ETZ 251 leaking carburetor

[thomaskwscott]

Hi Guys,

I have been fighting my carburetor for more than 2 weeks now. It seems that after i finish a ride and wait 20mins it begins to slowly leak fuel from the overflow. This appears to be due to float height but i don't understand the delay, surely the float chamber will be pretty close to full after a trundle round the block so it would start leaking almost immediately?

My confusion aside, i have set the float height according to the manual (28mm). This is still showing the same problem and frankly i am out of ideas....

Thanks

Tom

[DAVID THOMPSON]

the float if its made of brass alloy it may have fuel in side of it

take it out and shake it see if there's liquid inside

bing carbs on older bmw's were bad about getting a pin hole in float and sinking

make sure the needle and seat are clean
dave

[Skorpion]

Hi thomaskwscott

I would think it's the needle valve sticking thats is the problem, this is what stops the fuel entering the float chamber, take off the float and unscrew the valve, and give it a good clean.

[therealche]

If there's any signs of damage or wear its not expensive to replace http://www.themzshop.co.uk/product/floa ... er-nut_da/

[mr_luke]

Silly question, but I take it you turn the fuel off when you stop the engine? In my experience carburettor float valves often don't stop the flow of fuel completely, even when they're working fine in operation. I suspect the 20 minute interval you're seeing is the time it takes the fuel level to reach the overflow pipe, from its 'working' level.

Assuming you are turning the petrol off, I'd be tempted to investigate the fuel tap first - even with a dodgy float valve there shouldn't be any petrol to leak out if the tap's sealing!

[DAVID THOMPSON]

lot of people do not turn off the tap..
i never do on my rt125 but it is always parked out side if its in the work shop its OFF

now my old bmw is a different thing i always shut it off because the brass alloy floats
are known to sink and leak with out notice /this float looks just like some used in amal carbs...in bsa and triumph

the brass floats are so bad about failing that i now use wine bottle corks in place of them very fussy to adjust but work great after setting up
dave

[thomaskwscott]

Thanks for all the responses. The strange thing is that I have replaced both valve and floats with new ones and am still experiencing the same problem. My next step will be to leave the float that's in there in a glass of water for a while to verify it doesn't sink. I am interested in swapping for cork floats, what does this involve in terms of setup?

[DAVID THOMPSON]

I am interested in swapping for cork floats, what does this involve in terms of setup?

a carb that's easy to get to the float and the patience to spend a lot of time moving the cork up and down on the needle

i have only done this on old 1960's bmw as there carb is easy to do it to.... its a real pain any way
dave

check some one may make a plastic float for yours

and test the float in a jar of gasoline water weigh's different and also has surface tension

surface tension is the reason you can get a razor blade to float on water and some bugs can run on the surface
dave

[thomaskwscott]

Success!!! I'm happy to report that I finally got it to stop leaking. The answer turned out to be a bit of blue gasket sealant around the float valve thread. I'm not sure how long it will last but for now it works great.

When i first put it back together however, there was a tiny tiny leak (about one coke bottle capful every 12hrs). I put this down to badly adjusted floats and readjusted them to sit a little lower. The manual says when the carb is upside down the top of the floats should be 27 + 1mm from the float bowl seal. I have moved it to 29mm and now there is no leak. This is worrying me however as i have heard this can starve the carb when flat out for long periods of time. I've been thinking i could probably do a better job of the measuring but it's a pain to take it all out again. Do you think it's worth ripping it apart again or am i unlikely to have problems?

Thanks

Tom