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Johnson 140 bucking.

K

Kreeper

New member
Hi. I've got an 86 Johnson 140 that I'm having endless problems with, any help would be much appreciated.
I've had it at a shop (which was hard to find because apparently my motor is too old for most shops to work on). They said the CDI was done, so replaced it (with a supposedly good used one). I've changed leads, fuels lines, fuel/water filter, ultra sonic clean on the carbs. I'm nearly at my wit's end, I'm sure someone on here has had the same.
It may be from a couple of things. It will idle fine, but bucks like it's in some kind of limp mode? Also, when I've had it running right, I'll shoot out for a test and 10 mins in it will start coughing, and I'll have to idle home.
Has anyone got a solution for me?
Thank you
 
This sounds like a fuel restriction. I'm not 100% sure, but the suggestions below cost you $0 to check and fix.

Is your fuel pump diaphragm in good shape?
-- A bad diaphragm can be inefficient and not deliver enough fuel to the engine under high demand.

Did you change the primer bulb when you changed fuel lines?
-- A primer bulb (even a new one) can have an internal issue and create a flow restriction.

Have you checked your fuel tank vent to make sure it's clear?
-- Spiders and other gunk can clog up your vent which then creates a vacuum in the tank as the fuel pump removes volume from the tank. The vent should operate freely to let air in.

When you open the fuel filler cap, does it make a sucking sound?
-- If it does you definitely have a venting problem.

Does your fuel tank have an anti-siphon valve in your fuel pickup tube where the 3/8" line connects?
--This is a ball and spring valve that prevents fuel from getting sucked out of the tank through siphon action as the boat sets. This is most common in boats where the tank is higher than the engine. The vacuum created by the engine fuel pump sucks against the anti-siphon valve and compresses the spring to allow fuel to flow. When the engine isn't running the spring seats the ball and closes off fuel flow. These can get gunked up over time and cause a restriction which decreases fuel delivery to your engine. The fuel pickup can be removed and the anti-siphon ball and spring knocked out.

KJ
 
The term ---" bucking "----Might suggest it is jumping in and out of gear.--Any videos of this behaviour ?-----Could also be a lean condition.----Due to fuel starvation or crankcase compression.
 
Last edited:
Thanks KJ great thoughts.
Yes all new internals in the VRO pump.
The bulb is new and I checked it before installing and it seemed to operate well.
She's got under floor tanks that I swear breathe too much!
I will investigate more, and try to get a video up so you can hear it.
Much appreciated


kevinj said:
This sounds like a fuel restriction. I'm not 100% sure, but the suggestions below cost you $0 to check and fix.

Is your fuel pump diaphragm in good shape?
-- A bad diaphragm can be inefficient and not deliver enough fuel to the engine under high demand.

Did you change the primer bulb when you changed fuel lines?
-- A primer bulb (even a new one) can have an internal issue and create a flow restriction.

Have you checked your fuel tank vent to make sure it's clear?
-- Spiders and other gunk can clog up your vent which then creates a vacuum in the tank as the fuel pump removes volume from the tank. The vent should operate freely to let air in.

When you open the fuel filler cap, does it make a sucking sound?
-- If it does you definitely have a venting problem.

Does your fuel tank have an anti-siphon valve in your fuel pickup tube where the 3/8" line connects?
--This is a ball and spring valve that prevents fuel from getting sucked out of the tank through siphon action as the boat sets. This is most common in boats where the tank is higher than the engine. The vacuum created by the engine fuel pump sucks against the anti-siphon valve and compresses the spring to allow fuel to flow. When the engine isn't running the spring seats the ball and closes off fuel flow. These can get gunked up over time and cause a restriction which decreases fuel delivery to your engine. The fuel pickup can be removed and the anti-siphon ball and spring knocked out.

KJ
Click to expand...
 
You should not be opening throttle without advancing ignition .-----But a process called ----Link & sync -----might help.-----Or hook up a timing light ( one cylinder at a time ) and see if light shows a problem.
 
racerone said:
You should not be opening throttle without advancing ignition .-----But a process called ----Link & sync -----might help.-----Or hook up a timing light ( one cylinder at a time ) and see if light shows a problem.
Click to expand...

Thank you. I'll track down my timing light and have a look.
I take it you mean when I just hit the lever on the carbs? It does the same when using the shift lever, in neutral or in gear.
Thanks again.
 
Put a timing lite on each cylinder when it's doing it and look for black spots. You could have an ignition problem.
 
Looks like a fuel issue. If I was going through what you are going through I would do it this way

1. warm up engine for 5minutes.
2. test compression on every cylinder.
3. test spark on every cylinder. (I just keep 1 plug in and crank engine. If it does anything that’s not cranking that cyl has spark.
4. tear down those carbs and find the problem. I do think it’s a fuel restriction issue. But just to make sure everything else is good do the above steps first. Sounds like something is clogged in those carbs. Also make sure that the carbs arent leaking.
5. check your timing on #1 cyl at idle and at WOT.

I think it’s a fuel problem. But you should definitely check spark, compression, and timing as well.

the last thing you want is to fix the fuel issue and then take the boat out and realize there’s a couple cyl that aren’t firing
 
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