Halfway Can Be an Adder. When Cleaning Carburetors, It is Important to Completely Flush Out Adhering Chemicals

If the engine is warmed up only to stop it once in a while, water vapor will remain in the muffler and cause rusting.
The same applies to cleaner chemicals used to remove dirt from the inside of carburetors; be aware that residual cleaning ingredients may cause unexpected side effects.

Handle sticking throttle valves carefully while applying heat.

Check the piston-valve type carburetor: the starter motor spins briskly but shows no sign of starting, and the throttle is stuck and will not move. The piston would not come off even if the threaded top cover was loosened.

In piston valve type carbs, the throttle cable is directly attached to the throttle valve, so it is easy to try to force the stuck piston to move, but if the fuel in the gap between the piston and the body is varnished, it will stick like glue, so do not force it. On the other hand, there are a few cases of butterfly valve sticking in negative pressure type carbs, and when the throttle sticks and does not move, it is often due to rust inside the throttle cable.

Heat with a heat gun may soften the varnish and allow the throttle valve to move. To heat the entire carb evenly, boiling it in hot water mixed with water-soluble parts cleaner is also effective. In the case of a sticking piston on a negative pressure type carb, be careful because the piston diaphragm may be damaged when heated with a heat gun.

He removed the carburetor from the vehicle, heated it evenly with a heat gun, and still the throttle cable was pulled and the piston would not jerk, so I inserted a screwdriver through the venturi to help slightly and finally got it to nudge and remove it. The sticking was not caused by fuel, but by an altered carburetor cleaner.

If fuel inside the carburetor is left unattended for a while, varnish and corrosion can occur as it volatilizes from inside the float chamber. If the fuel cock is gravity-fed and left in the ON position, it is not uncommon for new fuel to flow in from the fuel tank every time the fuel in the float is depleted, resulting in a disastrous site that continues to get dirty without the float chamber drying out.

A carburetor whose jets and float valves no longer function properly requires an overhaul because it cannot be recovered simply by replacing the fuel in the float chamber, and care should be taken at this time not to overwork everything.

Piston-valve carburetors, which are popular in mopeds and mid-size single-cylinder vehicles, open and close the throttle valve directly with a cable. Therefore, when the throttle sticks, people tend to try to move the valve by twisting it forcibly. However, when fuel adhering to the small gap between the piston valve and the carburetor body turns into a varnish-like substance, it becomes like an adhesive and does not come off easily.

Attempting to forcibly peel it off by turning the throttle can damage the tycoon at the throttle cable end or damage the throttle valve itself. Also, removing the carburetor from the engine and inserting a screwdriver into the venturi to push up the piston valve is strictly prohibited as it can damage the piston and carburetor itself. It would be a waste of time if you destroy your precious car with the intention of maintaining it.

Incidentally, in the case of negative-pressure carburetors, the butterfly valve to which the throttle cable connects is not in direct contact with fuel as the piston valve, so it is less likely to stick. Instead, the vacuum piston sticks, causing symptoms such as the throttle opening and closing but the venturi not opening, and the engine not revving up even if the engine is started.

Heating is effective in such cases. By applying heat with a heat gun while spraying a sticking piston valve with lubricating spray, the hardened varnish is softened and replaced with the lubricant, thereby eliminating the sticking.
It is also effective to simultaneously heat and clean the carburetor by immersing it in hot water in which water-soluble parts cleaner has been dissolved.

However, when using a heat gun on a negative-pressure carburetor, care must be taken because of the risk of damaging the diaphragm rubber above the piston due to temperature. Similarly, carburetors that use rubber at the tip of the starter plunger for starting may also be subject to deterioration and dropout due to overheating. A heat gun is certainly easier to heat than hot water, but be careful not to overheat.

When using spray-type cleaners, disassemble the entire carb or run it after cleaning.

There was a white solid substance like a hot bond around the needle jet where the piston valve had been disconnected, which was the cause of the sticking. Judging from the color and condition of the foreign substance, it was not fuel, but rather a carb cleaner that had been sprayed to remove the dirt and remained in place.

Even if you use a good chemical cleaner, poor post-processing can lead to more trouble than it's worth. The chemicals clinging to the slow jet or the heat from the heat gun have made the jet slightly wet, but fuel will not pass through in this condition.

The jet needle holder is also in this state. It is necessary to clean the jets again, and at the same time, check the slow air and main air passages in the carburetor body to see if they are clogged.

Spray-type carburetor cleaners are convenient for removing dirt from the inside of the carburetor when the throttle valve is not sticking and the engine is still running. The appeal of this product is that it can remove carbon, varnish, and light corrosion from the jets at the same time as spraying. Some products can be sprayed from the air cleaner box and the intake pipe connecting the carburetors while the engine is running.

However, some products require cleaning of the cleaner itself after application. Spray-type chemicals can be washed off with fuel, but if the carbon and varnish inside the carburetor and in the jets are removed and the carburetor is left unattended, the remaining chemicals inside the carburetor may do something bad, and the problem may become even worse.

The carburetor shown here is an example of such a situation. The carburetor was not only sticking to the piston valves but was also unable to start due to foreign matter, apart from the altered fuel, adhering to the slow jet and needle jets.
The owner removed the carburetor, cleaned the float chamber, and sprayed the jets and air passages with carburetor cleaner.

Therefore, it seems that the adhering chemicals stayed in place without being washed away, and over time transformed into foreign matter that clogged the jets. Not all carburetor cleaners are like this, but it is reasonable to recognize that some sort of rinsing process is necessary after using a chemical with cleaning ability. Imagine washing clothes with detergent and then not rinsing them, or the detergent will remain forever, and it is only natural that parts cleaner or fuel would be used to flush out the cleaning components of carburetor cleaner.

If you don't want to disassemble the jets and needles and use carburetor cleaner to wash them with parts cleaner, the quickest way to rinse them out is to actually run them. If the fuel in the float chamber is sucked up from the slow and main jets, and the cleaner inside the carburetor is washed away, the residual components will not cause any problems.

Idling the bike in a garage only allows fuel to flow through the pilot outlet and slow ports, so it is important to actually run the bike and open the throttle wide to supply fuel through the main jet as well. For big bikes, it is safer to disassemble the bike and rinse it with parts cleaner and fuel, since a large throttle opening can cause excessive speed and be dangerous!

It is best to ride the carburetor as often as possible to avoid the buildup of dirt inside the carburetor, but remember that if you are unlucky enough to be cleaning the carburetor due to conditions caused by carbon or varnish, it is important to rinse the carburetor so that no cleaner components remain.