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Post by fishnfool on Aug 19, 2021 20:31:55 GMT -5
Could it be Hydra Locking? I had the same problem on a smaller 40hp Yamaha on a boat I have. It would bog after about 30min of running. I would turn it off let it sit and it would run fine for another 30-45min then bog again. I chased it throwing parts at it. Turned out it was the fuel pump inside the VST. Replaced the pump, problem solved. I dont know what it is, it only happens IN GEAR below 1500 RPM. It is intermittent. I have since replaced the pressure sensor too. This is the same motor I just had the mid section replaced. I also had mechanic do a link and synch on both motors, VST and F filters replaced. I also just last week replaced the spark plugs. I thought maybe low pressure fuel pump but the problem doesn't go away when I pump the primer bulb and the front fuel filter stays full so I am pretty certain it's not the fuel pump. I ran the motor with the cowling off to eliminate a failing VST float. The mechanic yesterday looked at the TPS readings and all looked good, no codes either. The RPM range this is occurring in is all within the ISC regulating range below 1500 RPM which keeps me coming back to it. Above 1500 RPM the ISC is fully open and basically a redundant function. Also my motors really seemed to change after cleaning the ISC. I cant clean the inside though. Before cleaning the ISC valves both motors would stumble and stall after starting, sometimes taking multiple times to fire up and stay running. But after I cleaned both ISCs today they fired right up! I've learned lots about the various fricken sensors my motor because of all of this though! I ordered the nearly $400 ISC valve tonight, should get it next week and will report back.
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Post by finatic on Aug 19, 2021 20:43:13 GMT -5
Good luck
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Post by abouttime2fish on Aug 20, 2021 8:10:50 GMT -5
Totally different motor but……. My Yamaha 70 2 stroke would do a similar thing. Putt along fine then almost starve for fuel, catch snd keep going. I’ll call it a leak in the fuel system. But fuel was not leaking out, air was leaking in.
In my case it was an engine mounted fuel filter. The cup was fine, the part that bolts to engine was cracked. The only way I found it was to run it cowling off on the muffs. I noticed the fuel filter would get low on fuel, then fill up. Every so often fuel level got low enough it stumbled.
Grab a six pack snd watch it run for a while? Good luck.
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Post by fishnfool on Aug 20, 2021 8:38:58 GMT -5
Totally different motor but……. My Yamaha 70 2 stroke would do a similar thing. Putt along fine then almost starve for fuel, catch snd keep going. I’ll call it a leak in the fuel system. But fuel was not leaking out, air was leaking in. In my case it was an engine mounted fuel filter. The cup was fine, the part that bolts to engine was cracked. The only way I found it was to run it cowling off on the muffs. I noticed the fuel filter would get low on fuel, then fill up. Every so often fuel level got low enough it stumbled. Grab a six pack snd watch it run for a while? Good luck. I also considered a vacuum leak. I inspected my fuel lines as best I could and did not see anything. I seated my fuel filter cup when I replaced the front filter and thr water/fuel separator filters are replaced annually. I haven't totally ruled it out but it's so intermittent and it only happens in gear, not at idle or even if I advance thr throttle out of gear that I'd think if it were a vacuum leak it would be pretty consistent, but who knows??? Very frustrating...
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Post by abouttime2fish on Aug 20, 2021 15:19:33 GMT -5
Call this guy….. www.burlesonmarineinc.com/index.htmlWhen Yamaha has a question, they call him. He won’t touch anything but a Yamaha. When my normal shop scratches their head and shrugs, this is where I go. He’s always horribly backed up, but maybe he’ll give you a direction to go.
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Post by abouttime2fish on Aug 23, 2021 15:15:25 GMT -5
Any issues when you fuel boat? Could fuel vent be not venting or partially blocked?
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Post by fishnfool on Aug 23, 2021 17:09:24 GMT -5
Any issues when you fuel boat? Could fuel vent be not venting or partially blocked? No filling issues. I've sort of deduced that anything fuel related causing an issue i would expect to be shared between the motors too. This is strictly the starboard motor. I have racked my brain over this for several years, addressing everything that I can research as a potential cause. The ISC valve is due here this week, fingers crossed. Next stop, pulling my injectors this fall to ensure there is a gasket on every injector. Then maybe replacing fuel lines. As much as I enjoy solving a good mystery this is getting annoying!
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Post by finatic on Aug 23, 2021 17:15:11 GMT -5
Dam Chris, you're going to have more qualifications than a certified Yamaha technician after you put this one to bed.
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Post by fishnfool on Aug 25, 2021 17:56:11 GMT -5
Installed the new ISC valve today, took boat on a short ride and dare I say the motor didn't act up. It's done this before, going periods without acting up, so thr jury is still out. Fingers crossed.
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Post by gatorman on Aug 25, 2021 18:03:04 GMT -5
Man I hope it works for ya, fingers crossed!
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Post by outtadblue on Aug 26, 2021 9:21:59 GMT -5
Maybe this is it. Good luck
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Post by finatic on Aug 27, 2021 14:49:18 GMT -5
Man I hope it works for ya, fingers crossed! X2
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Post by fishnfool on Sept 2, 2021 9:20:24 GMT -5
Bad news, the hunt continues...
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Post by abouttime2fish on Sept 2, 2021 11:50:18 GMT -5
That stinks. Wish I had more ideas for you. Seriously, call Burleson Marine. 252-622-4656
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Post by finatic on Sept 2, 2021 13:13:09 GMT -5
Bad news, the hunt continues... Sorry to hear that.
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