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Carburetor Tuning Thread for B Series

The choke cable sheath might be slipping at the clamp under the dash if the jet tubes aren't moving. The clamp will only hold the sheath if it has the plastic coating on it. It's common for the plastic to crack and come off the inner metal sheath. If the sheath is long enough it can be trimmed but the plastic cover is likely brittle and will break again eventually. It can also happen at the clips on the carb bodies but it will be obvious if that's the case.
 
Going back to Weber DCOE carbs. I am building a B20 with Tinus Tuning 2.6L stroker kit. It is assembled and waiting for some head work on a F head: porting, larger valves (46mm intake, 38mm exhaust), enlarged chambers for unshrouding the valves - probably to around 59cc, Isky double springs, stock rockers. The block has a 97mm stroke, 92mm bore, forged pistons and rods, balanced and mildly blueprinted. Pistons have 6cc dish and are .010" below deck. I will use a Cometic .027" head gasket, so squish will be about .037". Static compression will depend on how the chamber size turns out, but I expect it will be around 10.3:1. I don't know about dynamic. I have a Tinus Tuning TT7 cam.

I have a pair of Weber DCOE 45 carbs. I don't know the history on these carbs. I cleaned and reconditioned them and plan to use them on the stroker B20. I think they are early DCOE 9 carb bodies. They are Italian bodies with 2 progression holes. Here is the current jetting and configuration, which is what was in the carbs when they came to me:

Progression holes 2
Throttle plates 78
Main venturi (choke) 38
Aux venturi 4.5
Emulsion tube F2
Main jet 145
Air correction jet 160
Acceleration jet 45
Idling jet 50F9
Cold start (choke) jet 6055
Needle valve (spring) 225
Accel pump return 70

I would welcome any thoughts and suggestions as to jetting, etc.
 
It's my turn!

My recently installed Dellorto DHLA 40s are giving me quite the headache, literally.

Setup:
Dual DHLA 40s, non lettered early carbs via: For sale post
-55 idle jets in currently
-210 air correctors
-135 main jets
-32 mm chokes
Carbs baselined per typical DHLA setup, 2.5 screws out on idle screws
Volvo Comp Services intake
Throttle linkage setup
Misab vibration style carb mounts
Holley FPR set to 3 PSI
Facet 40007 Fuel pump
123 Distributor set to 12 BTDC at 1K RPM
Ran the valves to .016


I am having quite bad backfiring issues with the carbs. Full on fireballs out the intake.
Its really rough starting as well, can't get it to idle at all. Not using the choke mechanism at all.

The carbs appear to be quite wet in the barrel when I go take a look, also appears to be some wetness on the throttle shaft?

I've read that this can be a lean issue? This setup should be set to run relatively rich from my understanding.

Previously this car had a Weber DGV 32/36. While I wasn't a fan, it never exhibited any backfiring issues like this.

Would love any help as this car needs to drive up onto a trailer in about 3 weeks and I would prefer to not have to put the DGV setup back on.
 
GeorgiaTechFan12 said:
It's my turn!

My recently installed Dellorto DHLA 40s are giving me quite the headache, literally.

Setup:
Dual DHLA 40s, non lettered early carbs via: For sale post
-55 idle jets in currently
-210 air correctors
-135 main jets
-32 mm chokes
Carbs baselined per typical DHLA setup, 2.5 screws out on idle screws
Volvo Comp Services intake
Throttle linkage setup
Misab vibration style carb mounts
Holley FPR set to 3 PSI
Facet 40007 Fuel pump
123 Distributor set to 12 BTDC at 1K RPM
Ran the valves to .016


I am having quite bad backfiring issues with the carbs. Full on fireballs out the intake.
Its really rough starting as well, can't get it to idle at all. Not using the choke mechanism at all.

The carbs appear to be quite wet in the barrel when I go take a look, also appears to be some wetness on the throttle shaft?

I've read that this can be a lean issue? This setup should be set to run relatively rich from my understanding.

Previously this car had a Weber DGV 32/36. While I wasn't a fan, it never exhibited any backfiring issues like this.

Would love any help as this car needs to drive up onto a trailer in about 3 weeks and I would prefer to not have to put the DGV setup back on.
Click to expand...
Do you have any vacuum leaks and is the float height set correctly?
 
spock345 said:
Do you have any vacuum leaks and is the float height set correctly?
Click to expand...
I plugged all the vacuum ports to try and eliminate all possible vacuum leaks for the time being.

One thing I considered is it possible that the vibration mounts need to be super tight?

Float height is set to 18mm on both, with gasket, per some Alfa forum I found.

Edit: It has the 10g floats, Float height method
 
GeorgiaTechFan12 said:
It's my turn!

My recently installed Dellorto DHLA 40s are giving me quite the headache, literally.

Setup:
Dual DHLA 40s, non lettered early carbs via: For sale post
-55 idle jets in currently
-210 air correctors
-135 main jets
-32 mm chokes
Carbs baselined per typical DHLA setup, 2.5 screws out on idle screws
Volvo Comp Services intake
Throttle linkage setup
Misab vibration style carb mounts
Holley FPR set to 3 PSI
Facet 40007 Fuel pump
123 Distributor set to 12 BTDC at 1K RPM
Ran the valves to .016


I am having quite bad backfiring issues with the carbs. Full on fireballs out the intake.
Its really rough starting as well, can't get it to idle at all. Not using the choke mechanism at all.

