Engine stalls or doesn't start:
1. No gas draw even choking the carb.
a. Dirty screen filter inside carb. Remove the cover and clean the filter.
b. Tank pickup or fuel lines clogged. Clean.
c. Tank pickup loose from the fuel line. Fix.
d. Leaky fuel lines that suck in air. Replace.
e. Tank ventilation blocked. Motor stalls after 1 or 2 runs.
Even when the primer bulb is able to pull gas from the tank, the carburetor fuel pump will not be strong enough to work with a blocked vent tube. Eventually, if the pump overcome this resistance, the tank collapses. Clean the ventilation tube.
f. Check if the pressure hole on the intake port is aligned with the manifold and gasket; this hole is responsible for transfer the crankcase pulses to the carb, to operate the gas pump.
g. Defective diaphragm. Replace
h. Stuck regulator needle/seat. Clean.
i. Plugged internal fuel passage. Clean with compressed air.
2. Air in the fuel lines (bubbles in the system)Check the gas lines looking for cracks or loose fittings. If necessary, change them. If the fuel system has a quick fueling valve, check for proper operation. Test the system without the valve. Fix or replace the valve, if it is defective.
Disassemble and check the carb gaskets. Replace if necessary.
3. Poor fuel delivery while running. Leans out after a while
a. Check all of the above first.
b. Old age - can have a leaky diaphragm in the carb or the needle is worn out. Fuel flow can be surging. Rebuild carb.
c. Not properly vented tank
4. Water in the gas tank.
The water will be a lighter colored bubble at the bottom of the tank. Remove the tank, turn upside down & squeeze out the water through the vent tube. NOTE: Draining and refilling the tank may not remove all water.
5. Too lean carb.
Open H and L needles in small increments.
6. Carb breathing water at turns or by the rooster tail of other boat
Protect the carb.
7. From the Walbro site, technical tips:
Pressure testing a Walbro carburetor is an
excellent way to determine if there
The height of the metering lever on a diaphragm carburetor is very critical. A metering lever set too low may create an over rich condition. While a metering lever set too high may create a lean condition. The correct procedure to set a metering lever is to use a Walbro metering lever gauge (part number 500-13). Apply light pressure with a small screwdriver to the head of the inlet needle to keep it stable. Lift or lower the opposite end of the metering lever, run the 500-13 gauge across the lever so that the lever moves slightly, but does not restrict the gauge from moving across it. Each Walbro carburetor is clearly stamped on the metering lever gauge.
If your engine has sluggish acceleration, is difficult to start and seems to have low wide open throttle speed, check the exhaust port for carbon deposits. Also, check the spark arrestor screen for carbon build-up. This is a very common problem with engines that have a large number of hours of use.
Dirt is the most common cause of carburetor problems. When servicing your Walbro carburetor, be sure to check the inlet needle tip area as well as the low and high-speed adjustment needle tips for dirt. Compressed air is the best method to clean those areas without leaving fibers from commonly used items such as a cotton swab and pipe cleaner.
The best way to assure your Walbro carburetor will perform acceptably next season is to run the unit completely out of fuel. This will help to assure that the rubber components are not harmed by sour gas or that deposits don�t form in critical fuel passages of the carburetor.
1. Kill switch grounded
Disconnect the wires from the kill switch and test.
2. Kill wire touching ground
3. Fail safe
a. If you are using a 4 cells pack, try a 5 cells one. On 4 cells and big servos, the load at the servos may be too much and low voltage at the fail safe can trigger it.
b. Disconnect the fail safe and test.
a. Disconnect the wire between the low voltage coil and the ignition coil. Connect a 6v low amperage lamp at this wire (low voltage side). The lamp's other pole should be connected to an engine ground. Pull the starter a few times, the lamp should glow. If not, the low voltage coil is the culprit, otherwise, look for trouble at the high voltage and connections
b. Check the correct gap between the coil and the flywheel
c. In an engine with 2 coils (primary and secondary) check the correct connection between them.
d. Check if the coils have a good path to ground
e. Check the spark produced by the coil.
5. Spark plug
Try a new spark plug
Poor off idle to WOT transition
a. Low side needle to far in. Back out 1/8 of a turn each time and try again.
b. Blocked low needle circuit inside carb. Clean and rebuild carb. Clean with carb cleaner - Not gasoline!
3. High side blocked. Same procedure as above.
A tip from Jim Nissen:
problems typically indicate that the low end
needle is not out enough. I typically will
loosen the low 1/8 of a turn per adjustment. For
each 2 adjustments (1/4 turn out) on the low end
you have to compensate and turn the high side in
about 1/8 turn.
So if your in the ballpark - out on the low - in on the high. This will help balance the transition for your setup so that it will not stumble.
