73 25HP Johnson - a bit mystified

[CatfishMN]

Hi,

Hoping for a bit of help here. Model 25R73A.

So when I let the motor sit for an extended period (a day or more) it'll fire right up on the 2nd or 3rd pull and run as long as I want it to. When I shut it down and let it sit, it might pop over for a few seconds, then shut down, and no matter how many times I pull it, it won't start. When it does run, there's a good water spray (replaced impeller earlier this season).

I replaced the Atwood fuel line/bulb with an OMC one a month ago. When I pump it, it stays hard and fuel is sitting in the carb bowl. I even took it to a shop who cleaned the carb and tested the compression, which they said both were good.

Recently I looked under the cowl and the wires running to the defunct kill switch were bad (exposed copper), so I disconnected them. I have started and ran it since disconnecting these, so I think that rules that out as the problem.

The only thing left that I can think of is the ignition system. I ordered new points, coils, and condensers. Am I on the right track here? Does anyone have other insight to lend as to something I could be overlooking?

EDIT: Yes the tank is vented. Forgot that.

Thanks in advance.

 

[Daviet]

Re: 73 25HP Johnson - a bit mystified

I would check the spark when it wount start, if you have good spark, it has to be a fuel problem.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

I have checked the spark when it won't start, and I am getting healthy blue spark at least 1/4" on my spark tester. I 'd thought I ruled out the fuel system. Where would you start?

Thanks!

 

[Daviet]

Re: 73 25HP Johnson - a bit mystified

You might try running it for awhile and then shut it down and look in the carb and see if there is any gas puddling in the venturi causing the engine to flood. How do the plugs look, black and gas fouled?

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Hi. The plugs do get a bit fouled, and when I take them out after trying to start it, they are wet. When trying to start, unburned gas runs out the exhaust and into the water as well. Thanks!

 

[R.Johnson]

Re: 73 25HP Johnson - a bit mystified

Remove the two screws holding on the fuel pump, and hold it away from the engine. Pump the primer pump. and see if fuel run's out the back of the pump. Run a pressure-vacuam test on the whole fuel system.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Thanks. Do you mean to see if fuel runs out of the carb or the fuel pump?

I just remembered one other piece of the mystery. About a month ago I was out on a local lake that had a no-wake temporarily set up due to high water. Running at slow speeds, the motor would sputter and cut out from time to time. I was able to remedy this by holding the priming buld and pumping it whenever it sputtered. Sorry for not mentioning this earlier. Does this help in the diagnosis?

Thanks again for helping.

 

[R.Johnson]

Re: 73 25HP Johnson - a bit mystified

I changed my reply to back of pump, sorry about the mistake. It certainly does sound like a bad pump. Some times just to get you home you can put the fuel can up on the seat to help the weak pump, or slowly pump the prime bulb.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Thanks again, will do the pump test when I get home. So if fuel does run out the back of the pump, this means there is a leak in the pump, correct?

Would this manifest itself in the way I described as far as sometimes starting and running, and other times not? I have never had it cut out at WOT, only low idle and starting.

 

[kbait]

Re: 73 25HP Johnson - a bit mystified

When you test the pump, use a couple bolts/nuts to cinch down the corners of the pump where you removed the mounting bolts. If it's leaking out the back (where it gets it's pulse from the cylinder) it is flooding out that cylinder when running/starting. If that's good, scrutinize the plugs when it won't start. If you see ANY water droplets, you likely have a failing head gasket. And it may be bad w/o any water intrusion if it's leaking between the cylinders..

 

[AlTn]

Re: 73 25HP Johnson - a bit mystified

if your mounting screws also hold the pump body together, be sure to put a couple of nuts on them to hold it all together as you pump the bulb from the fuel tank..use your thumb or bolt to block the line going to the carb...the diaphram may not have a hole in it and your pump won't leak, however, just a weak diaphram can produce a weak stream that's unable to fill the carb bowl. In addition to the advice already given, try running a clear vinyl fuel line from the pump to the carb, no air bubbles should be present if the pump and all fuel connections are working properly. This clear hose is for test purposes only, do not run it as a permanent setup.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Thanks for all the replies. Will do some testing when I get home this evening and post what I find.

So if the fuel pump is bad, does it sound like the cause of the issue I decribed in the OP?

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Hi,

So I got home from work and took off the fuel pump. Squeezed the bulb hard as a rock and observed no fuel coming out the small opening in the back, or anywhere else. Does this rule out the fuel pump as the problem. I did notice the outside/bottom of the carb got wet with fuel after pumping the ball so much. Haven't gotten a chance to get the clear vinyl hose suggested above to see if air is making it through.

I also pulled the plugs again and did another spark test just to be sure. Both had healthy blue sparks. When I pulled the bottom plug, I did observe liquid on the threads, but when I touched and smelled it, it appeared to be only fuel.

Any thoughts?

Thanks!

 

[Daviet]

Re: 73 25HP Johnson - a bit mystified

If you have a fuel leak at the carb when squeezing the primer bulb, it sounds like you might have a needle/seat problem in the carb.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Hi,

So I went back out and squeezed the bulb again and actually observed fuel pouring out the front of the carb; a pretty good trickle. Would this be a needle/seat problem? Would this be something fixed by adjusting the float, or something else?

Seriously, thanks everyone for replying, this thing is driving me nuts

 

[Daviet]

Re: 73 25HP Johnson - a bit mystified

Yes it is a needle/seat problem. The needle valve is controlled by the float. You could have a piece of thrash in the needle/seat not allowing it to seal off. You need to remove the carb and overhaul it. make sure to clean all passages and orifices really good, and check your float level. It might not hurt to get the OEM kit, it comes with a new float.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Thanks, I overhauled the carb earlier this year, but it was probably me who screwed up the float level.

Questions:

Would this cause the problem I described in the OP? Was I flooding the motor by letting too much gas in, and thus fouling the plugs?

Thanks again for your attention Daviet, I really appreciate it.

 

[Daviet]

Re: 73 25HP Johnson - a bit mystified

Could be. If the fuel level in the carb is to high or the needle/seat is not sealing off, when you shut the engine off there is some pressure in the fuel system. It's possiable that the pressure could force fuel into the carb venturi and flood the engine. If the engine was allowed to set for a while (depending how much fuel had leaked), it would start properly and run fine until shut down. There may just be a piece of trash in there and only needs to be removed. If it is black in color, replace the fuel line from the pump to the carb, it's coming apart inside.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

Gotcha. Will break down the carb in the next day or two and post back with results.

 

[CatfishMN]

Re: 73 25HP Johnson - a bit mystified

So I broke down the carb, and not visible debris impeding the needle. Still sprayed it out for good measure. I noticed the float looked a little off, so I bent it back slightly. Put everything back together, and now no fuel leak! Too bad it is pouring rain outside or I'd give it a test. More to follow tomorrow.