Author Topic: 1979 CB650 vibration at 65mph and around 6000rpm (Read 5129 times)

checkflag · « **on:** July 16, 2009, 12:43:06 AM »

Anyone else experience a body tingling vibration at a similar speed/rpm combo?
It's a vibration that comes on strong and your whole body feels it. I would imagine
a girl might like this, but for me its a problem i would like to solve.

Also, I think my front brake caliber is dragging on the rotor because I hear a
shhushhing sound while moving. Normal, or well, what do you think?

Thanks.

Hush · « **Reply #1 on:** July 16, 2009, 02:22:03 AM »

Check your front axle bolts and any other life saving devices fitted to your bike.

Also your rear wheel alignment, back wheel may be off line and at a certain speed will cause vibration.
Old Honda CB350's suffered from this vibration but the 650 does not, find the cause, probably something loose like front mud guard or maybe even associated with your front brake dragging problem, check caliper alignment.

Gordon · « **Reply #2 on:** July 16, 2009, 08:17:27 AM »

Check all the engine mount bolts, too.

Frankenkit · « **Reply #3 on:** July 16, 2009, 08:37:55 AM »

I have a vibration like that at 6k rpms, too. I still haven't found the cause. Def. not in the handlebars, I feel it more in the foot pegs/seat/tank. Either it's not there or unnoticeable below 6k, though, unless I really press my knees to the tank. Motor mount bolts are all nice and tight, and so are the front axle bolts. I guess I'll have the rear checked, too? Vibes decreased significantly after using dynabeads to balance my tires, though, so I guess that's some improvement.

checkflag · « **Reply #4 on:** July 26, 2009, 01:35:35 AM »

Kit.. ever have any luck with that vibration? I just put new wheels and tires on
(finally) but vibrations are still there.

Who knows, maybe its normal.

jeepster · « **Reply #5 on:** July 26, 2009, 02:58:02 AM »

I have the same exact problem on my 650 Nighthawk...5500 rpm or so and the bad vibes start. In my case it has nothing to do with speed as it seems to vibrate just as badly when the bike is parked.

Johnny5 · « **Reply #6 on:** July 26, 2009, 05:36:24 AM »

Checkflag,

Are your carbs sync'd perfectly? You'd be amazed at how smoother the engine will run after this adjustment.

With that said, my 750K7 has a slight vibe after 4,000rpm. It goes away when I pull in the clutch, so it is engine related. And the carbs are sync'd, tires balanced, motor mounts tight, ect. I think some bikes just have some character.

CBJoe · « **Reply #7 on:** July 26, 2009, 05:44:59 AM »

Chain Lubed and Tensioned properly? I know you had the wheels off to change the tires, but thought I'd mention it anyway.

Joe

Johnny5 · « **Reply #8 on:** July 26, 2009, 06:30:23 AM »

Quote from: checkflag on July 26, 2009, 01:35:35 AM

Kit.. ever have any luck with that vibration? I just put new wheels and tires on
(finally) but vibrations are still there.

Who knows, maybe its normal.

Vibes go away when you pull in the clutch at speed? If so, it's engine related and you can rule out wheels, chain, ect.

manjisann · « **Reply #9 on:** July 26, 2009, 11:25:54 AM »

Harleys vibrate at any rpm range. Maybe the vibration is normal?

Brandon

tonycb650 · « **Reply #10 on:** July 26, 2009, 01:25:38 PM »

just got back from about a hundred mile ride on my 650 and i also get a "buzz" through the bike at 6 grand. when i pull in the clutch, it goes away. i've always known it was there, just didn't seem to be anything to be concerned about. but the only bikes i've ever ridden is a couple of old hondas and have learned to sort of dismiss most noises and vibrations. if you're new to old bikes but have ridden newer bikes, you would probably think your bike is falling apart. i would have to say its probably 'normal'.

Hush · « **Reply #11 on:** July 26, 2009, 02:25:07 PM »

I get my front Comstar balanced but don't worry about the rear, my 79 650 has no vibrations and it should with all the police junk on it.

