SB Needles to Resolve Lean WOT with SUs

[Jeff G 78]

There must be some other factor at work that we are missing.  I guess as long as you found a solution, all is good.  

[Captain Obvious]

I believe there are other factors at play as well, but as long as the problem is gone, it's hard to argue with success.

2 hours ago, duffman said:

I wish I had the RH needles to see how different they would be on my car.

I think I have a pair of RH needles if you would like to give them a try.  PM me?

[Stanley]

Don't see any RH or SB but this one in Riverside has a lot of needles.

https://www.aptfast.com/ListItems.aspx?RootCat=SU%3A Needles&page=2&

[german240]

I think it is incredible easy to get the SUs "working". However, fine tuning is difficult! 

What I did so far: 

1. Data logging with SM needles (AFR/Rpm with Zeitronix ZT2) -> too lean from 3000 rpm on, mixture nut had to be dropped by 4.5 turns as a base setting. I used the SM needle as starting point and selected the RH needles
2. Checking AFRs during hard acceleration -> changed to ATF damper oil, now my AFR drops perfectly to around 12,5
3. Setting fuel bowl level with clear hose and banjo bolt: The only way to do it right. I tried it according to the FSM before, and the fuel levels were way off. I also noticed, that my rear carb (short ears) had a long needle valve installed. Therefore, I ran out of adjustment and couldn't raise the fuel level high enough. So far, both carbs are at the same level but 2mm too low. I'm  not sure how this affects overall performance (much discussed topic). 

4. To do: Install some sort of LVDT sensor / potentiometer in order to record the actual piston position. I want to know where the piston sits at cruise speeds as the needle seems to be too rich just in this area (AFR 13,5-14)

 

[Jeff G 78]

I like the banjo bolt idea!  I will use that.  Do you have the banjo specs handy?

[german240]

Quote

4 minutes ago, Jeff G 78 said:

I like the banjo bolt idea!  I will use that.  Do you have the banjo specs handy?

 

It is M8x1

[Jeff G 78]

Thanks, I'll grab a pair.  I have always struggled with the float heights.  Several years ago, I posted my method which involved using a clear water bottle as a surrogate bowl so I could set the floats and not have to take the bowls off and reinstall them over than over.  It worked okay, but it still wasn't super accurate.  The banjo bolt setup should yield much better results. 

[Captain Obvious]

That banjo bolt is a cheap and simple way to check the levels, but it only works on the bowls with the drain hole. If you don't have that hole, you still need to splice into the hose between the bowl and the nozzle.

Same for this device:

[Mark Maras]

20 hours ago, Jeff G 78 said:

There must be some other factor at work that we are missing.  I guess as long as you found a solution, all is good.  

I'm curious the weight of oil everyone is using that is experiencing a lean condition at WOT. Heavier weight oil is supposed to richen the mixture at WOT. 

[german240]

Oil viscosity doesn't affect wot performance at all as it only determines the mixture during the first 1-3s of acceleration. 

Thin oil =faster rising piston = less vacuum to draw fuel = leaner 

Thick oil = richer 

Edited March 1, 2019 by german240

[Jeff G 78]

I run 20 weight.

[Duffman]

Just participated in a 200 mile drive through some old AZ mining towns yesterday, had a great time!  The Z ran outstanding on cruise and acceleration, good AFR numbers.  I did notice a few rich spots (around 12 AFR), but all around very good.  Got 25.5 mpg driving through the hills, am happy with that! 

Am going to order the RH needles for comparison purposes, and possibly lean out a few spots in the range.  Am very happy with the SB needles, just love to tinker!