Hey guys, I bought a boat a while back with a 1989 Yamaha 40hp 2 stroke, 3 cylinder that I've been raking my brains over trying to get it running right. Initially it had sat up for a couple years, so I went through the carburetors with a new rebuild kit (about 4 times now), replaced the fuel filters and cleared out the lines, pulled and capped the oil injection system (I'm running premix now), changed the plugs, and pulled the powerhead and replaced the lower crack seals and the gasket between the powerhead and middle shaft.
It will basically run like a charm for the first 15-20 seconds when you first crank it, but right after 15-20 seconds, it will begin to spit and sputter and die out. I bumped up the timing enough so that it will run like this, but you can tell it's only on 2 cylinders of the 3. I have narrowed the problem down to the bottom cylinder because you can pull that plug while it's running and it makes no difference to its tone. When you pull the middle or top plug, the motor will die. The bottom plug also looks a little cleaner to where it doesn't seem to be burning right. You can see the bottom cylinder is getting spark, so it shouldn't be the coil. I pulled the CDI Mitsubishi timing box module thing and went through the wires to make sure all the connections were good and it all checked out.
I ran it on the water a week ago, and it did the same thing. When you first crank it, it will run like a dream until about 15 or 20 seconds and it will start to die out (it starts running on 2 cyl). I also noticed that if you do a hole shot and floor it, it will kick up and throw you out of your seat (definitely on all 3 cylinders), but after about 3 seconds it will die back down. It seems that at certain points or situations it sends correct spark to the bottom cylinder, but other times it doesn't to where the bottom cylinder isn't firing right or making power. When you open up wide open, it will go but it spits and sputters and doesn't move very quickly, so it definitely is running on the top 2 cylinders only.
I just wanted to check with you guys and get your opinion. My last resort is to replace the CDI unit since I figure it isn't sending correct spark to the bottom cylinder, therefore causing all the problems I mention. It doesn't seem to have any damage or corrosion or anything (the entire motor actually looks like new under the cover). So, should I spend $400 on that darned CDI box, or is there anything else I can try? Also, does anyone know of a cheaper solution; can I send the CDI box to some place for repair at a lower cost? Thanks in advance!
Edit: I forgot to mention, but the compression in all 3 cylinders is spot on and I did a leak down test and it is almost literally perfect. It doesn't seem to knock or make noises, so it shouldn't be anything internal.
It will basically run like a charm for the first 15-20 seconds when you first crank it, but right after 15-20 seconds, it will begin to spit and sputter and die out. I bumped up the timing enough so that it will run like this, but you can tell it's only on 2 cylinders of the 3. I have narrowed the problem down to the bottom cylinder because you can pull that plug while it's running and it makes no difference to its tone. When you pull the middle or top plug, the motor will die. The bottom plug also looks a little cleaner to where it doesn't seem to be burning right. You can see the bottom cylinder is getting spark, so it shouldn't be the coil. I pulled the CDI Mitsubishi timing box module thing and went through the wires to make sure all the connections were good and it all checked out.
I ran it on the water a week ago, and it did the same thing. When you first crank it, it will run like a dream until about 15 or 20 seconds and it will start to die out (it starts running on 2 cyl). I also noticed that if you do a hole shot and floor it, it will kick up and throw you out of your seat (definitely on all 3 cylinders), but after about 3 seconds it will die back down. It seems that at certain points or situations it sends correct spark to the bottom cylinder, but other times it doesn't to where the bottom cylinder isn't firing right or making power. When you open up wide open, it will go but it spits and sputters and doesn't move very quickly, so it definitely is running on the top 2 cylinders only.
I just wanted to check with you guys and get your opinion. My last resort is to replace the CDI unit since I figure it isn't sending correct spark to the bottom cylinder, therefore causing all the problems I mention. It doesn't seem to have any damage or corrosion or anything (the entire motor actually looks like new under the cover). So, should I spend $400 on that darned CDI box, or is there anything else I can try? Also, does anyone know of a cheaper solution; can I send the CDI box to some place for repair at a lower cost? Thanks in advance!
Edit: I forgot to mention, but the compression in all 3 cylinders is spot on and I did a leak down test and it is almost literally perfect. It doesn't seem to knock or make noises, so it shouldn't be anything internal.