|#1: How To..... Tune Hitachi Carbs
Posted: Mon Oct 22, 2007 10:50 pm
Ok here is my first attempt to write a how to
on tuning Hitachi carbs!!!!! I am sure i will leave something out so
please feel free to chime in gurus!!
will need include
Allen to take off air filter and the bullet for the
12mm socket for bolt holding tank down
hold up tank
Snub nose screw driver
long flat head screw driver
carb adjustment tool makes things easy they are about 8$ at the auto
pliers of some sort
and the sync tool now i know there
is some controversy on this site about this but mine worked great
12 ft of 1/8" ID clear PVC tubing
2 plastic T's that fit vacuum lines
parts of vacuum lines
1 ink pen taken apart with the ink tube
clean of ink.
The tubing was taped to the yardstick with
transparent packing tape. The wire ties were put thru the hole in the
yardstick to secure the tubing on each side at the top. If desired a
machinists or carpenters square and a pencil can be used to extend the
1/8" markings to both sides of the stick or the level of the oil on one
side can simply be noted before testing begins since it must return to
this point to be in balance. Fill with oil to about the 26 or 27 inch mark
(36 at the bottom). You may have to leave the unit sit for a day or so to
get all the bubbles out. If you are careful not to introduce air when
filling this is less of a problem. Now take the ink tube and cut it in
half. At the top of the yard stick cut the PVC tubing and stick each end
of the ink tube in the ends of the PVC tubing secure it with some RTV i
used some high tack RTV. Let this try for 3 hours.
When in use with the engine running both lines must be connected,
one to each carb. The oil will be sucked up and out of the manometer if
only a single carb is connected and the other end is left open to the
Ok so now the actual procedure
the carb tool to the carb holders
Set you throttle stop screw on the front cylinder to
about 1000 rpm
* Synching Carbs At Idle: You will first synch the carbs at idle.
This is done by means of the two screw adjusters ("throttle stop screws")
on the sides of you carbs. The left one is a set screw, and the right one
is a thumb wheel screw. Loosen the retaining nut on the set screw so it
can be turned. Working these two screws, set you carbs to where the oil is
even in the towers with the idle at 1000 rpm on your tach. Leave the
retaining nut loose for now.
* Adjusting Your Pilot
Screws: These screws control the mixture in your pilot circuit, which
controls off-throttle running (idle and deceleration) and running when the
throttle is cracked open just a bit. The screws control fuel , not air!
You turn right (in) for less fuel (leaner) and left (out) for more fuel
pics for you enjoyment
Front Pilot Screw
Rear Pilot Screw
WARNING! Never bottom these screws hard. You can injure the seats
or the screws, making good adjustments impossible. If adjustments don't
seem to get results, this may be your legacy from an earlier tinkerer.
Very likely your pilot circuits are plugged.
These screws came set
very lean from the factory (EPA stuff) and what we want to do is set them
somewhat richer to help reduce warm-up time, improve low-end running, and
inhibit a tendency to backfire.
With the engine idling, turn one
screw in until the engine begins to slow due to fuel starvation in that
cylinder. Then back out say 1 and 1/2 turns or until the engine runs its
fastest and smoothest. Then do the other side. This should get you close.
If you chose, you can try doing one cylinder at a time, that is, if the
engine will run on the other cylinder. Pull one plug out and be sure to
ground the plug wire you pull off. Ungrounded plug wires on running
engines are hard on coils. You are searching for a smooth, strong idle
with each cylinder firing nicely. Once this has been achieved, you'll then
want to recheck your rpms at idle and your synch and readjust if
necessary. When you have decided that your idle is solid, tighten the left
side retaining nut on the set screw. If you experience backfiring,
"spitting" through the carbs, or other signs of leaness, back the pilot
screws out a tad more.
* Synching Carbs At 3-4000 rpm: Once
you've got your idle squared away to your satisfaction, you now need to
synch your carbs at higher rpms, where you will do your riding. This synch
is accomplished by turning the synch screw located between the carbs in
the back. You'll most likely need to remove the rear carb breather pipe to
get to the screw, and move the tank up out of the way a bit using the 30mm
socker works great if you have one. Once you get to it, it is usually
quite simple to rev the bike to 3-4000rpm, hold it there, and check your
synch. Then let go of the throttle, make a correction, and try again. A
couple of adjustments should get it. Note that on some carbs the linkage
between them has taken some serious wear and has slop in it which maybe
difficult to take all the way out. Due to play in this linkage, the
throttle valve of your right carb (where the throttle cable connects) will
always open just a tad before the left carb throttle. This maybe
noticeable at tiny throttle openings where your right cylinder will hit
harder than the left, but if you are synched properly at idle (using the
set screws) and at higher rpms using the synch screw, this effect will go
away as the throttle is opened further, and is not usually bothersome.
This is the Screw you are looking for, it is at the end of the
screw driver and difficult to adjust this is were the carb adjustment tool
comes in well
I cannot take much of the credit for this i just added the
following websites together and took some pics please let me know if i
forgot something and i will add it as i see it!!!