Back-fire on gilera

[rmsinaga]

Hi there!

Wanna ask about 'back-fire' phenomenon happened to my gilera scooter.

Recently I encountered several times of back-fire. Normally it happened when i rode my gilera on highway around 90-100km/h cruising speed. It was smooth initially but after a while it back-fired then suddenly lost of power then the engine stalled. Need to wait for ~10minutes before i could restart the engine again, otherwise i could only hear cranking sound using e-start. Then I changed the magnetic coil for the plug, unfortunately the problem still persisted. It back-fired several times during 90-100km/h cruising speed, but then the waiting time to restart was shorter ~5minutes. I could feel that the scooter really lacked of power, not like last time when i bought it. My gilera is already ~7yrs old, I bought it ~2yrs ago (2nd hand).

What can cause this back-fire? I googled it, some articles mentioned about incorrect carburetor setting, perhaps the air-fuel ratio is not optimized yet. Any advise on this matter?

Thank you.

[fion12]

eh this happened to me too last Wednesday. I was on the 2nd lane expressway driving 90-100km/hr then my bike suddenly back-fire. I started panicking and waving my left arm like a sotong to indicate I want to go to the road shoulder. lucky for me the cars were far behind me. in fact my bike back fire 3 times on the expressway, at locations where traffic is very heavy. so scary. each time I had to wait approximately 5-10 mins before the engine starts up. in the end got to amk where my bike completely broke down and had to be towed to the nearest workshop. in the end, what the uncle just did was to release the water from the carburetor( I had washed my bike the night before) and open up the fuel tank cover, let some air into the tank. and since then no problem with my bike. maybe your carburetor got water too?

 

p.s I know nuts about bike parts etc, just saying from what I experienced before.

 

oh and my bike is a decade old Honda rebel 125.

[ezzyoiler]

the phenomenom u have just described...doesnt sound like backfire..but engine stalling..

some may say engine cut out..this is common for parts/devices failure or as you experienced contaminated fuel..

 

backfiring is a condition where unburnt fuel gathers at the exhaust pipe...and sometimes literrally explode..

the bike will not stall...it can keep on doing this..

 

the following article explains backfiring..

 

Backfire in an automobile engine typically results from various malfunctions related to the air to fuel ratio. Backfiring can occur in carbureted engines that are running lean where the air-fuel mixture has insufficient fuel and whenever the timing is too advanced. As the engine runs leaner or if there is less time for the fuel to burn in the combustion chamber, there is a tendency for incomplete combustion. The condition that causes this is a misfire. The result of a misfire or incomplete combustion is that unburned fuel or flammable hydrocarbons are delivered to the exhaust manifold where it may ignite unpredictably. Another backfire situation occurs when the engine is running rich (with excess fuel) and there is incomplete combustion during the Otto cycle, with similar results.

Popularly the term is used to describe a sharp report produced by almost any type of engine. However, among engine professionals, "afterfire" is the term used to describe ignition of fuel within the engine exhaust system and "backfire" is the term used to describe this same process taking place in the induction system, primarily in internal combustion engines. The separate terms are useful when troubleshooting running problems.

When starting an engine, timing that is too advanced will fire the spark plug before the intake valve is closed. The flame front will travel back in to the intake manifold, igniting all of that air and fuel as well. The resulting explosion then travels out of the carburetor and air cleaner. A common air filter will allow the gases to escape, but will block the flame front. On many small marine engines, no air filter is used, but a screen is placed over the intake of the carburetor as a flame arrestor to prevent these flames from escaping the intake, and potentially igniting fuel, or fuel vapors in the enclosed sump or bilge of the boat and causing a fire or explosion. Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously.

[edit] Causes

 

Exhaust system backfires occur in engines that have an emission system malfunction, like an air injection system diverter valve problem, an exhaust leak, or when the catalytic converter has been removed. In some high-performance vehicles, when a driver shifts up and lets off the accelerator, the engine has a moment of running rich. This causes an incomplete burn which causes the fumes to explode in the exhaust system along with an audible clacking sound. However this condition is a result of working smog equipment, and is unlikely to cause any damage.

A fuel injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective.

Common causes of backfires are:

• Poor or unregulated engine timing is often a cause of intake backfires, but can also be responsible for exhaust backfires
  
• Improper wiring in the ignition can also lead to timing issues and backfires
  
• Low fuel pressure, clogged fuel filters, and weak fuel pumps could cause a severe lean air-to-fuel ratio during fuel injection
  
• Missing or damaged catalytic converter can result in backfires out the tailpipe
  

[crazydj]

I ever like rev very high on my bike on a really hot day with clutch in, moving very slowly. Rev and rev, then i hear like a couple of "PAKkkk!!!!" sound very loud. PAKKKK! PAKK-PAKKK! Like higher pitch gunshot.

