Reply To: 7.5hp Evinrude won’t idle

[Don]

Yeah, 37PSI is real low, I would definitely try a different gage.  You will probably only see 70-85PSI readings, which is normal for these engines.  If low readings are confirmed with a different gage, then you need to pull the cylinder head and have a look.  Perhaps the gasket is blown between the two cylinders.

OK, so the engine is new to you, so you don’t know how it ran before.  You serviced the ignition and carburetor.

The carburetor linkage should just start to open the throttle plate when the hash mark on the cam aligns with the throttle linkage.

So, the engine runs OK at the start position, but at a higher RPM than an idle.  Again, make sure that carburetor throttle plate is closing at idle, and that is not being held open slightly by a messed up choke linkage.  Just because the cam isn’t touching the carb throttle arm does NOT guarantee the throttle plate is closing properly.  I guess the only way to ensure proper throttle plate closure is to remove the carb and have a look at the throttle plate from the back side of the carb.

Again, I would try those inline neon spark testers to make sure you are not losing spark at lower speeds.  Just because parts are new, does not mean they are not defective.

So, first I would confirm the compression readings.  37PSI is too low.

Next, I would check that carburetor to be sure the throttle plate is actually closing at idle speeds.

Finally, I would invest in those inline neon spark testers to make sure you are not losing spark on one/both cylinders at lower speeds.

Again, just cuz parts are new, doesn’t guarantee they are any good.  Perhaps you have a defective spark plug, try some different ones.  Have a look at the plugs, and look for signs of water intrusion as well.