making a 125 fast

Edited Date/Time 10/4/2014 11:44am
just wondering what i could do to my 2008 yz125 to make it a little faster, or a lot faster. i don't want to bore it out.
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9/24/2014 5:34am
Hey guy Smile

When i was riding in 125cc I had a YZ
I have BUD RACING exhaust withs a V-Force 3
But I think if you want a really perfect YZ and if you have money
You can prepar the engine
Put a exhaust
Change front suspension ( WP con valve for me is the best or Ohlins )
Put a V-Force 3

Is my opinion maybe you don't like

9/24/2014 6:48am
If you're on the chunky side of things, lose 10 kg. On my clapped out 98 CR125 I was still neck and neck with my friends new (at the time) YZ125 (2011). He was a bit heavier than I was though.
HenryA
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9/24/2014 7:51am
VHM head + Vforce + a pipe will make it scream. Don't forget to jet it correctly!
quadmx301
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9/24/2014 7:56am
Lock your right wrist at full rotation! lol. But seriously.

I'm a 125 lover, I can't get off of them. I've had good luck with putting Boyesen Pro Series reeds in the stock reed cage, vs. the V-force 3 route. It's cheaper, and I can't notice a difference between the two systems.

Pipe-wise, I've always preferred Pro Circuit over FMF. I've had far better results with PC personally. Check out Bill's Pipes though, I've seen +4 HP over a PC pipe on certain systems from them.

If you're still not happy, I would send your cylinder and head to Eric Gorr for his Mo-Betta porting package. It's a broader, easier to ride powerband that makes power everywhere, and he is very reasonable. You could do the top end focused porting, but low end will suffer, and it will be harder to ride.

My best advice: keep the thing stock and get faster corner speed. YZs have AWESOME 125 motors. I would do reeds and a pipe, get your jetting dialed in, and ride!

Enjoy!!

The Shop

macz400
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9/24/2014 7:57am
Run non O ring chain
Port and polish
Head machined for race gas
PC pipe and R304 silencer
No heavy wheelsets or HD tubes
Most important jetting!
brocsdad
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9/24/2014 8:09am Edited Date/Time 9/24/2014 8:10am
I would always recommend suspension before anything.

As far as the motor - Pipe, Port and head mods, carb mod and good race fuel such as VP VPR. If that's not enough you can have the cases matched, coat trans and ceramic bearings.

Call Bobby Barr at barrscompetitiion.net

He built bikes for RC, Jeff Stanton, Mike Jones, Cooper Web etc.

Good Luck!

Todd
9/24/2014 8:56am
Check and see how thick the base gasket is and put a thinner one in and it will raise compression, I do this on all of my 2 strokes and it works good to boost performance
mgtkr1
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9/24/2014 11:22am
learn to ride it faster. a pipe and correct gearing should be ample, plus v force reeds. tuning is a waste of time unless your racing in a 125 class. if your just doing practice days for fun and want more power, get a 250
9/24/2014 12:45pm
quadmx301 wrote:
Lock your right wrist at full rotation! lol. But seriously. I'm a 125 lover, I can't get off of them. I've had good luck with putting...
Lock your right wrist at full rotation! lol. But seriously.

I'm a 125 lover, I can't get off of them. I've had good luck with putting Boyesen Pro Series reeds in the stock reed cage, vs. the V-force 3 route. It's cheaper, and I can't notice a difference between the two systems.

Pipe-wise, I've always preferred Pro Circuit over FMF. I've had far better results with PC personally. Check out Bill's Pipes though, I've seen +4 HP over a PC pipe on certain systems from them.

If you're still not happy, I would send your cylinder and head to Eric Gorr for his Mo-Betta porting package. It's a broader, easier to ride powerband that makes power everywhere, and he is very reasonable. You could do the top end focused porting, but low end will suffer, and it will be harder to ride.

My best advice: keep the thing stock and get faster corner speed. YZs have AWESOME 125 motors. I would do reeds and a pipe, get your jetting dialed in, and ride!

Enjoy!!
I agree with the reed and pipe. I put a V-Force III and an FMF Fatty on our 2006 YZ125 and it really punched up the midrange. Running 114 octane Base Race Fuel doesn't hurt either! The thing flat gets it!
9/24/2014 12:48pm
To help you with pipe selection, the Pro-Circuit pipe gives you more on top. The FMF Fatty tends to increase the spread of power throughout, but will not give you as much top end as the PC pipe.

