Mini ROK carb help!

[GregF (Greg Fine)]

Maybe this will help.

@GregF

The following in taken from E.C. Birt. A carburetor guru that is well known for his work with Tillotson Carbs. It gives good tuning instructions on how to find optimal settings for the HL and HR carbs. It can also be found on the ECcarburetors website at the bottom of the page under E. C. Birt Archives:

eccarburetors.com

EC%20speed%20secrets%2093.pdf

12.39 MB

“Your Tillotson carb earned the reputation of being “user
friendly” because if you got anywhere close to the above
information you carb will work for you. Track side there are a
few simple steps to follow on finding the right tune of your
carb. 1) Set the low side needle at 1 1/4 turns out from bottom
and the high side needle at 1 turn.
Now you’re ready to start the engine. Set the kart on the
starting grid and have it pointed at the race track. Pointed at
the privy or someone’s pick-up just could lead to major problems.
Never get into the kart without being dressed to race. Put
yourself in the kart, hit the throttle a couple of times and watch
the linkage of the carb. Make sure that it is going from full
throttle and have your handler put the starter into the starter
nut and spin the motor over. Watch the fuel come up the fuel
line. As soon as it disappears into the carb, count to two and hit
the throttle. The motor should fire.
lf the clutch is set up right, you’re still in the pits. lf not,
you’re on your way to the track. Now you know why you didn’t
point your kart at the privy. Hold the brake on and throttle the
engine a few times to get the clutch to hook up and move out
onto the track. lf the motor is loady, give it a chance to clear
out by itself. lf it won’t, you may have to take a touch of the low
side away. Turn the needle in a little bit at a time until the motor
cleans up. As soon as the motor cleans up brings the low side
needle back out where it was. Give the kart a couple of laps to
warm up. Once the motor is warmed up, come down to parade
lap speed then stand on the throttle. lf the motor bogs, it could
be on the lean side. Open the low side needle lust a touch.
Keep coming out with the low side needle in steps of 1/8 turn till
the motor pulls hard from the parade lap speed.
Now you’re ready to find the tune for the high side. On the
longest straightaway, bring the high side needle out till it goes
rich in the middle. This rich sound will be a splattering sound
or irregular firing. Better known as 4-cycling. Once you tind
this spot, start taking the high side in till it runs clean all the
way to the end of the straightaway and just 4-cycles at the
point where you’re going to lift for the turn. Once you have
found this spot, take the high side needle in lust a touch more.
Now go back to parade lap speed and make sure it pulls off the
bottom clean with no bogging.
Next check the feel ol the motor as you just come off the turn
after a high speed straightaway flat footed. lf the motor 4-
cycles here, the low side is just a touch on the rich side. Take a
little away from it. (Turn the needle in.) Watch your temperaturegauge. Anything over 350” F is starting to get too hot. lf you
don’t have a temperature gauge on your kart and the stickers
start to melt off the side of your helmet, that is also a good sign
that the motor is running on the hot side.
Once you are comfortable that the motor is tuned right,
come back into the pits and check the position of the needles.
lf you find that the high side needle is out more than the low
side needle you missed it somewhere out on the track. When
you’re tuned at the optimum, the low side needles will be out
just a touch more than the high side. Once you have found this
place for the needles you can start f ine lining the tune by the
plug color and temperature of the motor. Plug color will be a
light tan to brown color. Motor temp 250* to 350* F max on a
control. A lot of people tell me that a TS-40 or US-820 has to
run 500" plus to make good power. Try 375’ and put your stop
watch on it. Just maybe 500" is not the hot tip after all.
ODDS AND ENDS;
Never mix up any more fuel than you need for race day.
Dump left over fuel into your race hauler. Never use left-over
fuel for parts wash.
Service carb after every race meet. When pumps get
stretched, replace them. Stretched pumps make for a richer
running carburelor.
On real hot day set the pop-off pressure a bit higher. This
will let you run the needles out f urther and help coolthe motor
off without being too rich on the top end.
Cool weather, good air, high A.D. Set the pop-off just a
touch lower. Carb can stand to be a touch richer.
When setting pop-off pressure never have carb dry. Wet
everythng with WD-40 for safety factors.
When putting in new gaskets, wet them with your 2-cycle oil.
This way, if you have to pulla track side service you won’t have
gaskets stick and tear on you.
Pop-off pressure must pop then drop a touch and hold. lf it
doesn’t hold carb will not perform right. Will always be on the
rich side. Cure: reclean needle and clean seat with Q-tip (cotton swab) and
wD-40.
Always carry a spare cap, fuel screen and cork with you. lf
carb starts acting lean, pull cap and check screen. lf trash is in
it, replace with brass screen and hope that none of it gets to the
needle, causing it to leak.
Torque carb pump plates like you would a cylinder head.
Every other one till tight. Any leaks here will cause lots of
tuning problems. lf lap times are not fast, it’s always easy to
blame the problem on the carb. But just maybe you will find
that faster lap time by tuning the driver or the chassis.
Keep your fuel dry and have a good time at the races."

• E.C. Birt

(Minor edits for points of reference, i.e Q-tip = Swab & Degrees in F not C)

It was more for the Tag Senior engine, but the tuning explanation is spot on.