2012 YZ125 Jetting Issue

JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619
Edited Date/Time 2/4/2021 4:52am
Wondering if anyone has had any issues with jetting? I have taken the carb completely apart, cleaned and replaced every jet and the float. I'm still having an issue with it being "flat" or a "sumble" in the mid range area. Any idea's? Generally I'm pretty good with jetting but this is kicking my ass!
|
DynoDan22
Profile picture for user DynoDan22
Posts
769
Joined
9/7/2011
Location
Victorville, CA, USA
DynoDan22 2/2/2021 12:26pm
2/2/2021 12:26pm Edited Date/Time 2/2/2021 12:26pm
Try replacing the jet block gasket with a JD replacement gasket. Mikuni's have been know to have this gasket fail and make jetting difficult.
1
doitinthewoods 2/2/2021 3:00pm
2/2/2021 3:00pm
Make sure your reeds are good. I chased jetting for a while on a 125 and that was the issue
2
CornflakeJackson 2/3/2021 11:30am
2/3/2021 11:30am
What jetting, fuel, premix ratio are you currently running?
As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and replacing it definitely helped with a 1/8th to 1/2 throttle burble I was struggling to get rid of.

Is the powervalve functioning correctly? If not, that could be hurting mid-range power until there is enough RPM to blow open the powervalve.
JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619 2/3/2021 12:24pm
2/3/2021 12:24pm
DynoDan22 wrote:
Try replacing the jet block gasket with a JD replacement gasket. Mikuni's have been know to have this gasket fail and make jetting difficult.
Good copy, I'll get this on the way.

The Shop

See All »
JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619 2/3/2021 12:25pm
2/3/2021 12:25pm
doitinthewoods wrote:
Make sure your reeds are good. I chased jetting for a while on a 125 and that was the issue
First thing my dad reminded me to do. They looked fine but they have been in for a while so at this point I'm going to replace them.
JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619 2/3/2021 12:29pm
2/3/2021 12:29pm
CornflakeJackson wrote:
What jetting, fuel, premix ratio are you currently running? As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and...
What jetting, fuel, premix ratio are you currently running?
As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and replacing it definitely helped with a 1/8th to 1/2 throttle burble I was struggling to get rid of.

Is the powervalve functioning correctly? If not, that could be hurting mid-range power until there is enough RPM to blow open the powervalve.
Im running 32:1 Yamalube R. Bike has a Pro Circuit pipe and silencer, Vforce 3 and I currently have a
420 main, 38 Pilot, stock needle 3 from top, and airscrew at 1 and 3/4 turns out.

I haven't checked the power valves, totally slipped my mind. I'll check those. Wasn't there an issue with these on the YZ's? I seem to recall something being an issue.

Thanks for the insight.

CornflakeJackson 2/3/2021 6:09pm
2/3/2021 6:09pm
CornflakeJackson wrote:
What jetting, fuel, premix ratio are you currently running? As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and...
What jetting, fuel, premix ratio are you currently running?
As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and replacing it definitely helped with a 1/8th to 1/2 throttle burble I was struggling to get rid of.

Is the powervalve functioning correctly? If not, that could be hurting mid-range power until there is enough RPM to blow open the powervalve.
JBlain619 wrote:
Im running 32:1 Yamalube R. Bike has a Pro Circuit pipe and silencer, Vforce 3 and I currently have a 420 main, 38 Pilot, stock needle...
Im running 32:1 Yamalube R. Bike has a Pro Circuit pipe and silencer, Vforce 3 and I currently have a
420 main, 38 Pilot, stock needle 3 from top, and airscrew at 1 and 3/4 turns out.

I haven't checked the power valves, totally slipped my mind. I'll check those. Wasn't there an issue with these on the YZ's? I seem to recall something being an issue.

Thanks for the insight.

I would think that jetting is good then unless you’re at crazy temperatures or altitude.
Yes the power valve pins are know to back out or fall out completely as shown on the right PV in the photo below. If one or both are out of place you can replace with roll pins from the hardware store.
The PV can also just get dirty/loaded up with carbon and sludge which won’t let it move as easily as it should. Should slide really smooth and easily when assembled. A properly functioning powervalve is critical for allowing the bike to stay in the pipe in less than WOT situations.

