Best screwdriver for adjusting 70's Ford Carburetor idle mixture screws?

After fixing a leaking power-valve, I now need to re-adjust my Ford truck’s idle mixture screws, located at the base of the carburetor. The screws are a straight slot on the head, not a Phillips. It’s a very frustrating job b/c of the slotted screw head and their location. The distributor and fuel filter are both in the way. A long screwdriver doesn’t meet the screw dead-on b/c of the distributor, but allows me to see what I’m doing. A short screwdriver clears the distributor so it meets the screw dead on, but my hand is in the way then so I can’t see what I’m doing. In either case the screwdriver keeps slipping out of the slot as I turn the screw.

I got to thinking there must be a better way. My current idea is to wrap a short screwdriver with some elastic bands near the tip, then friction fit a piece of tubing over the end of the screwdriver, the tubing (copper, plastic, not sure?) just a little bigger than the head of the screw. Then – at least in theory – the screwdriver will be forced to stay on the head of the screw by the tubing. Any easier or more likely to work ideas out there in Car Talk Forum land?

Edit: Forgot to ask another related question. I’m thinking of using on old O2 sensor – which I think still works – to assist. My idea, I’ll shove the sensor as far into the tailpipe as I can, and read the voltage it produces while I’m adjusting the idle mixture screws. I’ll start with a rich mixture so there should be no O2 coming out the tailpipe, then adjust in the lean direction, and stop adjusting when the O2 signal just appears. What do you think? One problem I can think of, the O2 sensor may need to have the outside part out of the exhaust stream to work properly.

what you need is a “Slotted Screw-Holding Screwdriver”, or what I call a split tip screwdriver.

you can see one at here
but you need to go to a hardware store to find the proper size.

I made this screwdriver over forty years ago to adjust mixture screws on carbs.


That spring version might just work. And I have a spring like that on hand doing absolutely nothing at the momement. It may be time to put it to work. Good idea.

Sears sells this one in the store near me:

They also sell hundreds more on line. Just search for “screw holding screwdriver”. Maybe you will find something you like.


I don’t think these people know how hard it is to reach the idle adjustment screws on a carb.

That’s why I made the tool.


Yeah, there’s the keeping the screw driver in the slot and on the head part of the problem, and just getting the screwdriver to where it needs to go part of the problem.

...the O2 sensor may need to have the outside part out of the exhaust stream to work properly.

Yes, it does.

Carburetor adjusting tool;

I would highly recommend the tool shown by Nevada. I bought one of those way back in the day and it would get me to the screws on any carburetor made.
Mine is a Snap-On so that might be prohibitively pricy today. Maybe a more inexpensive version can be had???

I also strongly recommend the tool shown by Nevada. The Allen wrench shown on the far right is for adjusting the points through the window in the distributor cap on GM products.

I don’t use it often any more, but when I do, it’s priceless.

I thought that tool might be discontinued/obsolete but it is still available from Snap-On for only $106.40;

I probable paid just $80 for that tool 30 years ago while working for $5 per hour, just 16 hours of labor to pay for one tool.

There are a few on Ebay without the sockets for $15-27;

This is something to look for at swap meets/flee markets. This might be found for less than ten dollars, people selling old tools like this may not know what they are for.

While I seem to recall adjusting Ford idle mixtures with my bare fingers Rochesters did require that dog leg tool or for the shade tree DIY slipping a piece of vinyl hose over the end of a screw driver would help keep the screw driver in the slot. Of course the tamper proofs were sometimes difficult to remove and resulted in bent needles that were really difficult to keep a screw driver on.

Check Amazon for flexible shaft screwdrivers. You could use the Tygon tube over the flexible shaft.

The tool I used had the blade made out of bent wire crimped into an aluminum shaft, with a red plastic handle. Sound familiar to anyone?

Good ideas above. It sounds like this problem has already been solved and I just need to get with the plan and obtain the right tool for the job.

JayWB: I still have my GM dwell adjustment tool. It has a chuck and 5 Allen wrenches although all GMs seemed to use one size. It has a flexible shaft with screwdriver type handle. When used with a dwell meter it was really to easy. Idle air adjustment screws tended to have a generous slot. I just used a large blade stubby screwdriver.

Rod Knox: Ford Autolite and Holley carbs with the groves on the idle air adjustment screws could be adjusted with fingers. I had forgot about the stupid plastic tamper proof caps which allowed maybe a 1/4 turn of adjustment. with a little care they could be pried off without damage.

@GeorgeSanJose, have you considered replacing those adjustment screws with Allen head screws? You can probably find them, and they shouldn’t cost too much. Then you can adjust then easily with a flexible shaft screw driver and the proper Allen head attachment.

Vacuum hose works well.