Had a low reading on my Mercury on #5 cylinder last night. It was 95. The others were around 120. Could this be a reed valve problem? When my manual comes in will it walk me through what I need to check?
dstuard,You could inject a little two stroke oil into that cylinder and re-run compression reading .If it increases momentarily,your low reading is either ring and or cylinder wall related.
I did squirt in some oil and it did not change the reading at all. Any ideas what to check now? I am sure my manual will say but you know it is hard to wait. Do you think it is possible rings are ok if the oil did not change it? I can tell you now I reaved it up too much trying to get it to run on three cylinders. It did backfire also one time when I first started it. So do broken reeds affect compression?
I have to disagree with OB (for a change).<br /><br />Though a bad reed will affect scavenging compression in the crankcase to the point of making the cylinder powerless, cylinder compression will not be noticably affected at testing speeds.<br /><br />On the other hand, debris from a broken reed can interfere with compression if it gets into ring grooves.<br /><br />A broken reed is easy to diagnose. You will get pulses of fuel/air mix out of that carb.<br /><br />Your problem could be related to head gasket leakage or a badly scored cylinder.<br /><br />Good luck.
You beat me to it JB. The reeds won't affect cylinder compression.<br /><br />A 2-stroke has two different kinds of compression. Primary and secondary. Primary compression is the cylinder compression (this case) and secondary is crankcase pressure. Crankcase pressure can be somewhat affected by reeds.<br /><br />Hopefully these compression readings are being done with a warm engine. Pulling the head will allow you to get a good look at the cylinder walls.
dstuard, I'd do a de-carb before I'd start taking things apart. I don't know your exact motor, but a lot of Mercs have integral heads that can't be removed.
I was just told that mine can't be removed. I guess I will do a decarb after I get the electrical problems figured out. Maybe I am just spinning my wheels. Anyone intersted in a pretty motor with power t&t? LOL
Just checked my compression again after letting her sit in a little oil last night. Compressed up to 120 and then started to back down again. Thought it might be my gauge so I tried it on all of them and it did the same thing. Shouldn't the gauge stay the same? Can I think positive that it pumped up to 120? Looks pretty clean inside the spark plug hole other than all the carbon. If I ever get the ignition system running I will do a decarb. Any ideas on what would make it have compression today but not yesterday? All I did was squirt some oil in and leave it over night.
If you dont mind my askin, what did ya come up with on the thing runnning out of fuel at wot.I have a 150 merc. doin the same trick with me.All new fuel stuff.Gettin check vaves this week.
Still not quite there yet. I am assuming I blotched up my fuel pump rebuild. If I ever ge the electrical stuff fixed I will take a stab at the fuel. Let me know what you find out also. You might fix my problem.
