125 RT Idle unstable

[FlyingRt]

Hi folks,
the cold start of my RT is good if the choke is not pulled, even if the temperature is at 4 degrees (Celsius). After starting, it idles at ~1600 U/min but not stable. Pulling the choke let the engine die. Even after a distance of 4 km, it frequently happens that the idle brakes down and the engine dies if I don't pull the throttle. The further you drive, the better it is, but it can also happen after 20 and more km. I have the following carb settings: Idle mixture screw is 1,75 turns out, idle is set to 1800 U/min when engine is hot, needle is in position 4, floater (new) is adjusted to 21 mm. Carb is cleaned. Air and gas filter are new, also gaskets and several O-Rings in the carb. Any ideas how I can improve this behavior?
Martin

[DAVID THOMPSON]

mine does better at about 1900 and your tach may have some error
mine is fussy about the fuel quality

and my enrichment valve (choke) is stuck in the off posotion so mine will not start

dave

[FlyingRt]

Normally I take 95 octane fuel. It contains max. 5 % ethanol. Today I tried out 100 octane premium gas (expensive stuff). Contains also <5% ethanol. No difference yet (after 15 km).

[DAVID THOMPSON]

the ethanol. is the problem mine just does not like it
and see if you have any air leaks in the intake rubber between the carb and engine
dave

maybe at a boat yard the small outboard boat motors hate the ethanol.

[FlyingRt]

Unfortunately you have the choice between less than 5 % and less than 10% ethanol here. Fuel without ethanol is rare in Germany.
The intake rubber looks good. I tested it for leaks with break cleaner. Idle didn't change when spraying. The crank case ventilation tube has started to crack, but is not leaking.
Martin

[DAVID THOMPSON]

if your tach is erratic and uneven that is some times signs of faulty power supply to the ignition box
mine went crazy when the voltage regulator went bad
i have had problem with the spade lugs (power connectors) they loose tension and do not hold a good grip on the other part
female end is loose and falls off the spade

but Murphy's law says if your looking right at the problem...it will not be seen by anyone present until
it has caused max damage



one of my favorites is the BMW 1950 to 1969 issue with weak spark at plug ..
making every one think they have carb problems
DAVE

[FlyingRt]

[quote="DAVID THOMPSON"
i have had problem with the spade lugs (power connectors) they loose tension and do not hold a good grip on the other part
female end is loose [/quote]

Ok Dave, I will check the power connectors and clean them. I have already cleaned the ignition coil connector and the switch off relais spade lugs because they were rusty. A few weeks ago it happend that at high speed the engine suddenly died and could not be started for 5 min. Thought it was the switch off relais.
Martin

[MichaelTorre]

Your cold start behavior is trying to tell you something.
It should really require the choke when normal.
M

[FlyingRt]

Yes, could be too rich.
This brings me to another open question: What is the right carb settings? If have found different carb settings recommended. My "drivers manual", (from 2000) says needle position 3, mixture screw 0.25 - 0.5 turns out, idle 1400 + 100 U/min, the 2003 drivers manual says needle position 4, mixture screw 1.5 - 2.5 turns out, idle 1800 + 100 U/min whereas the repair manual (2001) says needle position 3, mixture screw 1.5 - 2.5 turns out, idle 1800 + 100 U/min. My is build in 2003. I actually have needle hanging on position 4, mixture 1.75 turns out and idle at 1800 when engine is hot. There are also other differences in the official MZ literature, e.g.oil volume and position of intake pipe. What I will try is to made it leaner by adjusting the mixture screw according to the 2000 manual.
Martin

[DAVID THOMPSON]

mine is sick and i will have the carb off asap i will check mine it is as stock from July 2002
other than the screw on the bottom rear
and the idle adjust

my choke is stuck

dave

[breakwellmz]

Hi folks,
the cold start of my RT is good if the choke is not pulled, even if the temperature is at 4 degrees (Celsius). After starting, it idles at ~1600 U/min but not stable. Pulling the choke let the engine die. Even after a distance of 4 km, it frequently happens that the idle brakes down and the engine dies if I don't pull the throttle. The further you drive, the better it is, but it can also happen after 20 and more km. I have the following carb settings: Idle mixture screw is 1,75 turns out, idle is set to 1800 U/min when engine is hot, needle is in position 4, floater (new) is adjusted to 21 mm. Carb is cleaned. Air and gas filter are new, also gaskets and several O-Rings in the carb. Any ideas how I can improve this behavior?
Martin

Hi

Sounds like the carb jets could do with a flush through.
Do the easy stuff first!
Get a can of aerosol carb cleaner and spray it into the pilot jet screw hole(After taking out the pilot screw!)