Front SU Carb pulling in a TON more air than the rear - Help...

[research monkey]

This is another one of those "i purchased "rebuilt" carbs, instead of rebuilding them myself" threads.   I've been sitting on some rebuilt carbs (purchased online), MSA 6-1 Header, and MSA exhaust for almost a year now... Finally had the opportunity to install them this past weekend.  I ended up pulling the ARA AC unit out as well. 

Before I end up pulling the front carb completely, just wanted to hear more opinions. 

Installed all the parts mentioned above and cleaned up anything I could as I went.  Also threw in some BSPT 1/2" and 1/4" plugs in the balance tube.  New blocks/gaskets for the carbs as well. 

Car fires  up cold with the choke.  Then after its @ operating temp, it'll start right up each time.  Idle is about 1500ish.  I started out originally with the jets turned all the way up and then down 2 full turns and the throttle adjustment nuts all the way in and then back out 2 turns. No matter what i did with the front carb, i could only get it to increase air flow, never reduce.  The synchrometer i'm using shows 7 kg/h on the rear carb and 20-30 kg/h on the front carb. 

Fast idle screw is all the way back out, and I pulled the throttle adjustment screw out of the front carb completely just for the hell of it (thinking that maybe the butterfly wasnt closing completely).  I took some time last night to search on the forums and google for anything.  Everything pointed to maybe a vacuum leak somewhere.  So today, i went and checked all the vacuum lines and plugs.  I sprayed a little carb cleaner in various areas (balance tube gaskets and blocks, intake manifold where it meets the head, line that goes to the brake booster, carb blocks/gasket area etc) and never got the rpms to increase. 

Also pulled the dashpots and cylinders and made sure they were clean on the inside.  I used 3 in 1 oil for the dampers.  Return springs on the throttles look good and i believe attached correctly.  Vacuum advance is plugged into the front carb. 

I have new plugs, points, rotor, cap, plug wires, coil etc. and they are ready to go in but I wanted to make sure I could get the car to idle under 1000 before i started messing with any of that.  The car ran fine on the old SU carbs, compression was good, i believe the timing was at 10 degrees @ idle 700 rpms 

 

 

[siteunseen]

Shouldn't the choke cable be all the way down? Looks like yours is up.

[siteunseen]

Here's mine with the choke off.

[research monkey]

47 minutes ago, siteunseen said:

Here's mine with the choke off.

Thanks, it did seem a little stuck on the return.  I unhooked the choke cables and the air flow dropped down to between 15-20.  The throttle adjust is still basically all the way out though so still trying to mess with it. 

[research monkey]

Going to swap the front carb with my other one at this point to see if the issue continues. 

[research monkey]

Welp, without even an adjustment a simple swap over to the old carb and voila... issue gone.  So now I guess I need to breakdown this carb and see where it went wrong with the previous owners rebuild. 

[research monkey]

I think I found the problem.  Butterfly had ZERO play and the shaft holding it looks bent... 

[siteunseen]

This may be of some help. I've never seen that before myself.

Here's a bunch of threads on those shafts...

https://www.google.com/search?client=ms-android-americamovil-us-revc&ei=S44PX-W8LsuOggebw6ngCA&q=bent+su+butterfly+shaft+classiczcars.com&oq=bent+su+butterfly+shaft+classiczcars.com&gs_lcp=ChNtb2JpbGUtZ3dzLXdpei1zZXJwEANQAFgAYJ41aABwAHgAgAHdAYgB3QGSAQMyLTGYAQA&sclient=mobile-gws-wiz-serp

[Mark Maras]

 Sell it to ZTherapy.

[research monkey]

1 minute ago, Mark Maras said:

 Sell it to ZTherapy.

They buy carbs? 

I think i'll purchase the parts I need for the "rebuilt" carb and put it back together.  Then throw it back in the car.  Then maybe I'll rebuild and clean up the old pair that I have. 

[7tooZ]

One of the problems with old SUs is the butterfly shaft bushings get worn and leak. Z therapy replaces them with roller bearings instead of brass bushings. Good luck though and post up your journey. 

[Patcon]

2 hours ago, research monkey said:

I think I found the problem.  Butterfly had ZERO play and the shaft holding it looks bent... 

The shaft screws are normally staked. It looks like someone got a little carried away staking that one. the shafts bend easily...