high rpm motor fail

[mjfogarty]

Own a OXY 66 Salt water Series II two stroke 150 hp two stroke with 800 hours. Has been serviced regularly and always treated to a generous fresh water flush after my son and I return from offshore or the river system here in the Martin County, FL area. Last week the motor shut down while we were running at 2700 - 3000 rpms. I mean shut down like turning off a light switch. After some head scratching, we turned the key, motor started up, no problem. Another 10 minute run down Indian River and it happened again. After restarting, we returned home but kept the boat at wake speed, maybe 900 to 1200 rpms. No shut downs at this low rpm. Our mechanic says its probably faulty fuel lines due to ethanol fuel use in the past. We have used non-ethanol fuel in this motor for the last three years and when we did use ethanol fuel, we always added a labeled protective additive. Fuel in the water separator is residue free as is the VST. Could it be that the fuel lines have debilitated to the point where they collapse under load and cause the motor to shut down? If this is the case, it seems motor would lose rpms first before just turning off like room light. I think it's an electrical issue. Help!!

[99yam40]

Hard to look up a motor without a model #, so is this a fuel injected motor?

if so when the VST gets low on fuel the pump does not pump fuel so the rail pressure drops and motor dies

could be other things that keep the VST level from keeping up to the motors use at higher RPM

[TownsendsFJR1300]

I've had the innerds of my fuel line (between the transom water /fuel separator) and the under cowl filter literally turn to mush and get stopped up in the Yammy filter.

Just happened to be doing maintenance and noticed it. It pulled out like mushy spaghetti... (It was Mercury Marine grade line too).

The lines are easy enough to check, check the primer bulb for any goo inside it as well..


Had the innerds break down, it would tend to clog and hamper flow, especially at higher RPMs / higher fuel flow...

[walleye1]

Any mercury fuel line that has the red lettering get rid of it.

[TownsendsFJR1300]

Any mercury fuel line that has the red lettering get rid of it.

I don't remember, (think it was white lettering), but it WAS Marine grade.

I believe when it was installed when re-powered in early 2007, the shop put it on.

Guessing it lasted 5 years, WITH Non-Ethonol fuel.

Just that short section. Still have the original tank to transom filter line (21 years old).

[mjfogarty]

Forgot to mention in the original post - the motor is fuel injected and the model # sx 150txra.

[mjfogarty]

To add to the high rpm motor shut-down issue. No, I haven't checked the primer bulb for goo. No "goo" in base of VST, water separator nor on filter that sits under the electric fuel pump when checked for fuel clogging mid way thru this issue. Problem continued on subsequent high-rpm trials. Seems to me that if the problem is related to poor fuel delivery due to degrading lines the motor would stutter somewhat before shutting down like turning off a light. 99yam40 stated "other things" can cause a low amount of fuel in the VST. Is there a sensor that reads this low fuel level and immediately kills the motor?

[pstephens46]

Sure sounds electric if dies “like a light switch being turned off”. No surging or wavering in rpm. May be tough to test if it immediately starts again after it dies. May take the issue getting worse in order to find a solution.

[DennisG01]

There is no sensor that reads low fuel and kills power.

If it indeed turned off like a light switch, that sure sounds like an electrical issue. If it was a fuel issue, there would be, at least, "some" type of initial stumbling.

I would think this is maybe something spark-related (or computer). If they lose power, the engine would turn off immediately. Start the good 'ol fashioned way... Start at the battery and inspect (closely) every wire connection (both+ & -). Remove, inspect, clean replace and make sure it's tight. Follow the wires everywhere they go and to the engine - check all major connections there, as well.

What type of "kill switch" do you have? You may want to check that to be sure it's functioning properly. I've experienced one where the "key" was slightly cracked and didn't hold the button out quite far enough and caused intermittent issues.

[99yam40]

To add to the high rpm motor shut-down issue. No, I haven't checked the primer bulb for goo. No "goo" in base of VST, water separator nor on filter that sits under the electric fuel pump when checked for fuel clogging mid way thru this issue. Problem continued on subsequent high-rpm trials. Seems to me that if the problem is related to poor fuel delivery due to degrading lines the motor would stutter somewhat before shutting down like turning off a light. 99yam40 stated "other things" can cause a low amount of fuel in the VST. Is there a sensor that reads this low fuel level and immediately kills the motor?

no there is no sensor for level.
But as I said if the level drops below the pick up screen there is nothing to pump

restrictions in pick up,filters, or in lines, sucking air can all limit flow of fuel.

why not test/monitor fuel pressures to see if that drops when it dies

[walleye1]

Mercury gray fuel line with the red lettering was the bad crap, made me alot of money.

[mjfogarty]

High end stator perhaps?

[99yam40]

service manual should tell what type of ignition system it uses and if it has a low and high speed charge coils