Odd misfiring problem - SV650.org

26-01-06, 11:50 AM

After replaceing my plugs and air filter I found I had this popping in the exhaust on tick over and sometimes a real loud misfire on the over run.
I put the old air filter and plugs back but still it popped and banged.
So refitted the new filter ensuring it was fitting correctly. But still it popped.
Then I noticed when I lifted the tank the revs increased slightly and the popping vanished. I have checked to see if any pipes and hoses are getting trapped but everything seems to be OK.
I chalked the round intake of the filter to see if the sponge under the tank touched but it doesn't. The spacers at the front of the tank are there.
I would guess it is running rich on tick over and it the unspent fuel igniting in the exhaust.
A new air filter should make it run leaner on the same settings so what is causing this. Has anybody else had this problem?
I would add this is not the first time the tank has been raised and refitted.

northwind · 26-01-06, 11:55 AM

I'd have said it was a restriction around the top of the tank too... Is there any chance your airbox has lifted up at all? It needs to be right down hard on the carbs, and they need to be right down on the intakes. I doubt you touched those but they might have simply loosened over time, or taken a knock... Not the likeliest of suspects tbh, but you never know.

fizzwheel · 26-01-06, 12:11 PM

My bikes been doing the same since I had it serviced last

Cheers for the tips, I'll have a look at all of that at the weekend I think

26-01-06, 12:13 PM

Northwind - Thanks for your input. I'll give the airbox a push downwards to see if it clicks into place.

26-01-06, 12:28 PM

Maybe an air leak, lift tank, run engine, spray some Easy-Start or similar round air-box to carbs joints, if engine speeds up when you do this then you have a leak somewhere... the Easy-Start is getting sucked in through the leak. WD40 might do it too. Look very carefully when you are putting the airbox back on. I find the air box sometimes needs a little help from a long, thin, screwdrver to help it "pop" fully onto the carbs.

26-01-06, 01:53 PM

Triumph5ta - The air box hasn't been off, only the filter has been changed and that is a very easy fit and just a matter of lifting out the old filter and dropping in the new and doing up the screws evenly. That is why it is such a mystery. Especially as Fizzwheel has the same problem after I presume a proffessionally done service.

30-01-06, 04:31 PM

Well the problem is still there, am I missing the obvious?
Fizzwheel - have you sorted your bike yet, if so what was the cause?
Has anybody got any idea what is wrong?

30-01-06, 04:43 PM

Just rang JHS Racing and they are certain it's an electrical fault and I know nothing about electrics. Blast.

31-01-06, 05:15 PM

Well I think I found the cause of the problem. As it was bright sunshine I took a break from removing wall tiles in the bathroom to have another go at the bike. I took the bike outside and lifted the tank and had a good look around. Whilst moving the tank up and down I noticed the fuel hose from the tank to the carburettor was kinking slightly at the tank end. On closer inspection I could see a split which just couldn’t be seen when working in the garage due to the artificial lighting. As I couldn’t get the hose off the carburettor I glued the split with rubber solution from my bicycle puncture repair kit and taped it up with plastic insulating tape. It seemed to run OK and the revs didn’t drop and there wasn’t any popping in the exhaust so I’m hoping there will be no backfiring when riding.
I think the hose could be a little longer to avoid the kinking and therefore causing the split.

26-01-06, 11:50 AM	#1
drumwrecker Guest Posts: n/a	Odd misfiring problem After replaceing my plugs and air filter I found I had this popping in the exhaust on tick over and sometimes a real loud misfire on the over run. I put the old air filter and plugs back but still it popped and banged. So refitted the new filter ensuring it was fitting correctly. But still it popped. Then I noticed when I lifted the tank the revs increased slightly and the popping vanished. I have checked to see if any pipes and hoses are getting trapped but everything seems to be OK. I chalked the round intake of the filter to see if the sponge under the tank touched but it doesn't. The spacers at the front of the tank are there. I would guess it is running rich on tick over and it the unspent fuel igniting in the exhaust. A new air filter should make it run leaner on the same settings so what is causing this. Has anybody else had this problem? I would add this is not the first time the tank has been raised and refitted.

26-01-06, 11:55 AM	#2
northwind Moderator Mega Poster Join Date: Jan 2004 Location: In the garage where I belong Posts: 17,083	I'd have said it was a restriction around the top of the tank too... Is there any chance your airbox has lifted up at all? It needs to be right down hard on the carbs, and they need to be right down on the intakes. I doubt you touched those but they might have simply loosened over time, or taken a knock... Not the likeliest of suspects tbh, but you never know. __________________ "We are the angry mob, we read the papers every day We like what we like, we hate what we hate But we're oh so easily swayed"

26-01-06, 12:11 PM	#3
fizzwheel Super Moderator Mega Poster Join Date: Dec 2003 Location: Somerset Posts: 3,614	My bikes been doing the same since I had it serviced last Cheers for the tips, I'll have a look at all of that at the weekend I think __________________ Look Dave, I can see you're really upset about this. I honestly think you ought to sit down calmly, take a stress pill, and think things over. K5 GSXR 750 Anniversary Edition

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26-01-06, 12:13 PM	#4
drumwrecker Guest Posts: n/a	Northwind - Thanks for your input. I'll give the airbox a push downwards to see if it clicks into place.

26-01-06, 12:28 PM	#5
triumph5ta Guest Posts: n/a	Maybe an air leak, lift tank, run engine, spray some Easy-Start or similar round air-box to carbs joints, if engine speeds up when you do this then you have a leak somewhere... the Easy-Start is getting sucked in through the leak. WD40 might do it too. Look very carefully when you are putting the airbox back on. I find the air box sometimes needs a little help from a long, thin, screwdrver to help it "pop" fully onto the carbs.

26-01-06, 01:53 PM	#6
drumwrecker Guest Posts: n/a	Triumph5ta - The air box hasn't been off, only the filter has been changed and that is a very easy fit and just a matter of lifting out the old filter and dropping in the new and doing up the screws evenly. That is why it is such a mystery. Especially as Fizzwheel has the same problem after I presume a proffessionally done service.

30-01-06, 04:31 PM	#7
drumwrecker Guest Posts: n/a	Well the problem is still there, am I missing the obvious? Fizzwheel - have you sorted your bike yet, if so what was the cause? Has anybody got any idea what is wrong?

30-01-06, 04:43 PM	#8
drumwrecker Guest Posts: n/a	Just rang JHS Racing and they are certain it's an electrical fault and I know nothing about electrics. Blast.

31-01-06, 05:15 PM	#9
drumwrecker Guest Posts: n/a	Well I think I found the cause of the problem. As it was bright sunshine I took a break from removing wall tiles in the bathroom to have another go at the bike. I took the bike outside and lifted the tank and had a good look around. Whilst moving the tank up and down I noticed the fuel hose from the tank to the carburettor was kinking slightly at the tank end. On closer inspection I could see a split which just couldn’t be seen when working in the garage due to the artificial lighting. As I couldn’t get the hose off the carburettor I glued the split with rubber solution from my bicycle puncture repair kit and taped it up with plastic insulating tape. It seemed to run OK and the revs didn’t drop and there wasn’t any popping in the exhaust so I’m hoping there will be no backfiring when riding. I think the hose could be a little longer to avoid the kinking and therefore causing the split.