4 cyl CARB question

[R.White]

As I have been having a few problems with the carb I thought it would be a good idea to strip and clean everything while making a few repairs. I must say though, I have never encountered a carb quite like this!!

My question is: I understand from what I have read that the air valve should be removeable from the body of the carb. How do I get it out?

It moves up off it's seating as it should but does not come right out. Could someone steer me in the right direction please.

Ray

[Pete K.]

[ATTACH=CONFIG]171412[/ATTACH]Hey there Ray-- So far I've re-done 3 of those carbs, one of which is on my '25 & running well. That air valve un-screws from itself. The slightly earlier carbs are a wee bit different 'tho. I believe the air valve comes further apart on those, (with the cast brass float covers). The sheet brass float bowl cover type (as the '25 should have), you need to get at the bottom of the valve by removing the 4 screws of the choke assembly, otherwise called the rack&pinion. Don't forget to MARK the shaft where the choke lever clamps to it before you take it apart. This will help when you reassemble the monster. After you've got that off, you'll see the round base of the air valve piston. There will be two small holes where a special spanner wrench is used to un-screw the piston from the valve. I didn't have that tool, so I clamped a pair of needle-nose pliers in my heavy bench vise, opened jaws about half way, to align into those two piston holes. I then placed the carb "onto" the pliers and used the bulk weight of the carb to break it loose, then unscrewed it by hand the rest of the way--no problem.Just be careful not to scratch or nick any of the working surfaces of the brass parts of the carb. You will need a set of new gaskets and the packing can be found in your local hardware store's plumbing section. It is just the graphite impregnated string. It goes in the pinion shaft for the choke lever. Soak everything in a gallon bucket of "real" carburetor cleaning acid. You'll be surprised how spotless it comes out! Don't worry, the cleaner is quite caustic but won't hurt the brass. Best regards & happy New Year Ray, --Pete

Edited January 6, 2013 by Pete K.
add picture (see edit history)

[R.White]

Thanks for the advise, Pete. It worked a treat!

Ray.

[MikeC5]

These carbs remind me of the S.U. carbs on my MGB. They both use a tapered needle to meter the fuel flow based on engine load/manifold vacuum. The main difference is that the in the DB carb the jet moves relative to a stationary needle while in the S.U., the opposite occurs.

[R.White]

Yes Mike, I thought the same. The thing I noticed was that the two types of carb sometimes seem to suffer from the same problrm; ie. the piston will stick and give a peculiar symptom which can leave one scratching one's head unless you are expecting it. I was once up all night trying everything I could think of to get a friend's mini started after replacing a valve. Yes, you guessed it, the carb piston had stuck!! A little metal polish will keep it free. I am very familiar with the little MG and the B series engine which was fitted it to many different British cars as you probably know. My neighbour has a few MGs in his collection including a 'C' with the Austin Healey engine (6 cyl.) As you probably know, there was even a V8 version!.

One problem with my Stewart carb is the rack and pinion choke mechanism. One of the teeth has broken off the little brass pinion leaving it free to turn on it's shaft. Not having a spare, I thought I could solder the pinion in place and arrange it so that it works on the undamaged portion because it looks like the rack will move the metering needle enough - just! Perhaps a photo would explain it better so I will try and post one.

Jason, I cannot be certain because there are several types but it looks like a two speed version of the permanent magnet, three brush, 14 W type which is recognised by the circular yoke. This type of motor is polarity sensitive and must be wired negative earth or it will run backwards. The advantage of this type of motor over it's predecessor is that it's self parking switch not only interupts the current supply, it also short - circuits the armature windings. Regenerative braking thus results, ensuring that the wiper blades always stop in the same position. I am not 100% confident that this is exactly what you have there or quite when this type of Lucas wiper motor was introduced but my 1973 Triumph GT6 has a similar one. As you say they were widely utilised.

Not much help I'm afraid if you are stuck for one.

Ray.

Edited January 7, 2013 by R.White (see edit history)

[Pete K.]

