesitations or loss of power you could feel on the street.
The Holley carb stopped blubbering at lower speeds.

This is one of Tuners posts (much appreciated)

“On the lean side of stoichiometric, as the AFR is made progressively leaner there is a larger percentage of unburned oxygen in the combustion gasses. As the mixture is leaned, the increasing amount of (now very hot) oxygen in the residual gasses improves combustion. 

Generally, as you jet leaner, the small throttle opening area (light load, vacuum above about 8” or 10” hg.) some engines will get crisper and actually get more power with less throttle, up to 17/1 or so (indicated on a WBO2) before the ‘fishhook’ phenomenon of increased consumption occurs. Some engines with excellent distribution respond increasingly better as high as 18/1, while some engines with poor distribution are struggling at 16/1. The break point is when the leanest cylinder misfires. Before smog tuning began in the mid 60s, most old-school OE engines were tuned to run at about 16.5-17.0/1 up to 50%-75% load. The extent and characteristics of this phenomenon, of course, depend on the valve timing and headers, backpressure, etc, and varies from engine to engine. 

It will help to understand this about the sensors. On the lean side of stoichiometric there is an increasing amount of nitrogen oxides in the exhaust product. The O2 sensor is affected by the presence of the oxygen in the NOx and is reporting a leaner AFR than there actually is. This is not a fault of the sensor or sensor system of any manufacture. It is the physics of the catalysis and ion pump processes by which the sensor itself operates.”

[Right hand drive]

Nah, I’m not in the photo, I’m the good looking guy behind the camera

Not a bad guess on the weight. I had it on a weigh bridge with me in it, it weighs 3350lbs (1520kg). What makes your guess good is it has fiberglass doors and nose cone and aluminum top end on the engine. Things you weren’t to know.

With AFR I tried various target ranges above and below stoich but the way I wanted the car to drive and feel I settled on .94 lambda (13.5 AFR with 14.4 stoich fuel) target @ 60kp/h ramping up to .98 lambda @100kp/h.

Something I had noticed through different tuning strategies is lean surging either occurring or not at the same AFR. Main bleeds and emulsion more like old school Holley would lean surge not much over stoich at lower speeds. When opening up the bleeds and adjusting idle circuit accordingly the lean surge over stoich would all but disappear. It might be as tuner has said in your post, my engine has poor distribution at lower speeds and more emulsion air helps with that and/or the way the sensor is reading the gasses is influenced by a different burn. I guess it would take a 5 gas analyzer to pin that down.

Some info here on how wideband sensors work so I can see what tuner is getting at

https://www.innovatemotorsports.com/resources/news3.php

[Robban 54]

Hello
Was about to mount my boosters.
Discovered that on the underside or the outlet there is a gap around between the insert and the booster.
If I spray with brake cleaning or 556 in the inlet on the booster from the float side, it will of course come out of the 12 holes but also a lot in the gap.
Is there anything to worry about?
Robert

[Right hand drive]