johnsw
Well-known member
'04 Yam 150 carb 2 stroke
OK. Launched boat back in mid-June. Ran good for 2 short trips. 3rd trip, got into the bay on plane for just a few minutes and RPM suddenly dropped from 4500 to a labored 2200-2400 RPM. Limped back to the dock but in neutral RPM drops and engine stalls. Engine would start but not stay running without a little cold start lever assist. So called the marina mechanic to check it out. Would not idle for him. He noticed gas dripping from middle carb, so he overhauled them. Did not correct the issue. Diagnosed bad pulser coil. So he hauled me out and took boat to his shop inland (he services 2 marinas). Replaced the pulser coil and ran the boat several miles on the water back to my slip, no apparent issue. I went to use the boat about a week later. Boat started fine and idled OK. Left dock going though a long no wake area to the bay. Once on the bay, gave it the throttle and best it would do was low 2K rpm, and once again stalls at idle. Went back the next day to check a few things out, and issue was still happening. So long story short, same problem even though the boat was run after being serviced. So that's how this season started.
I checked fuel separator, and no water in the fuel. Checked resistances of the new pulser coil, and looks good at about 380 ohms each. Low and high speed coils reading correct resistances.
I wasn't able to get to the boat since then but mechanic went to check it out last week and didn't seem to have a problem with it. Couldn't get into the bay much because the wind was blowing pretty good, so sounded like he just did some full throttle starts in the no wake zone outside the marina. He was going to take a second look, but haven't heard anything yet.
So I'm open for ideas on what may be going on. Since the problem is apparently intermittent, looks like I need to diagnose this when it happens. If it takes a few days before the mechanic gets to it, he may or may not see the problem. I'm kind of leaning towards a fuel delivery issue, but that's just a SWAG based on very little. Carbs were rebuilt a few weeks ago and didn't resolve the problem originally. The fuel pumps were replaced 2 seasons ago and have less than 40 hours on them. Priming the fuel system with bulb, no smell of gas or visible signs of a leak and the bulb seems to be working OK feeling resistance as the lines and carbs fill with gas. Primer bulb was not collapsed when this was happening, so guessing not a clog between the primer bulb and the tank.
I'll be at the boat a few days next week and planning on taking my tools and diagnostic gear to try and narrow this down if I can make it happen again. Got a winky-blink harness on the way in case the computer is throwing any codes, got spark testers, extra fuel line and whatever else I think I may need. Got a spare CDI module from a misdiagnosis from way back, so I'll have that just in case it's ignition. But not really sure of what I'm looking for, so all ideas are welcome.
OK. Launched boat back in mid-June. Ran good for 2 short trips. 3rd trip, got into the bay on plane for just a few minutes and RPM suddenly dropped from 4500 to a labored 2200-2400 RPM. Limped back to the dock but in neutral RPM drops and engine stalls. Engine would start but not stay running without a little cold start lever assist. So called the marina mechanic to check it out. Would not idle for him. He noticed gas dripping from middle carb, so he overhauled them. Did not correct the issue. Diagnosed bad pulser coil. So he hauled me out and took boat to his shop inland (he services 2 marinas). Replaced the pulser coil and ran the boat several miles on the water back to my slip, no apparent issue. I went to use the boat about a week later. Boat started fine and idled OK. Left dock going though a long no wake area to the bay. Once on the bay, gave it the throttle and best it would do was low 2K rpm, and once again stalls at idle. Went back the next day to check a few things out, and issue was still happening. So long story short, same problem even though the boat was run after being serviced. So that's how this season started.
I checked fuel separator, and no water in the fuel. Checked resistances of the new pulser coil, and looks good at about 380 ohms each. Low and high speed coils reading correct resistances.
I wasn't able to get to the boat since then but mechanic went to check it out last week and didn't seem to have a problem with it. Couldn't get into the bay much because the wind was blowing pretty good, so sounded like he just did some full throttle starts in the no wake zone outside the marina. He was going to take a second look, but haven't heard anything yet.
So I'm open for ideas on what may be going on. Since the problem is apparently intermittent, looks like I need to diagnose this when it happens. If it takes a few days before the mechanic gets to it, he may or may not see the problem. I'm kind of leaning towards a fuel delivery issue, but that's just a SWAG based on very little. Carbs were rebuilt a few weeks ago and didn't resolve the problem originally. The fuel pumps were replaced 2 seasons ago and have less than 40 hours on them. Priming the fuel system with bulb, no smell of gas or visible signs of a leak and the bulb seems to be working OK feeling resistance as the lines and carbs fill with gas. Primer bulb was not collapsed when this was happening, so guessing not a clog between the primer bulb and the tank.
I'll be at the boat a few days next week and planning on taking my tools and diagnostic gear to try and narrow this down if I can make it happen again. Got a winky-blink harness on the way in case the computer is throwing any codes, got spark testers, extra fuel line and whatever else I think I may need. Got a spare CDI module from a misdiagnosis from way back, so I'll have that just in case it's ignition. But not really sure of what I'm looking for, so all ideas are welcome.
