25 hp mercury wont prime

[txcutter]

I have an 1985 25hp mercury/tiller handle/ with a portable 6 gal fuel tank.

I took it out and primed it, started it. It idled fine. At full throttle it would lose prime. I would simply squeeze the primer bulb and it would pick back up. It would run fine at half throttle.

I took it back out the other day and same thing. Except this time I could not get it to prime at all. Now it won't even start.

I bought a new tank, fuel line with fittings, and primer bulb. I cleaned the fuel filter and the fitting that the fuel line plugs into on the motor. Oh, and the filter/bowl was almost empty when I took it apart.

It won't prime one single bit. I can't even get it to get fuel into the filter/bowl. I even turned the motor over some to see if it would pull some fuel into the filter/bowl but nothing.

One thing is that the fuel fitting that is on the motor, the pin inside it is very corroded. I cleaned it up the best I could. As far as I can tell, it functions like it should.

Any suggestions? I'm no mechanic unless it's a simple fix. I talked to a mechanic and he said that the fuel pump may be bad. But this was when it was just losing prime when running at full throttle.

Bryan.....

 

[JGra]

Re: 25 hp mercury wont prime

You might have a needle and seat problem in the carb. My 20 hp was doing the same thing. Fixed that and adjusted the float level and its seem to be running ok at the moment.

 

[Kirscher]

Re: 25 hp mercury wont prime

I had the same problem on my 35hp. I found it to be the diaphram in the fuel pump. I don't know anything about your engine but it should have a fuel pump just after the fuel line comes into the engine and prior to the carborator. It is possible your engine has a built in pump on the carb.

 

[madanorak]

Re: 25 hp mercury wont prime

I had this problem on my 18XD, which is virtually the same engine. The solution is to rebuild the carb with a full kit, as it has an integral fuel pump which you will find that all the diaphragms & seals will have distorted. Also get a new needle valve as they have a rubber point which becomes sticky and so blocks the fuel inlet. This is about 1-2 hour job, but fairly easy, just make sure everything is spotless and all holes in the carb are clear when you put it back together. Whilst the carb is off, check the bleed pipes connecting to the reed block under the carb, as I found mine to be perished, and there is very little access once the carb is on. After doing this, my engine runs like a dream, and have had it for 6 years, giving it some serious abuse, constant WOT pulling a ringo, and it has never missed a beat.

Kev