Trying to decide whether or not this is all in my head, but would love to know if anybody else has had any similar experiences?

(CBR600 F3 (1995))

So changed the spark plugs (long long overdue - I've had bike for 2.5 years and not changed them before, and no idea what the servicing was like before)
Bike had been getting increasingly sluggish to respond, noisy, hard to start, and eventually blew out the spark plug cap from chamber 2.
New plugs immediately rectified that, starts straight away, throttle is so much more responsive and smooth, flat spots in engine almost gone.

What I've noticed however is that when cornering, it feels like either the front or rear tire (at different times) slips a tiny bit. Now that could be my imagination, or me being overly cautious and so changing my riding style, but has anybody else experienced this?
Logically I can imagine that the throttle is a bit more sharp, so as I ease on the power it's putting a bit more torque to the back wheel so I need to readjust to that (no explanation for the front wheel though).

Have also noticed that it's much more liable to locking up the rear on downshifting with heavy engine braking, especially even with a very slight angle on it. I know, I know, be smoother and don't downshift whilst leant over, but this is a few degrees and is definitely not something that it did before the plug change. Again, logically I can imagine that could be somehow linked to the better power delivery from new plugs.

Any thoughts, any experiences?

 

Just a thought... but how loose were the old plugs? Cause a leak through the threads is pretty much the only thing that could explain the increased resistance at engine braking and the jumped plug cap. They would have to be in finger tight though. However to me it sounds you`re downshifting a bit too early if you`re getting tire locks frequently, you might consider easing up on that a little.

 

How are the tires? How old are they?

Maybe it really does have a problem and you are just more sensitive to it now.

 

Plug in chamber 2 was well loose, basically didn't have to unscrew it to remove it. Was worried about the threads in the engine, but the new one seemed to screw in just fine. So yeah, that could definitely be a factor. I'm not knowledgeable enough on engines to know exactly what that could cause. All plugs a wee bit blackened as well. Could just be age, could be when it's been knocked over a few times (perils of on street parking) or could be that it runs a bit... rich? I think?

I think I do downshift a bit early, to be honest the wheel locking up doesn't bother me (although it probably isn't great for the bike), it was more the fact that it is different now to what it was before.

Tires (Pirelli Angel ST) have about 5000 miles on them but they've been relatively gentle miles this year and there's still plenty of tread. I would expect the grip to be less than if they were new, but again it's more the stark contrast to just before the change.
Ultimately the dropping temperature could also have an effect, but it was only off the road for a week, and I don't remember it being so twitchy previous winters.

Yeah, don't know if it's a 'problem' or just that my riding style was being disguised by lack of power. Obviously if I'm too aggressive on throttle going in and out of corners then it's going to spin up or lock up, and an increase in engine response could have an effect on that, I just don't think I'm being 'that' jumpy with it.

 

You literally didn't have to unscrew it and just pulled it out? Or it was just extra loose?

 

Uncertain... I popped the cap on and off a few times whilst examining it and it didn't come out then, but then another time it came out with the cap. Would suggest to me extra extra loose and then my cap on/off-ing unscrewed it the rest of the way.

New plugs been in for a week now and checked tightness again, nothing has loosened up there.

 

A plug that comes out with the cap means that cylinder isn't doing anything. So you've just received a 25% increase in power and engine braking. I think that would have a significant impact on all things relating to performance, throttle, handling, and engine braking. For future reference, always try to use a torque wrench to get the proper amount of tightening on things like spark plugs and such. BTW, I love F3's, enjoy the ride.

 

agreed, also on down shifting, try rev matching to prevent the rear from locking up/skidding.

 

Thanks IDoDirt, that's pretty much what I was thinking, good to have somebody else affirm thoughts. Yep, I torqued up with good old torque wrench, mistake was not checking the plugs when i bought it or changing them for 2 years!

Thanks for the tip sjona2011, I try to do that, but think I need to re-learn my throttle a bit with the increase in power.

 

Yeah, you basically had a cripple-triple before you changed plugs if that plug came out with the ignition wire.

The bike should also sound drastically different too. And you should have noticed quite a bit more power or at the very least, more consistent throttle.