YZ125 bogging/dying exiting corners.

Lasse
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529
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11/5/2015
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DK
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2940th
6/3/2021 2:40pm Edited Date/Time 6/4/2021 9:04am
Hi!

I have a 2006 YZ125, with an HGS pipe and Vforce3 reeds. I've been trying to get it running right and have come a long way.

Current settings:
MJ 430
PJ 40
AS 2 turns out
Stock "74" needle, top notch
8.7mm float height

Will rune OK the first few laps, then it will start bogging/cutting out exiting corners, even at full throttle.
It *feels* like if I pull over and let it idle for a bit, that the issue disappears, but I might be wrong, as i am typing this late at night after a practice day.

What could it be? I tested the gas cap ventilation and I can blow through the venthose, though not sure how free it should feel.

Fuel flow seems fine when opening the tap, with the fuel hose disconnected.

Any leads would be nice.
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6/3/2021 3:00pm
im no pro but it sounds like float height? but you say you checked it? and you have put the float height to 8.7mm? how are you measuring bud? with the caliper type? ot the bung and pipe from sump drain plug hole? in the manual you measure the fuel level on the yz, and thats normally 9.5-10.5mm above the float mating surface area
FGR01
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5091
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AZ US
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1334th
6/3/2021 4:26pm
Might be an air leak that only appears when things are good and warmed up and expanded and then goes away when things cool down. I had this on my YZ125 at the reed block when using a V-Force. Had to seal it up good with a thin coat of Moto-Seal. Use some gas-proof sealant. Do you see any evidence of gas seeping out around the reed block?

You seem a bit lean on the needle and pilot. I was running a 42.5 and the stock needle in 2 or 3.
Lasse
Posts
529
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11/5/2015
Location
DK
Fantasy
2940th
6/3/2021 10:55pm
im no pro but it sounds like float height? but you say you checked it? and you have put the float height to 8.7mm? how are...
im no pro but it sounds like float height? but you say you checked it? and you have put the float height to 8.7mm? how are you measuring bud? with the caliper type? ot the bung and pipe from sump drain plug hole? in the manual you measure the fuel level on the yz, and thats normally 9.5-10.5mm above the float mating surface area
I measured the height with a caliper from the mating surface, to the top of the float, in the middle portion, where it is tallest.

I already read about the leaky reed blocks and made sure there are no leaks there.
6/4/2021 7:20am
Check the torque on the cylinder and head bolts.

You say you are running the needle on the top clip? If that is the case, you may need to look into a leaner needle and try towards the middle.

The Shop

6/4/2021 7:42am
im no pro but it sounds like float height? but you say you checked it? and you have put the float height to 8.7mm? how are...
im no pro but it sounds like float height? but you say you checked it? and you have put the float height to 8.7mm? how are you measuring bud? with the caliper type? ot the bung and pipe from sump drain plug hole? in the manual you measure the fuel level on the yz, and thats normally 9.5-10.5mm above the float mating surface area
Lasse wrote:
I measured the height with a caliper from the mating surface, to the top of the float, in the middle portion, where it is tallest. I...
I measured the height with a caliper from the mating surface, to the top of the float, in the middle portion, where it is tallest.

I already read about the leaky reed blocks and made sure there are no leaks there.
here is a pic out of the manual buddy, ive always done mine this way, i had the same symptoms as you after changing my needle and seat a few years ago, if you dont have the manual, send me a email address and ill mail you it over, also i didnt buy the fancy kit they try to sell you, i used a rubber bung and a piece of clear pipe,
gristle568
Posts
306
Joined
6/30/2014
Location
Newton, NC US
6/4/2021 9:04am
How fresh is the top end and cylinder plating? I had bogging issues with an out of spec cylinder.
b8res
Posts
511
Joined
1/30/2014
Location
Lodi, CA US
6/4/2021 11:07am
Metering block gasket.... replace it and report back.
Pretty sure JD Jetting sells those gaskets.
Give that a try.
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