Re: OT: Chinese carburetors

default wrote:
On Sat, 21 Feb 2009 22:19:19 GMT, Jan Panteltje
<pNaonStpealmtje@xxxxxxxxx> wrote:

On a sunny day (Sat, 21 Feb 2009 16:40:28 -0500) it happened default
<default@xxxxxxxxxxxxx> wrote in <9as0q41a9m439plfnsnoljadhoiaa6pate@xxxxxxx>:

Any suggestion?
I hate to spend $$$$ to have it picked up by the dealer in an other city,
where it then probably will work, and get charged 250 Euro for a new <whatever have you>//

Fuel air spark is all you need so . . .

Do you have a service manual?
Yes.


Spark coming at the wrong time Timing light or Ohm meter if it has
points (or obvious physical problem like mechanical link stuck in full
advance if it has a mechanical advance)
No points, pick up coil with potted electronics ...
It says it has a thyristor in it, that is all I know :-)

Manual should say. Most thyristor sets use an electronic timing
advance. The other choice is a centrifugal flyweight that shifts the
trigger magnet relative to the flywheel as speed increases.

They sell a kind of emergency ignition system that fires the plug at
about 4,000 times a second and that will sub the system, so something
like a "model T" vibrator coil might sub it and allow it to start as a
troubleshooting technique. I had a DC/DC converter HV CDI ignition on
my BMW motorcycle that failed in a way that caused the plug to fire
rapidly. The engine ran more or less normally but overheated and
sputtered now and then, but it was drivable in that condition.
Fuel contaminated Rig temporary fuel supply with known good fuel
Possibly, but why just stop like that, no prior indication
of 'sputtering' was just doing max speed no problem.
Was gone for maybe 45 minutes in the shop, fuel does not
go bad in half an hour, seems unlikely.

Possibly, not necessarily likely. A warm engine will tolerate more
out of spec conditions than a cold one unless it is out of spec when
warm only. The fuel could have some contaminate that was in the tank
and not in the float bowl allowing it to start the first time and warm
normally. Like something introduced into the fuel deliberately by
someone else . . .

Fuel mixture way off No good safe ways to test that, but you can
restrict the air or fuel and see if it tries to start.
I will try that tomorrow.


Carb float
could be sinking or float valve could be sticking, allowing excess gas
to flood cylinder when engine is off.
I had the carb on the workbench, diafragm seemed OK (inspected with magnifying glass,
fuel level seemed OK, plenty of fuel there (all over the workbench when I turned it over,
was pure gasoline, evaporated right away, if any water it should have stayed.

Fuel level is critical to correct mixture. A dribbling needle (float)
valve may seat some of the time and not others. Too high a fuel level
is too rich even if it can't spill over into the cylinder. AND how it
sits when parked can influence that.
Compression too low Compression gauge (bent valve stem or stuck valve
or broken valve spring, broken ring(s), etc..)
mmm, I feel compression with the kick starter.

Is it 140 PSI or 85 PSI? Your leg may not be able to differentiate.

Valves normally make noises when defective, or not adjusted right, no such thing.
I am beginning to think some flash over in the potted electronics, or perhaps HV cable, as that
would explain why I smelled ozone, twice.

Not necessarily. A valve closing a smidgen too late will cause a puff
of gas back into the carb disturbing the even flow.

Yes, go with your gut and what the symptoms tell you. If it doesn't
pan out, you still need to keep an open mind and treat it like its the
first time you looked at it.

Ozone - More is formed with corona than an arc, but more corona may
form if the spark plug isn't connected - open circuit = higher peak
voltages.

Ozone? You shouldn't smell ozone, ever. If Jan really smelled it,
that'd mean exposed high voltages are afoot. Broken / intermittent spark plug wire? That could fail abruptly.

But accurate smelling is dicey in a parking lot next to a stinky,
flooded scooter. A spark test with the plug removed (possibly in
darkness, to look for corona along the wire) should tell the tale.

Cheers,
James Arthur
.

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