TO MUCH FUELL ON THE PLUGS 618
in 2 Stroke Technical Questions
13 years ago
-
Re: TO MUCH FUELL ON THE PLUGS 618
by bill martin » 13 years ago
Yanis,
Can you shorten the adjustment at the throttle? That would raise both slides, then you could lower the high one with carb adjustment.
Bill.
-
Re: TO MUCH FUELL ON THE PLUGS 618
by yanis karvas » 13 years ago
BILL THAT IS BRILLIANT!!!!!
Thank you,
I will report as soon as I look things over,
Yanis
-
Re: TO MUCH FUELL ON THE PLUGS 618
by Nick Axworthy » 13 years ago
Yanis I have copied these instructions off a yahoo web site....they are written by a guy that taught me a lot about 2 stroke and they work for me....I still have a lot to learn....
It maybe worth reading what Bob say in them and starting with a clean sheet of paper,
----------------------------------------------------------------------------------------------------
From Bob Metzler
Check for water or crap in the carb bowls. Make sure carbs are mounted
square with the engine since a tilted carb can cause one cylinder to run
hotter than the other on some engines. Cracks in the carb mounting
sockets can cause lean mixtures so replace them if they are brittle.
Check for adaquate fuel flow to the carbs. Any time you notice higher
than normal EGT or if the plane won't reach normal full throttle RPM
install a new fuel filter before you waste a lot of time looking for other
problems. See my article on fuel systems for more info.
Each carb has an idle jet, a needle jet with a jet needle and a main jet.
All have tiny numbers on them which tell you the size. Check to be sure
they are the factory recommended jets and the jets are the same in both
carbs because its common to find that a previous owner has installed
different jets. The factory recomendations are almost never wrong so
its very important that the factory jets are used during testing.
Check that all throttle cables are routed to drain out any water inside the
cable outer jacket. Water collecting in a low spot can cause corrosion
or freeze in the winter to lock the cable in one position.
CABLE ADJUSTMENT FOR A SINGLE CARB
Pull the throttle all the way back against the lower throttle stop. Where
the cable enters the top of the carb there is an adjustment that is covered
by a rubber boot. Slide the rubber boot up the cable to get it out of the
way then gently pull upwards on the outer jacket of the cable. There
should be a tiny amount of free movement before you feel the inner cable
start to move the slide upwards. That tiny amount of free play is critical to
be sure that the cable is not holding the slide up off of the idle speed
adjustment screw. If you have trouble feeling it you can remove the air
filter and look inside the carb throat to watch the slide move. Loosen the
lock nut and turn the adjustment screw until you have that tiny amount of
free play if needed. Lock the adjustment and work the throttle back and
forth a few times to be sure the cable outer jacket ends are fully seated
in their sockets correctly then pull the throttle all the way back against the
lower throttle stop. Double check that the amount of free play is still
correct at the top of the carb before you reinstall the rubber boot.
Push the throttle all the way forward against the upper throttle stop and
look in the carb throat. The slide should go up far enough so that it does
not block any of the carb throat opening. Its okay if it goes up just a little
extra but if it goes up too much it will bind and put a strain on the throttle
cable. You should install some sort of upper throttle stop to prevent that.
CABLE ADJUSTMENT FOR DUAL CARBS
Dual carbs must be mechanically matched or one cylinder will have a
higher EGT than the other and/or you can not get a smooth idle. Pull the
throttle back against the lower throttle stop. Where the cables enter the
tops of the carbs there are adjustments that are covered by rubber boots.
Slide both boots up the cables to get them out of the way. Loosen the
locknuts and turn both adjusment screws down two turns. That makes
sure that the cables are not holding the slides up off of the idle speed
adjusting screws.
Remove the air filters and use the smooth ends of drill bits as round
feeler gages to check the clearance between the bottom of the slide and
the bottom of the carb throat on each carb. Pick a drill bit that will barely
slide into the smaller of the two openings and use it to adjust the idle
speed screws on both carbs until both openings are the same. Your
carbs are now mechanically matched. To keep them matched you must
ALWAYS turn the idle speed screw on both carbs the same amount
when makeing idle speed adjustments. NEVER adjust just one idle
speed screw.
