Pointy running poorly.

[sKiTz-0]

Ok first off, apologies for what is probably going to be a long post but I want to accurately describe the symptoms on the problem I've been having, so if you're sat back with a beer after your Sunday roast and have 5 minutes to spare, I would appreciate any input

Bit of background in case of relevance - bike has been sat all winter, when I dug it out a couple of months ago the battery was knackered so I bought a new Yuasa battery and an Opti-mate to ensure I didn't let a battery get in that state again.

Bike has been running fine since then, no problems at all - been using it daily for past few weeks, then last week 14 miles into my 15 mile journey home it suddenly lost all power and felt rough and spluttery as if it was running on one cylinder. I managed to make it home and thought I would take a look at weekend.

Took it for a quick spin yesterday morning, and still doing the same thing - idling absolutely fine, starting fine, just whenever I'm pulling the throttle it is choking and bogging down. So I checked the spark plugs, both sparking, but I thought I would change those before checking ht leads/coil etc. Swapped them over yesterday morning and the bike was running fine after that. Hurrah I thought, that was easy

So I thought before I rely on it to get me to work Monday morning, and seeing as though the sun was shining, I'd go for a spin to Buxton to make sure everything was ok. Well, 25 miles in and it is bogging down again. Grrrr. I'm now 20 miles from home and had to nurse it all the way back. I'm kinda thinking it is something fuel related now though as while I was stuck behind cars trying to keep the speed/momentum up whilst not being able to overtake (some dodgy old people doing 25 in a 40 zone which was killing my revs and almost killing my bike) I noticed that it was not a specific amount of revs it was hitting which was bogging it down, but rather exactly where the throttle was. So I could pull a little throttle, and accellerate veeeeeery slowly up to the point where I could do 70mph in top gear comfortably, just that whenever I am pulling any more throttle than that the fuel is blip-blipping in. So I pull the throttle, the revs shoot up to 6-7k and then fall back down to around 4k (without moving my throttle hand) and then suddenly it is as if fuel gets through and the bike jerks and shoots up to around 7k revs again before bogging down / repeat.

I thought then that maybe it was the throttle position sensor, so I have just taken everything apart to look at that and realised I don't actually have the security style torx bits to get it off. Although while I was there I noticed one of the hoses had come loose from the air box - it seemed to run from down near the bottom of the engine (so that'll be where that nice streak of oil down the left hand side was coming from!)

Great I thought, maybe that is why it was choking. Just been for a test ride and still no improvement!

I don't really know what to try next - anybody any ideas? Anybody had the same problem before? I need my baby up and running so I can make the most of this weather - it's just my luck to be stuck in my car when the weather is like this.

Thanks

sKiTz

Air leak? Choke sticking? is fuel flowing well? Assuming its a pointy here..

[sKiTz-0]

Yes, pointy. K3 model, fuel injection. I was sure I had put that info in there somewhere! Apologies.

[mattSV]

Dodgy (old) fuel
Kinked fuel line
Blocked breather

[sKiTz-0]

I can rule old fuel out as I have been using the bike for at least 250 miles a week for the last 3 weeks so have gone through a fair few tank fulls.

I'll make a point to check breathers, fuel line, air leaks first off.

What's puzzling me is why the problem suddenly went away for 25-30 miles when I changed the plugs and then came back again. The old plugs looked ok when they came out, not oily, not too sooty, not corroded. I'm wondering if maybe a pipe or something could be caught/twisted under the petrol tank. Although I'm sure that is unlikely to be the case as I have had the tank totally off a couple of times since, and wouldn't explain why it just suddenly started as I was riding down the road. hmmm......

Cheers for all the suggestions so far guys.

[Bibio]

have you checked your oil level?

[muzikill]

Fuel pump ?

[sKiTz-0]

Oil level - forgot to say, I did check it after putting the new spark plugs in and am ashamed to say that it was below the low line! (probably thanks to that loose hose throwing all the oil out!) So I topped it up all the way.

You don't think maybe it could be a piston ring? If so then I don't understand why it would be ok again for 25-30 miles.........strange.

Fuel pump - there is nothing on the dash to indicate (no FI warning) but could be a possibility.

[sKiTz-0]

Actually, saying that, if it was piston rings I guess the spark plugs would be covered in oil.....

I had exactly this problem on a previous bike. Ran ok for ~10/20 miles then suddenly jerky, almost like going onto reserve (yes it still had a petrol tap). Stop bike for 10 mins and all ok again for a while. Turned out to be the fuel pump windings failing when it got warm. New pump fitted and problem fixed. I dont know if the SV would throw up a FI fault for this or not TBH, but the pump may be a possibility for the fault you describe.