Special Tricks

1.  Installing a velocity stack on a Saito-82a engine:  A number of Saito engines are now sold without an intake velocity stack, presumably to save production costs. The addition of a velocity stack on the carb inlet helps stop some fuel spray coming out the carb when the engine is running. If you want to add a velocity stack to the Saito-82a you will need to buy the velocity stack (part number SAI50GK93) plus an O-ring. I got an O-ring from a local hardware store with dimensions 5/16” inner diameter, 7/16” outside diameter. The picture at left below shows the parts; the picture below on the right shows the engine after installation. This is probably not recommended by Saito, nor for ‘klutzes’ who can not use a screw-driver without stripping the threads in the plastic back-plate. This particular intake velocity stack part should also fit the the Saito 50, 56, 65, 80, 91, 72 engines but I have not tried using it on those other engines. 

Vel_stack_82a
Vel_stack_82a_parts

2. Access to Needle Valve With Cowled Engines: With a cowled engine the main high-speed needle valve is often inaccessible. Even with the extension provided this is usually not long enough to extend outside most cowls. A good solution is to omit the wire extension piece, and grind a screwdriver slot on top of the needle valve. A screwdriver can then be inserted through a small hole in the cowl to adjust the main needle valve. It also helps to epoxy a short (about 1/2”) length of brass tubing over the end of the needle valve to help guide the screw-driver to the needle valve.

needle_valve_web

There is an even easier way shown above. After you have used your Dremel tool with a cut-off wheel to grind a screwdriver slot in the top of the needle valve, then put some heat-shrink tubing over the end (I used white-color heat-shrink tubing in the above picture for no good reason).  The heat-shrink tubing holds the screw-driver in place while you adjust the needle-valve.

3. Slowing the Throttle Servo: Some computer radios (at least my JR 10x does) permits the adjustment of servo speed. The speed of a servo may be slowed down by a preset amount and is set up with transmitter programming. Check your transmitter manual to see if you have this feature. This is particularly useful with the throttle servo.

As the throttle is quickly advanced from low to full throttle lots of air suddenly enters the engine which will cause the engine to quit unless the low-speed mixture is set sufficiently rich. The faster the throttle stick is advanced the greater is the tendency for the engine to quit. Therefore, if the throttle motion is slowed down the low-speed mixture can be leaned further while still preventing the the engine from quitting when the transmitter throttle stick is rapidly advanced. See the ‘Throttle Setup’ section on this web site; it is best to have the leanest possible low-speed needle setting. 

The amount the servo is slowed is a personal decision. Just slow it an amount you consider is the slowest you think is reasonable.

The overall result is a very reliable low-speed engine setting. No matter how fast you move the transmitter stick back and forth the engine will not quit.

4. Setting up the Throttle Linkage: This actually applies to any engine make. Use a good quality servo with no backlash or slop. Use a solid linkage between the servo and engine throttle arm - no floppy wires or plastic linkages - and make sure the friction is minimal. This is particularly important for getting a reliable fixed low idle position.

The following only applies if you have a computer radio that may be used for servo end-point adjustments to help set up the throttle throws.

First make the mechanical linkages such that the servo moves the throttle arm from approximate idle position to approximate full throttle position.

Next set the transmitter throttle trim lever to its center position (assuming you have a tranmitter with a mechanical trim lever and not electronic trim). Now move the transmitter stick to full throttle position. Next look into the engine carb and you should see the carb barrel approximately fully open. Now, using the transmitter programming, adjust the servo end point adjustment back and forth while looking down the carb - you want the servo end point adjustment set so that the carb just opens fully with the transmitter stick at the full throttle position - if it is not fully open you won’t get full power, and if the servo is pushing too hard you will get high servo current drain when at full throttle.

Next move the transmitter stick to full idle position. The transmitter trim lever is still at its center position. Now adjust the low-throttle servo end point using the transmitter programming function so that the carb opening is about 1/2 mm (this is a good starting point).

Start the engine, keeping the throttle trim lever centered and the transmitter stick a couple of clicks above its full idle position. Assuming you have already adjusted the carb needles for optimum running, the low speed idle setting is set using the transmitter end-point adjustment, and not the throttle trim lever that stays centered. With this procedure you always know that a centered trim lever corresponds to the correct idle rpm. For future changes to idle rpm that may be required always adjust the servo end-point adjustment using the computer programing function and not the trim lever position.

Remember, when starting the engine for the first flight of the day the engine will probably not maintain the same  lowest idle rpm as the last time you flew. The first flight of the day is usually needed to loosen up the engine. So don’t be tempted to adjust the idle rpm with the computer end-point adjustment until you have flown a flight or two. On the first flight of the day move the mechanical trim forward a couple of clicks and then back to center for landing and subsequent flights.

Having a reliable and lowest-possible idle rpm helps with landing a model. You always know that setting the trim lever to center will provide that lowest idle rpm. If you are paranoid about avoiding engine stoppages during a flight you can always take off with the trim lever a couple of clicks above its center position, then return it to center just before landing (this is a good procedure for a new engine).

[If you unfortunately  own one of those transmitters with an electronic trim on the throttle you will need to adopt a somewhat different procedure from that outlined above]

 

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