Ray, I had this problem of a missing tooth on the pinion once. The pinion only moves about two thirds it's rotation, so you can assemble it so as the missing tooth will not even come into play so to speak, when choke is pulled and the rack & pinion does it's thing. The only thing you'll need to do is reset the choke lever in a different spot on the pinion shaft at the end. Have car running and warmed up. Back off the carb adjusting screw, near base of carb. loosen choke lever clamping screw and slide it off the pinion shaft (it is knurled) Get the engine to idle fairly well, on the "lean side" by turning the shaft. you may need a pair of needle nose pliers for this, and put choke lever back on & tighten clamp screw. Now you can adjust the fine tuning with the adjustment screw on carb. I've enclosed a photo of a Stewart carb with the rack and needle valve taken out to show another scenario whereas the needle valve has come loose from the rack gear. The needle valve is made to "float" when it is attached to the rack gear by a small peened flange. Many times this will break loose. It is possible to re-peen this needle valve by un-screwing the top of the rack gear to get at the bottom side of it. By using a "Dremel" type tool, one can successfully cut a tiny portion of the base of the needle valve, annular grind, maybe only the thickness of your finger nail, (How's that for a US Std.-to- metric conversion!), enough to accept the tiny washer and go through the rack gear top and have enough there to start re-peening. Use a good set of tools and slowly peen the new flange.

[JACK M]

Basic Universal Wiper Drive Kit - Speedway Motors, America's Oldest Speed Shop

[R.White]

As can be seen, the small brass pinion has a tooth missing. If this was the only fault, the pinion could be repositioned as Pete has confirmed. However, the gearwheel must be cracked as it is loose on it's shaft. As this is my spare carb, I am considering a repair by soldering the pinion to it's shaft, though it would be nice to find another pinion.

The item to the left is the only adjuster screw which would normally be restricted by a tiny spring loaded indent located in the carb body and pressing against the side of the larger knurled knob. As can be seen, the thread has corroded away leaving it on the point of failure. While this could be built up and machined or filed to size, the easiest and quickest solution is to fit an ordinary screw with a spring in compression against it's head. Again, it would be nice to see the correct fitting returned to the carb.

Ray.

[Guest 1930]

Basic Universal Wiper Drive Kit - Speedway Motors, America's Oldest Speed Shop

Thanks Jack, I just bit the bullet and ordered a electronic voltage reducer kit for the factory wiper, hopefully that will be the end of it

[Guest 1930]

Yes Mike, I thought the same. The thing I noticed was that the two types of carb sometimes seem to suffer from the same problrm; ie. the piston will stick and give a peculiar symptom which can leave one scratching one's head unless you are expecting it. I was once up all night trying everything I could think of to get a friend's mini started after replacing a valve. Yes, you guessed it, the carb piston had stuck!! A little metal polish will keep it free. I am very familiar with the little MG and the B series engine which was fitted it to many different British cars as you probably know. My neighbour has a few MGs in his collection including a 'C' with the Austin Healey engine (6 cyl.) As you probably know, there was even a V8 version!.

One problem with my Stewart carb is the rack and pinion choke mechanism. One of the teeth has broken off the little brass pinion leaving it free to turn on it's shaft. Not having a spare, I thought I could solder the pinion in place and arrange it so that it works on the undamaged portion because it looks like the rack will move the metering needle enough - just! Perhaps a photo would explain it better so I will try and post one.

Jason, I cannot be certain because there are several types but it looks like a two speed version of the permanent magnet, three brush, 14 W type which is recognised by the circular yoke. This type of motor is polarity sensitive and must be wired negative earth or it will run backwards. The advantage of this type of motor over it's predecessor is that it's self parking switch not only interupts the current supply, it also short - circuits the armature windings. Regenerative braking thus results, ensuring that the wiper blades always stop in the same position. I am not 100% confident that this is exactly what you have there or quite when this type of Lucas wiper motor was introduced but my 1973 Triumph GT6 has a similar one. As you say they were widely utilised.

Not much help I'm afraid if you are stuck for one.

Ray.

Thanks Ray, I thought you were done, I removed my post. Sorry

[Pete K.]

I see what you mean Ray...Those parts should be the same in the earlier carbs (J2B5) with the cast brass float cover and the later L-254 Series carbs. I have rebuilt both. The one on my '25 is a series B-264 and works well, again,same pinion & screw. Those parts shouldn't be too hard to find.---Pete.

[MikeC5]

There always seems to be DB carbs on fleabay so I would guess finding decent spare parts shouldn't be too difficult.