A buddy of mine has a 115 Hp Yamaha 4 stroke that runs like a scared dog for about 5 minutes, then it backs off real quick on it’s own (like he pulled back and forth on the throttle quickly). At first it happened so quickly, I thought it was an electrical issue or a protection feature like low oil or high temp. There were no alarms and the oil level was fine. Once he backed off the throttle for a minute, we could get back at full speed for a minute or two but the problem came back. The motor runs fine between 800 and 3500 rpm without this issue occurring. To see if it was a fuel starvation problem, I sat in the back and pumped the primer bulb at full throttle and the boat ran fine without issue.
Couple of things I considered:
1)obstruction in the gas tank pickup line ( ruling out fuel line/filter since we just replaced the fuel supply line and water separator to include a check of the fuel tank connection w/ anti siphoning feature was clear)
2) check valve in primer bulb is sticking shut - (we just replaced the bulb, but have not tested the motor since)
3) low pressure fuel pump is going bad
4) getting in dangerous territory here…Vapor Separation Tank (VST) issue??? High pressure pump issue??? injector issue???
Could this be a VST issue/High Pressure Pump issue/Injector issue since it is intermittent? Any help will do and thanks in advance.
Update:
We just took the boat out after replacing the primer bulb and we have narrowed the problem to the motor. The motor began to perform its “song and dance” at the exact location from the dock as it did yesterday. This leads me to believe that the problem is either the low pressure fuel pump, the VST, HP pump, or injectors. I have confirmed that it is a fuel starvation problem at this point because the problem completely goes away when I continuously prime the engine with the gas bulb while at full throttle. Below 4000 RPM, the problem does not exist at all (we can cruise all day). Above 4000 RPM, the problem starts to occur.
Couple of questions that someone may be able to answer:
How does the VST (Vapor Separation Tank) work?
How does the High Pressure Fuel pump work?
If this was an injector/VST/HP pump problem, would the problem go away when I use the primer bulb?
Thanks in advance for any help.
“Highfly” the war horse of Major General James Ewell Brown (JEB) Stuart
very unlikely its an injector issue
its a restriction in the system somewhere between the injector and the tank
you pump the primerbulb and “force” pass the restriction
its not a complete blockage since it runs fine at lower fuel volume
by restriction i dont mean it has to be an actual blockage. the system could have a weak pump etc…
Thanks Chris…I am leaning towards the VST filter or the low pressure fuel pump. We have replaced everything up to the motor and I feel comfortable that it is not the fuel tank pickup…he doesn’t have a anti-siphoning valve, it is actually a fuel nozzle with a built in valve. I haven’t tackled the high pressure fuel system before, so I am interested in the difficulty level. We will keep you posted!
“Highfly” the war horse of Major General James Ewell Brown (JEB) Stuart
I had a similar issue with my F225 and the problem was debris in the VST filter and one of the fuel pumps had to be replaced (not sure if water or debris or age was the demise of the fuel pump). It took several trials of diagnosing and if the 150 is anything like the 225 that little filter is behind a lot, so i had a mechanic do it for me at that point. The fuel pump was expensive. Also replaced all the fuel and shocked with Ring Free Plus after that runs like a champ ever since. From my understanding it is very unlikely to be fuel injector issue, so be hesitant if someone tells you that route.
had almost the same problem, found trash in the inline filter coming from trash in the tank. pulled the filter out of the line an it now running like a champ
JIYC tiger and justretired, thanks for the response. My buddy is starting with putting on a new fuel filter (the one on the motor) and a low pressure fuel pump. If this does not fix the problem, we will be taking about the fuel system to get to the VST filter. We will keep you posted…heck maybe even a pic or two if we get to it.
“Highfly” the war horse of Major General James Ewell Brown (JEB) Stuart
We just retired our 2008 115 with 6,200 hours. Around 3000 hours it started the same thing and we changed the high speed filter and never had another problem with it until the adapter plate corroded to the point that water started getting into the oil(which could have been avoided by changing the cylinder head zincs). Definitely sounds like the high speed filter to me though.
Still learning about these motors…which filter is the high speed filter = VST filter? Please let me know if it is. Thanks!
quote:Originally posted by baseballfireh
We just retired our 2008 115 with 6,200 hours. Around 3000 hours it started the same thing and we changed the high speed filter and never had another problem with it until the adapter plate corroded to the point that water started getting into the oil(which could have been avoided by changing the cylinder head zincs). Definitely sounds like the high speed filter to me though.
“Highfly” the war horse of Major General James Ewell Brown (JEB) Stuart
If anybody is curious, we replaced the low pressure fuel pump and the motor mounted fuel filter…problem fixed. Thanks for all the responses! If we should have done anything differently, we should have replaced the filter…ran it…if the problem persisted then replace the low pressure fuel pump.
“Highfly” the war horse of Major General James Ewell Brown (JEB) Stuart