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Old 06-14-2017
oldmako69 oldmako69 is offline
Senior Member
Join Date: Feb 2017
Posts: 210


Welcome to my world. I have a pair of 2005 F225's and have had a similar issue since day of purchase (August of last year). At first it only affected No 1. I changed and checked most of the same things that you did. All to no avail.

I checked every inch of the fuel delivery and filtration. Everything was spotless and showed zero contamination. No cracks in fuel lines ends, loose clamps etc.
I replaced the squeeze bulbs with new from Yamaha.
I swapped out the inline check valves from one side to the other.
I pulled and cleaned the VST. When I did, I found evidence of gasket compound on the VST lid (which is not to be used) AND small bends all around the base of the HI-PSI pump as though someone had attempted to pry it open. Now bear in mind that these engines only had 125 hours on them! So, clearly this engine had been a problem child all along.

Eventually, the engine would not start at all even though the VST was full and the spark was fine.

I figured that the Hi-PSI pump within the VST had failed due to it running dry so many times. I replaced BOTH the hi and low PSI pumps and the engine has behaved flawlessly ever since. Admittedly that is only about 35 hours or so, but I'LL TAKE IT!

Now, the same symptoms are present on Eng No 2.

I read a thread on a different board written by an ASE trained auto mechanic who had similar issues with both of his engines. He ended up replacing both engines Low PSI pumps to solve it. Now he hasn't been to Yam school, but he clearly ought to know more than I when it comes to troubleshooting a modern gasoline engine's fuel and electrical systems.

Here's the problem as I see it, I can remove the cowling on my engine and put a finger on the low psi pump to confirm its operation (10 on 20 off). I can also watch the first stage filter quantity ebb and flow in response to the low pressure pump, yet sometimes the engine will still fail with fuel in that first stage and the pump running. Its got fuel. IF I have someone on the boat who can drive, if I run back and squeeze the bulb firm again the instant it starts to shut down, then I can prevent it from stopping. Sometimes.

It also seems the worst when the engine is the hottest. If you run it for a bit, then shut it down the whole mess gets heat soaked. If you then start it up and try and idle for a bit, it will usually die right away. All this is very frustrating.

Best of luck to you.

Last edited by oldmako69; 06-14-2017 at 09:36 AM.
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