YZ 125 Mods?

[stevied125]

Just recently bought my first dirtbike, an 05 YZ125. I am wondering what things would be good to do to the engine and still be fairly reliable. I have a FMF SST pipe and FMF Shorty silencer. I know I want to put a Delta VForce 3 reed cage, but not sure what else to do. Does anyone a bolt on head for stock bore and high compression with also a port and polish? What are some good ideas for these things?

 

[trial_07]

1- Good suspension
2- Good jetting
3- Practice, practice, practice...and oh...practice!

The performance upgrades you're looking at cost a lot and won't make a SIGNIFICANT difference. Get a big bore 144 or buy a 250 and you'll be a much happier man :nod:

 

[gurt]

I know athena makes a bolt on cylinder and head kit for the 96-04 yz. I have it on my bike and it really made a difference. you lose some bottom but the mid and top absolutely rips. it keeps it a 125 but raises the compression and is ported.

 

[husabutt]

Just recently bought my first dirtbike, an 05 YZ125. I am wondering what things would be good to do to the engine and still be fairly reliable. I have a FMF SST pipe and FMF Shorty silencer. I know I want to put a Delta VForce 3 reed cage, but not sure what else to do. Does anyone a bolt on head for stock bore and high compression with also a port and polish? What are some good ideas for these things?

Try a Phathead Racing head. We just ordered one for our new 06 YZ125. We chose the Flat top piston kit with a two step higher compression dome. with this configuration you must use 105+ octane fuel. About $250.00

 

[Zenith]

Or for $50 get a tuner to modify the head to a similar profile of that Phathead and you get the same power for 1/5 the price :P. Or let them do it their own way and maybe you get more power then the Phathead, for 1/5 the price. In case you haven't guessed I'm not a fan of these heads, if you don't need to change head profiles on a regular basis (and how many people do lets be honest!) they're a lot of money for very little.

Do a search in the suspension forum, there are a few reasonably simple mods you can do to the forks that make a huge difference. After that I'd recommend holding onto that money for the VForce etc. and going for a bigbore as suggested above.

 

[husabutt]

Other mods include:

V-Force reed assembly
FMF Fatty pipe w/SA silencer
Pro Moto Billet kickstand
Utah Sports skidplate
Ironman rear sprocker (50 teeth) up 2
Steahly flywheel weight
Works connection guards
All black Acerbis plastic
Tag upper triple clamps and handlebar
Metal Mulisha graphics
Guts racing black seat cover

We are still waiting for parts to come in in order to finish it.

We also purchased a 2003 KX 125 carb off free bay to get the needle and slide for tuning. This is unproven so don't go buy a KX stock needle and slide and just stick it in as it will be quite a bit leaner than stock. We will be testing that mod very carefully. BTW it did work great for our YZ85 :)

Yamaha does offer a slightly leaner 4.25 slide and many leaner needles. Leaning the jetting will probably as usual produce the biggest low end gains as the YZ seems to be jetted horribly rich. Just from starting the bike a few times and never riding it when we pulled off the stock pipe it was dripping oil. Yuck!

 

[husabutt]

Or for $50 get a tuner to modify the head to a similar profile of that Phathead and you get the same power for 1/5 the price :P. Or let them do it their own way and maybe you get more power then the Phathead, for 1/5 the price. In case you haven't guessed I'm not a fan of these heads, if you don't need to change head profiles on a regular basis (and how many people do lets be honest!) they're a lot of money for very little.

Do a search in the suspension forum, there are a few reasonably simple mods you can do to the forks that make a huge difference. After that I'd recommend holding onto that money for the VForce etc. and going for a bigbore as suggested above.

