TOPIC:

Although I have soaked both my '80 set and '79 set of carbs in lacquer-thinner for long periods of time with seemingly no ill effects, a cautionary note to this practice by "kawboy" deserves attention. Thanks to kawboy for this input on the following:


From “Kawboy”: Feb./15

“This is an excerpt from the Parker O-ring handbook which would explain what Scotch was describing as shrinkage of the orings noted on the air bleed screws after cleaning.

3.9.4 Fuel System
Gasoline and diesel fuels are used in normal commercial vehicles. Fuels are more aggressive than mineral oils and cause higher swelling of the elastomer which increases with temperature. Swelling of an elastomer in fuel is, however,generally reversible when the absorbed fuel vaporizes completely.
When parts of a compound are dissolved or leached out of the elastomer however, shrinkage takes place which is permanent. If a nitrile-based compound is required, a compound
must be selected which contains minimum amounts of plasticisers, anti-aging or anti-ozone additives. By careful selection of the seal compound, the tendency to shrinkage or cold brittleness is avoided.
Figure 3-6: O-ring Linear vs. Volume Change Relationship”

AND also from “Kawboy” : Feb/15

“For the record, I did a little experiment yesterday with a cut o-ring from the carb bowl drain screw. I dropped it in a teaspoon of lacquer thinner for 20 minutes. First I checked the diameter with my vernier at .064" and after 20 minutes it had swelled to .075" and was as soft as butter and I literally wrote my name in my hand with it.”

From "scotch": An amendment to cleaning with lacquer-thinner.

Based on this observation by "kawboy" it seems evident that the seals on the throttle shaft ends could be damaged if soaked excessively in strong cleaners such as lacquer-thinner. The use of lacquer-thinner for manual surface cleaning and gallery flushing using a syringe is OK. However: Best to err on the side of caution and keep the full submerged soaking in lacquer-thinner to 5 minutes or less. This solvent is strong enough to reduce varnish build up quickly. Exterior cleaning is successful with a small bristle-brush. Additional soaking for 5 minute intervals perhaps should be after a thorough blowing-out and complete drying to reduce any detrimental long term affect on the throttle-shaft seal.

Just trying to help Scotch any way I can. I've probably rebuilt 200-300 carbs during my time as a Chrysler mechanic back in the early 1980"s. We used some pretty volatile carb cleaner that ate everything except metal components so you had to be sure to remove every piece. The throttle bushing on automotive carbs never had seals only a tight tolerance between the shafts and bushings. Sometimes when we had a car that stumbled at idle and you couldn't compensate by richening the idle circuit, we had to replace the throttle shaft bushings and ream fit the shaft. Part of the bushing kit included replacement split end screws for the throttle plates. After you replace the throttle plates and checked the plate fit in the throttle bore you had to splay the ends of the screws.

Wow, Kawboy, I was just addressing that issue in the other thread on here!

I was reading an article the other night about rebuilding Mikuni carbs on a Yamaha. It was written by a race mechanic and tuner. He says that most motorcycle carbs have shorter screws than on cars to help with air flow since their bores are usually so much smaller. The screws on cars stick out far enough to peen over for security, but on bikes they just stake them below the surface of the shaft. More of a "swedge" effect, like securing the handle to an axe.

This mechanic suggested that for a restoration project, the chances of ever having to remove those screws again is pretty slim, so he suggested using red Loctite. Anybody who has ever used the stuff knows that it's almost like welding! The threads of the part usually come out with the screws! They do make a release agent, but it takes a long time to penetrate to loosen the red. Blue Loctite just isn't secure enough for such critical screws as butterfly screws!