• Engine

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    Electric (battery powered) boats, no doubt, have some advantages. No problems of starting the engine, smaller, easy maintenance, and the race electrics attain fairly high speeds. The recent advances in brushless motors and LiPo batteries has made electric powered R/C boats an exciting class to run.

    Glow engine

    Derived from the engines used for model airplanes, they are usually called "nitro" engines. In fact, those engines run on fuel blended from methyl alcohol, castor and/or synthetic oil and nitro methane. They belong to 2 groups, according to the placement of the engine. Outboard, in which the engine hangs over the transom, just like the real ones (picture below) and inboards in which the engine rests in the hull and power is transmitted to the propeller by means of a shaft (see picture below); Outboards engines are mainly used in the tunnel hull. At speed, just the prop and the last third of the hull touches the water. Because of the special design, speed creates an air flow beneath the boat, lifting it from water, reducing drag and allowing high speeds. But this kind of hull demands a very calm water, because it has a strong tendency to fly in choppy water.

    Outboard glow engine Inboard glow engine

    Gasoline engine

    Generally, two types of engines are used:

    The ones specifically made for hobby use, the most well know are Quick Draw and Zenoah (pics below), both are available in a range of displacement and power.

    The ones originated from engines developed for other purposes, normally leaf blowers and string trimmers. These are commonly known as "Weed Eater" motors. These engines are extensively modified for use in R/C boats. In USA the Homelite is the most commonly used engine, because of its availability and low price. Only your imagination, in the USA, limits the different brand of engine used. The pictures below show a stock, air cooled Homelite as found on weed eaters and the same engine prepared for R/C boating.

    Quick Draw Engine Zenoah engine

    Homelite engine for a weed eater Homelite engine ready to go on boat

    Husqvarna engine being prepared at 6 cylinder engine
    Shark Racing. v. water jacket.

    Breaking in

    Although some engine makers - Zenoah included - say that their engines don't need any special break-in procedures, some precautions should be taken until your engine has used at least of a gallon of fuel.

    Oil. Increase the amount of oil mixed to gas. We like to use 25:1 on engines already broken in, which comes to be more oil than the Zenoah suggestion of 32:1. During the first tanks this mix should be 20:1, for easier setting of the rings.

    Adjusting the engine. During this same period, open the needle 1/8 turn above the normal adjustment.

    Look for the color of the spark plug ceramic.

    • Light gray: too lean, adjust immediately. Turn the needles counter clockwise.
    • Brown, from light to middle dark: OK. During break in it's desirably that the element be on the darker side
    • Black: too rich. Turn the needles clockwise.

    For all those adjustments turn the needles 1/8 each time


    A tip from Mike Hoffmeister:

    Just cut two pieces of medium blue silicone hose, about 1/4" long, and slide them up on the shank of the needle valves. The pieces interfere with each other just enough to damp vibrations and keep the needles from falling out (especially the low-speed needle). The only concern is to make sure that when you adjust one, it does not cause the other to rotate!

    The picture bellow show how this work. Simple and efficient.

    Water pump

    A boat without a water pump relies on it's forward movement to push water through the water jacket. If your boat has a clutch, a water pump, which works even with a stationary boat is mandatory.

    Gas oil mixture

    A 2 stroke engine runs on a gas/oil mix. Period. It's unbelievable the number of engines that need reworking because the happy owner forgot this little detail. The result is an engine that will need a complete tear down and new piston and rings and maybe the cylinder itself. The engine makers recommend a 32/1 to 50/1 ratio mixture for their engines what means that, for each 32 (or 50) parts of gas you should add 1 part of oil. FORGET IT! This mixture is good for a engine running on a weed eater between 4 - 5000 RPM. Not on a boat, with a hopped up engine. It will be much happier with 25:1 mixture. Translating the math, each gallon of mixture should have 5 - 8oz of first grade 2 stroke oil. Don't try to save on fuel: it's the cheapest item of your equipment. Bellow, some recommendations from experimented boaters:
    • Amsoil
    • Blendzall Racing Castor
    • Golden spectrol
    • Honda HP-2 synthetic racing oil
    • Klotz Super Techniplate 80% synthetic 20% racing castor oil
    • Quicksilver, Mercury Outboard
    • Redline 2 cycle Racing
    • Silkolene Pro2. 100% synthetic

    Old mixture

    Mix just the amount of gas you intend to use in one or two weeks. Aged gas, especially if mixed with oil, looses its combustive properties and evaporates away part of its chemical components. This causes hard starting and low power.

