Cylinder #3 losing spark when engines warmed up

[alan0259]

Hey everyone.

My 2002 R6 (carb'd) isn't running right.

I've just bought the bike and it was running a bit rough so I've:

Cleaned the air filter
Put new fuel in
Changed oil/oil filter
Changed coolant
Stripped and cleaned carbs (every pilot jet was blocked, mixture screws are standard setting - not adjusted anything)
Balanced carbs
Put new NGK spark plugs in.

It's loads better but still not 100%, when you first turn the bike on and spray water on the headers the water evaporates instantly, but after 5-10 mins when the engine is warm cylinder #3 seems to cool down and the water takes twice as long to evaporate.

I've swapped two coil plugs around but the fault is still on cylinder #3.

Any ideas what can be causing this? I've done a 20 mile ride and it's no different...

[moonzoomer]

sounds like a faulty coil, switch with another coil from the same bike and if if another cylinder stops firing, if so the problem will be the coil which will need replaced. The insulation breaks down internally in the coil after it gets warm causing this common fault.

[alan0259]

[moonzoomer]

[DJP]

Well if it runs OK cold, that would tend to rule out physical engine damage such as dropped valves etc.

As you've swapped coils, that would seem to rule out electrics.

That just really leaves carbs. I don't really know much about them on this bike, but I'd be having another close look at carb #3. (eg Float heights? Bent needle? Another blocked jet somewhere that you haven't noticed? Correct jets fitted? etc etc).

Failing that, how about getting a used set of carbs and seeing if it runs OK with them?
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[Major Doss]

The pulse coil on early Hinckley Triumphs were renowned for breakdown when hot, dropping a cylinder. Fine when cold. Just throwing it out there.....
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[P.addy]

Do you mean you have changed the physical coil over so taking the one from 2+3 and using it for 1+4 or just switched the leads/caps round.

I'd do the first one. If the problem changes to either 1 or 4, its the coil.

[cb1rocket]

[P.addy]

Ignition coil for 02 R6

https://www.stuff4bikes.co.uk/ignition-coil-yamaha-yzf-r6-01-02-13041-p.asp?gclid=CLrwsbHyqr0CFe3ItAodijwALQ

I'd be swapping the coils over between 2+3 and 1+4[/img]

[weasley]

The title says "lost spark" but the analysis just shows a dropped cylinder, not the reason.

First off, check if the plug is sparking when in this failed mode. If not then it is electrical and would be either the coil, the lead, the plug cap or possibly the spark plug. You can test all of these with a multimeter to look for the right impedances.

If the plug is sparking nicely then it is something else. The fact that it is heat related would steer me away from the carbs (at least to start with) and I'd look at compression, maybe valve clearances or possibly a head gasket issue.

However, the rule I have learnt the hard way is to eliminate the easy-to-check things first (rather than get stuck into the thing you think it must be, only to find it isn't that).
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[alan0259]

Thanks for the replies everyone.

I've remembered that when putting the carbs back on, I was struggling to get to all of the clamps so a couple of carb boots aren't clamped down.

Do you think this could be causing the issue? The two that I tightened were just about accessible so god knows how I'll get to the other ones.

[0l0dom0l0]

[alan0259]

Right, weird update.

Last night when I swapped two coil plugs around the fault was still there but I was testing while the engine was red hot.

Today I've done the same tests three times (morning, afternoon,night), all four are now firing fine when first started and also when engine has been running for 10-15 mins.

But now the revs seem to creep up from 1.3k to 2k after 10mins of it running and it requires a big (ish) throttle blip for it to settle again, a small blip seems to keep it at 2k revs.

Also noticed that its making a clicking noise when I first turn ignition on (sounds like the wheel of fortune wheel as its about to stop spinning!).

Well and truly baffled!

[Pete.]

Your initial fault sounds like tight valve clearances on that cylinder but after the last post, well, who knows?
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[weasley]

The clicking is the fuel pump priming - it's normal. You will probably find it does it more after being stood for longer. That said, if it is doing it for a few seconds even after a day of standing that might point to a fuel leak somewhere along the way.
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[spikenipple]

Sounds like an air leak.

Edit: (The high idle problem)
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[salem1987]

on my old 99 R6 it turned out to be a faulty reg rec causing all sorts of issues with cylinders not firing. Might be worth checking the charging voltages when running.

(multimeter on the battery set to 12V DC, should read roughly 14v when revving engine. If you see big spikes up to 19V or anything around there its probably toast. Same applies if its just reading 12V or less)

[geordiecbrblo...]

[0l0dom0l0]

[orac]

while you are in the carbs check the diaphrams. i had an extremely similar issue with the little 400, found a tiny whole that could only be seen by stretching the diaphram, it was less than 0.5mm long.

i quick qay to diagnous this is to swap the daphrams, leaving the needles in there respective carbs, slders too if they can be seperated from the diaphrams
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[alan0259]

Fired it up again today and its running fine again on all four, even when it's been running for 10-15mins.

Maybe reseating the coil fixed it?

I've tightened the carb boots and it seems a bit better, the revs were rising ever so slowly until it got warned up, so once fully warm I turned the idle down to just under 1,500rpm.

The only issue now is that when its warmed up, when you blip the throttle the revs go lower than idle then slowly rise back up to idle, but I believe this is due to it running rich? The mixture screws on the carbs are at standard setting but its got an aftermarket exhaust

[alan0259]

Ok, decided to tweak the mixture screws on the carbs (whilst still on the bike like a magician!) whilst the tank and airbox was off, I turned them out another 1/2 a turn, so 2.5 turns out from the bottom, then altered idle to suit.

Bike was then idling and revving perfect.

Bingo i thought!

Then i put the plastic tray back on that covers the plugs, airbox, air hoses, fuel tank, seat.

Started it back up and same fault again!!!!!!

This to me is definitely looking like a trapped wire of some sort, maybe the tray catching the plug leads??

It's been running fine for two days then as soon as I out these bits back on it does it again, the first time I noticed the fault it was after putting things back together so it's a pattern.

I'm going to strip bits back off it tomorrow to try identify the problem...

Nightmare!!!!

[Nemo]

You can't really turn the idle screw a half turn and expect it to be peachy, sometimes it will, but majority of the time it won't.

You need to do it with the engine running, turn the mixture screw and listen for a change in engine tone, when it rises then starts to fall, go back to the peak, that's where you want it, set the idle then move onto the next cylinder.

Whilst you're at it, if you have the gauges, may as well balance them.
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[temeluchus]

replace the float valve needle and seat o-ring on that cylinder.
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[Ariel Badger]

Trying to treat an air leak by fiddling with an idle screw is not good science.
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