Weber DGAV 32/36 33B rebuild - leftover brass screw

[marlin1881]

I've looked and looked, but I'm not finding where this small screw should go.  Slotted head, no ports/jets. 

 

And, there are 2 identical springs in this carb, except for tension pressure; 1 in accelerator pump and 1 in the choke diaphragm.  It seems to me that the heavier tension goes in the accelerator pump.

 

Thanks in advance!

 

[TobyB]

That looks like it could be a drilling plug- is the carb older?

 

They cap the end of the cross drillings that carry fuel around

the carb- they look like bumps from the outside.

 

There's no choke diaphragm- do you mean the power valve?

 

t

 

[marlin1881]

This carb has a choke diaphragm as I just bought a new one to replace the old one with cracks in it.  In the attached pic, the assembled diaphragm housing is on the left, with the main shaft running horizontal through the housing where the water cavity mounts to, with the radial spring to pull the choke plates shut (I hope that makes sense).  This is a water heated choke system, and there's also a vacuum port going to the far left side of the housing.  This choke diaphragm uses the same diameter and length of spring as the accelerator pump, but one of them uses the lighter pressure spring.  They both "feel" about right with the lighter one in the choke, and the heavier in the accelerator pump.  If someone knows for sure, I'd like verification on that.

 

Good point on the screw used to block off some cross-drilling.  It's got to be there somewhere, or it's underneath some other plug/screw/etc.  It was so obvious when I took it apart...  That's the only thing keeping me from putting the carb back on the car.  The little screw looks like it's quite useful.

 

I also replaced the power valve as the diaphragm was shot on that as well, but it's bolted to the upper cover of the carb.

 

[TobyB]

Oh- right, choke pull- off.  

 

Try using compressed air to see if you can find a leak.

 

Having said that, the block- off screws often have a tapered seat, like the

diaphragm holding screws in your pic do.  So now I'm doubting myself

on that, too.

 

https://www.lainefamily.com/images/WeberTuningManual.pdf

 

if it helps.

 

t

 

[marlin1881]

Found it.  Can't say where, as you guys wouldn't think very highly of me...

 

OK.  Once I put the accelerator pump together I immediately saw it.  There's an extra threaded hole in the top rim of the bowl, just above the accelerator pump.  It looks kinda like a top cover mounting hole.  Little brass screw went below flush, and it looks to be in line with the fuel source for the pump.  Might be an important little screw...

 

Thanks for the help and the Weber reference.  I'll use that along with the Weber manual I bought from Pegasus Auto Racing, where I get a lot of my parts.

Edited March 26, 2023 by marlin1881

[marlin1881]

Once I got the idle and the mixture set, the motor purrs at 800 rpm just like it's supposed to.  Taking it off idle, it stumbles a bit and doesn't run smooth like it should.  You can smell it's running rich.  I'm on the front range of Colorado at 5000 feet.  From what I've read, I'll be increasing the air jet size.  I don't want to reduce fuel jets just yet.

 

[TobyB]

If it stumbles rich on transition, try a smaller idle jet.

 

????

 

Yep!  The 'idles' also affect the 'just off idle' mixture, too.

The idle screw draws its fuel through that circuit- is your idle screw 

in quite a ways?  Or is it almost all the way out?

That's the classic indication as to whether the 'idle' jet is too big or too small,

but it's not failsafe.

 

On a 32/36, that transition circuit's not fuelling by itself for very long-

in neutral, maybe from off idle to 2000 rpm or so, and then the main circuit of the

primary barrel kicks in.  Under power, it's really just preventing a bog when you start to let out the clutch.

It's also possible that the transition circuit's plugged- it has a couple of bends 

and turns in it, and then ends in a couple of tiny holes just after the primary butterfly...

  I know you said it smells rich, but if it's so lean it's misfiring, you may smell fuel, too.

But rich and lean feel and sound different- and if it feels rich,  then try a smaller 'idle' jet to see what happens...

 

As to air corrector vs. fuel jet, the jet itself sets the mixture at lower rpms, and then the air corrector

starts to affect the mixture as flow increases.  So if it's rich at lower loads/rpm, you start by adjusting (reducing)

the fuel jet. Then as revs and load increase, if it goes rich, you INCREASE the air corrector,

and if it goes lean, you DECREASE the air.  Think of it as diluting the fuel by adding air to it- 'cause that's what it does!

 

t

it's almost like science...

 

[marlin1881]

TobyB,  Thanks for the explanation.  That makes sense.

 

I bought the Redline high-altitude kit 701-DGV4-A and it should arrive early next week.  Here are the jets I'm getting, which should work well for Colorado at 5000'.

• Primary Idle Jets: 060, 65, 70, 75
• Secondary Idle Jets: 050, 55
• Main Jets: 135, 140, 145, 150
• Air Corrector: 180, 190, 200, 210, 215

What's not clear is whether the idle jets are Large or Small.  I've got the solenoid shutoff on Primary which requires Large.  The Secondary jet holder requires Small.  I'll report back.

 

I mentioned that my engine runs very well at idle, but the mixture screw is only open 3/4 turn, with 1-1/2 on the speed screw.  I'll need to bump the idle jet down a couple notches or so.

 

But, off idle, it runs rough.  So, I'm thinking I'll have to increase the air jets and/or decrease the main jets.

 

When the motor is cold and the choke plates are shut, it runs terrible rich.  Swapping Mains should help with that.

 

I've got some experimenting to do.  Pics and diagrams on this forum, along with responses have been very helpful.  Braden's Weber book is very good.

 

Edited March 31, 2023 by marlin1881