Yamaha 25 problem??

[mdb2]

Help me out. I have a 1998 Yamaha 25. This motor runs great for about 45 minutes. Then it will act like it’s not getting gas. It will bog down at full throttle. When this happens, I can just barely get it on plane to limp back to the landing. And it happens almost every time I run it for an extended amount of time. It’s not the gas as this has happened on multiple tanks.

It’s not the vent on the tank. I replaced the fuel line from tank to motor. Bulb stays hard. Have cleaned carbs. Again, it will run like a scalded dog for 45 minutes or so, then it bogs down on anything past about half throttle.

Any ideas??

mdb

[scquackaddict]

All I can think is maybe it is overheating and going into RPM reduction. I’m not a mechanic by any stretch but maybe look at water pump, impeller if it’s been a while since it was replaced.

[willyworm]

At first thought I considered too, that it might be overheating and going into limp mode, but if that were the case he couldn't get enough rpms to even get on plane. So that's out.

Just cause you've run multiple tanks don't mean much. You still could have water in your gas. Disconnect the fuel line from the motor and use the primer bulb to shoot some gas into a clear glass jar and see if there's water at the bottom. The water is heavier so the gas will stay on top and it'll be obvious. Also check the fuel line for potential leak spots. Also look at the little fuel cup under the cowl with the filter in it. Might have a little water settled in there, or even in your carb bowls.

Just spitballing here.

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[willyworm]

2 cylinder model, or 3 cylinder?

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[willyworm]

You or anyone else messed with the timing linkages, by chance?

Sounds like it's either fuel or timing is jacked up. If it's getting enough to run at half throttle but not at full, then it sounds like a fuel flow issue. I would say vent cap but you already checked that.

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[scdiver]

Check your spark plug wires, had a similar issue with a 25 where the wires were getting loose and only firing one cylinder.

[mdb2]

Willyworm, it’s a 2 cylinder. The screwy thing is that it will run like a top when I start off and up to 45 mins. Then it stalls. I was wondering, too, if it could be thermostat going bad???

I will check the field in a glass and see. It just seems like if it was water that it would run badly from the start.

[willyworm]

Forgot about the fuel pump assembly. Those things don't go bad often, but it's possible.

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[cam1195]

Ignition coil probably. Maybe fuel pump or carb acting weird.

IMO no timing issue if it runs well at all RPMs for 45 minutes.

Is your carb OEM? Aftermarket carbs can cause the problems you’re describing also.

[rp]

I had a bad gasket on the fuel pump. Took care of that and all was fine. I'm told I need to go ahead and do the carb gasket too. Mine is a 1998 model too.

[willyworm]

IMO no timing issue if it runs well at all RPMs for 45 minutes.

Good point

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[mdb2]

Ignition coil probably. Maybe fuel pump or carb acting weird.

IMO no timing issue if it runs well at all RPMs for 45 minutes.

Is your carb OEM? Aftermarket carbs can cause the problems you’re describing also.

Carbs are the carbs that came on it. This motor sat for about 15 years. I changed water pump, cleaned carbs, hot a new gas tank and line. And have been having this problem for a while.

[mdb2]

I had a bad gasket on the fuel pump. Took care of that and all was fine. I'm told I need to go ahead and do the carb gasket too. Mine is a 1998 model too.

What were your symptoms?

[mdb2]

Ignition coil probably. Maybe fuel pump or carb acting weird.

IMO no timing issue if it runs well at all RPMs for 45 minutes.

Is your carb OEM? Aftermarket carbs can cause the problems you’re describing also.

Y’all to me about ignition coil? What would be symptoms? How hard a fix is that?

[mdb2]

I did put all new gaskets in the carb when I cleaned them

[rp]

It would run and then start acting like it was choking out. Had to keep priming it.

[cam1195]

The ignition coil can be found on the other end of your spark plug wires. I believe there are two wires with pull apart connectors going to it on a Yamaha. Then two or three mounting bolts. Not sure about yours but the spark plug wires on some Yamaha 25’s are part of the coil... meaning to replace the plug wires you must also replace the coil since they’re one unit. I know you can check the resistance of coils to tell if they’re good or not but I have always had trouble ruling them in or out. They tend to heat up and cause spark problems when ran for a while. They are usually kind of cheap and if it includes wires you might as well swap it just to see. I’m not one to throw parts at things but if it can be categorized as a “tune up” I usually look at it as justified.

Have you checked compression? Might be a good idea also. If you want, you can always pull the thermostat out and run it without it to see if your problem persists.

To rule out the fuel pump, when it starts bogging down when you’re running down the river, start pumping the bulb and if the rpms increase, your pump is likely bad. If there is no change, your pump is probably still good.

[Palmetto Bug]

How long does it take for the engine to recover and run regularly again?

[Luvin' Labs]

Check compression and leak down. My motor would do that to. Would let it idle or sit for a bit, and then it would run fine again. I thought my issue was trash in the carb or something along those lines. Come to find out is bad compression/leak down.

[cam1195]

Check compression and leak down. My motor would do that to. Would let it idle or sit for a bit, and then it would run fine again. I thought my issue was trash in the carb or something along those lines. Come to find out is bad compression/leak down.

That’s what I am starting to think might be the issue too. If it comes back low, you can try de-carb spray.