Honda CB250 Nighthawk weird noise problem

[kingley]

I have a 1992 Honda CB250 Nighthawk that has a weird noise that only occurs when the bike is in motion. It's kind of like a slapping sound. It doesn't happen when the bike is stationary, If I put it on the centre stand and cycle through the gears and rev it, the bike doesn't make this strange noise at all. So I'm guessing it's probably not cam chain rattle or piston slap. The noise only ever happens when the bike is being ridden. I'm at a loss as to what it could be. Maybe it's a bearing gone or going bad, a cable slapping under the tank, fuel sloshing in the tank or just some strange unexplainable noise that's been there from day one? I'll see if I can record it on my phone (if possible) as I'm riding it tomorrow. In the meantime has anyone any ideas as to what might be causing the noise?
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CB250 Nighthawk

[Pete.]

Noise in motion is usually brakes or chain. Put it on the centerstand and turn the rear wheel. Inspect the chain for tight spots or broken sideplates. Inspect the discs in case one is cracked.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[kingley]

Thanks Pete. I'll check that out.
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CB250 Nighthawk

[numpty2]

I've had a Nighthawk for many years, and a loose chain can make that noise. It is mostly when you decelerate.

Another cause can be the centre stand. The spring gets weak with age/use and mine now bangs a bit when I go over big bumps.

Incidentally can I recommend the Yahoo users group: https://autos.groups.yahoo.com/group/CB250_Nighthawk/

...an excellent group with a huge archive of fixes & cures for this bike. It has saved me much time & money.

[kingley]

Thanks for the link numpty2. I'll check that out.
So far I've ruled out the chain, piston rods and cam chain. It could be the centre stand, but the noise seems to be coming from the front of the bike. I've padded the headlight to rule that out, checked the brake caliper. The sound is almost like plastic hitting metal. I suspect there might be a stray/loose nut/stone in the clock casings or maybe it's a cable hitting something. I honestly don't know. Further investigation should hopefully discover something. I'll check out the Yahoo group and see if that turns anything up too.
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CB250 Nighthawk

[bikenut]

hi dude,

balance chain, although you have tried bike on center stand and no noise, so front wheel noise|?? speedo cable or drive?

long shot, cotton thread trapped in tyre tread, difficult to see but a 40mph it made very loud noise, banging.........very worrying till i found the cotton thread........difficult to beleieve i know but it happened...... viva van so decades ago.

[numpty2]

I have a vague recollection that mine did have an under the tank noise for a while, and it might have been the clutch cable being slightly in the wrong route. I might be wrong though, memory not what it was. To be fair, I have had my Nighthawk for 8 years.

[kingley]

[kingley]

Finally diagnosed the problem I think. It's looking like it's brake chatter, caused by the pads rattling around a little (a very miniscule amount indeed). So I'm trying some copper grease on the back of the pads to ease it. I've also ordered some new pads as the old ones are getting pretty low. Hopefully that will solve the issue.
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CB250 Nighthawk

[numpty2]

The front brake is the only long running issue I've had with my Nighthawk. It seems really prone to sticking pistons after winter riding (I ride all year round in all weathers).
I've had to strip mine down fully 3 times, and I replaced all the seals & pistons once.
Not a big issue really, given all the other virtues, but we all like to moan about something.