Hyosung backfiring

[DarkLord]

Hi there

Just wondering if anyone can shed some light onto this for me.

Since I put the Screaming Demon can on the Hyo it has been backfiring like a mad thing, whenever I button off. I have checked the header systems and cannot see any obvious air leaks in it, I have checked the sparkies and it is definitely not running lean (if anything, it is running slightly rich) and there doesn't seem to be anything wrong with the engine from what I can tell, as it still sounds healthy.

I use 98 or 95 and I heard from a friend tonight that using 98 or 95 can cause the engine to start "knocking" or "pinking", an expression I've never really heard before, and that it is better to use 91 for the bike so when I gas up tomorrow I'm going to put 91 in it. Does anyone know if this is true, and if using 98 or 95 can cause it to backfire? I don't currently have the owners manual for the bike so I'm not sure exactly which octane rating the engine is designed for. I've had the carburetors checked recently as they were slightly out of time and that has helped a little but not much.

Any help would be much appreciated.

Thanks guys

DarkLord

[98tls]

Fwiw check the can,if its not sealed it will indeed backfire like a bastard,when i repacked mine i didnt seal one and it did as above.

[DarkLord]

Thanks 98, I have popped the can loose and put some gasket glue in it but it doesn't seem to have helped, however I am not sure if I used the right glue as it all went black and crispy after I rode it for a bit.

I've heard from some people that if the can is not fully sealed and it has gaps in it, it tends to backfire for a while, but eventually the carbon buildup from the exhaust plugs them up......... is this true?

[chaos rider]

is when the engine is still cold? or any time

i know that the hyo's with straight through exhausts have a tendancy to backfire when running cold

[DarkLord]

Nah it's anytime I button off. Has only happened since I put the new can on.

[steve_t]

Knock is caused by low octane fuel (91) or any fuel lower than what the bike is tuned for. The octane rating relates to the fuel's ability to resist pre-ignition (which is when the heat from the cylinder prematurely ignites the mix rather than the spark). Basically, it won't be knock.
However, if the mix is running rich and the timing is not allowing for a complete combustion, excess fuel may be igniting in the exhaust causing the backfiring. This is why it can happen more when cold as the chamber is cold and the choke means a higher fuel:air mix.
What's probably happening with your bike is that the new can is less restrictive than the stock one so the exhaust gas exits the cylinders more easily.
You may find the bike runs better on 91, but if you're gonna have your Screaming Demon on, I'd recommend you take it to a shop and get the bike tuned properly

[DarkLord]

Thanks Steve.

If it's just because the pipe is less restrictive, is my engine in any danger from damage at all? As I said I have checked the sparkies and it's definitely not running lean.

[98tls]

Thanks 98, I have popped the can loose and put some gasket glue in it but it doesn't seem to have helped, however I am not sure if I used the right glue as it all went black and crispy after I rode it for a bit.

I've heard from some people that if the can is not fully sealed and it has gaps in it, it tends to backfire for a while, but eventually the carbon buildup from the exhaust plugs them up......... is this true?

Carbon build up?Wont seal that gap,easy to find,start it up and run your hand round,any air will easily be felt,you need to use a high temp resistant silicone.

[DarkLord]

Carbon build up?Wont seal that gap,easy to find,start it up and run your hand round,any air will easily be felt,you need to use a high temp resistant silicone.

Thank you sir. I shall try that tomorrow.

[DarkLord]

Carbon build up?Wont seal that gap,easy to find,start it up and run your hand round,any air will easily be felt,you need to use a high temp resistant silicone.

I just went and tried it, and eureka - no problems around the can, a bit below that though, I could feel shitloads of air coming out of the pipe. So, it looks as if we may have found our wee leak.

I never would have thought of that. You are a champ. Thanks dude.

[98tls]

I just went and tried it, and eureka - no problems around the can, a bit below that though, I could feel shitloads of air coming out of the pipe. So, it looks as if we may have found our wee leak.

I never would have thought of that. You are a champ. Thanks dude.

Well done,as i said a high temp resistant silicone (spelling) is what you need,i used some horrible rust coloured stuff,plenty of it and let it set overnight and all should be good.

[DarkLord]

Sometimes you just have to laugh at life...

Once I find out how to fix something I have wanted fixed for ages, I always try and fix it straight away as I just can't wait... so I finally find out where this exhaust leak is and I go down at 12:00 am and try and fix it (patience is not one of my strong points!!) and hello, the bike won't start. I think the battery is dead as the engine won't turn over and light is fading etc. Perfect timing, it seemed fine a few minutes before.

I could have waited till the morning, but being the impatient bugger I am I tried to crash start it down my driveway and though it improved it still wouldn't start, so I got stuck at the bottom of my driveway. We live down a private road so no one else came down that way, and AA couldn't help as my membership has expired and I haven't been able to renew it (being out of a job and all). I tried to push it up myself but it was just too heavy and I had a mental image of the bike tipping over and a few smashed fairings etc, so I gave up on that idea fairly quickly. I had to wake my flatmate at 12:30am when he has work the next day to help me push it up the driveway.... I felt sooo guilty waking him up and promised to shout him a beer next time we're in town.

Yet another silly experience.... all you can do is laugh sometimes.

[steve_t]

Sometimes you just have to laugh at life...

Once I find out how to fix something I have wanted fixed for ages, I always try and fix it straight away as I just can't wait... so I finally find out where this exhaust leak is and I go down at 12:00 am and try and fix it (patience is not one of my strong points!!) and hello, the bike won't start. I think the battery is dead as the engine won't turn over and light is fading etc. Perfect timing, it seemed fine a few minutes before.

I could have waited till the morning, but being the impatient bugger I am I tried to crash start it down my driveway and though it improved it still wouldn't start, so I got stuck at the bottom of my driveway. We live down a private road so no one else came down that way, and AA couldn't help as my membership has expired and I haven't been able to renew it (being out of a job and all). I tried to push it up myself but it was just too heavy and I had a mental image of the bike tipping over and a few smashed fairings etc, so I gave up on that idea fairly quickly. I had to wake my flatmate at 12:30am when he has work the next day to help me push it up the driveway.... I felt sooo guilty waking him up and promised to shout him a beer next time we're in town.

Yet another silly experience.... all you can do is laugh sometimes.

It's ALWAYS the way! Good that you can laugh about it. I reckon half the people on here would be swearing and throwing things. Good stuff on getting it sorted

[DarkLord]

The gasket glue I put on there (and was recommended by the guy at Repco) was beyond hopeless. It just burnt to a crisp and then all chipped off so just an hour or so into my ride from Taupo to Tauranga and hello, bike is backfiring again. Needless to say, I was a wee bit ticked off, after all the shenanigans with the battery getting replaced (the new one crapped out as well, had to get it jump started) and me thinking I had finally got the backfiring issue sorted, when it turned out I hadn't as to being recommended the wrong stuff.

I got some stuff today called Gun Gum, which is specifically designed for patching up holes in mufflers. Greeny-brown coloured stuff, pretty awful to look at but it was like a thick, heavy paste. I went around all of the cracks in the header pipe and patched them up, haven't touched the bike since as it needs about 12 hours or so to dry, but I suspect that will have solved the problem, permanently.

The ride back to Taupo will be the judge of that.....

[CookMySock]

You are not too far from us bud, so bring it by sometime so I can have a listen for ya. It might be perfectly normal - just louder than what you are used to, or it might be problematic.

Steve