2004 YZ 125 must do mods/fixes?

[MXandy63]

Just picked up an '04 YZ125 cheap the other day with really low use.Was just wondering what mods are a good idea besides the front brake line fix and the usual maint.It already has a Pro Circuit pipe and silencer.Had the original tires(already fixed that),bars(steel now Renthal)and plastics.Just wondering what to look out for.This bike is just a back-up bike/play and practice machine for now.MX use only.Tore everything down and re-greased and torqued everything to spec and set the sag.Ideas and what to look for problems....Thanks!!!...p.s. already did some searches for this and came up fairly empty.If you guys know of a thread then let me know.

[MXandy63]

I guess nobody has any super secret mods to share...ha..ha!?

[95843]

When was the last time your shock oil was changed and re-charged?

Fork oil?

Is it the stock spring set?

What is your body wieght?

Org. piston or upgraded?

What is the compression?

What elevation do you ride at

What temp do you want to set the bike for?

Should I keep going?

Where are you riding MX tracks? Hills or flat?

Here: This will get you started in a direction I like for my kid. It is a good setting for the Sacramento area.

6CHY46-80 needle jet set at third ring from top.

410 main jet (standard)

37.5 Pilot Jet

Air adjust screw out 1.20 to 1.45 turns.

If you are better then a good Novice rider and do not mind the 1st 15 to 20% of throttle responce to be mush. Then have the power hit hard.

Go to a 40 pilot Jet, 420 main jet and 1.1/8 turns out on air setting but do not write back crying like a bedwetter.

The bike will smoke when cold and low RPMs. If it smokes when riding then go faster.

You are not giving any of us enough info. to help you out much. The bore kits are expensive. I check the piston ring for gap. Found the 55mm rings to have 25 thousands gap so I cut my own from a 55.5 or 56 mm ring to a 9 thousands gap.

Check your coil with an ohm meter now and then because you can not be down 20% on power with a dieing coil.

Keep an eye out for deals on clutch baskets and pressure plates if you are slipping the clutch in corners. Yamaha clutch parts are spendy.

If you have a good clutch and jetting set up, this bike will get it done for ya.

[95843]

Oh,

I polish the excoust (spelling?) port to a glass like shine and leave the intakes alone aside from checking the port edges in the cylinder to make sure they are not scubing a ring.

I have never had the need to split the case yet on the 04 YZ we have. so I have not been able to check how the cylinder match with the intake port.

[MXandy63]

When was the last time your shock oil was changed and re-charged?

Fork oil?

Is it the stock spring set?

What is your body wieght?

Org. piston or upgraded?

What is the compression?

What elevation do you ride at

What temp do you want to set the bike for?

Should I keep going?

Where are you riding MX tracks? Hills or flat?

Here: This will get you started in a direction I like for my kid. It is a good setting for the Sacramento area.

6CHY46-80 needle jet set at third ring from top.

410 main jet (standard)

37.5 Pilot Jet

Air adjust screw out 1.20 to 1.45 turns.

If you are better then a good Novice rider and do not mind the 1st 15 to 20% of throttle responce to be mush. Then have the power hit hard.

Go to a 40 pilot Jet, 420 main jet and 1.1/8 turns out on air setting but do not write back crying like a bedwetter.

The bike will smoke when cold and low RPMs. If it smokes when riding then go faster.

You are not giving any of us enough info. to help you out much. The bore kits are expensive. I check the piston ring for gap. Found the 55mm rings to have 25 thousands gap so I cut my own from a 55.5 or 56 mm ring to a 9 thousands gap.

Check your coil with an ohm meter now and then because you can not be down 20% on power with a dieing coil.

Keep an eye out for deals on clutch baskets and pressure plates if you are slipping the clutch in corners. Yamaha clutch parts are spendy.

If you have a good clutch and jetting set up, this bike will get it done for ya.

Thanks for the reply.In my post I stated It is used for MX.I have had this bike for like 2 days and do not know the "true" history.I'm just looking for problems or issues that others have had and the model years quirks.Already have jetting and suspension handled.Took it to Cal City MX on Sunday and am impressed with it(after my 450 ate 3rd gear for the 2nd time).Thanks for the clutch opinion....my sons YZ 85 had the same issues.Set-up is not a problem just looking for mechanical snafus that people have had if any with this model year.Like I said thanks for the reply and I appreciate it.Thats why I didnt give alot of setup info such as weight etc....setting the bike up is not an issue for me just the little things that are a problem with this year such as water pump seals,clutch problems,reeds and so forth...just things to watch out for.Thanks again for your reply and info 95843..appreciate it.

[95843]

We have found the 04 YZ 125 to be almost bullet proof.

I would have though my kid would have put a rod out the side of this thing long ago. Still no play in the piston rod to crank.

I would buy another one in a heart beat. This coming from a life long Honda lover. You will love this bike.

