DT175 runs rough

Hey
I don't know what is wrong with my motorcycle.
It runs rough, it must be something with the electrical system, because if
im taking my plug of and i kickstart it then i sometime can see no spark.
But one thing that is strange is that if i drive it for a long time and it
gets hot then if i turn the engine off and try to start it again then i
fail. and if i then start it then it runs very roughly. But if ill wait a
few minnutes then i have no problem starting it. What could it be??
I know almost certainly that it has nothing to do with the carb. i cleaned
it and the problems i experience only occour sometimes. if i try to take the
spark plug wire off and put it firmly back on then it sometimes solves the
problem.

 

Motorcycle ignition systems often don't use very much voltage, maybe
only 12,000 volts. Or less. The most incredibly weak ignition system I
ever heard of was piezoelectric. Some Whizzer motorbikes had a crystal
instead of ignition points. When a pushrod compressed the crystal it
emitted a few thousand volts at most, but that ran the engine.

Sometimes it's hard to see the weak spark put out by a low voltage coil
if you're in the bright sunlight. I remember how I was amazed at the
weak spark my CR-250M Honda's coil produced. It was a skinny and enemic
white spark.

But it doesn't take much voltage to light off a mixture that is within
the range of explosibility. So carburetor engineers make sure the idle
jet is big enough and there is enough idle mixture screw opening to
start the engine.

You might try adjusting the idle mixture screw 1/4 or 1/2 a turn richer
to help the engine start when cold and to keep it a little cooler when
it has warmed up. You'd be amazed at how much 1/4 of a turn richer
affects operating temperature.

If you have a slide valve carburetor, richening the mixture usually
involves turning the idle mixture screw clockwise, because you're
adjusting the idle air.

If you have a CV carburetor, richening the mixture involves turning the
idle mixture screw counterclockwise because you're actually adjusting
the fuel/air mixture.

Then there is the possibility that your engine is running lean because
of piston ring sticking or exhaust system plugging somewhere. A power
valve that is stuck in the closed or parlly closed position would make
the engine run hot and lean.

Then the spark plug overheats and quits firing until it cools down. The
spark likes to jump from the coolest point on the center electrode to
the ground electrode.

I was really embarassed on time when I had a piston ring sticking
problem. I was talking to the Husqvarna factory motocross team about
riding a long defunct motocross course at Saddleback Park in
California, but I couldn't show the guys any
tricks on the course because my piston ring was stuck and the 250cc
engine was running like a 125cc engine.

Or, maybe your coil wire (or the cap is old) and degrading internally.
Is the coil wire replaceable or is it molded into the coil? If you
could replace the wire and cap separately, that might be the key. Cars
had carbonized threads inside the ignition wires and that suppressed
radio static. But motorcycles sometimes have copper or steel conductors
inside the ignition wire.

If you can't replace the spark plug wire, maybe you can find a coil
assembly somewhere and swap it into your bike to see what happens.

Some spark plug caps have a brass screw inside and that goes over the
spark plug tip to hold the cap in space. I unscrewed those brass things
and found there was a
bluish ceramic-covered resistor inside that kept the coil from firing
the spark plug until the voltage reached a certain level.

I replaced those resistors with brass screws. I think the engine ran a
little better.

Another thing to consider is whether you are using the exact correct
part number spark plug. Some spark plugs have built in static
suppressing resistors, but others don't. That would affect voltage rise
at the spark plug gap.

 

This is a DT175.

 

Cheezus H. Crustaceans. Let Andras remind me of that. I'm volunterring
to help HIM by giving up my time to talk about general troubleshooting
procedures, I'm not trying to be a target of your criticism and debate
endlessly with you.

If everybody who needs technical advice has to wade through your
kibitzing, it's no wonder you see so many people asking a question and
never returning to say, "Hey, thanks to all that answered, I found the
problem with your help."

Will this simple thread have to run to 150 responses as the UK debating
team kicks around all aspects of quantum tunneling as it relates to
Scheurle loop scavenging?

If you want to have a circle jerk, couldn't you keep it on the UK NG?

 

Why not? Andras might learn something.

If I told everything I know, TOG might learn something (or he might go
nuts trying to find an exception to everything I say).

Anyway, as I recall, I was mentioning exhaust system restrictions that
might cause overheating. A power valve, whether the motorcycle in
question actually has one or not may be a source of exhaust sytem
restriction. Another problem might be exhaust pipe and exhaust port
deposits.

 

As a Yamaha power-valve is not connected to the exhaust *at all*, how
could this be?

As Mark says - you're knowledgeable. Stickjto what you know.

 

So why are you offering utterly useless and irrelevant information?

It is, in fact, off topic. he's asking about a DT175 - you're waffling
on about power valves.

A poster asks about a carb problem on a CG125 - you waffle on about CV
carbs...

 

Hey

I'll try to collect everything i can and try diffrent things that seem
logical and i got some reasonable suggestion from FD about the mixture that
i can handle!!
It is a DT175 yes. It has a air/fuel mixture screw that FD also talked
about!!!
I don't recall that FD said that it had my bike HAD a power valve.

Ive ordered a new ignition coil. Im gonna get a new spark plug and wire. And
ill try the things that were talked about. and hopefully it'll fix it.

I plan to drive 400 km through denmark and take a ferry to Faroe Islands so
it better not fail through those 400 km's.

Thank you.

"The Older Gentleman" <> skrev i en
meddelelse

 

It was arguably implied in the response, but I'm sure he knows it
doesn't, which was my point - why bang on about it?

It could be something as simple as a duff plug cap.

Indeed