    Gas tank placement

    Put your gas tank as close the CG of your boat as possible. Like this, you reduce the CG alteration when running your boat. Besides, the fuel line will be shorter - witch is always better.

    Tank ventilation

    Make a coil from 1.5 foot of gas line, coil it and connect to the gas vent outlet. In the event of a roll over, fill the tank by the return line until gas is expelled from the ventilation coil, and all water in the lines will be expelled.

    Auxiliary tank

    Connect a 2 ounce auxiliary tank to the vent line. Connect the main tank to the auxiliary tank with a fuel line and a brass tube that reaches the center of the auxiliary tank. The vent tube must be at the top of the tank, so, if water enters the system through the auxiliary tank, the main will not be affected. Position the auxiliary tank in a way it can be easily removed and any water removed. Look bellow. Using a film canister instead of the auxiliary tank is also a tip that have more than few users.

    Ultimate gas tank setup

    This is a tip that Ron Frank posted at Jim's board. Not being enough, he posted also pics about it..

    After running an IV bag fuel tank for a year I finally came up with the best of both worlds.

    A plastic tank is easy to fill and vent BUT will pickup water in a flip/blow over.

    The "bladder" or IV tank needs no vent and will not pickup any water in a flip/blow over BUT is a pain to fill & get the air bubbles out, Especially in the confined space of a mono when the bag is under the motor.

    SOLUTION: A hybrid setup using a standard tank BUT the vent goes to a 250ML IV bag. It's filled thru the return line (WA-167 or any carb with a primer bulb), A Quick-Fill valve or a separate sealable fill line(WT-257 or other carb without a primer bulb}. The vent is a sealed system so no water can enter the tank.

    It's worked well with a plastic tank /IV hybrid and an IV/IV setup. On the IV/IV I mount the primary (500ML )bag under the motor, run 1 feed line to the carb & a vent line to the 250ML bag mounted in the bow. The vent bag is elevated so the air flows into it when refilling. No need to worry about air in the primary bag, Just gas & go..

    As Mel Gibson said in "Lethal Weapon", "Works for me"

    Good luck

    IV Bags

    To the best of my knowledge, Don Betz (db) was the first one to come with the idea of using an IV bag as a gas tank. The pros are so many that this setup is quickly becoming a unanimity between us. Here, he explains how to install one:

    1L I.V. Bag
    Outputs facing aft, end of the bag about even with the output side of motor, span the rails at forward side of bag with zip-ties and loop them through the hanging hole in bag.
    Different bags have different line configurations but you'll get the idea. Go to the auto-parts store and get a barbed plastic "T" fitting (vacuum, or windshield washer fittings). Stick one of the tops of the "T" into the output line in the bag. Attach large Tygon to the other top of the "T" and run that to an inline filter then to the carb. The other part of the "T" is your filler line, you just attach another several inch long piece of Tygon that you can just plug and unplug to add fuel.
    Fill the tank, once nearly full lift the aft end of the boat and pump the air out of the tank. Unplug the filler and replace the plug in the boat filler line.
    • LOW center of gravity.
    • Changing weight very near the fore-aft C of G.
    • Closed system, NO water contamination potential.
    • Supersimple.

    The main reason I came up with this idea was to get the changing weight near the C of G. Think about it, with a normal tank mounted in front of the motor the bow of the boat gets lighter as it runs lower on fuel. This is also interestingly enough around the same time that the race water is getting really churned up, right?

    I still can't seem to finish races but Oh well. Hopefully the L45 will get me to the finish this season

    Fuel lines

    The Walbro 167A carb uses 2 fuel lines, both connected to the fuel tank. The first one is the feeding line, the second is the return line. As the carb works on any position, I suggest using the primer (clear plastic bulb) up. This makes priming the fuel a lot easier. In this arrangement, the return line is the one by the primer, the supply line is at the opposite side. If you are using a quick fill valve, look at the drawing bellow to connect the lines.

