1987 Evinrude 15HP idles fine but then stalls once increasing the throttle

[badboybill88]

Evening all,

As outlined in the subject line, I have a 1987 Evinrude 15HP that idles fine but then stalls once I increase the throttle. It happens every time within a few seconds, and doesn't matter if it is in gear or not. The engine would probably idle all day if I let it. The outboard is also pumping the very best. Plugs are new, and does the same with the old plugs too, both plugs appear to be firing. I checked the fuel filter and it is clear of any blockage. The tank and hose are also new, and appear to be clear of any defects. Not sure what other information I can provide, but please ask if there is something else you would like to know.

I'd appreciate any help!
Bill

 

[oldboat1]

Did you take the carb apart, clean and rebuild it yet? Will it keep running if you squeeze the bulb to pump gas to it? poss fuel pump issue. could have the square little one, or the larger model. Kits for both (if the smaller pump, replacement sometimes easier. pretty tiny kit parts.)

 

[badboybill88]

I tried running the motor and squeezing the bulb, but that didn't make any difference. I believe the fuel pump is of the smaller variety, I've attached a photo below, and am going to get a price on replacing it. As for the carburetor, I don't really know the first thing about cleaning/rebuilding one. How would you suggest that I do this, or do you have a webpage or reference that you could point me in?

Thanks,
Bill

 

[oldboat1]

sounds like a carburetor issue to me. If it were mine, believe I would put in a carb kit before replacing or rebuilding pump. It sounds to me like a plugged high speed jet, if idling well but stalls with throttle increase. The most difficult part about that carb rebuild is probably getting it out of there, but the second time will be easy.

edit. suggest finding a parts blow up before disassembling. Not rocket science, but a little tricky to remove the air horn and the starter assembly -- first time, anyway. Can't reset carb/throttle adjustment without that, either.

 

[OptsyEagle]

I doubt it is your fuel pump. The fuel pump's purpose is to get fuel into the carb bowl. Once you have fuel in there you can basically disconnect the fuel line and the motor should run in neutral or in gear, until the fuel in the bowl is used up.

The first thing I would do is enrich the fuel mixture a little. Turn the knob on the front counterclockwise 1/2 turn and then another 1/2 turn and see if that helps. If it does, report back and we will tell you how to set that properly. If it doesn't then I would assume that the problem is in the carb itself and you may need to clean it with a new carb kit.

 

[badboybill88]

Makes sense, I'll give that a go. Could it have anything to do with the grade and mixture of the gas? I'm currently just running Regular mixed 100/1 with oil. Could this be part of the problem? I could try premium? I've read people saying go 50/1.

 

[Chinewalker]

Clean the carburetor. That means a complete disassembly, thorough cleaning of all jets, and reassembly with modern ethanol resistant carb kit. Other than getting the float level as described above, there's nothing really beyond putting everything back the same way it came out.

And get some 50:1 mix in there. The 50:1 isn't causing your issue, but it is an issue. OMC pulled back from the 100:1 mix in a service bulletin in the early 1990s.

 

[1983 ercoa 21']

You might also check to make sure the timing base is moving and advancing the timing.

 

[OptsyEagle]

Yes, use 50:1. Not your problem but is the correct oil mixture.

Also, speaking of timing plate. You will notice that when you turn your throttle, a plate under the flywheel, will turn and a cam will push on your carburetor's roller that controls the butterfly/fuel to the motor. That needs to synchronized to ensure proper spark timing at all the throttle ranges.

To by in sync, there should be a mark on that piece that pushes on the carb's roller. Either a line or an arrow or something like that. That line/arrow should be in the middle of the carb's roller JUST as it touches the carb roller. If it is not, then it is out of sync and may be causing your problem if it is out of sync too much (more then 1/8 inch on either side of the roller). An easy check anyways.

 

[badboybill88]

So I've completely disassembled, cleaned and put in a repair kit for the carburetor. There was a lot of gunk in the bottom of the bowl, so I'm sure that wasn't helping anything. I've reinstalled the carburetor and it sounds like it's running smoother, but the issue is still happening when I increase the throttle.
I uploaded a video to Youtube of what it's doing, you can find it here;
https://youtu.be/V5ysy0sLNjM

Any ideas?

 

[oldboat1]

Think it sounds pretty good throughout the range. Appears you are running on muffs, though -- if so, need to dunk it deep in a barrel to test or run it on your boat. Need the back pressure to make finer adjustments (sounds to me like it could be leaned out a bit -- rpms likely to increase, and smoother running. My idle needle needs to be set a little richer for cold starting, then set back for leaner running when the engine is warm.)

 

[OptsyEagle]

Did you check if the carb is sync'd with the throttle cam/timing plate?

 

[badboybill88]

No Title

If this is what you are referring to regarding the throttle cam/timing plate, then I believe it's bang on.

Please advise.

 

[badboybill88]

So I put the motor down into the barrel, which made it quieter, but didn't really notice any difference. I tried tweaking the low idle needle, and she did run a bit smother once warm, but the issue still existed when I increased the throttle.

However, after trying and testing a few different things, I figured out that if I slowly opened up the choke while I was increasing the throttle, it wouldn't stall. Furthermore, I was able to keep the engine running where it normally would of stalled, but at that point the choke was almost wide open...I have no idea what this means, but I feel as though it is a significant break through.

Thoughts?

 

[oldboat1]

well, IMO that use of the choke to keep it running would indicate to me that there is still a carb issue. The high speed jet is at the bottom of the carb (horizontal bolt). Normal cleaning is to remove the carb and the bolt and soak the body of the carb, then blow through the orifice with compressed air or carb cleaner. If the carb was pretty well gummed up at the bottom, that's where the h.s. jet is -- and it doesn't take much to block it. Sorry.

 

[Thompsoncustom]

I'm having the same problem as you on a 1990 johnson 20hp and like you if I play with the choke I can help it along.

What this means is there is a fuel deliver problem, so it's the carb, lines, fuel pump, or anything between the tank and the carb.

I'll be curious to what solves your problem I've rebuilt my carb and now I'm on to the fuel pump.

 

[OptsyEagle]

Sounds like it has to be the carb. You did indicate that it was dirty. Focus on the high speed jet as oldboat indicated. A soaking in carb cleaner may help. Definitely give it multiple blow outs with compressed air and if you can poke any holes in the jets with soft wire (copper), that may help

Yes, your carb synchronization looks bang on.

 

[AlTn]

if you're unsure of the location of the high speed jet < OMC calls them an office plug >, it's screwed into the bottom of the upper carb body casting that extends down into the float bowl when it's attached...it's brass and is slotted...if you don't have a screwdriver that is an exact fit don't worry about removing the jet, just clean it in place...this goes for your early production '87 carb...the later production carbs with the plastic tops have the high speed jet in a different location