The most common fuel leak problem would be overflow. Fuel leaks can occur when the oil level in the carburetor is set too high or when the float valve becomes clogged with debris and cannot close. Sometimes, unexpected causes can lead to overflow or gas leakage, so carefully observe the disassembled parts.
Brass floats are prone to corrosion punctures.
For more than 20 years, as far as I remembered, the motorcycle had been kept idle in a motorcycle shop's warehouse, so there was no major external damage, and naturally, the inside of the engine cover looked very clean. However, the overflow did not stop. When I removed the float chamber and shook the float itself close to my ear, I heard a chirping sound coming from inside the float on one side. It was a punctured float. Many brass floats get punctured after years of neglect.
Puncture float can be repaired.
After degreasing and cleaning the affected area and draining the fuel inside (if it is difficult to get the gas out, you can widen the hole), apply flux for sheet metal solder to the affected hole and jiggle it with a warm soldering iron. Then melt the sheet metal solder and pour it over the affected area. After soldering, fill a bucket with water, submerge the float, and shake it to see if air comes out. The trick is to repair with the minimum amount of solder melt because too much solder will increase the weight of the float.
Condition of the overflow tube
The punctured float repair was definitely repaired, but for some reason, fuel is still coming out in titters. The carburetor is sealed by the engine cover, so the balance bend pipe and overflow pipe are all integrated into the float chamber. What a surprise! I found a vertical crack in this balance pipe! Since there were no spare parts, this pipe was also repaired with solder. After the repair, with the float chamber filled with fuel, feed compressed air (squeezed to a small amount) in the opposite direction from the outlet side of each pipe, and when closing the upper side with fingertips, see if air leaks out from the soldered part. Check carefully.
Air element can be made by yourself!
Since no air cleaner element was included, a universal turbo filter from Daytona was cut and wrapped around a metal net tube for use. By soaking it with a very small amount of 2-stroke oil instead of incorporating it in a dry state, the moisture in the sponge seems to absorb the inhalation dust.
Test ride after maintenance is important!
After the repair is complete, the engine must be started and test ride, and in the case of 2-stroke models, it is important to bleed air from the oil pump to the injection port. If a transparent oil tube is used, it is possible to visually check the air being released. Be careful when the oil flow does not quicken even with the oil pump throttle fully open. The engine continues to idle comfortably.
- Point 1 - Overflow can have various causes, so do not suspect a problem at a specific point.
- Point 2 - Brass floats can be punctured, so be careful.
- Point 3 - Check the condition of the air cleaner element when practicing carburetor maintenance when rebuilding an old motorcycle.
When starting a 2-stroke engine that has been repaired from engine seizure, it is ideal to use "mixed fuel" when starting the engine for the first time. This is because a malfunctioning oil pump or some other defect in the separate fueling system can re-damage the engine that has just been repaired. Generally, the mixing ratio for 2-stroke engines is 25 to 30 to 1. When making starting fuel in a 300 ml plastic bottle, mix a little more than 10cc of 2-stroke engine oil for every 1 plastic bottle of fuel. Supplying this in a drip tank for starting is the best setup.
It is also unclear why this engine broke down in the first place. If it was a situation where the oil pump was defective and could not be lubricated, that is scary to think about! I immediately made a fuel mixture (slightly increased the amount of oil from 20 fuel to 1 oil) and poured the fuel mixture into the carburetor. To begin with, many 2-stroke engines have oil jet nozzles in the manifold part of the carburetor (some types supply oil on the cylinder wall or in the chamber bowl of the carburetor), so if you feed the gas mixture mixed with engine oil in advance, you can expect good lubrication performance. Incidentally, if you have a habit of pouring a little 2-stroke oil into the fuel tank when refueling, a fatal seizure problem is unlikely to occur.
When I looked at the motorcycle to go out for a test ride, I saw a fluid leak right under the engine. The fuel had overflowed. I decided to leave the test ride at this point and started overflow shooting the carburetor. Disassembling the carburetor, I found two causes of the gas leak. One was a punctured brass float on one side, causing fuel to flow into the inside of the float, preventing it from floating and doing its job. The other was a crack in the brass overflow & bend pipe that is cast into the float chamber. Both of these troubles could be repaired by soldering. It is unclear how much durability can be gained by the repairs, but it is a good idea to keep spare parts in good condition when the opportunity arises, as you never know when similar problems may recur. Also, if an overhaul seems necessary when the carburetor is disassembled, it is very convenient and definitely reasonable to purchase a fuel adjustment kit made by KEYSTER, which has all the gaskets necessary for overhaul and can also set the fuel adjustment.
