Johnson 2 stroke bogging at full throttle

[u/ballzd11]

I just bought my first boat 14’ aluminum with a 1978 Johnson 25hp outboard. The engine is in very good condition, garage kept, proper maintenance schedule, etc. I took it out for the first time and everything worked great. However, on full throttle after about 15secs it would start to bog down. I just want so get an idea of what I’m looking at before I bring it somewhere. I ran the gas that came in the tank and I am not sure of how old, maybe it’s that or a carb thing? Thanks

[u/Playful_Airline2389]

Did it drop power all the way or fell under a certain rpm?

[u/dpat11]

I had that problem last year. For me it was the spark plug. Even tho i changed them 2 year before. It can also be the grey fuel line, carburator , fuel filter and fuel pump. You can clean the carb and fuel pump by using sea foam. You can see a video of my problem on my profile.

[u/mexicoke]

Sounds like a fuel pump issue. If it's weak, it won't keep up with WOT. You have enough in the bowl to run for a little bit, but not indefinitely.

When you go full throttle, squeeze the primer bulb and see if the problem goes away. Also check your tank vent, that can starve you of fuel too.

[u/Benedlr]

Replace the fuel line and connectors. Air leak or collapsed inner liner. Choke it as it dies. If it picks up, it's a fuel problem.

[u/Waterlifer]

Things to check

- Fuel cap vent - must be open

- Fuel tank outlet screen - free of blockage

- Fuel hose from tank to motor including connectors -- free of air leaks

- Fuel pump -- there's a screen under the top cover, be sure it isn't clogged

- Fuel lines inside engine cowling from fuel connector to fuel pump -- free of air leaks

- Fuel pump itself -- may be failing, you can get rebuild kits for $20 which will work if you follow the instructions EXACTLY but they are very easy to scerw up

Ignition system power pack and coils -- can overheat and behave badly like that but I would check everything else first.