MickeyX · « **Reply #12 on:** July 26, 2009, 02:30:26 PM »

Since Kit synched her carbs and put in the dyna beads, her bike is really smooth now. I agree with most of the comments here, there are so many things that could cause the vibration. Part of it is knowing what is normal and what isn't. If you're used to being in a car mostly up until now, you will notice vibration in a bike right away, no matter what kind it is. You are essentially sitting on top of the motor and wheels with about 3-4" of foam under you. That's it. In a car, you have all kinds of stuff between you and those components, besides being in an enclosed wind buffered space, to keep you from feeling it. I'd go through methodically and check everything these guys have mentioned. Then take it for a ride and see if it has gotten any better. I notice a big diff if I'm on a black top or concrete road. The concrete seems to wear rougher and gives more feedback compared to a black top. Things like this all add up. Pull in the clutch and see if it makes it go away. I'd put some money on your timing being off a bit and your carbs needing synched though. Good luck.

cb650PK · « **Reply #13 on:** July 26, 2009, 03:56:45 PM »

I do not believe, that vacuum carb sync at 1500 rpm idle, does much at 6000 rpm under load.

Frankenkit · « **Reply #14 on:** July 26, 2009, 04:18:36 PM »

but you're not JUST adjusting the carbs' vacuum against each other at idle- ideally, as you go through the RPMs, the vacuum should still stay the same between all four carbs.

NateTheBookie · « **Reply #15 on:** July 26, 2012, 02:20:23 PM »

I realize this is an old thread, but did anyone figure out if this is normal? I have the same vibration on my '82 650SC from about 5.5-6k RPM, but the vibration is there even if I just rev it in neutral, so I'm 99% sure it's engine related, is it just the carb sync? or could a badly adjusted chain tensioner or the like cause this (I've adjusted mine, but it never seems like just loosening and tightening that bolt while the crank is turned by a buddy does much)?

Hush · « **Reply #16 on:** July 26, 2012, 07:06:45 PM »

Place your bike on it's main stand (asuming some goof hasn't removed it to lighten the frame) and start bike, let it warm up in neutral, throughout this proceedure don't touch the throttle, let the bike idle!!!!!

Once you are happy running temp is achieved then slacken the cam chain adjuster lock nut then back the adjuster off until there is no pressure on the bolt, (bolt finger tight) this may be one two or three complete turns of the bolt but don't remove it alltogether.
If the tensioner is still doing it's job the chain will self adjust, yeah seems scary eh, first time I did this I expected the chain to rip through the head.
Now retighten the adjuster bolt (don't Swartzneeger it, tight is enough) and now the lock nut.
You should notice a change in engine noise as you slcken the adjuster and a lessening in that noise as you retighten the adjuster.
If this does not cure your problem (and you should do this anyway) have the carbs synched (synchronised) if they are slightly out they will pull against each other and you will lose power and create noise like a can of stones being shaken in worst case csenario.
Can sound like very bad clutch rattle but is carbs, get it done proffessionally the first time and then learn how to do it yourself later...just my advice.

trueblue · « **Reply #17 on:** July 27, 2012, 03:43:48 AM »

Quote from: Hush on July 26, 2012, 07:06:45 PM

Place your bike on it's main stand (asuming some goof hasn't removed it to lighten the frame) and start bike, let it warm up in neutral, throughout this proceedure don't touch the throttle, let the bike idle!!!!!
Once you are happy running temp is achieved then slacken the cam chain adjuster lock nut then back the adjuster off until there is no pressure on the bolt, (bolt finger tight) this may be one two or three complete turns of the bolt but don't remove it alltogether.
If the tensioner is still doing it's job the chain will self adjust, yeah seems scary eh, first time I did this I expected the chain to rip through the head.
Now retighten the adjuster bolt (don't Swartzneeger it, tight is enough) and now the lock nut.
You should notice a change in engine noise as you slcken the adjuster and a lessening in that noise as you retighten the adjuster.
If this does not cure your problem (and you should do this anyway) have the carbs synched (synchronised) if they are slightly out they will pull against each other and you will lose power and create noise like a can of stones being shaken in worst case csenario.
Can sound like very bad clutch rattle but is carbs, get it done proffessionally the first time and then learn how to do it yourself later...just my advice.

I thought you weren't supposed to adjust the 650's cam chain while running, but I could be wrong.

Hush · « **Reply #18 on:** July 28, 2012, 02:27:57 PM »

It's a trick Kit taught me, works great just don't have any dickhead mates around who might screw the throttle while you do it.
Gives you a much better idea how much difference there is between when the cam chain is relaxed and when it is adjusted up, I guess if you backed the adjuster off too much you could get a tooth jump on the cam sprockets but I never had that problem.

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Author Topic: 1979 CB650 vibration at 65mph and around 6000rpm (Read 5129 times)