Weber carb question...

[MWP]

Hi all,

Can anyone tell me exactly what adjustment screw #25 does?
Its down the bottom of the image below.

I rebuilt my carb a few days ago, and its now ideling very rich.
This #25 setting screw is the only change thats been made.



Thanks!

[ViPeR_NiPPleX]

idle fuel adjustment by the look of it. Looks smaller than a 32/36..

[MWP]

That image is just of a similar carb that has the same screw.
Mine is a 34ADM (off the Falcon 6cyl).

Guess ill try a few different settings, see what difference it makes.
Pitty the screw is a real PITA to access

[ViPeR_NiPPleX]

typical sorts of setting is screw it all the way in (not too tight now) and back it out two turns. From there you will have to fine tune it. I found mine would idle brilliantly with more fuel, as having it a bit lean it would idle ok for about 2-3 seconds after startup and then complain a bit.

[MWP]

Ok, thanks.
At the moment the idle speed is set very high to keep it going and it splutters.
After idleing for a while and then driving off i get a big puff of black smoke.
So i guess its wound out too far at the moment.

[toddw]

Usually you wind it in until it runs rough and then wind it out 1.5 turns or there abouts until it smooths out. It is only the idle mixture for the idle curcuit but it will run rich if it is to far out.

[brett_celicacoupe]

for motorbikes, we screw them in all the way, then screw them out 1.5

then make adjustments from there.

its best to take the screw out and check the needle in the end hasnt broken off inside the hole as this is common. people scremt them in too much and the thin part of the needle wedges and snaps.

spray some carby cleaner through it while you have it out.

make sure the o-ring is there as well

[gixer]

It's idle mixture adj screw, another easy way of adjusting is to screw it out say 2 turns, then start the car, if it is running rough screw out more if it runs rougher screw in. now when it gets to a point where it is running quite smooth, screw it in to the note of the engine changes(not smooth) when this happens start to screw out, as you screw out count how many turns it takes to start running rough again, now screw it back in about half the number of turns you counted, on just about every carb car I have ever worked on this puts it just about smack on. This is the sweetest way to adj carbs on rotors.

[allencr]

All the above is OK.
If it's out more then 3 turns, the idle jet is too lean - if it's in more then 1/2 turn, the idle jet is too rich.
ONLY adjust it when the engine it at operating temperature or 'stinking hot'. Idling for 15 minutes IS NOT at operating temperature!!!

I rebuilt my carb

usually scares me!

[MWP]

Thanks all!
Ill have a go at it tomorrow.

Rebuilding it was very easy... ive done a few different carbs now.

[Screamn_Sleeka]

When driving/accelerating, this screw does nothing. If you are puffing black smoke when you accelerate, you need to buy smaller sized components for the carby.

As for tuning the idel mixture, you adjust it to max revs, then back until it JUST starts to drop in revs, then u take it back to half way between the two. Thats the best way to do it without a oxygen lambda sensor.

[MWP]

When driving/accelerating, this screw does nothing. If you are puffing black smoke when you accelerate, you need to buy smaller sized components for the carby.

Nope, its just on idle.
Ive tuned the rest of the rev range (resized jets & air correctors).

[Screamn_Sleeka]

Then if the idle mixture screw can not tune the idle correctly, you need new idle jets.
If this is 34ADM for a M series engine, it defiantly needs smaller idle jets.
I don't know if you can buy small ones, you might have to make them

[MWP]

The 34ADM is on a 21R.
I dont buy jets, i solder them up and re-drill them.

[Screamn_Sleeka]

You'll get better efficiency with a 32/36.
34ADM is like a square ball.

But yeah, try re-sizing them a bit smaller.