Super4: Big 'bang' sound when starting engine

[enj]

Hi, I noticed that if i did not start my bike for a week, when i start the engine, there will be a very loud 'bang' (like a gun fire!) coming our from the exhaust. Is this normal? How to prevent this?

[MiddleAgedBiker]

It's not normal. It's called backfiring. It's quite harmful to the bike components.

 

Can you describe how you start the bike?

[enj]

Oh really?!?!? Oh dear!!

 

I just press the start button for the engine lor, did nothing else.

[crankcase]

A few questions:

1. Just to confirm: this only happens when your bike has been standing for a while, or does it also happen when you're starting it every day?

2. Does the bike backfire at the very first crank or after you have cranked it a few times?

3. How much throttle (0-100%) do you use while starting?

 

You might wanna read this for more info, though it's not very detailed: http://en.wikipedia.org/wiki/Back-fire

[enj]

A few questions:

1. Just to confirm: this only happens when your bike has been standing for a while, or does it also happen when you're starting it every day?

2. Does the bike backfire at the very first crank or after you have cranked it a few times?

3. How much throttle (0-100%) do you use while starting?

 

You might wanna read this for more info, though it's not very detailed: http://en.wikipedia.org/wiki/Back-fire

 

1. Yes, only when it stands more than a couple of days

2. First crank? Er... crank means? Only first engine start.

3. I do not turn the throttle when starting the engine. Am i suppose to?

[kaiq]

Possible that someone playing the throttle beforehand?

[crankcase]

1. Yes, only when it stands more than a couple of days

2. First crank? Er... crank means? Only first engine start.

3. I do not turn the throttle when starting the engine. Am i suppose to?

 

"crank" means when you turn the key and the engine goes eh-eh-eh-eh before it fires. As you know, sometimes it takes a few cranking attempts to start a bike, especially an old one.

 

Normally a backfire is caused by unburnt fuel being dumped in the exhaust, which goes off with a bang when you try to start it the next time. You can make it happen by opening the throttle and killing the engine at the same time, for instance. It can also happen if you are cranking with an open throttle - the fuel from the first couple of attempts may cause the backfire in the next attempt, before the bike finally starts.

 

But frankly based on what you said, my limited ideas are exhausted. I'm no expert on this anyway, but was hoping it might be a kinda obvious issue... sorry mate, hope someone more experienced can help.

[arthur_chan]

i always open throttle with cranking to start my bike, mechanic told me it's easier to start, so far no backfire.

 

since TS has left his bike for a while, shouldn't unused fuel in the exhaust dried up?

[crankcase]

i always open throttle with cranking to start my bike, mechanic told me it's easier to start, so far no backfire.

 

since TS has left his bike for a while, shouldn't unused fuel in the exhaust dried up?

 

In your case I would say if it starts at the first crank it should be fine. But if it takes several cranking attempts then it may cause backfire. It has happened to me a few times, so now I don't throttle until the engine starts to 'catch'.

 

Yeah, that's why I'm at a loss. Could it be that fuel is seeping into the exhaust system over the course of many days, which is why it doesn't happen when the bike is in regular use? I'm not sure if this is technically possible, just an idea...

[arthur_chan]

In your case I would say if it starts at the first crank it should be fine. But if it takes several cranking attempts then it may cause backfire. It has happened to me a few times, so now I don't throttle until the engine starts to 'catch'.

 

erm it's an old bike, takes several crank to start, no backfire...

[MiddleAgedBiker]

Oh really?!?!? Oh dear!!

 

I just press the start button for the engine lor, did nothing else.

 

No choke, no opening of the throttle correct?

[enj]

Possible that someone playing the throttle beforehand?

 

Don't think so cos i cover my bike when parking.

[enj]

I guess now i should be starting my bike even not riding...

[allenkey]

same thing happened to my s4 a few days ago after bike left unridden for almost a month

[MiddleAgedBiker]

Before starting the bike next time, you could remove all the plugs and smell them. Do they smell like petrol? Which cylinder is it in? I'd write it down.

 

Also I'd do a compression test.

[tupac74]

informative ...