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IndyEFI500

Older motor problems

8 posts in this topic

So I get up north on vacation and start having motor problems. The motor in question is an older Mariner 25hp. It idles and starts great as always. Intermittently when you try to get going or are already going, it starts cutting out. Sometimes to the point of almost dying. It is a pain sometimes as it shakes the boat quite violently. I noticed there was gas leaking around the hose connection at the bulb so I took it apart and cut the hose off a few inches and put a new clamp on. It is slightly better. What does anyone think? Should I try some carb cleaner? New plugs? I haven't had it tuned up this year so I am wondering could it be carb related. Could it be something worse? I am just tyring to get through the week and then will take it in but am really trying to at least make it through the week.

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Pull the plugs and have a look. Could have a bad one.

With the violent shaking, my first thought is an ignition problem. Sounds like it is running on 1 cylinder. Some easy things for you to look at before taking it in would be plug wires and boots, make sure you don't have a loose one. Look at the plug boots for cracks or splits. Look for loose wires on the coils.

The use of a timing light comes in handy for determining if you have an ignition problem or not. you can even pin point which cylinder is cutting in and out, swap coils around to see if it affects the same cylinder, etc. Just be careful in routing the light's wires.

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Since putting a new clamp on the gas hose seemed to help, I would try a brand new hose from the tank to the motor. There is a little flap in the bulb of the hose that can go bad or get sticky. Also, the fittings at the motor and at the tank probably have an O ring. This get messed up especially on older motors and tanks.

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Water in the fuel? Try fresh gas. Try the old stand by seafoam.

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Sounds like the fuel system in vacuum locking. Check the relief on the tank cap and all hoses and bulb would be suspect as well.

Air leaking into a loose connection when the motor is pulling vacuum can occur even if fuel isn't leaking out when motor is not running.

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Sounds like the fuel system in vacuum locking. Check the relief on the tank cap and all hoses and bulb would be suspect as well.

Air leaking into a loose connection when the motor is pulling vacuum can occur even if fuel isn't leaking out when motor is not running.

I'm sure you already tried this but just make sure the gas line is plugged in all the way. I got stranded one time out on a lake and had to be pulled back to shore. Once there I checked things out a little better and the darn hose was unplugged just enough to suck air and the motor would only idle not rev up. I pushed the hose in all the way and off we went not a problem.

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I took the tank apart per a friends recommendation and everything seemed fine. I then tried for the third time to get the sediment bowl open. It had tons of junk in it. When I took the little filter inside the bowl off, it too had junk inside. A carb clean will be a must. I think I'll also buy a new hose and bulb but put a good inline filter in it as well just to make sure. Thanks for all the ideas everyone.

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Is that sediment black? If so you should replace all the fuel line. Older fuel line was not expecting alcohol (Ethonal) to be run in the gas and that stuff will eat the rubber inside your fuel hose. A good test is buy some new fuel line at NAPA and compare how elastic the new stuff is to the rock hard stuff you are using.

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