[Stormchaser]

I have an 80s model 25 hp Johnson that's been mine for a little less than a year. The thing starts right up every time, and runs well...for a while. But then it just bogs completely down and when this happens, it "surges"...revving high then low then high then low...

I've had the motor in the shop twice, the first time was before I ever ran it...just to have it gone thru, impeller replaced, etc...then the second time was after I recognized this issue, and they went thru the carb and replaced spark plugs etc. Still does it.

It will run well for a few minutes, but then it does the above, and it seems as though it only does it if I'm at WOT. When it happens, I kill it, and start it right back up. Sometimes it's still doing it, sometimes it's not...and I can baby it in. But I want to be able to run it at WOT when going from dock to spot and vice versa.

Any ideas? Suggestions? Snide remarks?

 

[Brett]

Air leaks between tank and carb,
and replace fuel pump would be my first thoughts.
Check filters for leaks or water buildup.

Have you tried running off a new tank and new hose?

 

[Stormchaser]

Air leaks between tank and carb,
and replace fuel pump would be my first thoughts.
Check filters for leaks or water buildup.

Have you tried running off a new tank and new hose?

On the last question, yes. I replaced the hose when I bought this rig and have since replaced the tank. Although the first tank is fine, I just wanted an extra. The old hose was a POS, but I never used it.

Fuel pump was replaced as well.

Now, your FIRST point about an air leak, I just realized something. Mind you, I bought this boat a year ago, but I work out of town a LOT. In fact, I wasn't even here when I bought it lol. That said, I RARELY use this boat, and the last time I used it was last October (2012). On that trip, I had trouble starting it at the marina. Turns out, when I pumped the bulb, I noticed fuel squirting out where the hose connects to the motor, and unhooked, then reattached it, making sure it "clicked". Pumped it up, cranked right up. So now you have me thinking that connection is not as tight as it should be. I'll check that.

I should mention, I have played with the vent on the tank, thinking that might have been the problem, but that didn't work.

 

[AfterHours2]

A good place to start with air leaks is the fuel line connectors at the motor and tank. The style at the motor is a quick connector and should have a o ring to seal. If the type at the tank is the same, then I would replace with a screw in barb connector and clamp the line to it. Less chance for leaks with the barb fitting. These two were the culprit of my issues and drove me crazy for months. Off and on issues mainly but it will eventually get worse. Hope this helps. I can post pics of my tank connector if you need them. Let me know...

 

[Stormchaser]

I would appreciate the pics. I do think that's the issue now that I've thought about it, but haven't had a chance to investigate further. Most people do that kinda thing on weekends, but when I'm not working, my weekdays are more freed up than my weekends...because the kids aren't in school on the weekends and I have to spend time with them. I'll probably investigate more Monday, but I'm pretty certain you guys have nailed it. I just never thought about that until Brett mentioned air leak, and I remembered that time at the launch where I didn't have a good connection there.

 

[Stormchaser]

OK, drudging this topic back up.

As I mentioned in one post above, I work out of town a LOT, and rarely use the motor. I bought a little skiff with a 15, but rated for a 30. I eventually decided to put this '89 25 hp on it just to see how it does. It actually worked great the first day I put it on. I had cranked it and ran it in a barrel the day before, since it hadn't been run in so long. Worked great.

So then I go out of town for a couple months, and just got back in town. I took the boat out Thursday, and it ran like crap. Drives me nuts!

So while I was out there, I removed the cover and cranked it up. I noticed a leak (gas) where fuel leaves the fuel pump headed to the carb. I don't like the way this connection is configured, but checked a schematic, and it's supposed to be this way. Basically, there's a small (1 1/2") section of tubing that connects to the bottom of the fuel pump, then a plastic 'L' that connects that tubing to the line that runs to the carb. The leak seems to be where the tubing meets the bottom of the fuel pump.

Question is, is there any reason I can't just run a hose directly from the fuel pump to the carb? That's how it's run on the 15 I have. I know one issue is the ID of the hoses is different. The little section of tubing connecting to the bottom of the fuel pump is bigger than what comes OUT of the fuel pump going to the carb. Anyone know of an in line coupler I could use without the 'L' to go straight thru? The plastic L is a normal part with the motor, I just don't like it.

