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Throttle Cable Assembly


NEVER USE ANY TYPE OF PETROLEUM BASED LUBRICANTS ON THE THROTTLE CABLE.  All this will do is gum things up and make problems worse.

Use powdered graphite ONLY.  "Liquid Graphite" a.k.a. "lock fluid" does more harm than good because the solvent in it does not evaporates completely and forms gum.  To lubricate the cable properly, the throttle must be disassembled and the inner cable removed.  Do not be concerned about replacing the shrink wrap on the hand throttle assembly.  It is for cosmetic purposes only.

The Bowden cable must never be bent sharply or it will be ruined.  Ensure that the cable has smooth turns from end to end.  Sharp turns increase friction and make the throttle harder to operate.

As your throttle cable ages, friction between the inner cable and the sheath increases.  This is caused by wear and/or dirt.  Dirt is a particular problem if the cable was ever lubricated with anything other than pure graphite.

Sometimes, the throttle cable will stick completely.  Rather than buy an entire new throttle cable assembly, pilots can replace the inner cable, an item readily available from any bike repair shop for about $5.  A local shop can do the whole job which involves cleaning the inside of the sheath and replacing the inner cable.  They can also replace the entire Bowden cable itself.

The inner cable will last 50 - 100 hours.  When replacing the cable, be sure to thoroughly clean every trace of debris, grease, and oil from cable housing.  Over time, the Teflon coating of the cable wears off and the little pieces can jam the inner cable.

1. Checking the cable for damage

With normal use, the cable will rub on various parts of the frame.  If the cable has not been protected at these contact points by wrapping it with electrical tape or a piece of split hose, the kill switch wire can short to ground.  This will cause an engine shutdown at unexpected times.  In extreme cases, the cable itself can wear through to the inner wire and the throttle can jam or cease to function!

Carefully examine the entire length of the cable for damage.  Apply tape or hose to those areas where the cable rubs any part of the frame.

2. Cleaning the throttle cable

To thoroughly clean the cable:

Quality Bowden cables will have an inner sleeve that reduces friction between the inner cable and the sheath.  In addition, a quality inner cable will be Teflon coated.  These cables do not need any form of lubrication and will work smoothly until they are worn out.

Pilots who fly often will also appreciate this throttle spring modification which decreases the pull on the throttle, lessens throttle shaft bore wear, and provides a more positive return of the throttle to the idle position.

3. Throttle cable end attachment modification

The inner throttle cable will last much longer if this modification is done where it attaches to the carburetor.  It also provides a much more convenient way to disconnect the throttle cable from the carburetor.  Instead of removing the knarp and losing the cable adjustment, the ends of the cotter pin are bent together and quickly removed from the the throttle lever.  A new cotter pin should be used, however, as bending it more than once or twice will weaken it.

Parts needed: (1) knarp - use the existing one; (1) thin piece of sheet metal; (1) small cotter pin.  The correct size knarp a.k.a. "throttle clamp" is available from Miniplane-USA if yours is missing or damaged.

Make the small bracket of out sheet metal as pictured here.  Drill two holes, one just bigger than the cable and the other just bigger than cotter pin.  Then bend the sheet metal into an "L".

Top 80 throttle cable attachment modification parts

The cotter pin must be shortened so that when it is pushed through the new bracket and throttle lever, it will not catch on other parts.  Be sure to check for free movement of the throttle cable.  Failure to thoroughly check the throttle cable for free movement can result in a stuck throttle which can be EXTREMELY dangerous!  This modification can be used with the throttle spring modification.

Top 80 throttle cable modification parts installed

4. Cruise control

A pilot in England asked me about modifying the stock throttle for cruise control.  After thinking about it, I do not recommend it.  Runaway engines and emergency shutdowns are conditions that require instant control of the throttle and a cruise control adds more complexity to a cascading event such as a stuck cruise control, a faulty kill switch, a broken throttle spring, or a glider deflation.  The pilot who had the stuck cruise control rolled his trike and did a lot of damage (propeller, cage, etc.)  What if his lines to the glider had gotten into the spinning propeller?  Think about this sort of thing before making modifications to your throttle.

Lines getting caught in a spinning propeller?  Anyone who has experienced a runaway engine knows what I am talking about.  It is terrifying.  However, if the above throttle spring modification is done (applies to most paramotors), throttle pressure is greatly lessened and will be much more comfortable when flying for many hours.

For those wishing for a way to construct a cruise control, I would modify the existing throttle pivot (drill it out) and insert a screw with a plastic knurled knob.  Shortening the pivot will allow the throttle halves to be squeezed together by the knob and screw enough to lock it.

5. Kill switch

See the kill switch info section on how to troubleshoot kill switch problems related to the cable and the throttle assembly.