Weber selection and initial jet tuning

[240260280]

Properly tuned Webers. Tis a mechanical thing of beauty.

btw we are lucky with our forgiving 6 cylinders as one throat slightly off (16.7%) at idle  is not as noticeable as on a 4 cylinder (25%).

Edited April 26, 2017 by 240260280

[blodi]

With my brand new webers I was getting different readings between both barrels on all 3 carbs. The rear/right barrel was reading lower on all 3. But got them all dialed in now with the air bleeds. 

Bung is being welded in as we speak. Idle jets here tonight....

[blodi]

Ok Updates....

Bung welded in....so much more accurate and comprehensive readings than the tailpipe clamp the wideband setup came with!  Getting useable readings at idle now/etc. 

Put the 65F9 idle jets in and adjusted idle mixture as needed. Much improvement yet again. Overall...it's idling well..driving at low speed well and AFR's look good at cruise and full throttle.  I also put back in the 185 air jets since I didn't really need to richen up the top in in the first plate. 

The only issue now is if I roll in or stab the throttle quickly....so I'm thinking accel pump jets...right? I have 45's now....go to 50/55? the exhaust jet/valve is the closed off version. 

[240260280]

FYI Bung location in manifold will show fast transients but for sustained periods of throttle, the  tail pipe and bung  shows the same A/F.

Monitor the AF when you stab to see what is going on. That is when the accelerator jets are active. The stab could slow the velocity of the air-fuel charge and cause the fuel to drop out of the charge.

What is your a/f at steady 60mph on flat highway and at 70mph?

 

 

 

[blodi]

With the sensor in the tail pipe I was getting readings at idle in the 30's and 40's...which doesn't make any sense. Now at idle I have it in the 14's.  I'll have to recheck afrs at cruise but I believe it  was ~14.5. 

[240260280]

30's and 40's A/F readings  means outside air is contaminating the measurement.

AF of Stoch (~14.7) at cruise is great to hear! Congratulations!

 

FYI: You can make pipes to collect samples deeper inside the exhaust.  Here is a picture of my home-made copper tube in action:

The 3/4" pipe has a input hole at the far end where the exhaust enters (I used a 1/2" to 3/4" reducer to make the tip input).  The sampled exhaust then travels through the longe 3/4" tube and out to the sensor (still inside the copper pipes) and  loops back in the section below (4X 90 elbows) into a 1/2" pipe that takes the sample back into the tail pipe up to where the 3/4" pipe starts. The 1/2" pipe is capped at its end but a hole in the side of the1/2" pipe (near the cap)  is where the exhaust gas sample exits the copper system). It exits approximately  2 feet  upstream from the sensor you see.  The sampled exhaust is drawn out by the  scavenging effect of  the non-sampled  exhaust pipe gas flowing by the exit  hole in the side of the 1/2" pipe.  This architecture keeps the input and output of the sample way up inside the muffler to prevent outside air contaminating the measurement.

The O2 sensor is screwed into a 3 way coupler that has 2 X 3/4" and 1 X 1/2" ports.  I soldered a 3/4" to 1/2" reducer in the top port and tapped it for the O2 sensor.

 

 

Innovate make a cast fitting that does the same thing:

 

 

BTW:  for SU carb tuning, I often work with an A/F of 30 when disabling one carb at a time. This trick doubles the air so A/F goes from 15:1 to 30:1

 

Edited April 27, 2017 by 240260280

[blodi]

The innovate is exactly what I was using actually. I am using their lm-2 wideband tuner setup.  Ordered the next two larger accel pump jets today. I'll report back on that when they come. I also need to work on my throttle linkage for better idle return.

[240260280]

I guess the Innovative is too short for accurate idle measurements.  That is nice to know.  Makes me happy about my contraption. 

[sweatybetty]

i have read somewhere? that a smaller choke will help with the off-idle stumble. ill post it when i find it

[LeonV]

16 hours ago, sweatybetty said:

i have read somewhere? that a smaller choke will help with the off-idle stumble. ill post it when i find it

A smaller choke could help with a tip-in stumble but not an off-idle stumble. That's controlled by the idle/transition circuit. Tip-in is a function of the main circuit.

[blodi]

I think if the accel jets don't resolve my issue; smaller chokes will be my next step. 

[sweatybetty]

here is the link

http://datsunzgarage.com/weber/