3cyl johnson problem Help!

[brian931]

Ok, guys new here, hoping for some advice. I have a 1996 3cly 25HP that I bought new, the motor has been an excellent fishing motor but recently I am having problems. The engine will start fine and idle fine but when I put it in gear the engine will not rev up, it will bog down and die. Somtimes when it is bogging it will suddenly rev right up to full for a short period and then imediately die, restarts fine and repeats this bogging cycle. With enough times I have got it to run full out for extended periods and it ran like a top but next time same thing happens, and I think the problem is getting worse. It will also run bogging for extended periods of time start to speed up then die.
To this point I thought it was a fuel issue so I replaced the line from the tank and the fuel filter with no change in condition I also put new spark plugs in. Now I wonder is the the fuel pump the issue or should I be thinking spark or does a dirty carb sound likely?
Thanks.
Brian

 

[Dennisanoka]

Re: 3cyl johnson problem Help!

Once you have it running and it wants to quit, pump the primer bulb, if it picks back up I suspect the fuel pump or fuel filter is the issue.

 

[lexkyboater]

Re: 3cyl johnson problem Help!

Hey Brian - welcome to iboats! Sounds like you're on track to me. You can verify if it's a fuel pump problem by pumping the bulb when you're bogging and see if it runs better. I don't have your model number, but I checked the BRP parts catalog Fuel System breakdown for a BJ25AREDC motor at http://epc.brp.com/default.aspx?brands=ej&lang=e and looks like there's not a fuel pump repair kit, only a mixing unit repair kit. Looks like this model also has two fuel pumps, which surprises me. I'm guessing yours is not premix?

You can also further check the pump by cranking it over with the kill switch lanyard pulled and the fuel line to the carb removed and see if the fuel pumps are pumping gas. If your's has two fuel pumps and you verify both are working, sounds like you need a carb rebuild kit. If you rebuild the carb, make sure you pull the core plugs and clean behind there. Soaking the carb in cleaner is better than trying to use cans of carb cleaner. Make sure and blow out all the ports with compressed air after you're done. You might consider a good omc manual if you keep the motor. --Steve

 

[brian931]

Re: 3cyl johnson problem Help!

Thanks for the help. Does it seem likely that a faulty fuel pump would be intermintent though? As I said I have managed to get the motor to run perfectly over long periods of time. And the engine does idle fine. I checked my engine model number to be J25TKLEDC.
Thanks

 

[lexkyboater]

Re: 3cyl johnson problem Help!

I probably should have said that you should verify compression and spark first. Not sure how much it's cutting in and out? Compression on that motor will probably run around 120 psi. You can make a spark tester with the following - http://forums.iboats.com/showthread.php?t=213548&highlight=spark+tester. On your motor, spark should jump 7/16". That said, it's possible plug wires are your problem. You can take an ohm meter and hook it up to both ends and wiggle the plug wires. See if the meter always reads no resistance or shows an open circuit when wiggling. We've seen a rash of plug wires recently here when engines are cutting in and out.

If the fuel pump is loose on the block and it's not getting consistent suction, that could cause the fuel to not flow reliably. Or your carb could have some gunk in it and it's sealing off fuel flow. Another possibility we've seen is a bad check valve in the gas tank, or a bulb check valve that's going out (but you've replaced that). Does the bulb stay hard or does it go flat? Another possibility is a leak in the fuel lines at the engine and it's sucking air. Look for any splits on the fuel line or gas leaking anywhere. If questionable, that's a cheap fix.

Several things to try but try to isolate the problem. See if it's bogging (carburetion) or has a cylinder cutting out. Those two may feel like they're the same, but the cylinder cutting out will cause more vibration and probably will only let it put out about 1/4 of the power it should have.

 

[brian931]

Re: 3cyl johnson problem Help!

Been almost a year, I hoped that the problem would fix itself over the winter! LOL, anyways still there, so here is what has been changed so far, new fuel line from tank, new fuel filter, new spark plugs, new spark plug wires. This is a very intermitted problem, the engine does run fine at times, yet at other times it will either not rev up just bog, rev up and then die, rev up and bog, or run fine, idling is not a problem, the problem is only on the water under load. I have been leaning towards the Power Pack, but am reluctant to throw parts at a problem I have no idea what it is. Could it be as simple as vapour lock in the fuel system? When I get the engine running right it does continue to run right until I shut it off then it cools down and likely will act up again? Does this sound like a power pack failure, I'm thinking fuel? Can a fuel pump act up intermitently? Power pack intermitently? Oh yah I ran the motor with the igniton/kill switch disconnected with no improvement, so no problem there.
Thanks for any ideas?

 

[brian931]

Re: 3cyl johnson problem Help!

Should of mentioned that when the engine is bogging pumping the primer buld does nothing and it is only slightly soft. Also turn the engine over with the covers off the fuel pumps and gas spurts out.