MZ RT125 Carb Troubles

[yatesy2073]

Hi, please can anyone help. Am having troubles with my carb, it keeps overfilling and fuel is coming out the drain pipe when the fuel is on when the bike is switched off. I have tried everything to adjust the carb correctly but no joy. This carb I believe is a Mikuni VM24, I've seen a VM22 very cheap on eBay and my question is will this fit and work with a bit of bodging or a new performance air filter to fit, or can anyone help me figure out what's wrong with my carb? Many thanks for any help! Ben

[rodge70]

hi, not a serious problem really,sounds like the float valve is not shutting off,could be caused by a puncture to the float,bit of crap on valve seat, worn seat and valve or incorrect float height,once carb is off pretty easy to work out which,good luck

[DAVID THOMPSON]

take your float and set it in a small pan of gas if it sinks ..new float needed..
the little shut off needle tip or seat needs cleaned
mine is 10 years old and i very seldom have to shut off the fuel tank tap
dave

[yatesy2073]

Thanks for the reply guys, I will give it another try. It's just so annoying having to take it on and off to test it! I've fiddled with loads off carbs in my life this is only one I've ever had a problem with! Thanks again. Ben

[DAVID THOMPSON]

these bikes use so little fuel they get upset at crud in the fuel

where i live we can get gasoline with no ethanol in it
i use that in my rt125 and lawn mower and weed eater
the rt125 tells the truth about fuel quality by running really bad on the crap with ethanol in it...
on good gas bike runs good to about 65/68 mph due to my 52 tooth rear sprocket.. 69 mph is red line on tac o
on the bad stuff it just will get to 60 and complains a lot at any thing over 55mph
220lb rider + 20lb gear in saddle bags
dave

[djsbriscoe]

I still have trouble with the float chamber over filling and upsetting the idle speed after riding it for awhie. The carb is inclined slightly downwards towards the engine which means it tends to overfill. I also know this because I have put the overflow pipe vertically down so that petrol is evacuated from the pipe as soon as excess petrol overflows in the float bowl. Everytime I stop suddenly I see a SMALL amount of petrol drip from the pipe onto the ground, which confirms the overfilling hypothesis.
The float height is so finely balanced that if you try to cure the overfilling it completly upsets the fueling and makes it too lean.
I've learnt to just live with it and I put up with a slightly erratic idle. The idle speed is on the nose at start up presumably because any excess petrol has evaporated. It's only later when I ride the bike that the excess builds up. This may not be as much of a problem dependent on riding style I suppose.
Anyway I'm just riding and enjoying the bike.

David.

[DAVID THOMPSON]

do you ride on brick or cobble stone streets...a lot..
mine makes a fuss in Marietta Ohio USA a city near by my city
with a lot of brick streets.
guess the float gets up set with the ruff ride.
trust me its ruff at any speed and very slick when wet.
dave

[chadz]

just been searching some info on rt 125 carbs and sm 125 carbs as they both use same ones and i also have a issue but mine starves my carb with fuel.

It starts fine, idles fine and revs fine sat there in neutral but soon as its in gear it just bogs out and noticed a few people add on a vm28mm on there 125,s and it picks up a lot better etc.

[DAVID THOMPSON]

the float setting on this carb on this bike is a bit fussy will try to send you the shop manual page on setting the float

probably wed evening
dave

[chadz]

aye david would deffo come in handy, is the full name of the carb that's come on bike called mikini vm24?its so i can try get my local bike shop to get a float for carb,cheers

[DAVID THOMPSON]

may just need adjusted floats are not cheap

there's a tab on float that is bent to move the little sealing needle

i send file later today that explains it all
dave