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Motorcycle Repair/1983 Suzuki DR100 Carb Tuning


Hello, I have this bike and have been attempting to get it going.  I had it running once but I could not tune the mikuni carb properly, not used to four strokes yet.  I just cleaned the carb again and it just will not start.  It would catch just a little and pop a couple of times but would not start and I got worn out.  I don't know what screw does what and how many turns out etc.  Can you point me in the right direction.  Thanks, I would love to get this bike going for camping and fishing trips.

Randy Urry

Hi Randy,

Have you checked the valve clearance and/or the compression
on this bike? If your compression is above 130 it should run okay.
Two strokes will run on alot lower cylinder  pressures.

If it has enough pressure to blow your finger off the spark
plug hole it might be okay.

Next, make sure the carb jets have been removed and physically
cleaned with some smooth wire like fine guitar strings.
The needle or emusion jet above the center main jet
has small horizontal holes that can plug up.

Make sure the carb bowl is filling with fuel.

Use clean fuel as old fuel or fuel with water in it can stop
up the idle and main jets.

Check around the flanges where the carb connects to the
engine for air/vacuum leaks as this will impair it's
ability to draw the fuel in.

Make sure the spark plug is not fouled and the spark
looks good.

If your idle screw is near the rear it is an air screw,
if the screw is nearer to the engine side of the carb
then it is a fuel screw.

Turning the screw out can either richen or lean the mixture
depending on if it is an air or fuel type adjuster.

Start with about one turn on the screw and adjust it after the
bike is running and warmed up for the smoothest/fastest

Mid throttle fuel is adjusted with the clip on the carb slide needle.
Move the clip down to richen the fuel mixture and move the clip
up to lean the fuel mixture.

All these adjustments should ideally be done with
a warm engine after it is running.

If it won't start then you have fuel, spark or compression problems.

The valves need a couple of thousands clearance, if they are too tight
it will not run as the compression will be affected.

Check your fuel flow to the carb.
Check for carb air leaks and make sure the air filter is not plugged.

Spark should jump 1/4" gap.

Your spark plug color is used to determine carb tuning,
black is too rich and tan is about right. Too light a color
can indicate lack of fuel and overheating.

Idle jet tunes about 0 to 1/4 throttle opening.
Slide needle clip position tunes 1/4-3/4 throttle openings.
Main jet tunes 3/4 to full throttle

It should run with rough carb settings so you can tune it when warm
if everything is working otherwise.

Let me know if you need other details.


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Wayne S.


Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.


Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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