I own a 1998 C115 Yamaha 2 Stroke. I seemed to have solved one issue while uncovering another. Suspecting the motor was starving from fuel supply as my primer began to flatten, it was suggested by Boscoe to eliminate the built in tank by using a portable one. I made the new connection to a portable tank yesterday and the motor started immediately. Focusing on my primer bulb - within a few seconds - I heard what sounded like the motor was not dead center in the "neutral" position as I heard more of a "rattle" like the neutral gear was not quite engaged than a distinct engine knock. The sound seemed to have disappeared at times and reappeared. I disconnected the control cable @ the motor thinking I might have slightly misadjusted the gear shift cable when I recently decided to replace the ignition switch in my 703 control box. While still on my lift - but with the lower unit submerged to verify the pump was working with a strong water stream - I shifted the motor by hand quickly from neutral to forward; then neutral to reverse and still heard the "rattle" or knock. Concerned I'd cause more damage, I shut the motor down and decided to remove the spark plugs and check for compression. With the motor not quite warm, but recently started and running for a few seconds prior, I pulled my kill switch lanyard at the remote and removed all of the plugs to test each cylinder. I'm a weekend warrior repair guy in that I have an inexpensive Harbor Freight Compression tester. The tester has a few adapter fittings in its plastic suitcase none of which fit the cylinder head threads. I noticed without any of the adapters I could screw it directly into the cylinder, I attached the gauge to it to run my compression test. I noticed my battery was getting weak as I turned the key to crank the motor. While cranking the engine slowly about 10 times per cylinder, I got a consistent reading of 60 psi per cylinder which was alarming. The plus was that it was consistent; the minus was that if true, I'll need a powerhead rebuild. Discouraged, I decided to abandon everything and place the battery on charge for the evening.
I charged the battery overnight and plan to compression test the motor one more time this morning hoping the crank speed didn't give the engine the opportunity to develop cylinder pressure high enough to give me a true reading. Maybe it's wishful thinking. I'm a believer in good diagnostic tools, but purchased this inexpensive one to give me an indication of the powerhead's condition. Could it be that off in it's ability to give me a true reading? Anybody out there experience something similar to what I described and have any ideas as to what's going on?
I charged the battery overnight and plan to compression test the motor one more time this morning hoping the crank speed didn't give the engine the opportunity to develop cylinder pressure high enough to give me a true reading. Maybe it's wishful thinking. I'm a believer in good diagnostic tools, but purchased this inexpensive one to give me an indication of the powerhead's condition. Could it be that off in it's ability to give me a true reading? Anybody out there experience something similar to what I described and have any ideas as to what's going on?