Basically, it depends on your ability. If you're a very fast rider - go with PC. If you're a weekend warrior like us, go with the FMF.
9/24/2014 6:47pm
cheers for the feedback. I was thinking the FMF fatty because I don't really need that top end power, just more power everywhere. the problem I found with the 125 was at a recent trip to a motocross track, I couldn't keep up with my mates of 250f's. I just want it to contend with them. also i re jetted to a #420 main and a #55 pilot. thoughts?
brocsdad
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9/24/2014 7:03pm
Buy a 250 2 stroke or a 250f. 125s are a blast to ride but they are not really competitive against the modern 250fs
9/24/2014 7:55pm
brocsdad wrote:
Buy a 250 2 stroke or a 250f. 125s are a blast to ride but they are not really competitive against the modern 250fs
problem is I have no money, nor could I keep a 250f running. this is why I asked for mods, not a new bike.
FGR01
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Fantasy
9/24/2014 8:55pm
cheers for the feedback. I was thinking the FMF fatty because I don't really need that top end power, just more power everywhere. the problem I...
cheers for the feedback. I was thinking the FMF fatty because I don't really need that top end power, just more power everywhere. the problem I found with the 125 was at a recent trip to a motocross track, I couldn't keep up with my mates of 250f's. I just want it to contend with them. also i re jetted to a #420 main and a #55 pilot. thoughts?
420/55 sounds pretty rich. Especially the 55. Stock jetting is 410/40. (US Specs anyway)

On mine I have FMF Factory Fatty, FMF powerCore muffler (not the shorty), Boyesen Pro reeds on stock cage and jetted 400/42.5. Rips pretty good.
9/26/2014 5:31am
cheers for the feedback. I was thinking the FMF fatty because I don't really need that top end power, just more power everywhere. the problem I...
cheers for the feedback. I was thinking the FMF fatty because I don't really need that top end power, just more power everywhere. the problem I found with the 125 was at a recent trip to a motocross track, I couldn't keep up with my mates of 250f's. I just want it to contend with them. also i re jetted to a #420 main and a #55 pilot. thoughts?
FGR01 wrote:
420/55 sounds pretty rich. Especially the 55. Stock jetting is 410/40. (US Specs anyway) On mine I have FMF Factory Fatty, FMF powerCore muffler (not the...
420/55 sounds pretty rich. Especially the 55. Stock jetting is 410/40. (US Specs anyway)

On mine I have FMF Factory Fatty, FMF powerCore muffler (not the shorty), Boyesen Pro reeds on stock cage and jetted 400/42.5. Rips pretty good.
i chucked the 55 in just for some insurance in doing a top end as i back off the gas
im thinking FMF fatty with titanium 2 muffler with vforce3 reeds
FGR01
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Fantasy
9/26/2014 8:36am
i chucked the 55 in just for some insurance in doing a top end as i back off the gas im thinking FMF fatty with titanium...
i chucked the 55 in just for some insurance in doing a top end as i back off the gas
im thinking FMF fatty with titanium 2 muffler with vforce3 reeds
I can't believe it isn't a blubbering mess with the 55. Maybe it is compensating for an air leak somewhere? Just a thought.

The Titanium-2 is the same muffler as the shorty but with a titanium stinger and end cap. I had a shorty on before. I like the Powercore-2 better. It spreads the power out more and gives better overrev. The shorty is more punchy and you have to shift more quickly and more often.

I also tried the V-Force 3. I had horrible luck getting the thing to seal. It created an air leak. If you use the V-Force make sure you use a good gas-resistant sealant on all mating surfaces.
1
9/27/2014 9:40pm
cheers FGR01, ill look into the FMF gear

so i should chuck in a 40?
bd
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9/27/2014 10:13pm
Do the following:

- Send engine to Watts Perfections (complete engine)
- PC Pipe and Shorty
- Vortex Ignition
- V Force
- GYTR Clutch
brocsdad
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9/28/2014 1:49pm
bd wrote:
Do the following:

- Send engine to Watts Perfections (complete engine)
- PC Pipe and Shorty
- Vortex Ignition
- V Force
- GYTR Clutch
Is Watt's farming the work out to PC or is he doing everything himself?
bd
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9/28/2014 5:17pm
bd wrote:
Do the following:

