Ongoing Saga: Yamaha 150 TXRC & 1600 Rpm

[Psalm 99]

The problem: engine will be running great and then almost instantly cut down to 1600 rpm. I might be going anywhere between about 1900 to 3400 rpm when this happens. When this happens, engine responds nicely to throttle below 1600 rpm but no response if I try to go faster. Leaving the throttle set higher (say about 2700 rpm), engine may go for an hour @ 1,600 then almost instantaneously rev up to the throttle setting where it may stay for just a few seconds of even run great & maintain the throttle setting all the way back to the dock (about 1/2 hr). This has been a periodic problem since I bought the boat used about 3.5 years ago. I first disassembled and fully cleaned the carbs (no change), then replaced all the fuel lines, primer bulb, and filters (no change), replaced the fuel pumps (ditto). Disassembled all ground wires and cleaned (no change). Got what looked like a bad reading from the crank position sensor (CPS) which I replaced but problem persists. As per manual, checked output to coils from CDI unit (good), peak voltage and resistance from stator (good) and peak voltage and resistance from Pulser coil (good). No warming buzzer at helm with this occurs but I verified the correct operation of (1) all thermostats & temp. sensors, (2) battery charging, (3) oil level sensor. Got a Winky-blink which showed a periodic #13 code (problem with the Pulser Coil). Otherwise, Winky-blink indicated no other problems. Replaced pulser coil. Checked ignition timing, throttle settings & operation (fine). Went out today and engine ran great for about 8 minutes @ 3200 rpm then collapsed back to 1600 rpm again. Pretty much fed up. 1600 rpm is a decent *****ing speed so I left the throttle set higher and simply *****ed for about 2 hrs. Caught 3 small tuna and headed home. About 1/2 way home, engine sprang back to life and ran flawlessly at about 3200 rpm the remaining 10 minutes to the harbor. Sorry to carry on but its been a long road. About the only thing I can think that I haven't tried is disassembling all the wiring connections at the helm and cleaning. Boat is a HydraSport Lightning and the wiring job by the factory is about the best I've seen. Not sure if any bad connection at the helm could cause this problem but I did have my auto choke stop working which was simply a back electrical connection under the helm. Transom wiring connections including battery posts are all clean. One sort of strange thing: When this problem happens and I take the engine out of gear, engine responds accurately to throttle right past the 1600 rpm threshold. Placed back in gear, engine rpm can't go over 1,600 rpm. I appreciate you guys bearing with me on this.

[99yam40]

have you checked spark and timing when the RPM is limited?
what about the inputs and out puts of the CDI?
every one would expect it all to test well when the RPM is not limited, they need to be tested when problem shows up

have you checked to make sure you alarm sounds when over heat or low oil happens ?
how about the gauges ?
Do they indicate properly when over heat or low oil happens?

[JerEazy2]

Wish I had something wonderful to add - but the tests you’ve run have been while (assumidly) the problem wasn’t happening. You’ll need to run similar if not the same while the problem is happening. Something is either losing connection, or the engine is is dropping into a sort of slow mode (but I think that limits you to 2500 rpm).

[rodbolt17]

does the audible alarm actually work??????
it is easily tested and actually requires little effort on the operator.
do you realize you have no auto choke?
this issue,as it repeats, is easily tested.
the sequence is
suck
squeeze
bang
blow.

[Psalm 99]

Thanks guys. All testing has been on muffs at home. Finding out that the problem only occurs when the engine is in gear showed that testing on muffs with the engine out of gear is worthless. While on muffs and out of gear, CDI inputs and outputs exceed specs per manual. I use 'auto choke' to simply mean pressing the ignition key in while first starting the engine. I'd replaced the starter switch assembly and had a bad wiring connection that didn't allow the solenoid at the engine to work. I haven't checked the audible alarm but did check per manual the items which I think cause it to function: engine temp, oil delivery, electrical charge. The alarm buzzer is new as it was part of the ignition switch assembly which I recently replaced (bug got in and shorted switch which caused engine to start). I'm a little hesitant to ask but what is 'suck, squeeze, bang, & blow' as it relates to the engine??

