Outboard Motor Acting Up - Idle Speed Only

[MrAntigone]

I have an old Johnson 2-stroke 50 HP outboard that's been acting up. When underway, it runs fine for a bit, but after a while of increased throttle the motor dies down to idle speed. However, when the squeeze ball is pumped it has gone back up again, but then later again returns to idle speed.

We checked both carburetors and they look clean. We also replaced both spark plugs and the fuel filter.

We considered the fuel pump - but this would seem either to work not at all or work fine - not be "kind of needing replacement" - similar to a spun prop which we also considered and ruled out since it has managed to rise above idle speed at times.

Any other considerations/suggestions?

Thanks!

[sparrowhawk1]

Just to clarify: you can get it to run fine by squeezing the bulb?

[motion30]

You need a new fuel pump

[JPA Cate]

When you checked the carbs, did you blow out the jets? check the fuel for any kind of particulate matter?

[Had a spun prop, it would only work at idle.]

Ann

[Reefmagnet]

Check the tank vent is open/working.

[belizesailor]

Only realistic way to check/clean carbs is to tear them down, clean (careful w the jets), and reassemble.

Re fuel pump. Sometimes the diaphram gets perforated and can cause issues other than work/not work. That's inexpensive and easy to replace.

Maybe a vaccum leak. They can be intermittent and only occur after sufficient vaccum has built up...like after a few minutes of running.

Tank vent. On the outside chance that you have an obstruction there check/clean. You can also make a run with tank cap loose to confirm vaccum is not forming in tank.

Another thought along these lines: is it a portable tank or permanent install? If perm, is vent on cap or seperate vent line?

If you don't get off that easy then:

Clean the carbs.

Inspect the fuel pump (esp diaphram).

Check all fitings on vaccum side of fuel line from pump to tank.

[sparrowhawk1]

If There was a problem with the fuel tank vent you would not be able to pump fuel through the ball it would stay collapsed. Most likely it's an air leak. first place I would look is at the hose connector to the engine. Usually if air is leaking in if you pump on the ball fuel will leak out. second place: the hose connector to the tank which is easier because all you have to do is disconnect it put the hose in the tank. For checking for the leaks on any hoses on the engine or even the fuel pump case once again use the ball pump to pressurize the system and look for leaks

[Ex-Calif]

Observe the fuel filter while running - use opaque filters. You can see the air bubble growing.

Fix the suction air side leak.

Double check the vent - while it may not be totally blocked, it could be restricted.

There is no debris in the tank, right?

Only other thought is, "What boat is this engine powering and has the tank been relocated recently?" i.e. lowered in the hull so the lift is higher.

[belizesailor]

Originally Posted by Ex-Calif

Observe the fuel filter while running - use opaque filters. You can see the air bubble growing.
....

Cleaned/Changed your fuel filter lately? These symptoms are similar to a clogged filter too.

Should at least add that to the list to things to check.

[NoTies]

Don't forget the filter inside the tank on the pick up

[chouliha]

That is exactly what happened to my Yamaha 8hp Enduro a few weeks ago.. Exactly! Everyone said fuel pump. But what it turned out to be was an old hose fitting. Replaced the hose with a Yamaha version, cleaned the tank, removed and cleaned the carb. Blew the jets out, etc.

Been working like a champ now.

My suggestion. Is to do all the regular checks before you spring for a new fuel pump.

How old is the fuel?

Good luck

Chuck


Sent from my iPad using Cruisers Sailing Forum

[cwyckham]

A simple mistake that I've made three times now: Fuel goes bad, especially mixed fuel. If the gas isn't fresh, start by buying brand new fuel from a source that gets a lot of turnover. Only then start trouble shooting the engine itself.