- Send engine to Watts Perfections (complete engine)
- PC Pipe and Shorty
- Vortex Ignition
- V Force
- GYTR Clutch
brocsdad wrote:
Is Watt's farming the work out to PC or is he doing everything himself?
Doing everything himself.
FGR01
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9/28/2014 8:53pm
cheers FGR01, ill look into the FMF gear

so i should chuck in a 40?
I wouldn't recommend making such a drastic change. If the 55 is covering up an air leak, going straight to a 40 could be a recipe for disaster. Try small steps. Put a 50 in, assess what that does and then maybe go to a 45. If the bike gets too lean, I would start looking for air leaks, potentially one of the crank seals. Even the right side crank seal on theseYZ125's can create an air leak versus an oil suck. Look at where the crank is positioned relative to the oil level in the tranny. It is higher than the oil level and can suck air in through the tranny breather tube.
YZ125H1
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9/29/2014 5:55am Edited Date/Time 9/29/2014 5:58am
FGR01 wrote:
I wouldn't recommend making such a drastic change. If the 55 is covering up an air leak, going straight to a 40 could be a recipe...
I wouldn't recommend making such a drastic change. If the 55 is covering up an air leak, going straight to a 40 could be a recipe for disaster. Try small steps. Put a 50 in, assess what that does and then maybe go to a 45. If the bike gets too lean, I would start looking for air leaks, potentially one of the crank seals. Even the right side crank seal on theseYZ125's can create an air leak versus an oil suck. Look at where the crank is positioned relative to the oil level in the tranny. It is higher than the oil level and can suck air in through the tranny breather tube.
What would running a smaller pilot do? I currently have a 55 in my YZ125 and i checked FMF website and they show 45-50 on the pilot for my year.
FGR01
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Fantasy
9/29/2014 6:58am
YZ125H1 wrote:
What would running a smaller pilot do? I currently have a 55 in my YZ125 and i checked FMF website and they show 45-50 on the...
What would running a smaller pilot do? I currently have a 55 in my YZ125 and i checked FMF website and they show 45-50 on the pilot for my year.
What year is your YZ125? Everything I've said in this thread is intended for the current gen 2005-2014 YZ125. I have a 2006 and the OP has a 2008. Stock jetting (US Specs) for the 2005-2014 is 40 pilot and 410 main and the stock jetting is very good. Most people do not have to deviate very far from this. That is why I am surprised to hear that the OP is running a 55.

If I remember correctly, the previous YZ125's, say 1996-2004 era, did run a richer pilot jet. That was a completely different engine.
YZ125H1
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9/29/2014 11:14am
FGR01 wrote:
What year is your YZ125? Everything I've said in this thread is intended for the current gen 2005-2014 YZ125. I have a 2006 and the OP...
What year is your YZ125? Everything I've said in this thread is intended for the current gen 2005-2014 YZ125. I have a 2006 and the OP has a 2008. Stock jetting (US Specs) for the 2005-2014 is 40 pilot and 410 main and the stock jetting is very good. Most people do not have to deviate very far from this. That is why I am surprised to hear that the OP is running a 55.

If I remember correctly, the previous YZ125's, say 1996-2004 era, did run a richer pilot jet. That was a completely different engine.
I have the 96 model trying to get it to run better at lower throttle opening. Seems way too unresponsive down low. So many things that could be wrong with it though. I'm going to tear it down this winter and do the top end, check intake, power valve, and the exhaust. Since trying to dial in the jetting now its pointless when so many of the parts are worn.
rosebud441
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9/29/2014 1:52pm
Try to keep your weight under 150.. eat more salad, less deep fryWink
seth505
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9/29/2014 2:58pm Edited Date/Time 9/29/2014 2:58pm
1) jet it (close to) perfect
2) Keep the motor fresh
3) Weigh 150 or less
4) Become an expert at keeping momentum
5) Become an expert at shifting precisely
6) Maybe porting if you don't want to bore cylinder
7) Have reeds in perfect working order/good reed cage
8) smile and go weeeeeeee
YZ125H1
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10/3/2014 8:11am
Another thing you can work on if you are not doing it already is race changes and fanning the clutch out of corners.

endurox
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10/4/2014 11:44am
faster, change the gearing
quicker, install 144 kit

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