TOPIC:

Cleaning the Mikuni BSW32 carbs seems to be an ongoing battle and a topic that seems to dominate our Forum. The main problem being the Pilot Circuit and how best to clean out the debris/gunk that resides in these passages. A big thanks to Scotch for developing and having manufactured a "Cleaning Tool" specifically for cleaning the pilot circuit on the BSW32's.
One issue that seems to come up over and over is the type of thinner best used for dissolving the buildup of shellac/ gunk which has formed from gasoline evaporating leaving a residue in the pilot circuit and eventually blocking the circuit. Scotch's cleaning tool comes with an instruction sheet on how to use the tool and recommends the use of "Lacquer Thinner" as the dissolving/flushing agent.
Lacquer Thinner is a solvent primarily used to thin Lacquer paint for the purposes of spraying the paint, hence the name Lacquer Thinner. "Other" applications include cleaning parts prior to painting since lacquer thinner leaves no residue. It's also been found to be a great solvent for most hydrocarbon-based products like oil, grease, contact cement, gasket sealer and even breaks down most elastomer products i.e., rubber, nitrile, buna N etc. So, in general, as an all-purpose solvent, it's a great product to have available.
What's little known is the chemical composition of Lacquer Thinner and I write this topic to help us understand it a little bit more. in the painting industry, thinners are used to prepare the paint for spraying under different temperature conditions and Lacquer Thinner comes in various chemical compositions depending on the temperature range that the paint will be sprayed at. By varying the chemical composition, you can alter the flash point of the thinner. Ideally, you want to spray the paint and have it wet out on the surface, then have the thinner flash off and allow the paint to dry. Depending on the ambient temperature, sometimes you need a slow flash off, sometimes you need a fast flash off, so that being said, here are 4 examples of Lacquer Thinner based on temperature ranges and their respective chemical compositions.
Thinner #1 - 50° - 70° temp. range 
25%Light Alaphatic HydrocarbonSolvent
33%Tolunene
0.90%Ethylbenzine
5%Xylene
4%Methanol
10% 2-Propanol
21% Acetone
1% 2-Butoxyethyl Acetate  

Thinner #2 - 60° - 80° temp. range 
66% Toluene
7% 2Methyl-1-propanol
2% 2-Butoxyethanol
10% Methyl Isobutyl Ketone
15% Isobutyl Acetate

 Thinner #3 - 90° - 110° temp. range 
10% 2-Butoxyethanol
20% n-Butyl Acetate
70% 1-Methoxy-2-Propanol Acetate 

 Thinner #4 - Extreme Duty temperature range 
100%2-Butoxyethanol 

So why are we discussing Lacquer Thinner here on the Forum? One of main problems we seem to have is that “Lacquer Thinner” is not available in parts of the world and we keep getting questioned on this Forum for other names of the product or other thinners that will do the same job for us i.e. cleaning out our carburetors. Cellulose thinner has been suggested several times and yet cellulose thinner as near as I can tell is not necessarily the same. Acetone has been suggested as having similar solvent properties and able to be used for our cleaning purposes. What I can tell you is that Acetone has a very fast flash of compared to the Lacquer Thinner I use for cleaning. 

I've included pictures of the Lacquer Thinner I personally use and the second picture shows the chemical composition although not the specific percentages of each of the chemicals. As a solvent for cleaning the gunk/ residue in our carbs, this one works. I'm hoping this will help all of us better understand the name Lacquer Thinner and maybe help those in other countries with the procurement of similar solvents for the purposes of cleaning  your carburetors.


 

 

that's the lacquer thinner I use.  For cleaning carbs it's the only solvent I will use.  Works magic with The Cleaning Tool.

Hi Scotch, At one time here in the UK we had cellulose and nothing else. Now so many different things, starting with water based paints. This is used by 90% of the industry now. I think it's crap. Then we have acrylic, then we have 1 part acrylic then two part acrylic with hardener. Most of this is caused by tree hugging green plant savers.