Unstick a Stuck Pull-Start Cord on a Nitro RC

Businessman playing with an RC car in the hallway
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Radio-controlled vehicle enthusiasts know that troubleshooting a problem, like a stuck pull start, is often a process of elimination. The pull-start on an RC vehicle could fail for several different reasons, resulting in a pull cord that either won't pull out or a pull-cord that won't recoil. The first is often due to a condition called hydro lock (or hydrostatic lock), in which, basically, the engine locks up.

A failure to recoil is often caused by the cord coming off its track or flywheel. In either case, you won't be able to operate your vehicle until you fix the problem.

How Pull-Start Engines Work

RC vehicles are manufactured with several different kinds of engines. One of the most common is a simple pull-start engine, also called a recoil starter, which works much like the pull starts found on lawnmowers and chainsaws. The mechanism is made up of a starter rope, or cord, with some kind of a grip, usually T-shaped. The cord is wrapped around a flywheel located adjacent to the engine inside the vehicle. When you pull the cord, it uncoils and spins the engine's crankshaft, which starts it. Then the cord recoils back onto the flywheel.

When You Can't Pull Out the Cord

It's not all that difficult to unstick a pull-start chord, although it can be time-consuming. Plan to spend anywhere from a few minutes to an hour, depending on the cause, to fix your vehicle.

Before you begin, make sure you have a clean, well-lit place to work, and the following tools and/or parts on hand:

  • Wrenches
  • Screwdrivers
  • Needle-nosed pliers
  • New pull-start assembly (possibly)

Often when the chord is stuck inside the vehicle, it can mean that pressure has built up within the engine, a condition known as hydrostatic lock, or hydro lock for short.

In a regular internal combustion engine, hydro lock happens when a piston is prevented from completing its movement. In which case the engine either stops working or a mechanical failure occurs. Something similar can happen in an RC engine.

If you think your vehicle has hydro locked, then try this:

  1. Remove the glow plug.

  2. Gently pull on the cord a few times.

  3. If this releases it, replace the glow plug and restart your engine

If removing and replacing the glow plug and giving the cord a few gentle tugs don't work, the cord might have gotten twisted inside the vehicle or jumped its track or flywheel. In which case, you'll need to access these components by opening up your vehicle, then rewind the pull-start cord.

When You Can't Get the Cord to Recoil Back In

If your cord is stuck outside and off track, you'll also need to access the flywheel and rewind the pull-cord. 

If rewinding doesn't work, you may need to replace the pull-start assembly. Some RC owners prefer to just replace the pull-start rather than messing with the spring and trying to rewind the cord. It's your choice.

An Ounce of Prevention

To avoid pull-start issues altogether you may want to convert your nitro RC to a roto-start (shaft starter) system.