Hi all,

I have a bit of a problem with one of the air mix screws on my carbs.
As you can see the head is quite knackered:


Description

And should look more like this:


Description

After some advice for how I get this out?
I’ve tried hammering a small flathead into it but not getting anywhere….

Ideas welcome!

Thanks
Andy

Drill into it and use an extractor?

The other one is beginning to look iffy too.
Are they tight/seized??
Hammering should help release the threads. Heat may help. Looks like brass, so an extractor may spread the screw and make it harder to get out? You could try drill/tapping, threadlok a machine screw in and see if that works. Or keep drilling until only the threads are left and unpick those.
No easy options though.

Clean the top of the screw and where it sits. Try a little PlusGas penetrating fluid (not orginal WD40 which is a water dispersant) soaked in a number of times over a days. Clean the top of the screw again so no penetrating fluid is on it - go through your tool box for loads of similar sized flat head screwdrivers to see what fits best as there might be one that fits just right (sometimes cheap rubbish ones are usefully poorly made over size/there can be variation between screwdrivers). If the screwdriver is not slipping a slight further tighten (pressure in that direction) can help loosen a thread.. If you can’t get any screwdriver to fit (could even file/cut down the width of a cheap larger sized one) then perhaps a gentle drift anti-clockwise using a punch at a shallow angle in the remains of the screw slot at the right hand side end once you have done the long soaking with PlusGas.

What carb is it - twin choke sidedraft Weber or Dellorto? Maybe time for a rebuild and clean on the bench?

Cheers
Mike

[Edited on 3/12/23 by Mike Wood]

[Edited on 3/12/23 by Mike Wood]

[Edited on 3/12/23 by Mike Wood]

[Edited on 3/12/23 by Mike Wood]

Careful drilling and picking out the threads, as has been suggested,
Localised heat may well do the job, fine torch or heat gun.

If the rest of the assembly was in that state, I'd be doing a complete strip and refurb....

Have you tried a hand impact driver, the hammer blow will tend to shock the threads and help keep the blade engaged.

https://www.amazon.co.uk/Silverline-375291-Soft-Grip-Phillips-15-Pieces/dp/B014EKZMHW/ref=asc_df_B014EKZMHW/?tag=googshopuk-21&linkCode=df0&hv adid=222086461140&hvpos=&hvnetw=g&hvrand=10725824658657004664&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&a mp;hvlocphy=9180769&hvtargid=pla-421299777349&psc=1&mcid=3a6b1eb1b3a83ded8175bb8d390813b1&th=1&psc=1

I've had success with small left hand drill bits, drill gently in. Then an extractor to tease it out.

Approach with care and time and be gentle!

ALSO...it helps to centre punch the offending screw to give you an accurate start point for the left hand drill bit to stop it wandering around when you start!

[Edited on 4/12/23 by nick205]

Thanks all. The rest are all fine and not seized at all, move nice and freely, this one just doesn’t seem to budge.

They’re twin 40 dellortos btw.

I’ll have another attack with the suggestions and see how I do, removed plenty of steel bolts, but never a brass one!

Thanks
Andy

as mike wood said above, use proper penetrating oil **, and possibly try tightening it to break the bond.
** diesel fuel could also work.

Heat is probably your friend here but you'll have to really careful not to melt it! very strange for it to stick so bad, I've been taking apart some carbs so old my dad wasn't even born and they came apart no bother at all after a good soaking in hot petrol (and yes it was dangerous). I wonder if it was cross threaded? This is why its also super important to use good fitting screw drivers, especially on soft metals. Take your time & good luck.

@ pekwah1

Any joy with freeing up and removing the air mix screw?

There seems to have been plenty of advice given and I'm guessing some of us are hoping for success.