[rodbolt17]

suck is intake of air/fuel in the correct ratio.
squeeze is when the above is compressed.
bang is the moment of ign.
blow is when the ex gas exits and a new suck is about to start.
every other doohickey simply makes it more efficient.
we know compression is good because it sometimes works.
we don't know if the bang part is working all the time.
we don't know the suck portion of the fuel is working. we know it can blow cause it occasionally works.
to test the alarm simply pull the stop lanyard and crank it, if the audible sounds it works. if it does not either the emergency stop is bad or the ECU has an issue.

[Psalm 99]

Audible works fine. Wish everything about this engine was that easy. Because the problem has the performance of a loose wire, I spent the morning going over the wiring connections and spraying with CRC. Everything appeared real clean except the spark plugs. All caps were coated with a layer of gray paste. I'm assuming this is simply dielectric grease but I still cleaned it all off and used a 0.24" dia diamond abrasive bit to rough up the inside. As my problem only occurs when the engine is in gear and responds nicely to the throttle when out of gear, I'm not sure why a bad spark plug connection(s) would behave like this.

[rodbolt17]

because with no load you can disconnect 4 spark plugs and still rev it past 4000 RPM. that is why testing an issue that only occurs under a load on a flusher is a teat on a boar hog.
this aint a 69 chebby 350.

[Psalm 99]

Interesting thought on the partial blockage at the fuel pick-up. I've never removed the sov at the tank and looked at the intake riser. I did try priming the engine while it was in the 1600 rpm mode and the priming bulb acted like there might be air in it (wouldn't get hard, like compressing a balloon). I'll see if I can get to the riser this morning. Very much regret not completely draining the fuel tank and flushing it when I first got the boat. Seems like a no-brainer now. I go a little heavy on the Ring-tight and figured this would dissolve and tank residue.

[99yam40]

what is Ring-tight?

If fuel line is restricted the bulb would collapse.
might be sucking air somewhere tho

[Psalm 99]

Make that 'Ring-free'. Tried to remove the fuel intake riser. Boat is a 2004 Hydra Sport Lighting. Riser terminates in a 90 deg w/ ball valve. Ball valve seems to be integral with the riser (doesn't unscrew at top of riser block. Looked for a anti-siphon fitting but doesn't appear to have one. I'd like to remove the riser but it's really stuck in place & I'm leery about putting too much strain on the fiberglass tank. As an alternative, I can open the fueling port as a vent and give the riser a shot of 100 psi air thru the fuel outlet tubing; but, if the riser is getting gummed up while underway, this won't solve the problem. I can run the boat on an auxiliary tank to see if the 1600 rpm problem is due to a fuel blockage but the weather is not good and that riser is the only part of the fuel system which I haven't looked at or replaced. Any ideas for getting it out will be appreciated.

[pstephens46]

You mentioned fiberglass tank? Fiberglass fuel tank?

[Psalm 99]

I'm just assuming the boat's installed 80 gal fuel tank is fiberglass. It's definitely some type of structural plastic. This is a small farm here and every since seeing the positive result of Ring-free on my outboard carbs, I use it along with ethanol-free gas in all my farm equipment. it also did wonders on cleaning out my tractor's diesel injectors.

[pstephens46]

I'm just assuming the boat's installed 80 gal fuel tank is fiberglass. It's definitely some type of structural plastic. This is a small farm here and every since seeing the positive result of Ring-free on my outboard carbs, I use it along with ethanol-free gas in all my farm equipment. it also did wonders on cleaning out my tractor's diesel injectors.

Could be fiberglass. Wasn't aware Hydra Sport used fiberglass. Some used fiberglass years ago. Would expect plastic or aluminum. Read somewhere fiberglass does not like ethanol gas blends over a period of time. No idea if true or not

[99yam40]

I never heard of anyone putting Ring free in diesel tanks before