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Old 11-08-2010, 11:59   #1
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Help ! . . . Johnson 8hp Dies After 20 Minutes !

The circa 1990 8 hp Johnson outboard on my dingy dies after running fine for 20 min. It will loose power and then only run at just above idle for a couple of minutes and then die completely. After sitting for 1/2 hour it will run again.
Pumping the fuel bulb make no difference and it feels fine. Cooling water output stream remains fine. Plugs are fine. Is there some electrical component that what cause this situation? Because it takes so long to occur, it is difficult to trouble shoot.
Any suggestions appreciated.
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Old 11-08-2010, 12:06   #2
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Sounds like fuel starvation or vapor lock........maybe even dirty carb. But almost definetly fuel problem.
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Old 11-08-2010, 12:09   #3
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I have had similar problems in cars where the fuel filter has not been replaced and gradually blocks during use. It unblocks when the fuel pressure drops off.
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Old 11-08-2010, 12:26   #4
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Sounds like overheating to me. Are you sure the cooling water is flowing properly? Check the pump impellor.If it has lost a blade or two, it will over heat and sieze, then run again once it has cooled a bit.
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Old 11-08-2010, 12:28   #5
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had a similar problem. turned out to be the fuel pump. i just replaced all the membranes and haven't had a problem since (couple of months now)
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Old 11-08-2010, 13:13   #6
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An ignition coil that loses its oomph as it heats will give EXACTLY those symptoms. This is fairly common. Have you checked the spark just after it quits running? It should jump 3/8" with a bright blue intense "SNAP".

The clogged fuel filter issue mentioned by mintyspilot came to mind as well. That can cause fuel starvation that will then self correct over time after shut-down as the fuel seeps through the filter into the system allowing it to run again, for awhile, until the vacuum again over-powers the fuel pump. But your bulb pumped up hard does not support a clogged filter on the tank end of the bulb.

Debris in the lower end of the carb (bowl, float, needle valve, main jet and emulsion tube) can have this same effect, though the consistant timing of the problem you mention, with the gradually reducing speed, indicates maybe more like a normal-heating-caused issue, like a faulty coil, or an over-heating-caused issue, like vapor lock.

Overheating can occur even if its peeing properly - thermostat can fail, blockage due to accumulated salts and mineral deposits can clog certain critical cooling passages, as can debris from a rotten imepller that was not changed in time.

Overhaul your carb with a kit if its not been done in years. Cheap and easy.

The new 10% ethanol in gas has cost boat owners literally tens of millions of dollars in fuel system problems since it was mandated - an outboard mechanic I know sez his business has doubled since ethanol, all carb rebuilds. When you shut down the engine for weeks or months, disconnect the fuel line while running at a high idle and allow the engine to burn the fuel from the carb so it doesn't leave so much 'varnish', particles and crud in your carb as it dries over time.

Marineengine dot com has great outboard engine forums with many extremely knowledgeable folks that seem to live to help you with those engines... They will work you through the problem one step at a time.

That engine you have is pretty easy to work on once you dig in and go for it. You need to do the carb and check/replace the impeller every few years to keep reliability up anyway - I'd start with those of its not been done in three years.
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Old 11-08-2010, 13:33   #7
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A 1990 Evinrude 8 has 2 ignition coils and this engine will run on one cylinder, not well but will continue to run. The major ignition component that will effect both cyl. is the ignition module (Pack). On that engine this module is located under the flywheel. As stated above when the issue is present you will need to verify spark output. No spark - I would change that item. The other thing on that unit is the fuel pick up pipe in the remote tank can come loose from the fitting. If I read you right you just said pumping the primer is no help. If that pipe is loose you can pump all day and still get little or no fuel.
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Old 11-08-2010, 13:54   #8
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OK one obvious problem that has been mentioned in this forum (was a certain moderator who shall remain nameless but she is cute) had a similar problem and it turned out to be the fuel air valve on the gas tank was closed.
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Old 11-08-2010, 14:22   #9
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HEY!
...i resemble that remark....

And I was actually gonna offer up my own lesson learned... yeah, check that you have opened the tank vent, or cracked the fuel cap so that there is air flow...

; -)
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Old 11-08-2010, 14:32   #10
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OOPS, BUSTED.
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Old 11-08-2010, 14:35   #11
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Quote:
Originally Posted by S/V_Surya View Post
OK one obvious problem that has been mentioned in this forum (was a certain moderator who shall remain nameless but she is cute) had a similar problem and it turned out to be the fuel air valve on the gas tank was closed.
PRECISELY the cure I was going to propose!
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Old 11-08-2010, 14:35   #12
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Not sure (even though my engine has quit many times due to my forgetting to open tank vent ) but doesn't a closed tank vent, or a clogged tank-side fuel filter (in relation to primer bulb), result in a collapsed, or at least soft primer bulb?
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Old 11-08-2010, 14:41   #13
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For sure, but an air leak on the pick up side will only cause the bulb to seem wimmpy. I seen some after market bulbs so stiff you could't tell. Have also seen some of the cheapo bulbs lock the gozinta check valve and act wierd
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Old 11-08-2010, 14:49   #14
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Is this and older Johnson or a new one? I had an older Johnson with the same exact symtoms. Several carb rebuilds, and colling impellors lator. I pulled it completely apart with the intent to rebuild the engine. I found the cooling pickup line going from the pump to the engine goes through a cone shaped rubber gasket, that had melted shut into the line. scraping and drilling this gasket out of the cooling pipe fixed the problem. I talked to a johnson mechanic and he said every johnson outboard he has worked on had this problem. I had to pull the engine off of the lower unit to fix. (not as hard as it sounds).
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Old 11-08-2010, 18:02   #15
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I have a 58 year old "Johnson"

Still working fine!!!!!!!!!!!!!!!!!!!!!!!

Sorry....after the "day" I have had, I need to put a little humor into this.
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