When is a carburetor beyond rebuilding?

[MZ250]

Good afternoon, folks! I am working on an old carb, and am looking for advice regarding whether it's worth the trouble to rebuild. It has a bit of white, crusty build-up in the bowl and float chamber, having sat for a few decades. I got a kit with all gaskets, float valve, needle valve, adjustment screws, springs and clips. Advice I have found elsewhere on the web says that a carb with internal oxidation is beyond repair and should be entirely renewed. Is this accurate, or is there hope yet? The last carb I cleaned and reused (of similar age and condition) worked only for one day, then, in spite of repeated vigorous cleanings, NEVER ran the bike again, and I had to replace it. I did not use a full rebuild kit.  I have limited experience in such matters, and I am hoping that some of the more seasoned of you out there may be willing to offer their two pence. Much obliged!

[coxy]

You may need ultra sonic cleaning. Steve Reed may be able to help you

[slawsonb]

The ultrasonic cleaning advice is best, but a good set of small brushes and lots elbow grease will go a long way. My vote is that all is not lost.
...bert

[MZ250]

Excellent, thanks for your prompt replies! I almost forgot, I do have an ultrasonic cleaner, albeit a cheap one. I will give that a go, as I have already applied quite a bit of brushed on elbow grease, if you will...

[Old BS Guy]

There is a household cleaning product called CLR that is a lime and mineral descaler for showers and fixtures. I recently tried it in a diluted form on a carb. The jets were so plugged that not even my cleaning tool would touch them. I soaked the complete disassembled unit and parts in CLR for a day, and then rinsed with water, and blew it out. Came out perfectly clean. I chased all the jets with my cleaning tool,and they were clean. Just for good measure, I chased the passages with some aerosol carb cleaner, and blew them again. Carb was fine. On older carbs, pay attention in particular to the slide for excessive wear, and the needle and it's corresponding nozzle for wear, or being eccentric. Remember when you go back together to leave enough cable slack for proper slide adjustment when setting the idle, then readjust the cable to specified slack. Also, on plunger style chokes, don't expose the rubber sealing pad to caustic cleaners, as it will swell them out of dimension. Check that pad to make sure it will seal off the orifice when the choke is shut.

....KP

[slawsonb]

One other thing to look for is the float pin holes becoming oblong from vibration. The out-of-round condition will make it difficult to set the float height and get it to remain constant when the carb is mounted. These holes can be bushed with brass, but the drilling process really requires setup in a mill or industrial drill press to hold the bore straight and to get both holes drilled in-line.
...bert

[Old BS Guy]

Good Point, Bert. I usually use a precision drill press, or a 5th of whiskey to steady my hand.
....KP

[MZ250]

CLR---now that's brilliant. Had some in the utility room, got it soaking now. Thanks a bunch, guys!

 Now, a tip on "carburetter" cleaning from the operating manual for my 1974 MZ, which I find rather amusing: "Do not use a needle or piece of wire for cleaning the calibrated holes of the jets, because this will render them completely useless, use a bristle from mother's broom." 

CLR is much faster than going all the way to my mom's house...

[slawsonb]

Scotch please, KP.
...bert

[OldSwartout]

Now, a tip on "carburetter" cleaning from the operating manual for my 1974 MZ, which I find rather amusing: "Do not use a needle or piece of wire for cleaning the calibrated holes of the jets, because this will render them completely useless, use a bristle from mother's broom." 

I find it amusing that many places sell the set of ribbed wire welding tip cleaning tools as carburetor jet cleaning tools.  I wonder how many people actually use them for that and screw up the edges of the holes in the jets or resize them.

http://www.powersportsplace.com/parts/bkm-15-2212?seid=pspse1&gclid=CN7ijYSG4csCFQuPaQod9lAFrQ

If air and brake cleaner won't get the crud out, I usually pull a strand of copper wire out of some automotive wiring and use it. At least copper is soft enough not to damage a jet.

[BS Mechanic]

If you're serious about working on carbs, get yourself a set of jet reamers.  They are long and thin tapered reams with a square shape and sharp edges.

They come in a set from hair thin to quit large, enough to cover all jet sizes and also all the various small holes in carburetors.  These will clean out things that no amount of solvent or soaking will remove.  You do need to be reasonably careful, as you can also enlarge the holes if you aren't careful.

Not cheap, but very effective.

The set I have is Stahlwille, number 11085.  Amazon has them, several other places also and are less expensive.