Single cylinder when accelerating - in the dry!

[Al_Sweetman]

Hey dudes,

Bit of an issue ... '04 SV-S (40k miles, last big service @ 36k). Suffering from some bizzare behaviour that's just started happening (it seemed to start after plug replacement following a drop in September, and has got steadily worse).

When rpm is around 2-2.5k and I accelerate away, she seems to cut out , and only one cylinder is firing (not sure if front or back). Idling is fine, cruising at that RPM speed is fine, accelerating from higher rev range is fine... it's just on acceleration from between 1.8-3k (used to be sub-2k only!). To reproduce: Cruise at 28-30mph in 4th gear (around 2.8k rpm). Open throttle hardish and try to accelerate to 35/36 - struggles on one cyclinder and gets there eventually. Second cylinder kicks in at around 3.2k. If I roll off at any time, the second cyl kicks back in. This is particularly annoying at roundabouts / starting off from traffic lights as stalling frequently occurs :( It feels almost like fuel starvation to one of the cylinders.

My initial thoughts are:

1. Spark or lead need replacing as are fowled / knackered... However, I replaced the sparks less than a month ago (so about 1200 miles) and lead *seemed* OK. Plus, I'd have assumed that if it was leads/sparks it wouldn't idle fine, and wouldn't be limited to exhibiting this behaviour at such a specific rev speed.
2. When I changed the spark last, I think some crap fell into the combustion chamber and this could have fecked the engine?
3. Oil needs a change (clutching at straws here!) - due within 2k miles anyway
4. Fuel filter needs changing / injectors blocked?

I've had a search, and can't find any related threads to this kind of problem... Any advice would be very welcome!

Cheeses,

Al.

[maviczap]

Feel the header with the back of your hand, whichever is not firing properly will be cooler

Could be fuel or sparks

[the_lone_wolf]

Feel the header with the back of your hand

Yes, if the skin that peels off blackens immediately it's hotter than if the skin just sizzles like a bit of KFC:eek::eek::eek:


;)

[maviczap]

Yes, if the skin that peels off blackens immediately it's hotter than if the skin just sizzles like a bit of KFC:eek::eek::eek:

;)

If you feel it with the palm, then the reaction from the nerves is to grip even harder, which is bound to smart a bit:D

[Dicky Ticker]

Alternatively use a piece of wood[bit of "broom" handle],header pipe to your ear and listen------only the wood gets burnt.

[the_lone_wolf]

If you feel it with the palm, then the reaction from the nerves is to grip even harder, which is bound to smart a bit:D

Just a bit, there's still a little bit on the KTM header where I brushed it almost immediately after stopping...

[maviczap]

I used to have an imprint on my thumb and forefinger from picking up a square bar which I'd been heating to put a twist in it, and forgot it had been red hot just prior to me picking it up. Doh!

[Al_Sweetman]

Thanks for the replies :rolleyes: ;-)

With the wood trick, what would I be listening for? Mind you, the idea of riding along with my head on one side and a piece of 2x4 sticking through my helmet into my ear is quite an amusing one - as long as there are no speed bumps!

On a more serious note, this is proving tricky to analyse as idling and higher-rev riding is fine. Sigh.

Where does anyone suggest I should start first (and no reg-rec comments just yet :-D)? I'm thinking replace both HT leads and sparks and see what happens? It's just bizzare trying to work out what would cause it to only happen under low-rev acceleration.

Al.

[benji106]

can you not recreate in the lower rev ranges whilst the bike is static/in neutral? if so then you would be listening for the sound of the cylinder running (or not)

[yorkie_chris]

Drain the carbs and check for sh*t... it could be some oddness in needle circuit causing this farting about. Could also be coils and/or leads.

[maviczap]

Drain the carbs and check for sh*t... it could be some oddness in needle circuit causing this farting about. Could also be coils and/or leads.

Its an 04 YC :rolleyes:

[the_lone_wolf]

Its an 04 YC :rolleyes:

Yeah but he's really old fashioned...

http://i488.photobucket.com/albums/rr243/ktm_wolf/misc/amish_biker.jpg

;)

[maviczap]

Yeah but he's really old fashioned...

http://i488.photobucket.com/albums/rr243/ktm_wolf/misc/amish_biker.jpg

;)

The resemblance is uncanny :eye:

[embee]

OK, a bit of thinking out loud if you like.

It would sound like a fuelling issue but for the fact that it runs OK at the higher rpm, so it won't be any form of flow restriction/blockage. By far the most likely thing is ignition.

The spark voltage requirement increases with compression pressure (i.e. throttle opening) so it may run at idle and light load but won't at wide throttle opening, OK that fits. The ECU will almost certainly change the coil on-time (or dwell) with speed so it's possible that there's a certain speed range where it isn't producing sufficient voltage to spark effectively if the components in one cylinder are defective for any reason, but if you close the throttle (so demand reduces) or move to a different speed it might be just enough.

I'd change the plugs for a start, they can be defective and are low cost items, I'd suggest getting some NGK Iridiums off ebay, a fiver each. Check that the gaps on the old ones are OK, might give a clue. Also as you say double check the HT leads, coil end caps are clean and not damaged in any way, and check the plug caps are not damaged and clip onto the plug firmly.

Defective coils tend to start playing up when they get hot, so it doesn't sound like your problem as described (though can't be ruled out).

[Bibio]

does it do it in all gears and only at that rev range?

could be wrong but it could be a sticky TPS sensor. or dodgy connector on coil. and as said defective spark plug, wouldn't be the first time i've had a duff brand new one.

[Al_Sweetman]

Right sorry for the lack of replies but I've been wrestling with BT and an Infinity install - not good. Mind you, the connection here in Wetherspoons is pretty rubbish too

Anyway, as-per posts I used a block of wood as by the time I got back the idle was god-awful to. It was the front cylinder that was mis-firing so decided to start by examining the HT wire as I could here a distinct "sparky clicking" as it fired ... Took the spark-plug boot off (ie separated from the HT lead) and the lead inside the sheathing was blue and knackered! Trip to Suzuki dealership to get a new bit of cable, then came the fun of removing the airbox filter body etc, only to then find the cable is moulded into the coil! I tried getting fingers down to remove the two bolts that secured the coil but bugger me if they're not inaccessible. Due to lack of internet, I thought "bugger this for a game of soldiers" and have dropped it into the garage - currently suffering mental confrontation with myself at having a garage do something I know I can do but just don't have the time (further dismantling takes too much time out of a working day)...

Pick it up tomorrow and hopefully it'll be good as new (along with new BT-023 - hopefully going to last on the DC much better).

Thanks for all the suggestions - hopefully this'll fix it - and that hint about the stick of wood was genius at allowing to hear what's going on

Cheers,

Al.

[the_lone_wolf]

currently suffering mental confrontation with myself at having a garage do something I know I can do but just don't have the time

I know the feeling, just before Morocco I ran out of time and ended up paying ~£400 for a full on service for the KTM

Bugger me if they didn't hide everything you need to service under the airbox, tank, crash guards, seat, headlamp, fairing dashboard etc etc:rolleyes::D