    Return line blocking

    Matthew Waldron, from MD Designs, uses to block the primer exit to the tank. He states that, under some circumstances, vibrations from the engine may cause problems on the diaphragm or valve. It never happened to me, but Matthew is a very experienced boater and his advises must be taken in consideration. I quote him, when answering a question posted on Jim's Board:

    "We observed that while running the motor at some speeds the vibrations were enough to make the diaphragm or valve open up in the primer bulb and lose fuel out the fitting, after blocking it off the motors were easier to set the needles and the ran better with out have to adjust for different fuel flow rates. All we do now is prime the carb and put a cap on the exit fitting from the carb.

    Fuel line length

    The shorter, the best. Don't use a fuel line longer than 1 foot, place your fuel tank near the engine. By the way, the close the tank to the engine the less the CG will change when the tank empties.
    Needles settings

    Carburetor WT-257, engine QD 25 or Zenoah: low side: 2 to 2.50
    high : .75 to 1.25

    Zenoah engine, modified: low side: 3/4 to 1
    high : 2 to 2-1/4

    Premium gas

    Well, I was maybe the last one to be convinced about this matter. I read a lot about it, and now things make sense. High octane gas has additives to SLOW the burning time, as to prevent detonation on high compression ratio engines. Our 2 stroke engines are LOW compression engines, so this kind of gas is not necessary and even undesirable because they tend to burn - part of it - into the tuned pipe, making no useful power over the piston. I have a very good reason to taking so much time to see the light: Brazilian gas has a lower octane rating when compared to USA pump gas. In Brazil I do use - and recommend - special gas, which has the same octane rating as regular on USA. Thanks to Mike H., Ron Frank and other that showed me, with facts, that I was wrong.

    Clearance between the coil and flywheel:
    0.015 - 0.016 inches( 0.38/0.4 mm). This allows a good spark and, at the same time, avoids the coil touching the flywheel which cause drag, loss of power and radio interference. If necessary, to adjust the clearance, file the mounting holes of the coil.

    Jim asked Zenoah about specifications for the manufacturers coils. That's the response:

    RED Coil: Secondary voltage Ignition Timing
    @1.000 rpm 16KV @ 7.000 rpm 30 BTDC
    @7.000 rpm 28KV @10.000 rpm 28 BTDC

    GRAY Coil: @1.000 rpm 20KV @ 7.000 rpm 28 BTDC
    @7.000 rpm 20KV @10.000 rpm 25 BTDC

    "As you maybe know, the gray coil has good performance at low (idle-7.000rpm) and the red coil has good performance at high (over 7.000rpm) range."

    "This difference is set up according to the engine purpose, red coil (G230PUH/PUM is for high power at high rpm range, gray coil G230PU) is for easy starting by propeller flipping and good power at mid (7.000)rpm range."

    Komatsu said the coil/flywheel gap should be .3mm, and .2mm if you can get it. The smaller gap the hotter the fire.

    Not a word on the mysterious black coil.

    Additional information from the 260 Zenoah Manual

    Source Coil 1160-71211:
    Between Coil core and Red wire = infinite resistance (open)
    Between Coil core and Black wire = 185 ohms

    Source Coil 2629-71210:
    Between Coil core and Red wire = infinite resistance (open)
    Between Coil core and Black wire = 255 ohms

    How big is a big bore Walbro?

