Im compression testing a carbureted 2 stroke Yamaha 175 hp outboard on my Grady. I just wanted to triple check instructions so I don’t mess anything up. It seems I can adequately disable ignition by pulling the kill switch lanyard. Is that correct? Then perhaps I advance the throttle in order to open the carburetors? Of course removing all spark plugs. I’m just a little confused what can go wrong with the process. I’ve watched YouTube videos…but not quite the explanation I was hoping for. Any help is appreciated
Proper steps for compression test
- Thread starter Noble Savage
- Start date
You can open the throttle more than a little. half is OK
It is better if you use a remote crank switch so that you can jump the starter solenoid and not need to turn on the ignition.
Remove all plugs, and place them in cylinder order ( or bank order) so that you can inspect them and make notes on condition.
Do your compression test and write down the data. If you seem to have low compression, do the test again. If still low, squirt a little bit of 2 stroke oil in the cylinders and test again. A large change in compressions reading may be a sign of bad rings. I don't know for sure if the 175 is similar to the 150. On that engine, the two lower cylinders will normally have a tad lower compression.
Here is a link to a few starter switch
https://www.amazon.com/INNOVA-3630-...hy=59981&hvtargid=pla-4584345016115248&psc=1h options
It is better if you use a remote crank switch so that you can jump the starter solenoid and not need to turn on the ignition.
Remove all plugs, and place them in cylinder order ( or bank order) so that you can inspect them and make notes on condition.
Do your compression test and write down the data. If you seem to have low compression, do the test again. If still low, squirt a little bit of 2 stroke oil in the cylinders and test again. A large change in compressions reading may be a sign of bad rings. I don't know for sure if the 175 is similar to the 150. On that engine, the two lower cylinders will normally have a tad lower compression.
Here is a link to a few starter switch
https://www.amazon.com/INNOVA-3630-...hy=59981&hvtargid=pla-4584345016115248&psc=1h options
You're good - just open the throttle all the way (not in gear, of course). If you've recently run the engine on the hose, you are OK to do the compression without running the hose water. Otherwise, either run the engine on the hose or just hook up the hose to the flush fitting for 30 seconds. This isn't about heating up the engine - it will be just fine - it's more about making sure your impeller isn't bone dry.
hey thanks for the advice. Everything checked out with 130 pounds across all six cylinders. I got crazy and spent $81 for the quality mightyvac compression kit. My head gaskets are leaking, but it looks like I’m in good shape otherwise. Just wanted to triple check in case any of you had seen it go bad. Thanks again
Lightly leaking head cover gaskets are not serious. On the other hand, leaking actual head to block leaking gaskets can either be or become a serious concern