Motorcycle start failure usually occurs in cold winter, however, this failure also occurs in the hot summer.

1. Motorcycle start failure usually occurs in cold winter, however, this failure also occurs in the
hot summer. To solve this problem, we are now doing a brief analysis on all kinds of
technology of motorcycle engine warming and relevant matters.
In the hot summer, the temperature are generally more than 30 ℃. Due to the change of
temperature, the heat dissipation performance of engine become worse, especially in the
high-traffic areas of cities and towns, where motorcycle is often in a situation of starting and
stopping. Working condition of motorcycle engine will be worse when climbing or crossing over
the bridge. The running speed is low while engine speed is high so the cooling volume will
reduce accordingly. Sometimes motorcycle occurs an emergency stop suddenly running at a
high speed. These above situation will dramatically increase the thermal load of engine and
cause the excess heat hard to send out. At this point, the temperature inside the cylinder will
rise rapidly, the inlet temperature will rise to about 70 ℃ to 80 ℃, the temperature inside
the carburetor float chamber will rise to about 70 ℃ and the air density will drop sharply. So
the fuel will evaporate quickly under such a high environment and be in a status of active
gasification. If engine stop working, carburetor, inlet channel and combustion chamber won’t
get effective cooling, when starting again, the air going through these parts will instantly
transform into high temperature gas. While the density of these high temperature gas will
decrease due to the heat expansion, the proportion of gasoline in the mixture will increase. On
the other hand, these high temperature gas will make the evaporation condition of gasoline
become better, thus, there will be a overrich mixture in the combustion chamber. While this
overrich mixture will be hard to be ignited or can be ignited partly because of lack of oxygen for
burning, so it is hard to start engine at once. Besides, under the condition of high temperature,
the resistance coefficient of copper wire on the ignition coil will also increase and cause
current of the ignition coils in the primary coil assembly decrease, induced voltage of the
secondary winding reduce, and the spark from the spark plug not strong enough. If there is
carbon deposit in the electrode parts of spark plug, the mixture gas in the cylinder will be
difficult to ignite, which will cause start difficult or failure to start. Moreover, there is often
“air-resistance” phenomenon of gasoline in summer, it is also a main reason for the failure of
warm car start.
It is generally known that there will be some air mixing into the gasoline in the process of
production, storage, transportation and filling. When driving the motorcycle, gasoline in fuel
tank will swing back and forth due to the winding road and then air inside the tank will be mixed
with the gasoline. Even the air along the tube wall will also be absorbed into the gasoline in
gas flow, these air will form air bubble in gasoline and at the same time there is gasoline inside
the bubble. When temperature rises or atmospheric pressure is low, the air bubbles will swell
accordingly. When the vapor pressure is too high, the gasoline inside bubbles will evaporate
faster and the swell phenomenon will be more obvious. There will be more bubbles at the

2. bending part of gas pipe because of the negative pressure. When the air bubbles swell large
enough and is the same as the diameter of pipe, then there will be “air-resistance”
phenomenon, when the gas stops flowing and engine cannot be started. In general,
motorcycle with petrol pumps will more likely to happen this phenomenon.
When checking the failure of difficult start
for a warm car, you need to observe when motorcycle engine has stalled. If it stalls in a sudden
and there is blasting phenomenon at exhaust pipe at the moment of stalling, this should be the
failure of ignition system. If it stalls little by little, and the engine is obviously powerless before
installing, this should be the failure of oil supply system. Thus, proper maintenance and
reasonable usage of motorcycle is very necessary so as to avoid these failures. Please pay
attention to the following tips:
1. After driving the motorcycle for a long-distance or at a high speed, you need to downshift
and speed down the motorcycle before you want to stop it, so as to ensure the engine can
gradually reduce its load and emit the high temperature and heat before stopping. The
check standard is that the crankcase part is not hot and can be touched. Unless there is an
emergency, you should avoid emergency stop in the process of high-speed driving.
2. In the midsummer, you should drive the motorcycle in a moderate speed under high gear
and make the accelerator 10% more than the economic speed upper limit. When the speed
drops to 10% of the economic speed lower limit, you need to accelerate slowly until 10% of
the economic speed upper limits. Thus, the motorcycle is always in the circulation from low,
medium to high speed or from high, medium to low speed. This will make full use of the
inertia power of the motorcycle so as to save fuel, and can put the engine change from load
to offload frequently which will avoid overheat of the parts and engine will also get
reasonable cooling.

3. 3. If the motorcycle is in long driving, in addition to the rational utilization of inertial effect, you
should also avoid drive motorcycle around midday. Because it is extremely hot in the
midday, the temperature on asphalt or concrete road can reach 40 ℃ to 50 ℃, which can
suddenly rise the inlet temperature and make air density decline dramatically, then,
combustible mixture gas will be too thick and it will be very difficult to start the engine.
4. To avoid overheat of the engine, you need to clean the cover of engine and crankcase
regularly and remove the dirt or mud outside the engine, especially cooling fin. For those
motorcycles driving after ten thousand of kilometers, you need to do the maintenance
before entering the summer and clear the carbon deposit inside the combustion chamber,
spark plug, piston and piston rings.
5. Maintain and clean air filter regularly so as to reduce air inlet resistance, which will keep the
motorcycle well. Must check oil level before daily driving, don’t add too much so as not to
increase the crankshaft running resistance, which will impact heat dissipation for crankcase.
Change new engine oil before entering the summer and make sure its viscosity grade meet
the local standard. DO NOT mix engine oil from different brand or different viscosity, which
will make the oil produce chemical reaction and cause oxidation, then the engine will be
overheating and result difficult of warm starting.
6. When the mixture gas is too thick, there should be a higher ignition voltage, that is why it is
not easy to be ignited. Thus, you can full open the throttle valve so as to thin the mixture
gas. In a short period after starting the engine, you can rise the idle speed which is slightly
higher than the standard speed until the engine speed is stable. In order to ensure a
reasonable air fuel ratio, which can match the engine operating conditions, you should
make some proper adjustment of the carburetor. Under normal circumstances, when the
temperature rise 5 ℃, 20 ℃ as the benchmark, you need to turn gas bolt of carburetor a
quarter to a half back to the original standard circle. The actual circle number of gas bolt is
judged by NOT stalled after accelerating when starting a cooling motorcycle.
7. To avoid the air lock phenomenon of motorcycle in hot summer, you need to make sure
there is at least 70% fuel inside the fuel tank. Add the fuel at a regular time and prevent an
empty fuel tank. Choose a flat and broad road so as to reduce the severe shake inside the
fuel tank. At the same time, pay attention to the connect joint between the fuel rubber hose
and carburetor, avoid flat joint so as to fundamentally eliminate the air lock phenomenon.
8. If there are still failures even after several attempts to start the motorcycle, then you should
measure and record the resistance value of ignition coil, trigger coil and other electrical
parts while the motorcycle is still warm, and redo this after the motorcycle cool down. If
there is a big difference between the cooling condition and warm condition, that means the
insulation performance of the part is becoming worse and need to be replaced. If it is not
the electrical fault after checking, then you can move the motorcycle to a cool and

4. ventilated place and wait for the engine to full of cool down, then you can restart the
motorcycle.