 

Is this backfiring?

[ezzyoiler]

yes...sometimes it can be very loud...

suddenly boom...and you may be scared out of your wits..

yes the bike sometimes is damage by this explosion..

[MiddleAgedBiker]

Hi there!

Wanna ask about 'back-fire' phenomenon happened to my gilera scooter.

Recently I encountered several times of back-fire. Normally it happened when i rode my gilera on highway around 90-100km/h cruising speed. It was smooth initially but after a while it back-fired then suddenly lost of power then the engine stalled. Need to wait for ~10minutes before i could restart the engine again, otherwise i could only hear cranking sound using e-start. Then I changed the magnetic coil for the plug, unfortunately the problem still persisted. It back-fired several times during 90-100km/h cruising speed, but then the waiting time to restart was shorter ~5minutes. I could feel that the scooter really lacked of power, not like last time when i bought it. My gilera is already ~7yrs old, I bought it ~2yrs ago (2nd hand).

What can cause this back-fire? I googled it, some articles mentioned about incorrect carburetor setting, perhaps the air-fuel ratio is not optimized yet. Any advise on this matter?

Thank you.

 

The first thing I would check would be the plugs. Pull them out, ground them on the cylinder head, do you get a healthy and consistent spark when you thumb the starter on all plugs? Do they look healthy? They should be dry, and be a tan colour.

 

Then I'd check the carbs. Are the jets stock? Needle? Choke cable seating properly and not permanently being pulled out? I'd check the float height too, and that the float valves are seating properly on the seats. You'd probably need to go to the agent to get this done, unless you have the manual and know the stock jet sizes and float measurement and you can tell the mechanic who's checking the bike. When was the air filter last checked?

 

I'll also check for manifold leaks, they cause backfiring sometimes. The manifold is where your carb connects to your engine. Check that there are no tears in the rubber and the hose clamps are tight.

[fion12]

the phenomenom u have just described...doesnt sound like backfire..but engine stalling..

some may say engine cut out..this is common for parts/devices failure or as you experienced contaminated fuel..

 

backfiring is a condition where unburnt fuel gathers at the exhaust pipe...and sometimes literrally explode..

the bike will not stall...it can keep on doing this..

 

the following article explains backfiring..

 

Backfire in an automobile engine typically results from various malfunctions related to the air to fuel ratio. Backfiring can occur in carbureted engines that are running lean where the air-fuel mixture has insufficient fuel and whenever the timing is too advanced. As the engine runs leaner or if there is less time for the fuel to burn in the combustion chamber, there is a tendency for incomplete combustion. The condition that causes this is a misfire. The result of a misfire or incomplete combustion is that unburned fuel or flammable hydrocarbons are delivered to the exhaust manifold where it may ignite unpredictably. Another backfire situation occurs when the engine is running rich (with excess fuel) and there is incomplete combustion during the Otto cycle, with similar results.

Popularly the term is used to describe a sharp report produced by almost any type of engine. However, among engine professionals, "afterfire" is the term used to describe ignition of fuel within the engine exhaust system and "backfire" is the term used to describe this same process taking place in the induction system, primarily in internal combustion engines. The separate terms are useful when troubleshooting running problems.

When starting an engine, timing that is too advanced will fire the spark plug before the intake valve is closed. The flame front will travel back in to the intake manifold, igniting all of that air and fuel as well. The resulting explosion then travels out of the carburetor and air cleaner. A common air filter will allow the gases to escape, but will block the flame front. On many small marine engines, no air filter is used, but a screen is placed over the intake of the carburetor as a flame arrestor to prevent these flames from escaping the intake, and potentially igniting fuel, or fuel vapors in the enclosed sump or bilge of the boat and causing a fire or explosion. Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously.

[edit] Causes

 

Exhaust system backfires occur in engines that have an emission system malfunction, like an air injection system diverter valve problem, an exhaust leak, or when the catalytic converter has been removed. In some high-performance vehicles, when a driver shifts up and lets off the accelerator, the engine has a moment of running rich. This causes an incomplete burn which causes the fumes to explode in the exhaust system along with an audible clacking sound. However this condition is a result of working smog equipment, and is unlikely to cause any damage.

A fuel injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective.

Common causes of backfires are:

• Poor or unregulated engine timing is often a cause of intake backfires, but can also be responsible for exhaust backfires
  
• Improper wiring in the ignition can also lead to timing issues and backfires
  
• Low fuel pressure, clogged fuel filters, and weak fuel pumps could cause a severe lean air-to-fuel ratio during fuel injection
  
• Missing or damaged catalytic converter can result in backfires out the tailpipe
  

 

Wah, this is very very useful!! Thanks for explaining! So looks like my bike didn't suffer a back-fire. Still not too sure what is the problem though, have to go consult the honda rebel expert~