25hp Johnson outboard running problems

[rickatom]

We have a 25hp (not sure of date but older model @ 70's). We are having problems with the speed control. Engine fires and idles smoothly. When we get it out on the lake, while trottle in full postion, there is no power. Then on its own, it tends to speed up for only 8 seconds, then dies down again for @ 15mins before it will do it again. Engine stays running, but it has sparactic speed control. <br />We thought it may be diry ports.<br />Carberator has been dipped clean and blown out ports, and new gasket set used.<br />I read in an early forum about female gasline orings may seep air?<br /><br />Please email to rickatom@charter.net

 

[Paul Moir]

Re: 25hp Johnson outboard running problems

Welcome to Iboats!<br /><br />Yes, that could possibly be the problem. You can try pumping the primer bulb to see if that helps. If it makes no change, it's probably not a leaking o-ring, fuel pump, leaking needle in the carb, etc.<br /><br />You may be loosing spark on one cylinder at higher revs. Try seeing if you can draw a 3/8" arc off each spark plug lead.<br /><br />Before going much further we'll need to know the year. Check the transom bracket for a namplate. If it's missing, check around the engine block for a silver convex plug with numbers stamped in it. Those may provide the info we'll need.<br /><br />(in the 70's there's three ignition system styles and two very different 25hp engines).

 

[rickatom]

Re: 25hp Johnson outboard running problems

added question...the fuel line runs directly from the gas tank to the motor. There is no bulb in the line. Do I need to have a bulb?

 

[fishonboat]

Re: 25hp Johnson outboard running problems

I have never heard of anyone not having a primer bulb in the fuel line going from the gas tank to the motor. I would say that at higher speeds your motor is requiring more fuel and the line isn't pressurized and it's not able to supply the carb with enough gas. Is it hard to start? If you add a primer bulb I would also say that it would start much easier. I would add one and see if it helps. You can pick them up at Walmart for cheap. I think they are around $10.00-$15.00. Let us know what happens.

 

[Paul Moir]

Re: 25hp Johnson outboard running problems

I wonder if it's a pre-56 25hp that uses a pressurized fuel tank? Does it use a double-line hose?

 

[rickatom]

Re: 25hp Johnson outboard running problems

The fuel line was hooked up without a fuel bulb. I fear that has been our problem. From what I have read from the gracious info you guys have provided, I passed the info on to my dad. Today we started checking things, and he pulled out a line with a bulb and a sight glass filter. There was no gas getting to the filter after being pumped. There was an air lock. So he took a screwdriver and push the plunger while I pumped the bulb and filled the line with gas. So we wont know if this did the trick until we take it back to the lake.

 

[rickatom]

Re: 25hp Johnson outboard running problems

If the rain would just quit, maybe we can go on a test run Thursday. Question....I read the instructions on the fuel filter. One side in and the other out facing the carb. The glass in filter does not completely fill up. Does it really matter which direction the filter is aiming or is it just fule of thumb. I do have a reason for this question. thanks

 

[rickatom]

Re: 25hp Johnson outboard running problems

OK...after installing the primer bulb and filter, I bled the line from any air. The engine still idled fine and ran fine in low speed. It only surged to high speed maybe once or twice. Then I could not get anything else out of it but a steady run.<br />What else could be my problem???...recap ( dip cleaned the carb, and cleaned ports, added fuel primer bulb and filter).

 

[CATransplant]

Re: 25hp Johnson outboard running problems

Sounds like that used bulb has a problem with a valve. Get a new one, or, better yet, a whole new bulb and hose assembly. They're cheap.

 

[rickatom]

Re: 25hp Johnson outboard running problems

the bulb set up is practically new. Could it still be a fuel pump issue eventhough it is working somewhat?<br /><br />Removed the diaphram from the fuel pump and swapped it with another pump. Could this be a simple fix?? Motor was still not able to run at full power