Chirp when downshifting

[Gibbelstein]

Good morning all,
I think I finally got my carbs sorted out last night and it is quite nice to have a smooth idling/running bike again. The only issue I see now is that when I downshift without matching revs, I hear something that I assumed is the rear tire chirping. When I match revs (which I'm sure is a better practice anyway) there is no problem.

It started doing it when I was riding to the place where I tweaked the carbs, and I was thinking that it was just running poorly enough that the revs dropped too quickly between me pulling the clutch to grab a gear and me releasing the clutch that the speeds were out of whack. However, now that it is running properly, I don't think that is the case.

Does it sound like my suspicion is correct? How concerned should I be, since it performs fine otherwise? Anyone had this problem or want to offer a (hopefully) easy and (preferrably) free solution?

Thanks,
Chris

[Dogma]

Always best to match speeds when letting the clutch out, or let the clutch out smoothly if engine braking.

If this happens as soon as the gear is changed (while the clutch is still in) then you have clutch drag problem.

[Allie]

Are you also applying rear brake when downshifting?

[Gibbelstein]

Thanks, Dogma.

It seems to happen when I release the clutch, so I didn't think it was clutch related, but it was still something I was wondering about in the back of my mind. I'll try varying release speeds this afternoon to see if that changes things.

Also, I made a mental note last night to match better when shifting, but I'm still confused as to why it would start doing this seemingly out of the blue. I *think* i would have noticed it before on my trip to FL at least. There was not much else to pay attention to sometimes. =)

[Gibbelstein]

Allie,
Hmm. Hadn't thought of it. I really don't think so, but I will pay attention next time to see if I am doing it absent mindedly. I've certainly done stranger stuff than that...

[Allie]

Could be that or other drag on the rear wheel, such as tight bearings etc. I'd think the revs wouldn't drop too quickly just because of flywheel weight. Maybe you're running 346:1 compression??

[Steve]

Maybe you're running 346:1 compression??

Come ON, Allie, you know these engines won't handle anything over 345:1.

.

[Gibbelstein]

Well, I hate to leave any stone unturned so I guess I could check the compression, but if that's the case I'm kinda proud of my starter now. And I'm really glad it's not kick start.

[DanTheMan]

Tired clutch hand syndrome? Check your clutch cable. It might be that it's fully out when you think it's "just about there", and that would cause a chirp. On some of the MMSC (MSF) program bikes, I've chirped the rear tire on the downshift when demo'ing the excercise , and it was due to a stretched clutch cable.

[Gibbelstein]

Yeah, I think I need to attribute this one to rider technique. Took a long ride today and between warming up all the way and a slow deliberate clutch hand, the problem seems to have vanished. Thanks for the thoughts, everyone.

—Chris

[mike_of_bbg]

Also, I made a mental note last night to match better when shifting, but I'm still confused as to why it would start doing this seemingly out of the blue.

Maybe because your tires are wearing down or your tire pressure is off, reducing your rear tire traction. A heavy downshift will get a bit of a chirp from my tires at times.

[Gibbelstein]

Good point. I hadn't thought of tire pressure. I'll be checking that tomorrow...

[JEEPRUSTY]

Cheap hard tires would stop the chirping as they would just skid.
A slipper clutch would be cool to try.

[gearheadE30]

downshifting without rev matching is a darn good way to wear out a clutch, by the way. I don't think bikes are as bad as cars about it (street cars have clutches designed for mostly one-way operation, and get torn up if you don't heel-toe/double clutch downshifts) but it still makes a big difference. And if you ever drop the clutch like that on a downshift in a corner, not that you should shift in a corner anyway, there's a real good chance ending up in a lowside.

[Leigh]

I've done this deliberately into corners...
Go down two with the revs up, dump the clutch, the back wheel chirps and starts to slide in a compression lockup.
Lean in, power on.
Since you're already sliding it makes for a great powerslide out of the corner.

Gibbelstein, I don't recommend this technique for you just yet.
Just a feeling I get, ya know?