Vibration and misfire?

[Taipan]

Hi All

My bike has got very vibey lately. My fingers go numb its so buzzy. I thought it maybe carb balance but it has got worse on the way home tonight.

I'm pretty convinced its a misfire now. If I hold it a constant throttle at say 4k you can hear the exhaust note varying and the rev counter reading fluctuates.

I've searched the archives but can't find anythng definiive. Is this a classic symptom of anything? Or where would you advise me to start looking?

Many thanks.

[embee]

If it's a carb model, check out the choke cables. It's a common issue for them to corrode, usually near the ends at the carbs, and the plungers stick and don'y close off properly.

If you're lucky a clean and lube will do the trick, otherwise new cables are called for (also give them a lube).

The rear one is easy to get to, the front one isn't, and really needs the carbs off to do it. Youy might well find the screws corroded in, and they're made of finest cheddar so will almost certainly give grief getting them out. Plenty of penetrating oil, gentle taps on the end with a light hammer, and a very good fitting driver/bit and take it gently. The standard screws are phillips/crosshead, NOT pozidrive. Using a pozidrive driver will mess them up, don't.

That's a start anyway.

Then again it might be ignition...................

[Taipan]

Hmm, that's interesting as it runs very lumpy on idle when you first start it.

Thanks for the reply.

It could be loose coil connections, but doesn't quite sound bad enough (this can cause dropping on to one cylinder which is very dramatic).

If it persists it may be worth whipping the tank and airbox off and checking you have no loose connections. Although getting the airbox on first time can be a little fiddly...

[Taipan]

Originally Posted by Tim in Belgium

It could be loose coil connections, but doesn't quite sound bad enough (this can cause dropping on to one cylinder which is very dramatic).

If it persists it may be worth whipping the tank and airbox off and checking you have no loose connections. Although getting the airbox on first time can be a little fiddly...

I did this last night and checked the plugs, which I'm pleased to say were pretty much text book. The removal of the front plug is novel! I took the right hand fairing panel off to do this but I don't think it’s necessary? Do people on here remove the panel or can you do it without doing so?

I wanted to check the main jet sizes and reset the mixture screws but the light was fading and I needed it for the morning. So I'll have to revisit there.

I also put it all back together without putting the front plug cap on and for about half hour was completely baffled as to what I could have done to make it run on one cylinder.

It was my first chance to really look the SV over and get familiar with it. I loved the little tank prop! How cool is that! Carbs look very easy to get right off should you need to. I was only disconnecting the cables from doing so. The throttle cables looked a little chalky as did the metal pipe part of the choke cable. I pulled the splitter box apart and oiled it all up while I was there. This morning when I started it it still felt very lumpy on idle and it "hunts" at a constant 3-4k? When I've had this problem on a carbed bike before it’s been the overlap between the slow jet and needle. Sometimes I’ve gone up a size on the slow jet or even got away with an extra 1/4 - 1/2 turn on the mixture screws, or maybe raised the needle a notch on some carbs. I think the SV has adjustable needles doesn't it? I'll maybe play with the different circuits to see if I can smooth things out.

As I was giving the bike a once over I noticed the rear sprocket is past its sell by date. I thought the previous owner said it had new chain and sprockets, but it is clearly a new chain only. I'm sure when I reading the archives I read something about worn chains and/or sprockets causing vibration? I’ll be ringing B&C Express about replacements later.

I also seem to recall the naked has different gearing to the S versions? I'm more interested in extra grunt than top end. I'll search the archives for gearing options if I get some time later, but if there is a widely accepted set up please let me know.

[Biker Biggles]

A shagged chain will certainly cause those symptoms when you are moving,but obviously not when you are just revving it at a standstill.Have you checked the basic stuff like air leaks at the airbox to carb joins,and crankcase breather pipes coming adrift?Another vote for sticking choke plungers as a common fault though.

[tinpants]

I would say it sounds like you need to get your carbs balanced and the valve clearances checked/adjusted.

[Taipan]

Originally Posted by Biker Biggles

A shagged chain will certainly cause those symptoms when you are moving,but obviously not when you are just revving it at a standstill.Have you checked the basic stuff like air leaks at the airbox to carb joins,and crankcase breather pipes coming adrift?Another vote for sticking choke plungers as a common fault though.

I'm pretty convinced its the worn sprocket causing the vibration. I did check most of your list yesterday but didn't remove the actual plungers themselves. I'll do that at the weekend.

Originally Posted by Bellerophon

I would say it sounds like you need to get your carbs balanced and the valve clearances checked/adjusted.

I'm also pretty convinced the carbs need balancing too. I'll read the service history tonight see if I can find out when the valve clearances were last done etc.

[Taipan]

Well I was right about the mixture screws. One was 2 turns out and one was 3 turns out! Much smoother idle now and less hunting at small throttle openings but still not perfectly even?

Couldn't get the screws for the carb plungers out. They've clearly never been off before. But using a stethoscope type probe I'm pretty sure I can hear they are moving.

But still the vibration persists. Actually makes my throttle hand go really numb! Its mainly when filtering traffic and in thesub 5k rev range. I dont seem to suffer from it at motorway speeds, or 6k and above revs?

I'm not convinced its the chain or sprockets now as a closer look revealed the sprockets aren't that badly worn really, if at all. I've ordered a 46t for the rear anyway and will change that and just hope my chain will fit?

I think it must be down to carb balance? I sold my twinmax balancer when I sold my BMW and I never really trust my carbtune? So I guess i'll have to make up a manometer and check the carbs with that.

Anyone else had such a vibey SV your hand has gone numb? If so what was the cause?

Originally Posted by Taipan

......and I never really trust my carbtune........

Why's that if I may ask?! (It's just that i've only just bought one last week!)

I was under the impression after reading many peoples thoughts on these that they are pretty good.