Zenith 40 TIN 2.7 32mm venturi, need help jetting, data logs
 

Hi
I have a 74' 2.7 stock 150bhp i bought from a guy in this forum a couple of months ago.
After fixing a lot of errors from PO (2 different spark plugs, defect spark cables, 3 different idle jet sizes, drilled main jets, and a Facet fuel pump with open return line and the list goes on)
Zenith 40 TIN, i have rebuilt them and airflow calibrated them,and now idles at 12.5AFR
Float levels calibrated.
Ignition adjusted, and distributor cleaned

I have:
Venturi = 32
Main jet = 135
Air jet = 180
Idle jet = 55

My inlet head port diameter is 30mm.
I had to open the idle jet to 65 to get it to stop stumbling from Idle.
But my log now show way lean with this setup.

I tried to slowly accelerate to 4000rpm and then floor it to see if it was the fuel pump that could not maintain fuel level, but still lean.
So should i start increasing main jets?
I've read many people using the same jetting as i bought, and i guess they don't run lean?
http://forums.pelicanparts.com/porsche-911-technical-forum/501767-zenith-carbs.html

My log is going moderate uphill starting in 2.gear and going through 3.gear, but shifting at 5500rpm when i saw how lean it was

http://forums.pelicanparts.com/uploa...1370299189.jpg
http://forums.pelicanparts.com/uploa...1370299198.jpg
http://forums.pelicanparts.com/uploa...1370299206.jpg

Today i started to increase main jet in 3 steps

These graphs are 2.gear flat road, pull from 2k rpm

http://forums.pelicanparts.com/uploa...1370374542.jpg
http://forums.pelicanparts.com/uploa...1370374584.jpg
http://forums.pelicanparts.com/uploa...1370374593.jpg

It's getting better, i think i'm close to145 for the main jet now.
The top dotted line is 14AFR end the bottom 11AFR

Has anything else been done to the engine, ie, cams, pistons? Still have the cis cams?

Its nice to have the graphs.
A couple of thoughts:
1) If you are progressively opening the throttle from 2 to 5k consider that the accel pump is adding fuel, and the transition from the idle cicuit to mains is occuring at some rpm say ~2500.
2) An interesting graph would be steady state at say 3,4,5k.
then 3 to 5 at WOT and 3 to 5 with progressive opening.

George

As far as i know it is a stock engine, matching numbers for engine and tranny, but then again it's 39years old, and i don't have any history of it.

1) i'm cruising at 2k rpm, then flooring it to about 6k
I'm going to open up then main jets a bit more tomorrow, i can do som additional logs then

I have a few sets to Zenith. Just a couple of thoughts:

Nozzles for the Accel pump are tiny, make sure they are not plugged and are spraying? I've read here (from JW) that with our current fuel, he drills out the idle jet a bit.

Any accurate jetting involves taking temp and attitude into consideration. G'luck...

I've had the carbs in molecules to clean them, acc injectors are working, and i have adjusted them to give max.
Idle jet i have already opened up.

I have a modified stock muffler, i have now 2 outlets near center, so back pressure must be less then stock, noise is a lot more..

Getting close now. I might have to get a slightly smaller Air correction jethttp://forums.pelicanparts.com/uploa...1370730690.jpg

Yes, what are you up to now, 145s

That looks more like a fuel volume issue.

Your jet settings are close to realistic, I would have started with a 145 main and 55 idle is all you would need.

Is there corrosion in the emulsion tube wells?

I'm up to 145' main jets now
I think i should have increased the idle jet and main at the same time, instead of doing the idle jets first then the mains.
I now have 10,5AFR cruising at 2krpm , so i have to get some smaller idle jets now.
But the mains should be ok, there is a massive difference from when i started to how it's running now.

Emulsion tubes and internal are clean, no corrosion.

Hi Guys

I've seen heaps of these Zenith threads with data capture screens showing various results taken while the car id driven. This is something I'd like to try, how do i go about doing this, what s/w h/w do I need and what is the sampling mechanism on the car, i assume o2 sensor in exhaust.

would love to know the details on how this is done

cheers