Forgive me if this has been covered elsewhere, I could not find it.

My XT660X is completely standard from a suspension point of view, I have only added the Kev fork mod plus stiffer fork oil, nothing else. I have a problem with wandering from side to side when I get over about 140kph, (or even at lesser speeds if I have a topbox on, depending on the wind). I have made several tests and the problem seems to be a light front end, as things improve slightly when I transfer my weight as far as I can over the front end.

So I need to stiffen up the preload at the rear, to push the back up a little, and or to drop the front forks thro the yokes a bit to drop and therefore load the front end. Needless to say I use the bike only on road.

What do u experts suggest????? Thanks.

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(Now sold on, sob) 2011 Blue XT660X with gold wheels, was 26,500 km.
Engine mods: K&N Stage 1 filter, DNA Stage 2 filter, snorkel removed, Kev fuel mod fitted.
Plus: smoked Puig screen, Yam aluminium sump guard, Yamaha / Acerbis handguards, Givi Trekker aluminium side cases, Leo Vince X3 cans plus Kev front fork mod and Fender Xtender. Just fitted Michelin Road Pilot 3 tyres.

SOLD the XTX for a Super Ten 1200. And just bought a Raptor 700 so staying on here for some tips....

Mine does exactly the same,never tried to find out why, but it makes the ride more interesting

I agree Trev but it would be nicer and more er relaxing if the ****** would go straight and not behave like a boat on the waves, dont u think????

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(Now sold on, sob) 2011 Blue XT660X with gold wheels, was 26,500 km.
Engine mods: K&N Stage 1 filter, DNA Stage 2 filter, snorkel removed, Kev fuel mod fitted.
Plus: smoked Puig screen, Yam aluminium sump guard, Yamaha / Acerbis handguards, Givi Trekker aluminium side cases, Leo Vince X3 cans plus Kev front fork mod and Fender Xtender. Just fitted Michelin Road Pilot 3 tyres.

SOLD the XTX for a Super Ten 1200. And just bought a Raptor 700 so staying on here for some tips....

Are you meaning to say that you get a slight weave at a certain speed?

If that is the case you may want to check that your pressure on the front tyre does not exceed 28psi and also check if the tyre itself is beeded properly either side of the rim because even the slightest chink in the bead might be the cause of the problem.

If all fails then I would be checking your steering head bearings, in particular the one in the lower part of the fork just below the head tube because usually road bumps and constant vibration are causing wear and tear of these bearings.

It could be a million and one different things!

Check: Steering head bearings, swingarm play, rear linkage play, loose spokes, bent rim(s), incorrect sag/ride height or front rear balance (preload), worn/damaged tyres, tyre pressures, misaligned forks, bent forks, chain too tight or stiff links, knackered shock etc...

A few bits of info that would be useful to know in diagnosing your problem:

(1) Has this weaving issue started all of a sudden, or has it gradually appeared and steadily got worse, or has it always done it?

(2) Did it begin at the same time you fitted the fork spacers?

(3) What are the current condition of your tyres regarding wear, and what pressures to you run front and rear?

(4) How heavy are you and what is the current preload setting on the shock.

BTW - In my experience topcases almost always cause funny handling at speed, so I'd take it off, rule it out of the equation and concentrate on getting the bike to handle properly without it first.

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By doing the fork mod with oil you have tipped the balance of the bike from the front to the back,you have already answered you own question either dropping the forks or jacking up the rear will take you back to where you were plus the benefit of the stiffer forks.

You will get the same wandering results with a knackered shock,riding two up,too much weight in a top box,if you had an aftermarket shock you would cure it with the ride height adjuster(assuming your tall enough to still get your feet on the ground),altering the preload will cure the problem also but that means ending up with stiffer suspension,it would be a quick fix but not long term.