Poor WOT performance
a. Check ignition system: spark plug and ignition coils. Check spark and ignition timing. Correct as necessary.
b. High side needle to far out . Check plug for color. Should not be dark or sooty looking. Close needle in 1/8 increments each time.
c. High side needle to far in. Boat will start to run well then dies suddenly. Open needle 1/8 turn each
Out of balance engine. Check specially the flywheel.
Out of balance propeller. Check and correct as per the instructions bellow.
Flex cable with to much play. Use washers to reduce play.
Offset or bent square drive or collet. Replace
Resistor spark plugsA gas engine uses, as in you car, a spark plug to provide the spark that ignites the air/gas mixture that runs the engine. To avoid the plug interfering with the radio system, use only resistor type plugs in your engine. They normally have an "R" on the identification number. All our boats are assembled with resistor type spark plugs. The following plugs are appropriated for our engine. Use the one you can easily find.
2. Champion RDJ7Y
3. NGK BMR 7A or BM6A (1 degree colder)
4. NGK BPMR6F
Gap: .015" ( 0,4 mm)
pipes � the ones that there is no water
injection into them � use O-rings to seal
against the engine. Those rings need to be
protected against excessive heat e with this
purpose the flange between the pipe and the engine
is water cooled � exception made to Quick Draw
engines, with a water cooled cylinder and no need
O-ring additional cooling. Sometimes, those
O-rings leak and 2 problems occur: water inside
the hull and/or inside the pipe. Inside the pipe,
water hampers engine performance, inside the hull
may even sink the boat.. An interesting discussion
on Jim�s board offered some solutions to the
the obvious step is checking if the O-rings
are in good shape and correctly mounted on the
check for correct alignment
between the pipe, pipe coupler and engine;
keep some flexibility at the pipe mounting;
use a tad of grease when mounting the
5. check the seats for roundness.
Check your batteries. The voltage and capacity must be within
specification. If in doubt, use the biggest
capacity available, especially if using a 1/4
If using a fail safe � BTW what I always recommend � use 5 cells
packs for a total voltage of 6 volts.
Always use rechargeable batteries. As the name implies, they can be
recharged after use and, in a short time are
much more cost effective. However, they are not
eternal and must be well treated to offer the
best performance. After use, you should
discharge them completely, let them cool, charge
and store the pack for next use. We advise
reading your charger manual for better details.
But, if for any reason you are using non-rechargeable cells, fix then to
their support with elastic bands, duck tape,
whatever is available. Remember: engine
vibration tends to loose the cells from their
Never cut or coil the receiver antenna wire. It should be inserted in the
antenna support in a vertical position, to allow
for better reception. A 75 MHZ receiver should
have an 18" (45 cm) antenna wire. This
length is calibrated for best signal reception.
Turning the radio ON
Transmitter is always turned before the receiver and turned off after the
receiver has been turned off.
Avoid long wires from the
battery pack to the receiver; the resistance of
the wire reduces battery performance.
Keep the receiver and
batteries in a plastic bag or balloon, closed
with tape. Seal the radio box. Remember: water,
especially salt water, is enemy of your
Protect the receiver from
engine vibration by wrapping it with soft foam
Be sure the transmitter and
receiver crystals are matched pairs.
If your servos work
erratically, or oscillate, check for water in
the servo. Open and dry, or use the procedure
they buzz or hums at full travel, reduce the
travel, if your radio has this option. Otherwise,
connect the rod to the carb/rudder at the inner
holes of the servo arm and/or do just the opposite
at the carb/rudder end.
a wet receiver:
1.Take off the receiver and
2. Dip the electronics into
isopropyl alcohol for 1 hour.
3. Blow off the alcohol with
compressed air and let electronics dry for 2 - 4
4. Put a fully charged pack on
the receiver and leave it turned on until the
batteries discharge completely.
5. Check the receiver for
corrosion or some other liquid material in or
around it's internal components. If this is the
case, the receiver must be replaced. Remember:
it is expensive, but is not more expensive than
6. Connect the servos, a fully
charged battery pack and test for operation.
7. If the receiver does not
work, it should be replaced.
8. If the servos don't work or
oscillate, repeat the process
9. Protect all components with
anti corrosion product such as Corrosion X.
range � Interferences
AM radios are more prone to interference than FM ones. Interference may even cause loss of control of the boat and an accident with personal injuries. Besides all the measures you take to prevent interference, use a fail safe. This site has a chapter on how to install a fail safe that will give you the certainty that you did everything possible to prevent an accident.