True. If you don't get the Flat top piston kit it would only be $150.00

YZ125 2005-06 Phathead Flat Top Kit
YF12505

This Phathead Flat Top kit fits Yamaha YZ125 2005-06. Phathead Racing’s Flat Top kits include a Wiseco GP series 762 racers choice flat top piston kit and a Phathead set with domes designed to be used with these high performance flat top pistons. This kit will increase low to mid range power and resist detonation. If you are using fuel around 90 octane use the F11. If you run fuel around 100 octane the F12 works well. If you run race fuel with 105+ octane the F13 dome with this piston will produce an impressive amount of power. The standard two domes for this set are the F11 (7.8cc) the dome closest to stock, and one step higher compression F12 (6.9cc). The higher compression domes available are the F13 (6.0cc) and F14 (5.4cc) domes. When selecting domes, the smaller the cc the higher the compression. To order a flat top kit, choose the color of head body with the drop down menu below. Enter the 2 dome sizes you want with the set. By entering no dome selection defaults to the standard set of domes. WARNING. When using the higher compression domes you must run high octane fuel. Running low octane fuel in a high compression engine could cause serious engine damage. Experienced motor builders, to view a list of additional dome options available for this head set go to the F1 and Y1 series domes category
$259.00

 

[Nevada Sixx]

best mod i ever did to my 125 was lower gearing, and good jetting.. all the pipes, reeds, porting didnt make me feel like i was on a 250 as the ads want you to believe. i do recommend some some of those shock socks to keep dust out of your suspension.

 

[Pete Payne]

Bang for your buck would be the 144 kit. Stay away from the Jewelry engine parts :cool:

 

[MXP1MP]

upgrade the shifter stopper plate & bolt to the upgraded '07 parts the '05 - 06 had a bearing on the end and it breaks off which can cause all kinds of damnage. The '07 part uses a solid roller design parts from yamaha all together like $20 at most.

 

[MXRose3]

My son and I both have 2005 YZ125's. His stopper bearing went out and locked up the transmission. I'll be ordering the new part asap.

The new part number for the stopper lever assembly is:
1C3-18140-10-00

bolt is:
90109-06193-00

 

[stevied125]

YZ Mods??

I have a 2005 YZ 125. I am looking for a few things to help the launching of the bike in a race. I am relatively short 5'8". I know I need to get my suspension sagged a little bit so I can reach the ground better and also get the suspension revalved so I still have the travel and rebound. Has anyone tried the holeshot controller, as used in motocross? Also is the steering damper worth the money? Any help would be greatly appreciated.

 

[stevied125]

Well i already have FMF pipe and silencer, my next thing I am getting is the V-Force or Rad valve. I just need to get it to when I launch it, the bike doesn't try to flip over backwards. The bike is good enough for now, my future plans do include the 144 or phathead kit. I just need it so I can touch the ground better and launch better. I was considering the steering damper due to the fact it has serious tank slap at high speeds over small bumps and whoops, trying to eliminate that also. Has anyone tried the holeshot controller or the steering damper and what were your results?

 

[dirtracker]

Just recently bought my first dirtbike, an 05 YZ125. I am wondering what things would be good to do to the engine and still be fairly reliable. I have a FMF SST pipe and FMF Shorty silencer. I know I want to put a Delta VForce 3 reed cage, but not sure what else to do. Does anyone a bolt on head for stock bore and high compression with also a port and polish? What are some good ideas for these things?

You said its your first bike ,now I presumed your a beginner.My suggestion is before you spending your hard earned money.

1 Have your suspension set up for your weight
2 buy eric gorrs performance handbook read read read!!!!
3 Read your owners manual
4 Learn how to jet your bike
5 jet you bike for weather conditions type of fuel used
6 Throwing a v force + sst pipe on your bike no proper jetting will make bike peaky or sometimes run bad.
7 V force + sst pipe + Race gas + proper jetting will make bike run faster more snap response better mid to top but will be harder to ride for a begginer.
8 Now stock bike good suspenion set up ,proper jetting practice practice practice more seat time will make you go fast.
Big bore kits are the best mod you could throw in your bike will give you wider useable powerband but still useless if not jetted properly and if you dont know how to ride .

 

[endofsilence808]

the best bet would be practice. your mods wont do any good till you arent a squid, which will be a long time. money dont buy skill.