1
FGR01
Profile picture for user FGR01
Posts
6134
Joined
10/1/2006
Location
USA
Fantasy
908th
FGR01 2/3/2021 6:30pm
2/3/2021 6:30pm
doitinthewoods wrote:
Make sure your reeds are good. I chased jetting for a while on a 125 and that was the issue
JBlain619 wrote:
First thing my dad reminded me to do. They looked fine but they have been in for a while so at this point I'm going to...
First thing my dad reminded me to do. They looked fine but they have been in for a while so at this point I'm going to replace them.
With the VForce3, make sure you seal it up good with a thin coat of Permatex Moto-Seal or Ultra-Grey. I had one on my YZ125 for a while and it leaked until I did this and caused bogging and tuning issues. Ultimately, I ended up going back tot he stock reed block With Boyesen Pro Series reeds and that worked great.

2
JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619 2/4/2021 4:50am
2/4/2021 4:50am
CornflakeJackson wrote:
What jetting, fuel, premix ratio are you currently running? As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and...
What jetting, fuel, premix ratio are you currently running?
As DynoDan mentioned the jet block gasket is a good place to start. Mine was deformed and replacing it definitely helped with a 1/8th to 1/2 throttle burble I was struggling to get rid of.

Is the powervalve functioning correctly? If not, that could be hurting mid-range power until there is enough RPM to blow open the powervalve.
JBlain619 wrote:
Im running 32:1 Yamalube R. Bike has a Pro Circuit pipe and silencer, Vforce 3 and I currently have a 420 main, 38 Pilot, stock needle...
Im running 32:1 Yamalube R. Bike has a Pro Circuit pipe and silencer, Vforce 3 and I currently have a
420 main, 38 Pilot, stock needle 3 from top, and airscrew at 1 and 3/4 turns out.

I haven't checked the power valves, totally slipped my mind. I'll check those. Wasn't there an issue with these on the YZ's? I seem to recall something being an issue.

Thanks for the insight.

CornflakeJackson wrote:
I would think that jetting is good then unless you’re at crazy temperatures or altitude. Yes the power valve pins are know to back out or...
I would think that jetting is good then unless you’re at crazy temperatures or altitude.
Yes the power valve pins are know to back out or fall out completely as shown on the right PV in the photo below. If one or both are out of place you can replace with roll pins from the hardware store.
The PV can also just get dirty/loaded up with carbon and sludge which won’t let it move as easily as it should. Should slide really smooth and easily when assembled. A properly functioning powervalve is critical for allowing the bike to stay in the pipe in less than WOT situations.

Thanks for the picture brother!! I'll check that this weekend!
JBlain619
Profile picture for user JBlain619
Posts
1844
Joined
6/10/2010
Location
Severna Park, MD, USA
JBlain619 2/4/2021 4:52am
2/4/2021 4:52am
doitinthewoods wrote:
Make sure your reeds are good. I chased jetting for a while on a 125 and that was the issue
JBlain619 wrote:
First thing my dad reminded me to do. They looked fine but they have been in for a while so at this point I'm going to...
First thing my dad reminded me to do. They looked fine but they have been in for a while so at this point I'm going to replace them.
FGR01 wrote:
With the VForce3, make sure you seal it up good with a thin coat of Permatex Moto-Seal or Ultra-Grey. I had one on my YZ125 for...
With the VForce3, make sure you seal it up good with a thin coat of Permatex Moto-Seal or Ultra-Grey. I had one on my YZ125 for a while and it leaked until I did this and caused bogging and tuning issues. Ultimately, I ended up going back tot he stock reed block With Boyesen Pro Series reeds and that worked great.

Awesome, good info!! The bike came with the Vforce3 but I'll definitely make sure it sealed. May be time for a Vforce4!!

Post a reply to: 2012 YZ125 Jetting Issue