'97 90hp Mercury stalls after trolling 15 min

[gregBR549]

Hi all,
I am new here and I just got another boat (like I needed one). It is a used CC with a 90 hp Mercury, premix. We just put it in for a sea trial. It ran good but with a couple of problems that didn't show up at first. The motor only has about 25 hours on it. I think it was setting up for a while when I got it. We started trolling and after about 10 or 15 min, it would stall. We pumped the bulb, and we were good to go for another 10 - 15 min. Whats wrong here? Also, when we were trolling, sometimes a rattle sound was coming from what sounded like the foot at about 800 rpm. Like it wasn't quite in gear all the way. It was intermediate, not a continual sound, and it quit when we trolled at about 1200 rpm.
Thanks for any help,
Greg

 

[Silvertip]

Re: '97 90hp Mercury stalls after trolling 15 min

It sounds like the stalling problem might be fuel pump or fuel system related. You might check the spark plugs to see what they look like. Replacing them is just a couple of bucks. If the boat has an internal fuel tank, it is not uncommon for the anti-siphon valve to become sticky and restrict fuel flow. That valve is what the fuel line attaches to at the tank. Again, it can be removed and cleaned or replaced for just a few bucks. Check the fuel line for kinks and air leaks. The engine is also 11 years old so it may be the carbs are in need of cleaning even though the engine has low hours. As for the rattle you hear, that may be "clutch dog rattle" which is experienced when using certain props -- heavy stainless steel in particular. You should check installation to make sure the prop is tight on the shaft.

 

[CharlieB]

Re: '97 90hp Mercury stalls after trolling 15 min

You may have a very small air leak into the fuel line before the fuel pump, sucking in a very small amount of air until it addes up to a large amount of air and the upper carb runs out of fuel.

If you can rig a piece of clear hose just after the fuel pummp then watch it closely for any bubbles, indicating air sucking into the line.

DO NOT use aftermarket fuel link quick connectors, they are notoriously weak sealling, I very highly recommend OEM connectors for their better sealing.

 

[Texasmark]

Re: '97 90hp Mercury stalls after trolling 15 min

Silvertip is deadnuts on as usual. I agree with his prognosis. I currently suffer from "the rattle", but I'm not going to compromise my performance (by using a low pitched alum prop) for what Merc says doesn't hurt anything.

As far as the rattle, those gears rattle each and every time you cut the throttle while underway and they are built mighty hard (tempered) for that reason. You just don't usually hear it as other things are making too much noise.....it's an overrun clutch and it rattles when it overruns. If you didn't have it, you couldn't idle your engine if you were on plane (in F gear), for example. The engine rpms would follow the propeller rpms.......same thing as the old Ford 8N farm tractor with a rotary mower behind it. You have to add an "overrun clutch" on the pto shaft to keep the mower from driving the tractor through the fence when it's rotating and you are trying to stop. Grin

Mark