MZ/MuZ Riders

Hi Everybody,

Newby with a small problem.

Have posted this in Mechanical Talk but thought it might be better here?

Recently bought an old TS250. Always started second kick til I removed some tape which was attached to the throttle cable as it entered the top of the carb - just to see what was under it really!

Mistake.

As I removed the tape I noticed that the nut under the tape was moving - didn't seem like much. Now the top of the screw cap where the cable enters leaks a little petrol and the bike is hard to start - seems to flood easily. No other symptoms once I'm riding but a leak of petrol from the top of the carb noticeable when I stop.

My question is where should this nut be? There is currently about 1cm of thread underneath it.

Many thanks in advance for any advice.

Cheers,

Paul

That looks quite different from the cable adjuster on mine, it actually looks a bit like a brake/clutch cable adjuster from something else. Either way I don't think that's the root of your problem - The only purpose it serves is to set the amount of free play in the cable (could do with a locknut to keep it in place, probably what the tape was for.).

I can't really explain why it would leak petrol from there as fuel should not get that far up unless it's a really loose fit & is allowing it to blow past. (this would make the bike harder to start too as air would be able to get sucked past on induction)

If I was you then I'd just find & install a suitable locknut, adjust the cable till there's about 1mm of slack & wrap some more tape round. If the bike still seems hard to start then a good carb strip & clean should show up any other issues there may be, starting with the cold start piston & it's rubber seal as this would cause flooding if it was leaking.

P.S. Actually, while you're adjusting the throttle cable make sure the cold start also has a little slack when turned off in case the cable's holding the piston slightly shy of its seat.

Hope it's nothing too serious as it's a lovely day to go for a ride. Oh, and welcome to the forum.

Only me again!!!

Just looking at that picture, it seems the clip is missing on the carb to airbox rubber. Get a jubilee clip round there if you can as air leaks will mess up your mixture & possibly damage the engine if it goes too lean. If I'm honest it looks like the bike's suffered a bit from neglect and/or inexperienced fettling so I'd say also make sure there's an air filter in there & clean out the fuel filter while your at it.

Thanks for all your input!

I'm sure it is a clutch cable etc off something else as much of the bike is non-standard bodge - got it off ebay two weeks ago. Really pleased with it despite its non-standard quirks.

Reckon maybe I'll take it to a bike shop for a onceover - I'm not much of a mechanic and don't want the thing in bits on the kitchen table when the weather's so glorious for riding!

Cheers,

Paul

Might be worth doing that if you're not too confident yourself yet. MZ's are a great bike to 'learn the ropes' with though so I'm sure it won't be long before you're tackling most jobs yourself.

If you're going out today then just have a check of the plug & make sure it's not running too lean. If the tip looks like strong tea (with milk!!! ) then your about right.

Cheers, Dan.

Cheers Dan.

Paul

Hello Dan and welcome Paolo:

I would bet this is a original BVF cable adjuster. Paolo you need a locknut and rubber cap better than tape (no necessary original spare parts); very cheap and help you doesn´t go in water (rain, bike wash) or dirty and doesn´t go out the "carburator gas reflux".
MZ´s "sweat" , you don´t worry for this.

"just to see what was under it really! Mistake" Isn´t a mistake! is the way for you know and repair your motorcycle.

Best Regards, Manuel.

added some to picture
nut missing at top is used along with one at handle bar to take up cable free play and lock it
may have one at carb none at handle bar...
black line is rubber weather boot missing from cable
bottom of it will slip over missing nut to keep out water

idle screw is used to raise carb slide and with air screw to balance out idle
cable should have some free play and not raise slide till throttle has been turned just a bit
a well adjusted cable is great one that is not is a pain in the arse

Many thanks for the input and especially for your very clear annotations David.

There is no lock nut at the handle bar and the cable is pretty floppy in there - also the twist grip does not snap back.
(?????NOTE edit by dave ......check for return spring in carb.....)
I can't tell if the petrol leak is coming from the fuel pipe (which is pretty secure) or from the carb itself - my feeling is that the carb is 'overfull'.

I'm not sure if it leaked a little petrol before I untaped the cable but I think it didn't. And the bike certainly started second kick every time until I removed the tape. My method was simply to open the petrol tap, open the choke, switch on ignition and kick.

Since tape removal the bike is not keen to start and then when I've finally flooded it I turn off the petrol, twist the throttle open fully to expel excess petrol and kick til it starts with a blast of blue smoke, then turn petrol back on.

This could all be co-incidence and unconnected of course - but you know that feeling when something was working fine and you mess with it and suddenly it's not working fine?!

Paul

I'd be tempted to check the float & float height. I had a float sink on me a few years ago as the solder which joins the two halves of each float together became porous, fuel leaked in & the float sank. (30 miles from home, ES 250 sidecar outfit, big push uphill.........) Roadside bodge together by RAC mechanic who soldered it back together & got me home. replaced with a new one - no more flooding.
Float height should be 34mm from flange of carb body to bottom of float when held upright (needle valave fully open) , 27mm when inverted.(+1mm max,either way). Worth checking the needle valve is not sticking. Airscrew should be 3-4 turns out from fully screwed in. Set tickover by ear! Worth checking the rubber seal is OK on the bottom of the 'cold start' plunger as these can also cause problems.Think it would be worthwhile investing in a new cable as well.
Any more problems shout up ! I'm no mechanic but have bodged my way around GB & Europe on MZ 2-strokes for 30-odd years.
Regards,
Simon Greenwood.

not keen to start ...tells me a lot

rubber boot is missing it reduces air that is sucked in around the cable
you may be getting to much air in to carb around the cable
messing up the starting
this extra air reduces the vacuum pulled on the carb by the engine intake stroke
so the jet in the carb for starting spits out less fuel

my 4 cycle rt125 does not start if you do not crank for a second or 2 before
opening throttle same reason too much air = vacuum pulls in less fuel
dave
PS an air leak between carb and engine
can burn a hole in piston or at least make it run way too hot
do check for this

Hello!

Bisphaman, yes, bad quality control copper float. I have a old sunk float in the spare box because I mount a new float, perhaps 10 years ago.
Well, I shake it and the fuel still in the float .

Best regards, Manuel

float with fuel inside ..
place in sun on a few hot days bake it out
then flash seam with new solder
but make sure to not get to much on it or it weigh to much
dave
new ones store in baby food jar if they will fit
changes in air pressure from weather will make them go bad

bmw /2 floats and some amal bad about this

Thompson, thank you for the information.

Now I ride with Bing ,this morning I adjusted carburation for a rebuild engine. . Carburator have a white plastic float, people tell same sunk problem ...mine 30.000 km ok. . My experience for MZ ETZ 125 BVF and Bing carburators work ok.

Saludos, Manuel.