what exactly is a backfire

[vexed.]

Hey guys, I own a KRR 150.

 

I tried to kickstart my bike today and heard a loud bang noise. (comparable to a thunderflash)

 

I'm not sure what it is, and I naturally assumed backfire (even though I don't know what in the world that means, but it sure sounds like it).

 

A friend of mine thinks the spark plug died.

 

I'm not sure what to think ahah, all I know is that I can't start the bike and had to have it towed.

 

Oh, and one more question, what exactly is the "choke" ? no one has really told me. I have identified where the choke is, but I'm not sure if it's on the "on" position or the "off" position. And I'm not even sure how to use it.

 

Thanks guys

[Strong Eagle]

A back fire occurs when unburned petrol is released into the exhaust system. You could get a backfire when trying to start by having excess petrol in the mixture (too much choke) or a late spark. Then the exhaust valve opens and the mixture (already ignited or ignited by hot exhaust parts) eplodes in the exhaust pipe. BANG!

 

A choke is a device which makes for a richer fuel/air mixture to make it easier to start a cold bike (Not found on EFI bikes which set the mixture programatically). It is basically a small butterfly valve in the carb that blocks off the air so that more fuel is mixed in.

 

Singapore is generally very warm and most of the time choke will not be needed or only for a very short period of time when first started in the morning. As soon as the bike will run without choke it should be turned off.

 

Leaving the choke on too long can cause chrome pipes to blue.

 

Generally, if your choke is a push/pull knob near the carb, it will be on when the knob is pulled out, and off when pushed in. You can tell pretty easy when the bike is running (and warm). Set the choke. The motor will either speed up (due to rich petrol mix) or die (too much petrol for the air).

[FW1314A]

Originally posted by Strong Eagle@May 03, 2007 12:20 pm

A back fire occurs when unburned petrol is released into the exhaust system. You could get a backfire when trying to start by having excess petrol in the mixture (too much choke) or a late spark. Then the exhaust valve opens and the mixture (already ignited or ignited by hot exhaust parts) eplodes in the exhaust pipe. BANG!

 

A choke is a device which makes for a richer fuel/air mixture to make it easier to start a cold bike (Not found on EFI bikes which set the mixture programatically). It is basically a small butterfly valve in the carb that blocks off the air so that more fuel is mixed in.

 

Singapore is generally very warm and most of the time choke will not be needed or only for a very short period of time when first started in the morning. As soon as the bike will run without choke it should be turned off.

 

Leaving the choke on too long can cause chrome pipes to blue.

 

Generally, if your choke is a push/pull knob near the carb, it will be on when the knob is pulled out, and off when pushed in. You can tell pretty easy when the bike is running (and warm). Set the choke. The motor will either speed up (due to rich petrol mix) or die (too much petrol for the air).

gd info

[kmax]

i usually hear backfire when slowing down from higher gear to lower.

i.e from 6,5 to 4... that coming out from freeway to filter lane..

[Raptor]

Originally posted by kmax@May 11, 2007 02:10 am

i usually hear backfire when slowing down from higher gear to lower.

i.e from 6,5 to 4... that coming out from freeway to filter lane..

Your pilot jet is too small or you are tuned too lean.

[CABOOSE]

a backfire is what you get when you eat to many durians.

[d0n]

Originally posted by vexed.@May 03, 2007 01:14 am

Hey guys, I own a KRR 150.

 

I tried to kickstart my bike today and heard a loud bang noise. (comparable to a thunderflash)

 

I'm not sure what it is, and I naturally assumed backfire (even though I don't know what in the world that means, but it sure sounds like it).

 

A friend of mine thinks the spark plug died.

 

I'm not sure what to think ahah, all I know is that I can't start the bike and had to have it towed.

 

Oh, and one more question, what exactly is the "choke" ? no one has really told me. I have identified where the choke is, but I'm not sure if it's on the "on" position or the "off" position. And I'm not even sure how to use it.

 

Thanks guys

i encountered this same issue before as well

the spark plug has fouled

get it replaced and the bike will work fine again

 

the choke lever for KRR is found below the left side of the fuel tank (dont mix it up with the fuel tap)

it is in the form of a flat lever

when the lever is pushed downwards, the choke is on

to off the choke, simply pushed it back upwards

 

for some reason, i needed to use the choke most of the time i had to start my ex-KRR

 

[Stone]

2 stroke will back fire?

 

it will just fart rite....

 

very soft sound..

 

am i wrong??

[xxes123]

Originally posted by Stone@May 15, 2007 06:48 am

2 stroke will back fire?

 

it will just fart rite....

 

very soft sound..

 

am i wrong??

nope , 2 stroke bike also will back fire.. its a very loud thunder clap sound with blue flame coming out of my exhuast ... my bike has a habit of backfire every morning when i start.. dun understand why , everymorning the whole area so quiet then suddenly "bang" , everytime i act blur

[loufu]

nope , 2 stroke bike also will back fire.. its a very loud thunder clap sound with blue flame coming out of my exhuast ... my bike has a habit of backfire every morning when i start.. dun understand why , everymorning the whole area so quiet then suddenly "bang" , everytime i act blur

 

if u r the only 1 there i dun think act blurr can get u thru it.. haha:angel:

[vyzyl]

Backfire is caused when unburnt fuel in the exhaust continues to burn throughout the entire length of the exhaust pipe.

 

If the exhaust pipe is a "tong" one, the fire burns all the way through and is visible. It will burn up your fibre packing and sometimes damage certain parts of the exhaust (imagine carbon fibre exhaust... )

 

If you close throttle and go into engine braking, there will be less petrol flowing through the carb, hence a lean mixture (engine still sucking air through the carb), that will give rise to backfires.

 

There is a P.A.I.R. system that injects air to the exhaust port(s), the purpose is to let exhaust gas to burn cleanly (cleaner emissions), but usually that is intended with stock pipes with plenty of inner walls and plates to block off the backfire flame and cancel noise. The P.A.I.R. also contributes to backfiring in "tong" pipes.

 

Another factor is that there is an airleak somewhere along the header of the exhaust pipe. Or that the header gasket is not well sealed.

 

Without excessive air (oxygen) in the exhaust system, there will be minimal chance of backfire, even during engine braking.

 

Backfires may be "cool" but it's damaging if allowed to be done excessively on purpose, really.

[ah_hong]

Backfire is caused when unburnt fuel in the exhaust continues to burn throughout the entire length of the exhaust pipe.

 

If the exhaust pipe is a "tong" one, the fire burns all the way through and is visible. It will burn up your fibre packing and sometimes damage certain parts of the exhaust (imagine carbon fibre exhaust... )

 

If you close throttle and go into engine braking, there will be less petrol flowing through the carb, hence a lean mixture (engine still sucking air through the carb), that will give rise to backfires.

 

There is a P.A.I.R. system that injects air to the exhaust port(s), the purpose is to let exhaust gas to burn cleanly (cleaner emissions), but usually that is intended with stock pipes with plenty of inner walls and plates to block off the backfire flame and cancel noise. The P.A.I.R. also contributes to backfiring in "tong" pipes.

 

Another factor is that there is an airleak somewhere along the header of the exhaust pipe. Or that the header gasket is not well sealed.

 

Without excessive air (oxygen) in the exhaust system, there will be minimal chance of backfire, even during engine braking.

 

Backfires may be "cool" but it's damaging if allowed to be done excessively on purpose, really.

 

very gd info.