Motor Cuts Out at Low RPM

[chris4401]

1992 Grady 24 Explorer repowered in 03 with a 225 Yamaha 4 Stroke. Last year had some problems with the motor cutting out - had to pump the primer to get it to re-start and run. Possible leak (air?) in the water separator so I replaced the whole assembly with a SS one (Racor with the sight bowl).

While running the other day it would cut out at idle speed (no wake zones) and at trolling speeds. Same thing, pump the primer and it would start and run for about 10 minutes then cut out. Replaced the water separator filter, lines are clean (I have an in line filter prior to the W/S filter which is also clean) and the gas is about 2 months old. Boat runs great at speed (on plane) all day long. As soon as I throttle down for a no wake or trolling, it cuts out afer about 10 minutes at that speed.

My thoughts are an air leak of some sorts??? The fuel filter on the motor is full when this happens (visible filter - you can see the fuel) and the red ring stays on the bottom which is supposed to indicate no water. The fuel line from the motor is 5-6 years old but the primer ball appears to be original (17 years). Haven't had the time yet to trace the fuel line from the filter to the motor (Grady Drive) but I'm guessing that there is a splice in there somewhere.

Any other ideas or similar problems?? This is getting old!

Chris

 

[seasick]

Are you saying that you have to prime the bulb to get it to start?
When it dies was the bulb collapsed? If so, there is a blockage in th tank pickup, or tank vent.
If the bulb didn't collapse but the motor only runs when you pump the bulb, you have a fuel pump problem or a leak in the line between the pump and the bulb.

By the way, looking at the fuel in the filter only tells you that you are not out of gas. Is doesn't tell you if the gas is flowing ( at least it hard ti tell if it's flowing)

 

[chris4401]

Yes, have to prime the bulb. Update - hooked the boat up to a 5 gal. carry on tank. Ran fine (all rpm) for over an hour. As soon as I hooked back to the on board tanks (either one) it would die after 5-10 minutes. This is even when I hooked directly up to the fitting on the fuel tank. When I started the troubleshoot this AM, it ran for about 20 min. on the on-board tank. Then 5-10 min the dies. Prime the bulb and it would start. Switched the the carry on and everything was fine. switched back to the on-board and it would die.

Pumped out the tanks last Jan. New fuel in Feb (with stabilizer). Run the boat every couple of weeks. Ran fine on the on-board tanks last weekend but only on plane / at speed.

This is making me crazy....... anybody help???

Chris

 

[seasick]

The simplest thing to try is to run with the fuel cap off or at least loose. If that works and the motor doesn't die, you have a blockage in the tank vent.
The second possibility is that something is getting sucked up against the fuel pickup. Something as simple as a leaf can block the pickup. When the motor dies, the vacuum stops and the debries faal to the bottom of the tank. That one is harder to isolate. You may not be able to easily see the pickup tube .

 

[chris4401]

Ran with the caps open and still died (both tanks). Thought about the clogged pickup but what is strange is that it dies on either tank. Does not matter which tank is being used, it will not run at low speed. Either tank ran fine at high speed / on plane. The carry on tank will run fine ALL the time.


Just a note, the prime bulb does not collapse, and you are right about trying to see the pick up tube!

Chris

 

[LI Grady]

Its a long shot but when it dies on you can you inspect your fuel line to the motor? It is possible that the fuel line is collapsing.

Its a real long shot since I would think a fuel line would coolapse under high demand not idle but you never know.

Also...are these carb motors or fuel injected? I had a similar problem when my first mechanic (moron) failed to sych my carbs. Ran fine at speed but at idle was stalling since it was effectivel only running on half the cylinders

 

[chris4401]

Fuel line is OK (no collapse). FI motor. Mechanic thinks it may be a fuel pump that can not pull fuel at low RPM. Don't know what else to try.

Chris

 

[seasick]

Sounds like a pump to me. The portable tank probably sits higher and therefore the pump doesn't have to work as hard. It still could be an air leak somewhere bewteen the tank and the low pressure pump though.

 

[BobP]

Get a 1 ft or 2 ft length of clear hose form Ace or the Depot, 3/8 inch diameter, and install it in series with motor close to the motor (wherever you hooked up small tank), watch hose while motor is running, should be solid fuel, no bubbles. You will see right away any problems with bubbles.

Then if you find bubbles, you back track with the clear hose until you find where it is.

Don't leave clear hose in permanently, take it out when done.

It is actually good news motor runs ok on the portable tank, the rest is easy to find.

 

[BobP]

By the way, wherever you inserted the portable tank, from their forward into motor is OK, air leak wise, it's on the other side going back to tank - if an air leak is occurring.

If the squeeze bulk is collasping full , the motor will die but not initially, indicating a restriction on tank side of bulb. Get a new squeeze bulb to start. You have to observe squeeze bulb at exact time problem occurs, not later or earlier.

If there is concern motor pump is weak, disconnect tank side hose on squeeze bulb and hold finger to seal it while motor runs, does the squeeze bulk collapse while motor still runs at least initially? If so, pump is good.

If there is a fuel line that is internally parted and blocking, the squeeze bulb will find it too, just watch what it does when the motor dies. The squeeze bub will find any restriction, I presume you had the squeeze bulb in place when you connected the protable tank on the gas tank side of bulb (??).

 

[BobP]

The squeeze bulb is how many years old?

Petrified solid by now, no wonder it doesn't collapse.

 

[chris4401]

Squeeze bulb is new as are all of the filters. Squeeze bulb never does collapse. Good idea to try the clear tubing. Ran it yesterday and it again ran fine at speed. Determined that below 2000 RPM is when it would die. Above 2K it ran fine but as soon as I dropped it to 1900, it would die. Either tank.

Yes the portable tank was on the deck - going to place it on the ground to see if the "lift" will make a difference.

Chris

 

[lodgecreekgrady]

Did you bypass the lines going thru the grady bracket? When you hooked back from the protable tank did you try hooking the portable tank line directly to one of the tanks? That woud eliminate the fuel line or any filter or tank swiching valve problem if it ran ok then. If you haven't, then take the fitting out going to one of the tanks and look for a screen in the fitting. It will probably be under the 90 fitting that screws in the tank down in the pick up tube. You may have trash in there or they may be too resticted for a fuel injected motor. I had this trouble on my grady with a 2 stroke with VRO pump. It started smoking alot at idle and then cut off. I switched tanks and came in on the other which was fine and a clogged screen is what I found. I when thru that same thing with a previous boat and replaced everything trying to fix the fuel problem and after a very long and frustrating hunt that is what I found. That small screen is now somewhere on the bottom or the river in the place where i found the problem. As long as you have a good filter and fuel/water seperator you don't need that screen.

 

[JUST-IN-TIME]

check oil level
if high bad fuel pump

or you can pull them off and pump the primer bulb
if you see fuel, they bad