The carbs appear to be quite wet in the barrel when I go take a look, also appears to be some wetness on the throttle shaft?

I've read that this can be a lean issue? This setup should be set to run relatively rich from my understanding.

Previously this car had a Weber DGV 32/36. While I wasn't a fan, it never exhibited any backfiring issues like this.

Would love any help as this car needs to drive up onto a trailer in about 3 weeks and I would prefer to not have to put the DGV setup back on.
Click to expand...

Your list looks great except for your air correctors, those are way too big hence your lean condition assuming you have no vacuum leaks elsewhere. I would try something in the 180 range, rule of thumb for setup is main jet size +50 and then fine tune from there.

Assuming the timing and valves are set and float bowl is correct height, disconnect the linkage, set idle screws to 1/2 turn off their stops, then adjust each mixture screw while listening to best fast idle, work your way down the barrels, take your carb air meter (sync), go down each barrel, pairs should match, on my meter I believe at 1,000 rpm the meter reads between 5 and 6. Once all the barrels match, hook up the linkage and give it some blips. If it continues to backfire then richen up all the barrels a 1/4 turn on the mixture, if it bogs you have too much fuel and might want to step down a size on jetting.

Good luck. Aren't dual carbs fun?!?
 
R32RennSport said:
Your list looks great except for your air correctors, those are way too big hence your lean condition assuming you have no vacuum leaks elsewhere. I would try something in the 180 range, rule of thumb for setup is main jet size +50 and then fine tune from there.

Assuming the timing and valves are set and float bowl is correct height, disconnect the linkage, set idle screws to 1/2 turn off their stops, then adjust each mixture screw while listening to best fast idle, work your way down the barrels, take your carb air meter (sync), go down each barrel, pairs should match, on my meter I believe at 1,000 rpm the meter reads between 5 and 6. Once all the barrels match, hook up the linkage and give it some blips. If it continues to backfire then richen up all the barrels a 1/4 turn on the mixture, if it bogs you have too much fuel and might want to step down a size on jetting.

Good luck. Aren't dual carbs fun?!?
Click to expand...
The carbs only have a idle screw on one with one of those interlink linkages like an Alfa. I'm pretty sure these carbs originally came from an Alfa.

Another approach is to unscrew the plugs over the progression holes and get them close to balanced by shining a light down the throats and looking at where the throttle plates are.
 
^^^ This method also works very well for initial setup. With an interlink setup (I have one as well), I always keep an extra idle screw handy for set up as I left a lever arm on the outside of the slave carb.

 
Problem appears to be solved.

I can't take any credit for this, CoPilot came up with the solution.

I took apart the rear carb Idle jet and sprayed it down with carb clean. I'm not sure if it was clogged or air locked but it runs insanely better.
There are still some ITB popping and burping, but no more fire.

Thanks for the help TB, I'm sure I'll be back in this thread for more soon.
 
My 164 is currently set up as the following

Engine:
  • B30A Standard bore
  • 9.3:1 compression, Standard
  • Full teardown and rebuild with <2k miles.
  • Twin cast 3-1 manifolds with 2" dual exhaust
  • Skandix DCOE intake manifolds
  • Standard timing
Carbs: FAJS - Chinese reproduction, Australian re-tooling, genuine Weber internals
  • 45 DCOE
  • 36mm main venturis
  • 4.5mm secondary venturis
  • 1.65mm main fuel jet
  • 1.75mm air reduction jet
  • F-16 emulsion tube
  • 50 F8 Indle Jet
  • 0.35 mm discharge opening on the acceleration Jet
  • 0.6mm bleed/return valve
  • F5 65 choke jet (not married to this, but I don't do a lot of cold-weather driving)
  • 1.5mm needle valve for the float.
I've been sitting on this project for three years. I put it down to rebuild a '79 Goldwing last summer, and only YESTERDAY started it with proper float levels. Cranked right over with full choke and a gravity drip....
 

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Last edited:
cbevis said:
My 164 is currently set up as the following

Engine:
  • B30A Standard bore
  • 9.3:1 compression, Standard
  • Full teardown and rebuild with <2k miles.
  • Twin cast 3-1 manifolds with 2" dual exhaust
  • Skandix DCOE intake manifolds
  • Standard timing
Carbs: FAJS - Chinese reproduction, Australian re-tooling, genuine Weber internals
  • 45 DCOE
  • 36mm main venturis
  • 4.5mm secondary venturis
  • 1.65mm main fuel jet
  • 1.75mm air reduction jet
  • F-16 emulsion tube
  • 50 F8 Indle Jet
  • 0.35 mm discharge opening on the acceleration Jet
  • 0.6mm bleed/return valve
  • F5 65 choke jet (not married to this, but I don't do a lot of cold-weather driving)
  • 1.5mm needle valve for the float.
I've been sitting on this project for three years. I put it down to rebuild a '79 Goldwing last summer, and only YESTERDAY started it with proper float levels. Cranked right over with full choke and a gravity drip....
Click to expand...
You should move that pump back towards the tank. Electric pumps do best pushing, not pulling.
 
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