1974 15hp Evinrude outboard kills under load when in gear.

[bbassett]

I have a 1974 15hp Evinrude that had been sitting around for a few years. Before starting, I removed the carb, cleaned and installed a carb kit, changed fuel filter, installed new NGK spark plugs, and used fresh gas. Motor starts well and will idle good. Will run in forward or reverse but only at slow speeds. As soon as I try to go fast, it will kill unless I back off. I checked spark and both cylinders will jump a 1/2 inch gap. Checked points - just to make sure and adjustment was OK. Did a compression test and both cylinders were the same at about 80 psi. Changed fuel pump and have tried pumping bulb - all without success. I took motor off and put in a tub of water and seems to run fine. Have seen comments in this forum about checking the sync and link but not sure what that is or if it could cause the issue I am seeing. Have also seen comment about maybe old plug wires causing but not if that would cause issue either. Motor ran fine when it got put away. Any help would be appreciated.

 

[oldboat1]

Could be something missed in the carb cleaning, or technique. I would use the oem plugs (L82C gapped at .030), but that alone probably isn't the issue.

 

[TyeeMan]

Sounds like you might have some schmutz in the high speed jet on the carb. Or, if there is an adjustable high speed jet it might be set too lean or too rich. Try screwing the high speed jet in until it lightly seats, then back it out 3/4 turn, use that as your starting point.
Either in a test tank or on the lake fire up the motor and warm it up some. Adjust your idle jet, cuz if that's not set correctly you will have a hard time transitioning into the high speed jet.
Turn your idle/low speed jet in (clockwise) slowly until the motor start to stumble, it will be running lean, remember that spot. Then turn the jet out (counterclockwise) until the motor again starts to stumble, now it will be running rich, remember that spot. Now turn the jet clockwise half way between the two stumbling points and that will be your setting.

Do the same thing with your high speed jet but BE CAREFUL if you are on the lake.

 

[racerone]

Adjustable high speed jet on a 1974 model 15 hp ???----No such thing.---It is a fixed jet.

 

[bbassett]

Thanks. I will try resetting the low speed jet and let you know what I find.

 

[oldboat1]

If referring to an extra filter, I would remove it. Compression on my '80s 9.9s is in the 120s, for a point of reference. Maybe consider a head gasket -- while in there replace the thermostat and gasket, and resurface both the head cover and t.stat cover. (You have to pull the head cover to get at the t.stat).

 

[flyingscott]

Your compression is just a little low but that could be your gauge. I have had 15-20 of those motors over the last 2 yrs and all of them have had between 90-95 psi and were all good running motors. My low hrs 77 model is about 92psi per hole. These are not high compression motors

 

[scout-j-m]

Did you try to choke it a little when you gave it some throttle? If not maybe give that a try and if it has little more power then it almost has to be your high speed jet still being partially clogged.

 

[bbassett]

I reset the low speed jet based on Tyeeman recommendation but still same issue. I removed the additional filter but still same issue. I did try to run with the choke on and that worked. I took carb apart again and high speed jet - assume this is the one in the middle of the float but want to make sure - was clean but cleaned whole carb again. Still only works with choke on. Any other suggestions?

 

[oldboat1]

That carb may be a difficult one to clean. An orifice plug screws out at the bottom what looks to be the nozzle running up vertically -- not sure what comes apart in yours. In older styles, a brass nozzle with small openings screws out -- but maybe not on yours.

In any case, the top half should be disassembled and soaked. All of the jets/openings need to be accessed, either removed or soaked/opened up. The domed fitting(s) need to come off prior to soaking. Afterwards, spray all openings with carb spray before reassembly. The needle should be removed as well, and the needle passage sprayed out after soaking (plastic hose on the carb spray). Given your issues, I carefully would go through everything with fine wire or mono as well. Make sure there isn't the point of an old needle jammed in the needle housing (would see that if the domed fitting is removed). You do not seem to be getting a response to idle needle adjustments, and that still hints at a blockage somewhere -- as does the inability to run with the choke off.

 

[bbassett]

Going to order another carb kit and go thru it again. Will soak in parts washer until I get the kit. Will let you know how it turns out.

 

[bbassett]

I just took the carb apart and I think the needle hole was slightly plugged. One question I have is should the needle be sharp or slightly dull. Mine is slightly dull but when fully inserted you can see it coming into the hole on the other side.

 

[oldboat1]

Sounds like the needle is probably fine -- good to check the fit like you did. Doesn't take much of a blockage to cause issues.

 

[bbassett]

Thanks. I remove the two aluminum plugs but wondered if I should also try to remove the other plugs. I read somewhere that they're lead plugs but I see they don't come in the carb rebuild kit. So if you do recommend taking them out what do you use to plug the holes afterward.

 

[oldboat1]

Would leave the lead plugs sealed up. Soak the carb top with them in. (Don't need to remove the springs and linkages before soaking, btw.)