Front end problems

robwbright · May 23, 2010

2003 YZ250f

Took it to the track for the first time yesterday (my buddies new used bike). the prior owner had the rear shock nut turned almost all the way down - the guy said "I'm heavy, so I jacked it up."

I replaced the front wheel bearings and fork oil. The steering stem bearings feel tight and smooth and adjusted properly (as much as I understand that).

My buddy is a beginner, 6'2" and 200 lbs. We do not know what the spring rate are on either end - presumably stock from what the prior owner said, but I pretty much don't trust anything that guys said anymore. My buddy is barely jumping and just wants to learn to ride a bit before spending money on new springs or whatever - so the goal is to simply make the bike useable until he progresses some.

Anyway, the track we went to is really sandy. The front end felt really heavy and wanted to push a lot. It also felt like the front end wanted to stay on center - required some effort to turn it left or right.

I suspected the jacked up rear end was part of the problem, so we loosened the shock nut and moved it up the shock to about 1/2 way. the situation improved 50-60%, but was still there.

I can move the nut up further, but I was thinking that compression damping would be a good place to start next.

Am I on the right track?

Thanks

robwbright · May 23, 2010

btw, we'll work on the sag, but as he's new to this, we don't have anything but a triangle stand at his place here in NC. Thus, no way to check/set it at the moment.

IndyMX · May 23, 2010

Where are the forks in the clamps??

Patman · May 23, 2010

How ugly was the oil you drained from the fork legs?

robwbright · May 23, 2010

IndyMX said:
Where are the forks in the clamps??

Exactly where they are on my bike - there's a groove in the fork leg just below the cap groove. i set both bikes with the second groove dead level with the top of the upper clamp. Thus, the fork could be moved up in the clamps a whole lot more than it could be moved down in the clamp.

Doesn't make sense to me to move the forks up in the clamp and lower the bike for a 6'2" rider. . . but I don't know what I'm doing with suspension, either.

robwbright · May 23, 2010

Patman said:
How ugly was the oil you drained from the fork legs?

I haven't looked at a lot of used suspension fluid, but I wouldn't say it was terrible looking - just dirty.

One leg had a seal leak, so I replaced the seal and dust cover. The bushings showed some wear, but not nearly as much wear as the bushings on my RM were when I had it rebuilt - and those RM forks still handled/cornered really well.

Anyway, I replaced the oil in both legs of the 250f with Mobil 1 ATF.

Again, we're dealing with a beginner who just wants to get up to 10 mph on the track and jumping more than 24 inches off the ground.

I've never seen a bike do anything quite like this before - seems like it's setup issues to me, but, again, I don't really know what I'm doing or I wouldn't be posting this.

robwbright · May 23, 2010

IndyMX said:
Where are the forks in the clamps??

BTW, this is the bike that had the starting issue. Down here in N.C. it's 90 degrees and the bike has wanted the hot start lever when cold. However, on Saturday at the track, it started easy everytime after it got warmed up - even after it sat and cooled off. No coolant leak, either - which was the main thing I had to repair on it.

I'm sending him to have the valve clearances checked, but other than the valve clearances and this front end problem, I think he's good to go.

Thanks again for the help.

Chili · May 23, 2010

I'm missing something here, by shock nut are you referring to the lock collars on the pre-load rings? If so having the proper race sag can have a huge effect on cornering ability and feel.

If the track is really sandy try dropping the forks down in the clamps almost chopper it out and stay more neutral on the bike and steer more with the rear like a 2 stroke.

robwbright · May 23, 2010

Chili said:
I'm missing something here, by shock nut are you referring to the lock collars on the pre-load rings? If so having the proper race sag can have a huge effect on cornering ability and feel.

If the track is really sandy try dropping the forks down in the clamps almost chopper it out and stay more neutral on the bike and steer more with the rear like a 2 stroke.

the forks are virtually as low as they can go in the clamps. might be able to drop 1/8" then we'll be clamping onto the fork cap.

I realize sag makes a big difference, but I spent years riding bikes without even checking the sag - and never had one feel like this.

Plus, we have no way of getting the whole bike off the ground at the moment.

Anyone know of an online suspension troubleshooting guide or something like that?

robwbright · May 23, 2010

Chili said:
I'm missing something here, by shock nut are you referring to the lock collars on the pre-load rings? If so having the proper race sag can have a huge effect on cornering ability and feel.

If the track is really sandy try dropping the forks down in the clamps almost chopper it out and stay more neutral on the bike and steer more with the rear like a 2 stroke.

"shock nut" = "lock nut" and "adjuster" in the manual. The two nuts on the threaded section of the shock at the top of the spring.

robwbright · May 23, 2010

ok - he got a couple concrete blocks.

as I said, the shock was jacked all the way up - only about 5 threads were showing below the bottom shock nut.

we moved it up to about 40% threads left from the top and the front end started working better - but not great.

however, now we have measured the sag and it's 5.75" - WAY to much. Of course, the solution is to turn the shock nut down again - in the direction we came from that helped the front end.

i'm guessing that the bike has stock springs - which would be too soft for a 200 lb rider.

are the springs contributing to the problem? Seems to me that the sag would be excessive if the spring is too soft - yet we seem need to lengthen the spring to get the front end to work properly.

Confused. . .

robwbright · May 24, 2010

I'm headed to Myrtle Beach for 4 days and won't be on the net much, so I/we will check on this on Friday. Any further assistance will be much appreciated.

whenfoxforks-ruled · May 24, 2010

So far so good, yes the springs being too light is an issue. BUT, where are the clickers at? Buried would my guess, or at least the compression dampening? I do not need the bike off the ground to check the sags, just to baseline the static sag. You can achieve that by pivoting it on the triangle, or just lifting it till it tops out. No matter what I have tried, this job requires at least 2 people on the same page, most times 3! Measure the sag with rider and gear till it reaches 4 inches, against the bike sitting under its own weight sag. Then measure it topped out, unloaded. Subtract the sag with the rider, from the bike unloaded, topped out, this gives you the static sag. And that will tell you if the spring is correct. Are we on the same page? Vintage Bob

helio lucas · May 24, 2010

if you have the manual, follow it, if you don´t there are plenty of threads on the sag subject.
try to set every clickers half way. if they have 20 clicks, set it 10 clicks out from full closed position. they are a good baseline setting.

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