bassboy1
Lieutenant Commander
- Joined
- Jun 23, 2006
- Messages
- 1,884
1986 Johnson 50 hp. VRO engine, VRO has long been removed/disabled by previous owner. Unknown history, other than 'ran when parked,' and has been sitting for 6 years.
I've got everything running fine, except I'm currently dealing with a shaky idle. Engine starts very easily (this one has enrichment solenoid instead of choke), I don't have to push the key in to get it to start, nor use fast idle - it just starts with a turn of the key. Runs great at high speed, turns a 17p prop at 5300 revs, so everything seems to be correct at the higher rev range.
It idles fine, just rough - it'll plug along all day long at 750 rpm in gear, just shakes a bunch, and sounds more like a tractor than an outboard. During acceleration, it'll speed up fine, then at a certain throttle position, it'll suddenly sound like an outboard, then back to being a tractor when slowing down.
Compression is 135 on both cylinders, so I can rule that out.
Spark jumps a 7/16 gap (gap style tester), on both cylinders, so ignition seems fine.
Carbs have been rebuilt, and floats set per the included paper (level when upside down, hang down 3/4" when right side up).
I've done a link/sync. That's how I got it idling at 750, and not dying when putting in gear.
I've done cyl. drop test, both by pulling a plug wire when running, and by starting with one unplugged. Engine runs fine on the lower cyl, but does not like running on the upper one - running drop test kills the engine when lower plug wire is pulled. Starting with it pulled, it'll only run on the upper cyl with some fast idle added.
On the surface, this simply sounds like a clogged low speed jet on the #1 carb, and I'm not too proud to accept the possibility that I missed something when cleaning the carbs, however a few things make me think it's running rich on that cylinder, not lean:
1 - with brand new plugs, and about an hour of off and on running in a test tank trying to tune it, the lower plug comes out clean, but the upper one comes out oily.
2 - putting 2 fingers in the carb throat to choke it has absolutely no effect.
3 - it smokes like a steam train, and has a lot of unburned fuel coming out the upper exhaust ports. Changing the plug gap from .030 to .040 seems to improve this a bit (and maybe smooths the idle a little bit, but I can't really say on that).
The fuel pump on this engine is the kind with the 3rd nipple and a hose for crankcase pulse (unit is mounted on the back of the air cleaner - I'm assuming due to the former VRO system), not the kind that's mounted straight to the crankcase. Best I can tell, the pulse hose comes from the #2 cylinder, so I can't even blame a rich condition on #1 cyl on a fuel pump diaphragm leaking. Also, carbs on this model do not have adjustable jets, just fixed ones.
Any thoughts on what I should check next? Or, are the symptoms that I'm thinking are a rich condition actually a red herring, and the #1 carb needs a better cleaning?
I've got everything running fine, except I'm currently dealing with a shaky idle. Engine starts very easily (this one has enrichment solenoid instead of choke), I don't have to push the key in to get it to start, nor use fast idle - it just starts with a turn of the key. Runs great at high speed, turns a 17p prop at 5300 revs, so everything seems to be correct at the higher rev range.
It idles fine, just rough - it'll plug along all day long at 750 rpm in gear, just shakes a bunch, and sounds more like a tractor than an outboard. During acceleration, it'll speed up fine, then at a certain throttle position, it'll suddenly sound like an outboard, then back to being a tractor when slowing down.
Compression is 135 on both cylinders, so I can rule that out.
Spark jumps a 7/16 gap (gap style tester), on both cylinders, so ignition seems fine.
Carbs have been rebuilt, and floats set per the included paper (level when upside down, hang down 3/4" when right side up).
I've done a link/sync. That's how I got it idling at 750, and not dying when putting in gear.
I've done cyl. drop test, both by pulling a plug wire when running, and by starting with one unplugged. Engine runs fine on the lower cyl, but does not like running on the upper one - running drop test kills the engine when lower plug wire is pulled. Starting with it pulled, it'll only run on the upper cyl with some fast idle added.
On the surface, this simply sounds like a clogged low speed jet on the #1 carb, and I'm not too proud to accept the possibility that I missed something when cleaning the carbs, however a few things make me think it's running rich on that cylinder, not lean:
1 - with brand new plugs, and about an hour of off and on running in a test tank trying to tune it, the lower plug comes out clean, but the upper one comes out oily.
2 - putting 2 fingers in the carb throat to choke it has absolutely no effect.
3 - it smokes like a steam train, and has a lot of unburned fuel coming out the upper exhaust ports. Changing the plug gap from .030 to .040 seems to improve this a bit (and maybe smooths the idle a little bit, but I can't really say on that).
The fuel pump on this engine is the kind with the 3rd nipple and a hose for crankcase pulse (unit is mounted on the back of the air cleaner - I'm assuming due to the former VRO system), not the kind that's mounted straight to the crankcase. Best I can tell, the pulse hose comes from the #2 cylinder, so I can't even blame a rich condition on #1 cyl on a fuel pump diaphragm leaking. Also, carbs on this model do not have adjustable jets, just fixed ones.
Any thoughts on what I should check next? Or, are the symptoms that I'm thinking are a rich condition actually a red herring, and the #1 carb needs a better cleaning?
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