Carburation Problems

I set about sorting the carb on MZ wreck (MZ TS 150). I'd fitted a 22mm
with a 115 main jet to get it running, its supposed to have a 24mm mixing
body. It was ok, started, ran, idled but was wooden, IYSWIM

I've since fitted a new 24mm body and good used ancillary bits (floats,
needle valve, jets, slide etc).

On the factory specified jets - 95 main, 60 needle jet, 40 pilot, 75
'choke' jet it won't run unless the choke is operated, which is basically
an enriching jet that's uncovered by a piston in the carb body.

After *much* pissing about I've got it to run reasonably (its not had
full proper testing) cleanly on 115 main, 75 needle jet, 40 pilot and 75
choke.

It's still a bit fluffy under 4000 rpm. But good up to and past the 6000
red line.

I've not got it screaming hot and done any plug chops. Mainly because it
was dark and starting to sleet.

The inlets, both engine and air filter sides are clean, tight and appear
to have no leaks.

The only fly in the ointment may be the air filter. I haven't got a
decent 125 OE filter which are thick and heavy paper, metal and card
affairs. So I used a new one from a Hillman Imp, perfect fit. Usual
British type cylindrical concertina filter.

Its not uncommon to use car filters in the MZ world. ETZ 250s work
really well on Morris Minor paper filters.

Would a different paper filter make such a huge difference? The bike's
been stood for at least 6 years but perhaps as many as 18. I'm concerned
that the crankcase seals maybe drawing air (dynamo side as it doesn't
burn gearbox oil).

Any thoughts?

 

sweller wrote

Conventional wisdom has it that by making the airflow easier i.e. a
lighter or no filter you are going to make it leaner. Has it got a
refinement like a low end mixture control screw which might need undoing
a quarter turn?

Given what it is though I expect; if it is running then it is going to
be a close to perfection as ever you will get.

 

I appreciate that but am surprised it was such a big difference, leading
me to be concerned that it may be crankcase seals. I was looking for
something that I've missed that may prove or disprove the seals.

Only affects the idle circuit.

Despite common belief, MZs are not that unsophisticated.

 

sweller wrote

LOL

 

The filter might make that much difference, you've gone up about 20% on
mains which is what you would expect if you removed the air filter totally.
Are you sure there's no way air can get past the Hillman Imp Filter. Are
you getting any petrol in the gearbox oil?

 

It gets worse...

This morning I found a used OE 125 filter in one of my boxes of scrap
panels, blew the spiders out and it doesn't look too bad, not damp
anyway. Set the all the jets to standard...

...and it runs as badly, if not worse. The two giveaways are the new
random idling speed and that faint, but detectable, smell similar to
frying onions. Which is either I'm using bio diesel chip oil or its
started burning gearbox oil.

Engine on the bench time. Probably not too much of a bad thing, I've got
some seals somewhere. Although I'd preferred not to have had to piss
about.

 

That's a bit of an arse but just to rub salt in, I've just come back from
visiting my Mum in Bolton on the RS. A nice 150-mile round trip including
about an hour on the motorway at 60 and it didn't miss a beat. Bit of a top
end rattle but new little ends should sort that. The seat was designed by
Vlad the impaler though.