Make sure the throttle is pulled all the way back then go back to the cable
adjusters on top of the carbs. Screw them out to take out ALMOST all of
the free play. You check that by feeling how much you can lift the outer
jacket before you feel resistance. It takes a delicate touch but you need
just a tiny amount of free play to make sure that the slides are not held up
by the cables when the throttle is pulled all the way back. If the free play
is not the same on both carbs then one slide will start to rise before the
other so this adjustment is critical. Tighten the locknuts and work the
throttle back and forth a few times to be sure that all the cable outer
jacket ends are fully seated in their sockets correctly. Double check
that the free play is still correct on both carbs then slide the rubber boots
over the adjustments. If you have done it correctly both slides will start
to move upwards at the same time and the bottom of both slides will be
flush with the top of the carb throat just before you reach full throttle.
Set the throttle wide open and check that both slides go up far enough
so that they don't block any of the carb throat openings. Its okay if they
go up just a little extra but if they go up too much they will bind and put
a strain on the throttle cables. You should install some sort of upper
throttle stop to prevent that.
INITAL CARB ADJUSTMENTS
Because the jet RPM ranges overlap you should make the idle speed
adjustments first and work up to higher RPMs. If any large adjustments
are made it will be necessary to repeat the idle adjustment procedure to
fine tune all adjustments. Make sure a clean air filter is installed before
makeing adjustments.
There is an AIR MIXTURE adjustment screw which will fine tune the
amount of air at idle speeds only. The IDLE SPEED screw limits how
far the slide can come down to close off the air flow. If you aren't sure
which screw is which you can see the end of the idle speed screw
sticking out inside the carb air inlet if you remove the air filter. A spring
above the slide pushes the slide down against that screw.
To prevent engine shake and gearbox chatter our engines need an idle
speed of around 2000 RPM so warm up the engine and adjust the idle
speed screw for about 2000 RPM. Remember to turn BOTH idle speed
screws the same amount to keep the carbs matched if the engine has
dual carbs.
Adjust each air mixture screw to get the highest RPM at that idle speed
setting. 1/8 of a turn on adjustment screws can make a big difference so
keep the adjustments small. You will have to go back and forth between
dual carbs a couple of times to get the best possible idle because they
interact.
As the mixture gets better the idle speed will increase so adjust both idle
speed screws the same amount then fine tune the mixture screws again.
Keep at it until the engine idles smoothly at the lowest speed which has
minimum engine shake. Check the cable adjuster on top of both carbs
after you finish to make sure there is still the same tiny amount of free
play on each carb.
Be aware that it's easy to get an arm cut off by the prop and anything you
drop may go through the prop. I usually tie a short safety rope around my
waist and the base of the wing spars so that I have to stretch way out to
reach the adjusting screws. That way I can't forget and move toward the
prop. Fortunately you won't have to do this again until you notice an idle
problem.
------------------------------------------------------------------------------------------------
Hope you find it useful I did.
Nick.
-
Re: TO MUCH FUELL ON THE PLUGS 618
by bill martin » 13 years ago
Yanis,
If you follow the instructions Nick posted, The carbs should be tuned perfectly. Based on on what you have said so far, I would check one thing first. Back the idle speed screws out and pull the throttle all the way off. The slide should go all the way to the bottom. Then push the throttle to full and the slide should open completely. If you don't have that full travel, adjust the cables until you do, then follow Nick's instructions.
Another useful website is http://www.800-airwolf.com/ and look under tech support. They have a whole section on 2 cycle maintenance.
Bill.
-
Re: TO MUCH FUELL ON THE PLUGS 618
by Dennis Richardson » 13 years ago
Yanis - One thing that I have not seen addressed yet on your 618 is the wear that you will have on the slides and idle stop screws. As you have noted you are not able to adjust the idle speed, this is because of the wear on the contact area of the slide and slide stop screw. You either replace the slides and stops or use what you have available to true up the end of the stop screw, as it will have flat spots, then increase the depth of the screw travel or the length of the screw. The slide and the slide cut-away are critical components in the proper fuel/air ratio that the carb controls. Wear on these components will be accelerated by the amount of idle time, quality of idle and the efficiency of the air filtering system. It is my experience that when you accumulate enough hours to wear these components that the simplest and cheapest way of repair is to source complete carb assemblies.
Dennis
.png)
You do not have permissions to reply to this topic.
Related Topics