SiLiconD17
Seaman Apprentice
- Joined
- Jun 21, 2007
- Messages
- 44
I have a 1989 Yamaha 40hp 3 cylinder that came on a boat I purchased just recently. I went through rebuilding the carburetors, replacing the fuel filter, replacing plugs, etc. For some reason, it just doesn't want to idle.
As far as troubleshooting goes, I've made a few rounds. The bottom plug is cleaner than the top 2, but it seems to be making spark. I tested each cylinder for spark by disconnecting the other 2 plugs, leaving only 1 plug, and the motor would fire just fine and run on each cylinder just fine, even the bottom one with the cleaner plug. I also did a compression test and all 3 cylinders are on-spot. Basically what it does, is that it will crank and idle just fine, but just about every 20 seconds, it will all of a sudden want to die out (if it is running low enough RPM it will die out). If you bump the throttle up enough it will run, die down, then go back to normal and repeat the process over and over again. When it's on the higher RPM range, it seems to be fine; no hesitation or anything.
My guess is that it has something to do with the timing. Each cylinder has compression, spark, and fuel; and each cylinder is capable of running the motor on its own. The only thing I can guess is that the timing box is bad, and every 20 seconds it doesn't spark right or something, then it will go back to normal. The reason it runs fine at higher RPMs is because when it is almost near WOT, the spark is almost constant, so there wouldn't be a problem there. Does anyone else have any ideas? If it's timing, do I need to adjust that or do I need to replace some parts? Thanks in advance for your help!
I'm ready to unbolt this POS and put on a Johnson/Evinrude... (I'm an OMC guy at heart, don't hate me please)
As far as troubleshooting goes, I've made a few rounds. The bottom plug is cleaner than the top 2, but it seems to be making spark. I tested each cylinder for spark by disconnecting the other 2 plugs, leaving only 1 plug, and the motor would fire just fine and run on each cylinder just fine, even the bottom one with the cleaner plug. I also did a compression test and all 3 cylinders are on-spot. Basically what it does, is that it will crank and idle just fine, but just about every 20 seconds, it will all of a sudden want to die out (if it is running low enough RPM it will die out). If you bump the throttle up enough it will run, die down, then go back to normal and repeat the process over and over again. When it's on the higher RPM range, it seems to be fine; no hesitation or anything.
My guess is that it has something to do with the timing. Each cylinder has compression, spark, and fuel; and each cylinder is capable of running the motor on its own. The only thing I can guess is that the timing box is bad, and every 20 seconds it doesn't spark right or something, then it will go back to normal. The reason it runs fine at higher RPMs is because when it is almost near WOT, the spark is almost constant, so there wouldn't be a problem there. Does anyone else have any ideas? If it's timing, do I need to adjust that or do I need to replace some parts? Thanks in advance for your help!
I'm ready to unbolt this POS and put on a Johnson/Evinrude... (I'm an OMC guy at heart, don't hate me please)