"Now the problem is it does not have enough power in
high revs."
One more thought: Given the problem described, that sounds like main jet.
Here's a procedure I found on the web for Harleys:
********************
Adjusting Intermediate Circuit(s)
Adjusting High Speed Circuit(s)
Adjusting the main jetting requires a long stretch of open road with no
traffic. You must be in fourth or fifth gear and running at 3500-4000-4500
RPM. then open the throttle all the way to the stop, noting the feel of the
bike. Immediately let off about 1/8 turn and note the feel of the bike. If
the engine just slows a little, the jetting is very close. If it seems to
accelerate some when you let off the 1/8, your main jet is too lean. If it
hesitates or the top speed is poor (i.e. less than 80 MPH) you are too
rich. Adjust the main jetting accordingly. Use your common sense and seat
of the pants feel and you will get close enough to do plug reads.
Plug reading is as much an art as a science for most people. Lots of
experience is needed to REALLY do it up right. For most street riders,
making sure your plugs are a nice tan color is usually good enough. Don't
bother reading the plugs until you have done preliminary fine tuning. You
will need several sets of new plugs, gapped and ready to use. After your
bike is properly warmed up, after installing a fresh set of plugs, you will
need to do a full throttle acceleration test, making sure the bike gets to
full RPMs in 4th gear. (The Motorcycle Performance Guide staff recommends
you take the bike your local drag strip for this testing. Your local
sheriff usually has no sense of humor about a motorcycle running down his
roads in excess on 90 MPH). At the peak RPMs, you will need to shut down
the engine before you let off the throttle, and coast to a stop. Remove the
plugs and look at the general color of the porcelain. If the porcelain is
black, the engine is running rich, requiring the installation of a smaller
jet. If the porcelain is bone white or a very light tan the engine is
running lean, requiring the installation of a larger jet. If the porcelain
is tan to light brown, the jetting is close. If additional tuning runs are
required to adjust the carburetor, make sure you install a fresh set of
plugs before each run. You can not read the condition of the plugs unless
the plug is fresh.
If you are in doubt as to the jetting, make sure you jet on the rich side
(tan>brown>black). Because of potential engine damage, you are better off
slightly rich rather than lean. A lean engine can detonate, causing
permanent damage.
The 5 second overview:
When you are limited to street riding, take note on how easily and quickly
the engine reaches the proper RPM for shifting gears. The engine should
accelerate smoothly and quickly through all gears. When the main jetting is
to rich, the engine will feel sluggish and acceleration will 'feel' slow.
You can check the main jet by quickly closing the throttle from wide open
to 7/8 position when the engine's RPM is greater than 4500. If the engine
accelerates slightly, the main jet is to lean. A larger main jet is needed.
If the engine hesitates or misses slightly, the main jet is to rich. A
smaller main jet is needed. If the engine just slows a slight amount, the
jetting is very close to correct.
Another test is to accelerate through the gears at full throttle. If the
engine backfires through the carburetor, misses, cuts out or quits running,
the main jet is lean. Increase the size of the main jet. If the engine
acceleration seems sluggish, does not react to the throttle or sounds flat,
the main jet is rich. Decrease the size of the main jet.
The main jetting can be set quickly at a 1/4 mile drag strip. For this
test, you can ignore the ET (elapsed time). Making sure the engine is
warmed up, make your run down the strip making note of your final MPH. Keep
increasing the size of the main jet until MPH begins to drop. Then drop
back one jet size. Your jetting should now be correct.
******************
Personally, I've not found plug reading very useful. I've also read that
plug reading is way overblown, and that today's gas doesn't leave the same
signatures on the plug that we all read about. I've also not experienced
the full throttle effects mentioned here. My butt dyno is probably just
numb. I've also read about too rich causing a "blubbery" sound, or a "wet"
sound. I've yet to figure out what those sound like.
Finally, I have the same perception of my bike, that the top end is a
little lacking. This condition is from 6000, maybe 6500 to redline. And
I've done some internal work on mine such that I thought it would run
nicely at that range.
Jeremy
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