[2stroke63]

Don't you think 40 and 410 is kind of rich? I run 25 350 and the power makes my nuts want to fall off lol then again I have an 01 125.

[95843]

"Don't you think 40 and 410 is kind of rich? I run 25 350 and the power makes my nuts want to fall off lol then again I have an 01 125".

If you are an intermediate rider and need the very max out of the bike. The 40 with the 420 jet setting will flat haul the mail.

This setting is for a rider who is at idle and pinned with little in between.

The other setting I posted was for an average (or below) Novice rider who needs the entire range of power.

The 01 and 04 are close to the same bike. Maybe a little differant bend in the pipes? What needle are you running? Notice I am also one step richer there also.

If you are trying to run with a KTM 125, you have to throw the kitchen sink at em.

[MXandy63]

We have found the 04 YZ 125 to be almost bullet proof.

I would have though my kid would have put a rod out the side of this thing long ago. Still no play in the piston rod to crank.

I would buy another one in a heart beat. This coming from a life long Honda lover. You will love this bike.

Thanks....I really am starting to like this bike the more I ride it.Honda guy here too.But since my 450F ate 3rd gear Sunday it looks like Im racing this thing Sunday at an SRA gran prix.Two classes 45 mins. each.....bring it on!!! Ha Ha!!

[95843]

I am sure you have found there is no place to be lazy on a YZ 125.

The larger bore bikes are so much more forgiving of momentum type mistakes where the 125 makes you pay.

[MXandy63]

I am sure you have found there is no place to be lazy on a YZ 125.

The larger bore bikes are so much more forgiving of momentum type mistakes where the 125 makes you pay.

Yeah its been years since I rode a 125.Total fun though.Momentum is my friend now.

[2stroke63]

"Don't you think 40 and 410 is kind of rich? I run 25 350 and the power makes my nuts want to fall off lol then again I have an 01 125".

If you are an intermediate rider and need the very max out of the bike. The 40 with the 420 jet setting will flat haul the mail.

This setting is for a rider who is at idle and pinned with little in between.

The other setting I posted was for an average (or below) Novice rider who needs the entire range of power.

The 01 and 04 are close to the same bike. Maybe a little differant bend in the pipes? What needle are you running? Notice I am also one step richer there also.

If you are trying to run with a KTM 125, you have to throw the kitchen sink at em.

i have no idea what the needle is but when i tried running 40 410 a while ago my bike spooged like crazy. and the way i have set gives it crazy power from the bottom to the top. must be different elevations.

[95843]

Sacarmento is about 200 feet.

The 420 setting will have sponge the 1st 20% of throttle.

The 410 setting should not sponge much.

If your plug is burning good and the bike rides nice then you are golden.

If you are to lean then these things can be blow up monsters.

I will try your setting some day for giggles and see what happens ; )

[2stroke63]

I'm about 700 feet sea level. whats weird is my plug is always black but never wet and really dry. i just replaced the head gasket and the clutch side crank seal so nothing is leaking in. and the the reed pedals are pretty new. i have no idea whats up with that but it hauls so I'm not gonna worry:thumbsup:

[mrgrabow]

We have found the 04 YZ 125 to be almost bullet proof.

I would have though my kid would have put a rod out the side of this thing long ago. Still no play in the piston rod to crank.

I would buy another one in a heart beat. This coming from a life long Honda lover. You will love this bike.

If you've left the suspension stock, what clicker/sag settings are you running (both front and rear suspension)?

[95843]

If you've left the suspension stock, what clicker/sag settings are you running (both front and rear suspension)?

My kid is only 130 lbs with gear on and wet.

We set up the rear shock with 140 lbs of nitrigion gas (forgot the shock oil setting) Oil is from Dave here on Thumper Talk / Smart Performance, Rebound Return set slow 6 clicks out, High Speed Dampening is set at 2 turns out and Low Speed Dampening is set at 8. We can only get about 2.5 inches of sag because the lightest Shock Spring I have been able to find is set for a 140 lbs. Rider. Need the kid to gain a few pounds. The rear spring is set with the chain off the sproket, Bike on the stand with swing arm fully extended. Then I turn the top nuts until the spring is firm on the bottom mount. I am trying to get as much extention from the spring as I can with out throwing the C type holder out the bottom of the shock destroying the lower shock retainer.

Fork oil is at 120 MM with the Compression Clickers at 10 and Rebound a 12. We get about a 1 1/3 inch of Front Fork Sag out of it. The triple clamps are set at 20 MM from the top of the tube to the top of the clamp.

Most of the riding he does is at Hangtown which gets huge breaking bumps going into the corners from the 4 strokes. When we ride a smaller track I move the triple clamps higer (to first ring on the fork tube) and stiffen the bike up with two to 4 turns out on the fork clickers.

Keep in mind my kid can not tell me what he needs in his suspention. All he will say is it works good or it sucks. I have to watch him ride and then try to figure out what is going on from there.

Let me know if this helps any? Or maybe someone might have a better set up?

D.J.