    There is a lot of discussion about how big is a Walbro carb. You can do one of two things to discover: look at the 11 pounds Walbro Service Manual (if you can find one) or do what Mike T. says:

    "On a Walbro, there is a number in a small circle at the air inlet. That denotes the venturi (the small part) diameter in 64ths of an inch. A WA-167 has the number 28, which is 28/64. That fraction reduces to 7/16th of an inch. A wee bit less than a half inch. About 11mm. "

    Intake manifold for big bore carbs:

    Jeff Thompson offered this tip on how to make an intake manifold for a big bore carb, using the stock one as a starting point. This guy knows what he says:

    I have seen a few Big bore intakes on the market and here's a tip for the new guy's ,it will save you some buck's, I have used this trick for a while and it work's, and I get asked this a lot so here goes, Take your stock intake off and JB weld up the vacuum port's and the other void area's, let it dry and lay out some 180 or 220 sand paper on a good flat surface then sand it just enough to take off the excess epoxy, Then measure your throat on the carb and drill out the intake to match the big bore carb. word to the wise when you start to drill it out go in about 1/8" on both side's then drill all the way threw, Best to use a drill press. OK now that you have that. To operate the carb correctly take out the big screw on the top of your carb, you will see a beefy raised area on there by the screw hole on the cover plate drill it out and tap it using a 10/32 tap and install a nipple. and put the cover back on the carb, next install a nipple in your case on the side or in the crank cover, make up new intake gasket's and run a 5/32 vacuum hose from the case to the nipple on the carb.


    A tip from Paul Govostes

    The Walbro (WYK-33 Barrel Carbs), have just the (one H-Jet) needle visible. The Low Jet is a tiny screw which is hidden under a very small plastic cover. These Walbro Carbs come standard on the 35cc QuickDraw Engines and they are great carbs.

    Quick-Fill valve installation

    A Quick-Fill valve makes easy filling and, mainly, emptying the tank, witch is mandatory at the end of the day, when there is some fuel left. The drawing bellow shows how to make the connections to a carb with primer bulb. If you carb doesn't have a primer, just ignore that specific connection.

    Fuel filter/filler valve

    This is a tip from Jim Jellison, replacing, at the same time, the line filter and the quick fill valve.

    "This is a KJS fuel filter. The part number is 419,T Type Clear Fuel Filter. There is a filter screen in the body of the unit at the end facing the fuel line shutoff clip. This end of the filter goes to the carb. The other horizontal barb is connected to the fuel tank. The barb facing the tape measure is the fuel filler/drain barb. Just put the filter in line between the tank and carb, and then install a filler/drain line on the 3rd barb that is long enough to get over the side of the boat and connect to your fuel jug outside the boat. No mess, No fuss, No leakage. Nothing to break. In addition you need a fuel line plug for the filler line. I have found the fuel line shutoff clip is not necessary, as the carb never gets flooded during the fueling process. Of course you drain the fuel tank through the same line. Works great. Price $3.50 per filter"

    Coil test

    Testing the coil is not a easy task. First, because the small gap at the plug, the spark at the spark plug, when out of the engine, is not a secure indication that the coil is in good shape. Out of the cylinder, and having not to overcome the resistance of the compressed mixture, even a defective coil may produce a spark. Second, the spark gap makes a very small and hard to see spark. Solution? You may improvise, with leftover material, a very effective tester for your plug. Look the picture bellow.

    Basically, what we have is a metal shaft with a conical tip, fixed to a metallic base, electrically isolated from the base by a nylon or similar material bushing, soldered to a piece of spark plug wire. At the other end, a screw that can came close to the conical tip. This screw is not isolated from the metal base. Fixed to the base, making electrical contact with it, a wire with a alligator clip.
    Utilization: First, establish the maximum distance from what the coil is able to produce a spark. Connect the alligator clip to a good ground at the engine. Take of the plug and connect the two plug wires together - the one from the engine to the one from the tester. Separate the screw from the conical tip ant pull the starter. The spark will be easily seen. Continue the process, until there is no spark anymore. Go back with the screw to get the spark back. You have just discovered the maximum gap your coil is capable of making a spark jump. Register the information. From now on, whenever you need to check the coil, connect it to the tester and check the distance you have a spark. If much less than the registered, you have a defective coil. Believe me, it's easy to use and works.

    Carb fuel inlet

    Sometimes, you would like having the carb inlet in a different angle. Don't force it. It's plastic and breaks half the times you try it. Larry has a better option:

    Pull the fitting out, take the bottom off the carb. The hole is the right size for a 10/32 tap, thread the hole and then you can put any kind of fitting you want. Blow out the hole and put the bottom back on the carb. you can find straight or angel fittings so you can point the fitting any direction you wish.

