Yamaha 150 Power Loss Solved! - Saltwater Fishing Discussion Board Including Inshore Fishing, Offshore Fishing, Saltwater Fly Fishing and Kayak Fishing
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Old 07-04-2007, 10:10 AM   #1 (permalink)
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Default Yamaha 150 Power Loss Solved!

This is sort of a heads up to other Yamaha owners so they don't go through the troubles we did to solve a power loss issue.

We have a 2006 Parker 2520 with twin 150 Yamaha 4 strokes. They each have 450 hours on them and until recently ran flawless. Two weeks ago coming home from Clemente I noticed one engine was about 400 rpm's off sync with the other. I didn't think much of it since it did not effect performance, I could also bump the throttle up to put them in sync.

The following weekend we were headed back to Clemente and when I started up at the dock I noticed the out of sync motor had a slight vibration but nothing serious. Once underway things seemed fine. As we came close to the island we noticed the motors were about 800 rpm out of sync and we were feeling a definite vibration.

We shut down and anhored up for the night. The next morning we started up and the bad engine was idling rough and definately had a problem. We tried to see if it would run and we could not even get the boat to plane. Max rpm's for the bad motor was 3000, not good.

First solution was to change the plugs. When changing them out we noticed they were very light colored meaning we were running lean. New plugs made no difference. Next was f/w seperators, changed them out and no difference. We checked the main fuel filter and it looked fine. We pulled out the injectors and cleaned them the best we could, no luck. We did all we could out there and had no luck.

I kept thinking about BiteSomething's recent posts on power loss issues and all the headaches in solving the problem and it had me worried we were in for some frustration.

We still fished the island and there is a ton of YT over there on the frontside, fun fishing.

For the trip home we had to limp so I figured we might as well troll so I put the jigs out as we left the island back to Newport. 2 MILES off Pyramid we had a jig strike and I figured it was a bonito, nope Albacore! Way cool.

Anyway, back at home we did some research and spoke to Maurer Marine Yamaha dealer and decided it was the VST filter. We took that all apart (very fun) and cleaned the filter out. Put it all back together and no difference, arrgh! We tried bypassing all the filters and run the motor directly from a gas can and same problem.

Finally we decided to swap the injectors from the good engine just to check. Fired up and it was perfect! BAD INJECTORS, or at least one bad injector.

We took them to the yamaha dealer and had them cleaned out. Figured that was better to try than buying 4 new injectors at $160 each. Put in the clean injectors and we are all fixed! Both engines running perfectly.

So if any Yamaha owners have these symptoms, try the injectors before tearing into everything else.

I was told there has been some bad fuel at the docks which could cause this. Coincidentally, the Newport Shell fuel dock we used to use is now shut down for "quality control violations" from what I was told. Hmmmm....

Also, if the Parker owner who loaned us some tools at CLemente is reading this, Thanks Again!
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Old 07-04-2007, 12:09 PM   #2 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Informative post, thank you I will keep this in mind. I have the same power on my Parker. 300 hours so far so good. I run only Chevron.
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Old 07-05-2007, 12:41 PM   #3 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Great to see someone share what they learned.
Whether fishing, boat, motor, trailer, well it makes no diff.
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Old 07-08-2007, 08:36 AM   #4 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Thanks for posting how you solved your problem.

