Stuck Slow Idle Screw

[Pianoman]

My slow idle screw is stuck. Previous mechanic has obviously unsuccessfully had a go at it. Any ideas? I tried spraying wd40 but it still hasn't budged.

[abowie]

First question. Do you really need to remove the screw? As a temporising measure you can use the fast idle screw to increase idle, pending a full carb removal and rebuild in the future.

If yes...

There are 2 common problems. First, the o ring seal at the top fossilizes. The second is that the screw itself rusts on the threads and the conical section.

Many options for removal, but some require removal of the carburettor which is a bit of work.

First, try firmly tapping the screw head using an appropriate sized screwdriver and a steel hammer.

Don't go crazy as you don't want to damage the aluminium housing. Do this repeatedly, and every now and then try rotating the screw in BOTH directions to see if it will budge. Make sure your screwdriver is a good fit as you don't want to mar the screw head any more. This often works, but takes a while.

If you can get a pair of mole grips onto the handle of your screwdriver try this; you'll get more torque. Make sure you are applying a lot of downwards force as well as you don't want to strip the screw head.

If you have one you could try an impact driver, but be gentle. Rotate the handle of the driver in the direction to take up the slack then tap with a hammer. Lots of small taps are best. Again it's worth trying it in both direction.

If you have no success you'll need to take the carby off because this is the point where you start using heat, and you can't do that on a petrol containing device in an engine bay.

If you still can't get it out consider sending it to a carburettor specialist. IF you drill it out and damage the seat in the body you will be up for a new body.

FWIW, if you get to the point where you need to remove one carby I'd take the lot off and take the opportunity to strip and rebuild the whole set.

It's actually easier to remove all 3 carbs as a unit, on the manifold, especially on a RHD car.

[Robbiee]

I rebuilt mine ..really fun job
Take lots of photos
Don’t swap parts between carbs
Good luck

[christopher storey]

One of the best releasing agents is diesel fuel ; try infiltrating small amounts into the screw/body interface at intervals of a couple of days over perhaps 2 weeks, and then try the measures Andrew has suggested above

[steve3.8]

Some have had success with the freeze spray from screwfix , you could cycle heat and cold by using a heavy duty soldering iron on the screw--

[Phil P]

My carbs were in a terrible state as the car is non-runner and 2 of the slow running screws were stuck. Fortunately, my carbs were already disassembled and I tried the usual methods - Plus Gas, heat gun to get the differential expansion of the aluminium/zinc body over the steel screw but all to no avail. I ended up shearing the 2 screws and eventually found a local garage who could remove them by spark erosion. This was successful at a cost £150 (albeit cheaper than £300/body to replace them and retain the original bodies) but I discovered that the jet (seat) of one body had corroded completely. As a result, I manufactured a combined jet and sleeve for the body from brass with a 5/16 BCS thread and spark eroded cross hole. This had a sliding fit into the enlarged hole in the body and was glued in place with Loctite 577. It's essential that you drill the jet and tapping hole for the thread in one operation so that the screw is concentric with the jet.
I tried to attach a couple of photos but even at only 340kB it said that they were too big.
Yours,
Phil

[Pianoman]

Thanks everyone, I am going to take all your suggestions on board and see how I go. Total novice here so sorry if my questions are newbie grade
thanks