    Larry Ingelson

    Fuel filter

    Always use at least one filter between the tank and the carb. Whenever possible, use another one between the fuel line/quick valve and the tank.
    Water lines connections

    The water cooling system of your boat includes the water pickup, water pump (optional), water inlets and outlets at the water jacket, header and coupler water cooled or not. The pictures bellow show how to connect the lines on each one of those systems. We always recommend 2 pickups, if one of them clogs, the other will take care of the cooling. If the water pickup has only 1 inlet, use a Y to connect both pickups to the engine. The water pump is normally only used on engines with a clutch. If this is not the case for you, just ignore the pump at the pics. I like, whenever possible, having all the water inlets coming to the engine water jacket - it's the most critical part of the system, if something fails an expensive engine may be lost. From this basic setup. you may adjust your connections. On a system where neither the header nor the coupler are cooled, the engine outlet(s) conduct the water to the outside of the boat. One last word: use the lower connections as inlets - outlets at the higher ones. This way, the cooling water has to travel trough the entire system before leaving.

    The letters at the pics are:

    A: pickups
    B: water pump
    C: water inlets at the engine
    D: water outlets at the engine
    E: water inlet at the header
    F: water outlet at the header
    G: water inlet at the coupler
    H: water outlet at the coupler

    Lines without connections are the outlets from the boat.

    System 1: Engine with 2 inlets and 2 outlets, cooled header and coupler.
    System 2: Engine with 2 inlets and 2 outlets, cooled header and no cooled coupler.
    System 3: Engine with 1 inlet and 2 outlets, cooled header and coupler.
    System 4: Engine with 1 inlet and 2 outlets, cooled header and no cooled coupler.
    System 5: Engine with 1 inlet and 1 outlet, cooled header and coupler.
    System 6: Engine with 1 inlet and 1 outlet, cooled header and no cooled coupler.

    Checking compression

    Checking the engine compression is an excellent indicator of it's health. While new or in good conditions, check and register the compression. This number will be a parameter whenever you need to check the engine condition after some time of using it (months, years, any time you feel it necessary). The pics bellow show how simple is the operation. Use a gauge from automotive line, that reads, at least, 200 PSI. They are trustful and accurate instruments.

    As compression must be measured with a fully open carb, if you are operating alone it's easy to take the carb off.

    If you have someone helping you, you may skip taking off the carb. At the pic, the engine is fixed to a mount we use for this purpose. A very simple one, just a very strong wood base, with 2 aluminum rails on rubber mounts, set apart 5 inches, and with holes for different engines. Take off the spark plug, thread the instrument in place and pull the starter a few times, up to the needle stops. This is your engine compression. Take note and keep for future reference.

    Homelite - Taking off the crankshaft

    Homelite engines, beside being very popular have a point in common: all use bearings of the worst quality available at the market, that can't stand with the additional effort of a hopping-up. Replace bearings is not too hard - the most complicate part is taking off the crankshaft. Pics bellow show how to do this, using a press, to prevent damaging the crankshaft with a hammer. The part # are 6001 - front and 6201 rear.

    Take the opportunity and replace also the oil seals.

    Finally, the totally disassembled engine

    Homelite insulator block

    Homelite dealers have an insulator block that allows for a straight pull carb installation. On hobby shops it can costs as many as ten times the US$ 2.00 price tag at the dealers. Part # 06445

    Aeromarine motor mounts

    David, from Dallas RC Thunderboats, likes the Aeromarine mounts, for the 6 isolators in line with the crankshaft e for strength. Nevertheless, taking the engine out is a lot of work:

    The solution came from the old Hyper Torque mounts, simple and efficient.


    The most efficient exhaust systems include a special projected manifold and a tuned pipe whose dimensions take in consideration such variables as: engine c.c., RPM, exhaust and transfer ports duration, sound velocity at the pipe, exhaust temperature and so one, creating a complex equation that results in a design that vastly improves engine performance. (picture below). The cooling water for the engine, after leaving the water jacket may exit in two ways: exhausted out the boat side, by means of a outlet on the hull, or into the exhaust system, injected into the exhaust header and going out at the pipe outlet.