Cheap DIY Two Stroke Leakdown Tester

December 8, 2012

So for a while now I’ve suspected I’ve got an air leak of some sort on my Tomos. It runs a little hotter then it should, and doesn’t like to idle very consistently even though the timing is spot on. The first thing I usually do is spray some starting fluid around the intake area of the engine, if the engine revs up you’ve got yourself a leak. Unfortunately it didn’t do anything for me, so my intake area was free of leaks, but that’s not to say my whole engine was leak free.

My next step was to do a leakdown test, but buying a real deal tester seems to run around $200. I decided to make my own. I used the following…

  • chunk of radiator hose
  • gas pressure test gauge
  • 3/4″ male to spigot connector
  • extra header for a puch
  • expansion plug (I forget the size)
  • bike pump
  • spray bottle

I spent around $30 on everything would have been roughly have that, but the spigot connection was surprisingly spendy. I bought the gauge, spigot and expansion plug from menards although they can be bought at most home improvement style stores home depot, lowes, etc  or many places online. Everything else I already had lying around.

Basically all we want to do is plug the engine up and put a little bit of air pressure in it, roughly 6-10 psi. So really all you need is a gauge that goes to around 15 psi, but mine was all they had in stock so it goes up to 100psi. Once your plugged up and you’ve pumped some pressure in, it should hold and shouldn’t go down more then 1 psi or so every minute. If it goes down faster then that you’ve got a leak somewhere.

To find they leak spray some soapy water along the seams of the engine, cylinder, cylinder head. Put a little air pressure in and you’ll start seeing bubbles where you’re air leak is.

Here’s a video of the tester in action…