There are 2 kinds of interference: external, caused by sources out of the control of the R/C boater, and internal, for what the main culprit is the engine. Not much can be done to external interference, except, maybe, look for another spot to practice your hobby. A lot of those interference are caused by radio transmission on the neighborhood and/or other cause out of your control.
the interference caused by your equipment, steps
can and should be taken. The most usual
interference and the solutions for them are:
coil scraping the flywheel. The obvious signal are
scratches on the rotor. Adjust the coil gap as
recommended above on Motor segment.
b. loose and unprotected receiver into the radio box: Protect the receiver from engine vibration by wrapping it with soft foam, to prevent engine vibration to be transmitted to the receiver. Hold it to the radio box.
spark plug: the spark from the spark plug is the
main source of interference on radio. Always use a
resistor plug, to minimize the problem.
half charged batteries: batteries not fully
charged, by themselves, to not cause interference
but make the radio more prone to them. Always use
fully charged batteries when putting your boat on
interference picked up by antenna or servos wires:
keep those wires away from the coil and as short
engine vibrations: any metal vibrating is a
potential source of noise (interference). Always
use rubber mounts to fix the engine.
throttle and rudder cables and rods: if feasible,
use non metal rods for throttle and rudder or, at
least, non metallic connectors at the tips.
h. too long antenna wire inside the hull: if the antenna wire inside the hull is too long, it will pick up noise from the engine more easily. Keep it as short as possible. Close the receiver to the exit point for the antenna.
i. try soldering a 10 microF/16v capacitor on servos terminal, to filter noise on the wires.
j. never use a multistrand cable to run the servos and battery wires.
l. if you are using a fail safe and a kill switch keep the wires far from each other.
Some time ago, Jim Nissen offered a tip on his board on how to check if your servos are suffering from interference problems. I couldn't find it, so I am not able to use his words:
the receiver on a Dremel, wire it to the servos
and turn the Dremel on at maximum speed. If the
servos vibrate, change crystals. If vibration
continues, change the receiver.
Check the range of your radio
before putting your boat on the water: Turn on
the transmitter and collapse it's antenna, turn
on the receiver and start the engine - for gas
boats - and move away 30 yards
(15 for FM radios). Ask a friend to
check the operation of the servos while you
operate the transmitter with the antenna
collapsed. Be sure the servos are not vibrating
or making strange noises. Don't launch your boat
if your radio is erratic.
you don't have enough range, check first if
there is humidity at the receiver. If this is
the case, dry it and use Corrosion Block or
Corrosion X and test again.
If you don't have enough range, check first if there is humidity at the receiver. If this is the case, dry it and use Corrosion Block or Corrosion X and test again.
Note 1: FM radios have a
Note 2: Just collapse the antenna, don't unscrew & remove it. Some radios don't appreciate not having a load on the output transistor(s). You should get over 50 yards with a collapsed antenna. (Ron Frank tip)
1. Problem even with the
engine turned off.
If there isn�t enough range
do the test again with the engine turned off. If
the problem remains, it�s eliminated the
engine interference as the source of the
problem. Take those actions, which presume all
the above points were already verified.
Note: when, during the test,
the replacement of a component is recommended,
this doesn�t mean you have to take the older
component from its place and put the new one
there. For instance, the recommendation of
replacing a serve just means: disconnect the
older and connect a new one, leaving the old one
in its place
if using a fail safe, by pass it, just to be sure
that it is not it the culprit.
visually check all electrical connections, from
the battery on. Use a multimeter to check the
voltage at the battery, at the receiver and
servos. Bad or corroded connections cause
voltage drop and can be responsible for the
with a multimeter check the antenna electrical
continuity. Antennas that are externally in good
shape may by broke inside.
replace the crystal from the receiver and
transmitter for another matched pair. Sometimes,
crystal apparently good is damaged.
e. if only one of the servos is erratic, replace it.
f. if both are, replace the receiver.
replace the receiver and the transmitter
by a set you know is OK.
2. Problem only with a running
If the problem only
occurs when the engine is running, check first:
a. non resistor spark plug: substitute immediately;
j. check if the coils have a good connection to ground.
l. check the gap between the coil and flywheel, to prevent contact.
n. do the tests for item 1 above.
Let�s see what Jim Nissen has to say about this:
the wires from the motor going into the kill
switch. Tie them together and away from the
motor. The test is to see if you have ignition
noise migrating into your box from these wires.
A lot of electrical ignition noise flows right
up the wires and if the switch/failsafe is
anywhere near your receiver you can have
trouble. I layed out my box to place the
failsafe on one side of the box (closest to the
motor) and the receiver and associated servo
wires/power are on the opposite side.
EMI (electromagnetic interference) can be a real pain the in the boat. The single largest contributor is the high voltage spark cable. You should check to make sure you magneto has good clean grounds where it attaches to the motor. Verify the magneto is not hitting the flywheel. Clean grounds are important, as the electrical energy will try to find a path to ground somehow. Lets hope it's not through the kill switch wiring!
That all said it could be you just have a bumm radio. Was the radio new or used? Dropped? Anytime you drop a transmitter you run the risk of damaging the crystal or ferrite cores in the RF section. Another reason to wrap your receivers in soft pliable foam. Good idea to have a radio expert looks it over and tests the sensitivity and tune for that channel.