QuestionI have a 1999 Kawasaki KLR 250 dual sport. The bike starts on 1st or second kick, idles great and revs like you would expect. When traveling, 1st through 4th are great, 5th ok when on level ground or downhill and 6th will only maintain 60 mph unless going downhill. Others report this bike has no problem running 75 on the highway and when I first got it, I had no problem, then one day this started.
I have taken the carb apart so many times, I could do it in my sleep, boiled it, soaked it and still no change. Put a new coil, spark plug and spark plug wire on. Checked and rechecked all connections for loose or bare wire, set the valves, checked fuel flow and removed the stator housing to verify all is connected correctly. Compression is around 110 and does not leak. I am at my wits end and don't know where to look.
I also notice as I go over rough roads I get an intermittent cutout, but cannot find any loose connections.
Please help!
Stan
Answer
Hi Stan,
Engine power is mostly related to size and the inflow and outflow
of air. Your bike has a decompression unit which may be
worth looking at as lower compression equals less power.
Your reading of 110 psi is okay if the decompressor is
working but low if that is the total compression.
Another power stealer is a narrowed or plugged exhaust pipe
or air intake tract. Anything that lowers the flow
of air through the engine will steal power.
This includes air leaks around the carb mounting tube.
Lowered compression or air flow through the engine
must be considered along with carburetor condition.
The other thing that affects the flow of air/fuel
is the opening and duration of the valves.
A worn camshaft lobe or cam follower can cut down the valve
opening and timing so there is less fuel drawn into the engine.
In the ignition department the ignition timing and
advance are critical. Even if the timing is spot on
at idle it may not be getting the proper advance
at higher speeds. Some bikes have mechanical advance
units. Most later bikes have electronic advance
built into the pulse and CDI system.
This can be easily checked with a timing light.
Some bikes have the idle and advance timing marked.
The "F" mark is usually the idle timing mark.
When you speed up the engine the timing marks
should change as it automatically advances the ignition timing.
The KLR was built for low speed torque so intake and exhaust
ports are smaller. High speeds require a fast flow
of air so performance exhausts are less restrictive
and bigger carbs provide more fuel/air as well.
Gearing can also be lowered to provide more power.
Your engine can provide clues as to what is happening
inside the combustion chamber by reading the spark
plug at various throttle openings.
http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
If your bike is running too rich fuel/air the plug will be black.
Too lean fuel/air plug will be light colored.
If it reads light brown or tan color after a high speed
run then the mixture is correct.
If you have been losing power over time it might
be either a compression loss or camshaft lobe wear
or some problem with intake air or exhaust flow.
Of course things like rider weight and brake drag are also possible
but I will leave you to check those out too. ;)
Good luck!
Wayne S.
-------------------------------------------------------------------------