I'm sure there will be someone out there that WILL have a similar

problem and this post will help them out!!
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Old 07-08-2007, 10:06 AM   #5 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Great info. Here are some more tasty tid-bits. This may sound like confusing/incoherent ramblings to some, an over simplification of the issues to others, but if it helps at least one person, I guess it?s worth it. Here goes: A clogged VST filter was a very good first guess. However, if an engine is running rough, a few simple tricks could have saved you some time. One of the first tricks is to see if the engine is running on all cylinders: pull one spark plug wire off at a time (alternatively on fuel injected engines you can unplug the wires going to the fuel injectors). If the engine runs rougher without that spark plug wire connected - that cylinder is OK. If there is no change in RPM's when you remove a spark plug wire, then that cylinder isn't firing and something is wrong. If only one or two cylinders aren't firing, then you can rule out systems that are common to all the cylinders (like fuel pressure, computer sensors, etc.) The question now becomes "is the problem spark or fuel or compression"? It's easy to check for spark with a spark checker (mine can check up to four cylinders at a time). If you have spark, it's time to check the fuel side. In your case it was the fuel (injector(s)), but in my experience (mostly with Honda's) when the engine is running rough all the time, and one or two cylinders aren?t firing, it?s a bad spark plug or two. Of course, it could be other things but you get the picture on how to go about a systematic diagnosis. If all cylinders behave the same on the "drop test" (as we call it) above, then it's probably the fuel system, though in some rare cases it's a computer sensor or something else. Best bet is check fuel pressure next. All four stroke motors have a port where you can hookup a fuel pressure gauge downstream of the electric high pressure fuel pump. Had this been done in your case, you would have seen that the pressure was normal and immediately started looking elsewhere for the problem (i.e, NOT the VST filter). If the fuel pressure is low, then the question is why? It could be the VST filter, could be the high pressure fuel pump, the low pressure fuel pump, the hi or low pressure fuel filters, a fuel check valve (only on Yamaha's), the fuel water separator, the anti-siphon valve, the fuel tank pickup tube, etc. Running the engine on a separate tank, hooking it up at various locations on the fuel system can help eliminate (or pinpoint) some possible problem areas. Based on my experience, the following info may be helpful in pinpointing exactly where in the fuel system the problem lies. This info does NOT the gospel, but more often than not, it will lead you to the problem quicker than random guessing. If nothing else, it's a method for trying to make sense of the madness: 1. Engine surging, fluctuating RPM's, or sudden drops in RPM at higher throttle settings tend to be RESTRICTIONS in the fuel line UPSTREAM of the fuel vapor separator. What's happening is that the fuel vapor separator is running out of gas, when that happens, the high pressure pump (which is sucking gas OUT OF the fuel vapor separator) can?t get fuel and the fuel pressure drops quickly, albeit only for a fraction of a second. Since the low pressure pump is still pumping gas INTO the fuel vapor separator, as soon as a little more gas into the fuel vapor separator, the high pressure pump again has something to pump and can get the pressure up to where it should be ? until the separator runs out of gas again. 2. Steady low power, constant rough running, or engine runs great but won?t reach normal max WOT RPM, tends to be caused by a restriction in fuel system DOWNSTREAM of the fuel vapor separator. Typically this is due to, presented roughly in order of the likelihood of the failure: a clogged high pressure filter (vst screen on a Yamaha, vst screen and/or high pressure fuel filter on a Honda), a failing high pressure fuel pump, clogged screens on the fuel injectors, or a faulty fuel rail pressure regulator valve. What's happening here is that fuel pressure is steady because the fuel vapor separator is not running out of fuel, however the pressure is low because the engine is taking more fuel out of the system than the high pressure pump can replenish once the engine reaches a certain RPM. Unfortunately, these problems can be time consuming to diagnose in real life. A consistent, systematic approach in diagnosing the problem is extremely helpful ? more so than a ?shotgun? or ?start replacing parts? approach. I apologize for the long rambling post, but again, hopefully this info is helpful to someone.

This post edited by HondaDude 10:11 AM 07/08/2007
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Old 07-08-2007, 04:15 PM   #6 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Thanks for the info, I have the same boat, 250hrs and so far so good, but you never know, glad you made it back ok !
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Old 07-10-2007, 12:45 PM   #7 (permalink)
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Default re: Yamaha 150 Power Loss Solved!

Thanks for the heads up. I have the same motor on my 06 Parker with over 500 hours and will keep that in mind.
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Old 05-15-2016, 08:19 AM   #8 (permalink)
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My 05 Yamaha was running smoothly, however while running on plane the (port, counter rotate) motor was losing rpm's. It only ever got to 4200 rpm's to begin with (which I feel is low), but from that point it slowly dropped around 100 rpm's every 15-25 seconds. My thought is fuel filters but reading some of the above post, I'm now thinking I'll should check the VST as well. Any thoughts?
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