I bought a used 2020 YZ125 from a young kid last fall
I knew early on in the relationship that float height was a problem. It would leak out of the overflow sitting on the stand with the fuel on. I was able to eye ball the float height and make adjustments so it would no longer leak sitting there. The problem was.... The tab was bent at a pretty extreme angle. I have seen others carbs on youtube, and it seems the tab is flush. Something is was wrong.
The book says to replace the needle valve. So I did with an OEM assembly.
To make a long story short, there were still problems with plug fouling and spooge in the exhaust. So I bought the OEM tester kit from Rising Sun Cycles.
The tester arrived, and confirmed the float level was way too high.
The tab bent at a 45°ish angle would still have fuel level being too high. And the tiniest adjustment more than that, and fuel just does not flow.. Its like it vapor locks. When you disconnect the fuel hose, there is no residual fuel that drains from the fuel line when you disconnect from the carb...
Any tiny adjustment to to reduce the tab bend ends up with a fuel level too high again. A viscous cycle.. The tab bending is not linear and does not respond like it should.
I ended up buying a new $60 float assembly. Same problem. I have dumped a LOT of fuel out. Been round and round at least 30+ times.
Help...!!!! ???
Does the center plunger on the needle valve have it's spring tension? Can you compress it in? Did you replace the o-rings on the needle seat?
You are right I think. It has to be that. It could just be that the new unit is an out of the. box failure..... I had to throw away the needle valve holder because it was deformed. The valve looks good though. As does the O-ring ect.
I have put a lot of money and time into this carb. Lost in the sauce I just ordered a brand new one. I will compare it with the one that came with the bike and see what I come up with.
Will post results
So the new carb came in today. Turns out the problem was me. Some how I had it in my head that the fuel level should be at the mating surfaces. Turns out it is supposed to be 10mm/1cm above.
The new one tested right in there... Oh well.... Expensive mistake. The old original is back on the bike, and it runs fine so far.
Will see if the splooge and plug fouling comes back.....
New carb will be a back up if it does.
Remove the screws and replace them with socket head cap screws, so you can remove them in the future...
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I have found Brand new genuine Mikuni VM carburettors with incorrect float levels also. set to flood
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