Also, is it possible it's just an issue with the short tubing? Maybe due to ethanol?

Lastly, considering the problem described in the original post (same thing still occurring), I assume if fuel is leaking, air is replacing it. Is this likely THE problem?

 

[Stormchaser]

I bypassed the 'L' and rigged the fuel line straight out of the fuel pump, connecting it to the smaller line, in line.  There is no leak that I can see/hear, and I can clearly see the connections.  But...

It's still doing what it does.  Cranks right up, idles decent, but when I give it enough gas, it starts to rev up, then goes into spasms...

Someone please tell me this.  Considering that every now and then, it runs GREAT, there can't be anything TERRIBLY wrong, can there?  There has to be some little pain in the arse thing going on, right??  It's really frustrating me. 

And before anyone asks, yes...I have had an outboard mechanic look at it.  He clearly doesn't know what he's doing.  He's rebuilt the carb, replaced the fuel pump, and still, NO change in how it acts.  Cranks and idles fine, then spazzes out when you give it power.  Sometimes. 

I have a video on my phone of what it does.  Would it help if I can figure out how to post it here?

 

[cutrunner]

Maybe i can help.
next time you have it running and it starts "spazing out" pull the choke (assuming its a manual "pull to choke" motor), for a couple seconds. If it starts running good while the choke is pulled you got a carb issue, if it kills it then the carb is good.
its more than likely the carb. All johnsons leak a little fuel, if they dont then you gotta worry

Does the motor have one or two carbs?

 

[Stormchaser]

One carb. FWIW, when it did run good last Thursday, I had pulled the choke out. I had to keep doing so every couple of minutes. Sounds like carb issue. I had the thing rebuilt a couple years ago, but it does sit...

 

[cutrunner]

Obviously i cant guarantee anything but if i was a bettin man..
carb

 

[nmcphail]

When you take it to a competent mechanic to clean/tune the carb, I'd specifically request him to check/replace internal fuel lines (didn't note you saying this was done already).

I've had a few older outboards' lines eaten up/degraded such that the small pieces dirtied up newly cleaned carbs.

 

[Stormchaser]

I am concerned about that, Nate. Since I got it, nothing but non ethanol has gone in. But prior to me? Who knows?? And it is a 25 year old motor.

Regarding competent mechanics, I don't exactly live in a place full of good marine shops. I need to find an individual that knows what he's doing around here. For one, I'm no expert. For two, I work out of town so much and when I'm home, I would MUCH rather spend my off time using the boat than fixing it.

 

[jimsmicro]

I replaced the stator on mine because it was doing the same, a high speed surge, almost like it was cavitating.  It went away when I replaced the stator. I also had a similar problem on a 9.9 and it was an air leak on the fuel line at higher throttle.

 

[riptide]

also check the pick up tube on your gas tank , tempo had a bad run of plastic pick up tubes, they crack at the top where the tube is pressed on the hose barb . you have to take it out of the tank to check it

 

[Stormchaser]

I purchased a carb kit back in September (I was home at the time), but before I could get it installed, I was deployed to Michigan (AGAIN!!). I enlisted the service of a local yokel with a rep for making things run, and told him (mistakenly) to take his time, since I was going out of town. Well, once a month, I come home for a 4 day weekend, and that was this weekend. It wasn't ready...until today. He texted me earlier and said "it's ready to roll, son") lol. Unfortunately, I am heading back to Michigan tomorrow AM. Hopefully he'll deliver it before too late today so I can go run it. And HOPEFULLY he's right...and it's really "ready to roll, son"...

 

[Stormchaser]

I'm happy to post this video...
In the latest post, I told you guys I had the carb rebuilt by a young kid here in town, and he advised "It's ready to roll, son".
Fast forward and I came home for Thanksgiving weekend, finally got a chance to run the boat today.
32.9 mph is the highest I actually saw on the GPS, but I'm gonna go ahead and call it 33! 14' Mitchell with a 1989 Johnson 25 hp, and that 33 is with the front deck installed adding weight. Of course I was solo for the 33, but I got it up over 32 with both of my sons on board, which total about 160 lbs put together.

https://www.youtube.com/watch?v=rlry1hZcgsM&list=UUjB0p4_pThCiUH2Xkq9Rg_Q