Help troubleshoot handling issues.

[Ickis]

I haven't been on the forums in quite awhile. But I'm having a hard time figuring out handling issues I seem to be having, so I need your guy's help.

I've got a 93' CBR600 F2 that I ride daily (rain or shine). My FZR is in pieces, haven't had the money to get it put back together.

Anyway, recent work on it is the bike is:

- I upgraded the rear shock. Which required some minor grinding to the mount, however I don't think this is an issue.
- Installed upgraded fork springs, fork oil and fork seals.
- New Michelin Pilot Road 3's with around 1250 miles on them.
- Rear bearings replaced.

The suspension was upgraded because I'm a heavy dude, and the stock suspension was built for someone around 130lbs.

The issues I'm having are pretty recent. Nothing that happened directly after any modifications. At highway speeds (and above) I seem to have some front end wobble. I can attribute this to it being a naked bike, and it's much more prominent when windy. However, I'm not going to rule out the idea that the wind is only making a problem worse. I'm also getting surging feeling at highway speeds, but I think this may just be bad gas. Also, when turning, even when dry and tires are at operating temp, the bike feels like it's wet out. The bike doesn't seem to grip and hug the turns like it used to especially after the upgrades.

So, here's what I've done to troubleshoot or relieve the issues:

- Checked tire pressure.
- Checked front and rear bearings.
- Jacked up the bike and wiggled the swingarm to check for any play. Nothing.

After checking the front wheel bearings, I do know that I have a leak in the left fork at the drain by the axle. It doesn't seem to be a large amount. The reason for the leak is when I worked on the forks, I lost the seal for the drain bolt. It was dark out and late at night, not in a shop, finding it was going to be impossible. So uneven fork oil may very well be the or part of the issue.

The only thing I can think of that might be the issue is the steering stem tightest, or bearings.

So at this point, I guess I'm looking for any ideas I may have overlooked.

Thanks for your help.

-Ickis

[DonTZ125]

Do you have a 'wobble' (aka head shake - sharp and short pulses left and right) or a weave (slow, gentle sway back and forth)? You've checked or replaced all the other bearings; a weave is caused by notchy or overtightened steering head bearings.

Get that fork drain seal sorted - draining oil can contaminate your brake disk. Also, uneven damping can lead to erratic front end operation.

Between the revised shock and overhauled fork, you may very well have increased your rake and trail. Is this 'upgraded' shock shorter than stock? The FZRs normally need modified relay arms / dogbones when upgrading to an R6 shock. Do a search on suspension set-up; see if you can get your sack adjusted.

Measure your tire pressures cold and hot; you want a 10% pressure rise. A too-high cold pressure won't allow the tire to get up to operating temperature.

[Ickis]

It's more of a head shake as you described. The rear shock is actually the same length as stock. I doubt the tire pressure is an issue in regards to operating temperature. The reason being is that the Pilot Road 3's are specifically designed to be a cold-rainy weather tire, so it's designed operating temperature is lower than even most street tires.

And yeah, I intend on getting that fork oil leak fixed. I've got to do front brakes soon, so I'll probably do it then.

[reelrazor]

Front wheel assy. out of balance, front rim not straight.

[Stig]

head shake CAN be a rear end issue...as in tail wagging the dog

[Ickis]

Wheels are straight and were balanced when the tires were put on. I talked with a buddy about it and he suggested that the rebound and/or dampening may be too hard in the rear. So I turned them both all the way down and took it for a spin around the block. The change seems to have alleviated the cornering issues, but I'll have to do some more riding to be sure. After that assuming the issue is indeed fixed, I'll start making finer adjustments to the suspension, starting with making sure the sag is adjusted properly.

I'm guessing this has been an issue all along, but given the dramatic difference between old and new, it took me awhile to notice the nuances.

Admittedly, I've been quite lazy about tuning the suspension, but now I'm seeing why it's necessary.