Here we have force by Mercury 40 horsepower, two stroke, two cylinder, about 1994 vintage engine that has a hard time starting even when it starts it doesn't run for very long. So what we're going to do today we're going to check the compression on two cylinders and see what those measurements are. To do that we have to remove the spark plug wire caps. I'm going to take the spark plugs off. Working on the engine is a little bit harder because the boat is in the water. If you have it out on a driveway it's a different story. It's easier to work on it. But on the other hand even if it starts right and it seems to run right you cannot load it on your driveway. So you still need a water eventually to try it out to pull it out. In the second spark plug it's a little bit harder to get to because of the cover that eventually comes off. Here we have a compression tester, a very basic tool. It has a gauge and some connections and it has a thread of three different kinds for three different spark plug sizes. We're going to take our spark plug and we're going to try to match which one will fit. Obviously it's the largest so that's the hose we're going to be using to test the compression. So to get the hose inside the cylinder just screw it in the spark plug thread. The thread is with my hand no tools needed. It's got an hole ring on the bottom and it just turns as much as you can by hand. That's it. And connect the gauge. Rest it somewhere. That is secure. And then crank the engine. So all reading is just about 95 psi which is very low. Obviously this is not very good cylinder. It should be at minimum 120 psi. So we don't consider this cylinder to be good. We're going to go to the next one. It's a little bit harder to install because of the cover again. The engine, but yeah if you get it straight center it with the engine bore or the thread for spark plug. Yes, it'll be fine. And just turn it as much as you can by hand. See what this one is going to do? Before you go you have to reset the instrument by pressing the reset button. Let the pressure come out of the hose and the gauge. And now we're going to crank it again. So this again is 95. The same as the other one. It seems to be low on both cylinders. One good thing is that they are both equal. So we can try this one more time. But it looks like it's about 95. So we're going to unplug it. Let's replace the pressure of it. Try to torque this little bit better. No, this one is still rather tight. Try one more time. Just to make sure there are no leaks. So the measurement has repeated. It's 95. Once again. So this is kind of a low. And this engine needs an overhaul. Thank you for watching. You