69 johnson 25hp half power

[Saintnowhere]

ok i got a 69 johnson 25hp. it starts and idles fine, but when you go wot it just kind of falls on its face slowly accelerating, never reaches full rpm and just kind of stumble/surges slightly when it tops out at its low rpm. kind of like its getting too much fuel. It runs a lot better with the hood off but i know its not good too as it leans out the mixture. I know its not a fuel delivery issue, lines replaced, fuel pump replaced, full cleaning and carb kit installed float properly adjusted. carb has been off 2 more times since to check for debris and dirt. also been link and synched. also hoses fittings and tank are ok and vented.

Head gasket has been changed, new thermostat also, compression is 120 on both cylinders.
new points and condensers, adjusted to 020. coils that were in it are the new light green aftermarket has new plug wires also
it was getting oily so i changed the crank seal completely cleaned ignition components and mag plate checked for worn/damaged wires. gets nice blue spark at 1/4 gap on tester.

So i am stumped only thing i can think of now is blown base gasket, someone damaged or drilled the main jet or reed problem. those are my next 3 to go through. like i said taking the hood off helps tremendously but still not 100%.

Its on a 14/36 flat bottom with 9x10 prop and does 18mph
with the same boat and load and my 68 evinrude 18hp with same prop it gets 24mph

So before i tear the power head off if anyone has some ideas on what to try or check let me know

 

[oldboat1]

Prop in good shape? (18 mph doesn't seem too bad)

 

[racerone]

Maybe a reed valve issue.-----That 25 hp should scream at 5500 rpm !!----But is the serial # on the block the sane as the tag on the transom bracket ?

 

[Saintnowhere]

yeah original block/head/carb etc. 18mph is bad for this motor there was a couple times it kicked into full power for a few min did 28mph on my gps, thats why i went through the fuel system completely it was first on my list of suspects. also pumping the bulb does nothing before anyone asks and i know its not the fuel tank as i took a second one and tried it out.

 

[Saintnowhere]

prop is fine, not spun or damaged also not cavitating

 

[Saintnowhere]

I'm leaning towards reed valves also if i do those i'm changing the base gasket and lower seal also

 

[racerone]

Some will argue.----I would run with a timing light hooked up to see if spark is misbehaving.----Reed valves would not suddenly start working properly.

 

[oldboat1]

once had similar symptoms, finally resolved by pulling a mouse nest out from the exhaust, way up the leg under the powerhead. Might be worth probing up there with a flashlight and a coat hanger. Easy enough to check.

Removing the intake manifold and inspecting the reeds for a broken or missing leaf might be in order. If doing that, some disassembly and checking of the carb again would be reasonable. Make sure the choke linkage is holding the choke open when appropriate, also that the high speed orifice is squeaky clean. If you decide to remove it for inspection, the oem jet should be 72D.

 

[Saintnowhere]

You know a mouse nest or something simmilar is possible, i remember one time i left a fuel line hanging loose one night on a fourwheeler. the next day it started running like crap, turned out a spider crawled in the line and got stuck before the needle restricting fuel. took awhile to figure that out, anything is possible i will check. thanks

 

[oldboat1]

yup. Weird stuff.

 

[boobie]

You got to remember, it takes four things to make a motor run. Ignition, compression, fuel and EXHAUST !!

 

[Chinewalker]

I'm leaning toward ignition. Intermittent burst of wide open is typical of an ignition component failing. Check condensers and CLEAN points. Make sure coil wires a tucked out of the way of flywheel and cam.

 

[Saintnowhere]

I think i may have solved it. I pulled the mag plate and carb off today for testing and re cleaning.
pulled the coils disconnected condensers. coils checked out fine, the condenser for #2 cylinder was
discharging too quickly So i swapped it out for a spare i had. So when i was putting it all back together
I noticed under the linkage the kill switch wires were flattened pretty good near the screws. i twisted
it around and saw a little shiny spot. Well it just so happens to run to the #2 points. I think it was grounding due
to the vibration under load and shorting that cylinder and killed the condenser.

So i fixed those issues and will be testing it this weekend, hopefully that takes care of it.

 

[Willyclay]

Thanks for the update, good luck!

 

[Saintnowhere]

Ok sorry for the late response, have been busy. It helped a little but problem was still there so i decided to pull the powerhead. Turns out the base gasket was blown in two places between the exhuast and driveshaft ports and a 1.5 inch section on the front near the carb on the driveshaft section so i'm assuming if the lower seal was leaking it was sucking exhuast into the crank case there and also blowing out under the cowling sucking it into the carb also. So ordered some new seals and gaskets hopefully have it back together by this weekend. gonna pull the intake and check my reeds while im at it. i will report back when i get it done and test

 

[Willyclay]

Great find and, hopefully, that will get you going again!

 

[Saintnowhere]

It should, i pulled the carbon bearing and it was broken on top so that's another part i had to order, So i may not have it out this weekend. also realized it was missing the water pump spacer and throttle cam was "modified" ill get pics once i get the replacement i do not know what was trying to be done. plenty of time to clean and inspect everything else. she should be in tip top shape when i'm done.

 

[Saintnowhere]

well i took it out last weekend and it ran smoother but it was bogging even worse, even with the cowl off i could only get 21mph out of it so it lost a few mph and rpm, so over this weekend i replaced the reed plate and intake gaskets and all the rest on the engine, i smoothed the reed side of the plate with 1200 grit sandpaper adjusted the reeds.

I also bought a new #72 jet turns out someone did drill the original the new one measured .072 and the old one
measured .088 but both are marked 72 so i'm guessing by fixing the air leaks caused the lower performance due to it being even richer. plus the nasty black oil running out from where the lower meets the leg was a little bit of a give away.

So in a few days i'm taking her back out, the motor has been completely gone through i Believe it will do good now, if not i'm going to throw it off the back of the boat and paddle back.

 

[oldboat1]

Good sleuthing on the jet!

 

[Newfin]

Okay, this is going to sound weird but I have the same motor with what sounds like the exact same problem. I had installed all new electrical components on the motor after I bought it. I would take the motor out and once it got hot it would cut out on me. It seemed like the power was draining from it suddenly, then sputter out and stall. After a few pulls it would restart and repeat the stall again in a while. I was stumped. Everything was new. While inspecting the plug wires (new) I noticed one seemed a little shorter. I began to wonder if at WOT one of the plug wires might be pulled too far and start to lose contact with the coil. I decided to replace the shorter wire with a longer one and the problem went away. The reason I focused on an electrical problem is because of the way the motor would run at 5500 And then suddenly die. That doesn’t seem like a fuel problem. It was the way it died. It felt like the spark was being robbed. Also check the connection of the plug spring with the conductor in the plug wire. Hope this helps.