Tweet
Im experiencing loss of power, and think motor is only coming up to about half normal rpm. No lights or alarm sounding to indicate trouble with oil system or overheating...timing is good, good spark to all cylinders, fuel delivery through all 3 carbs good. I wonder if whatever mechanism Yamaha uses to cut rpm down on overheat or low oil level is failing? Any Ideas?
-
-
Kenai,
You can test the overheat alarm by unplugging the two wires that lead to the thermoswitch and shorting them together with the ignition on.
If you do not get an overheat alarm by doing this, then the alarm and/or wiring is bad and your motor could well be going into rpm reduction.
If you do get an alarm, then I would do a compression test on the cylinders - bad compression can cause the motor to not get up to full power.
Good luck,
Ken K -
Didn't get any alarm while shorting the wires leading to the thermoswitch, but did get a noticable increase in rpm at idle when I took the wires to ground. Tested the thermoswitch, and it went from no contunuity to a closed circuit when it was subjected to heat, so I know it is in good order. From following the wiring from the thermoswitch, it appears to go into the CDI unit, so is the reduction possibly caused by the CDI?
Something I didn't mention in my original posting was that compression on all 3 cylinders is 120-125#, all the carbs have been dismantled and cleaned, reed valves inspected...Comment
-
Kenai,
The thermo switch is designed to close at around 185 degrees - I have personally experienced one on my 2000 C115 close at 130, giving me a false overheat signal to the CDI unit. The CDI then does its job, and that is to sound the alarm and cut back on the spark, i.e. "rpm" reduction. When this happens, you will know it - the motor will shudder and shake and the CDI will reduce the rpm to around 1200 (on my C115). The motor will continue to s-and-s until you throttle back to neutral - then it will idle fairly smoothly.
You should have gotten an alarm when you shorted the two wires together (motor does not need to be running, just ignition on - also, I would not advise shorting either of the wires to ground). The CDI could be bad and not sending an alarm signal to the alarm, or the alarm/wiring could be bad.
Are you able to get up to high rpm, and then are losing power and rpm reduces. Or just can't get up to higher rpms? Maybe a bad fuel pump - can't deliver enough fuel at higher rpm.
Ken KComment
-
Fuel pump is good, priming bulb remains firm. I've tested this thing under load, but it won't come up to speed, and the discription Ken discribes is right on. First time this failed, I had been up to full throttle for aprox. 4 miles. Finally made it back to the launch, took it home and checked everything out...good spark, timing correct, all carb bowls full. Put it back in the river and ran good for rest of that day. Next day traveled about six miles before failure mode again, and have not had it run right since. Checked the enrichment manual switch, and note its in the normal position. If it was the emergency speed reduction function doing this, wouldn't the timing be retarded to cause the rpm reduction?...because I took the timing light with me last time and had perfect timing while motor was still underperforming. (by underperforming, I mean just barely able to get up on step)Comment
-
Kenai,
Sure starting to sound like bad ignition to me - either a bad CDI or the timing advance mechanism - I'm not familiar with the spark advance on that model - recommend you get a Yamaha shop manual and check the area of spark advance.
Now that the motor is showing its symptom all the time - have you checked spark again to all cylinders? Maybe a bad coil or spark plug wires. These are a lot less expensive than a CDI. I would check these out before I replaced the CDI.
Good luck,
Ken KComment
Comment