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Old 12-08-2010, 06:57   #16
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Clarification

Thanks for all the suggestions. I have the motor apart in my basement now, I cleaned out the fuel pump last night, found a nice online diagram for it and it looks like its in good shape. I will clean out the carb tonight. In response to some of the comments:

The 8 hp Johnson engine is a 2000, not a 1990.
The tank vent was open.
While the engine was dying, I squeezed the fuel bulb, it was firm and lots of gas was getting to the engine.
The plugs fired fine the next day.

I think that this is an issue caused by normal heat buildup affecting an electrical component such as the power pack or coils (or are they all the same part?) I guess the only way to find out is to run it till it quits and check the spark.

Can't rule out overheating though. I felt the cooling water discharge as the engine was dying and it felt warm, but not hot. Is there any way to clean the cooling passages other than circulating fresh water? I will check the impellor.
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Old 12-08-2010, 08:26   #17
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Still working fine!!!!!!!!!!!!!!!!!!!!!!!

Sorry....after the "day" I have had, I need to put a little humor into this.
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Old 17-08-2010, 16:04   #18
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Still no luck

Still can't solve my 2000 8 hp engine issue although it is getting worse which should make it easier to diagnose. It now dies after just running a few minutes so it is not overheating. There is still spark so I now believe it is a fuel issue. I added a new fuel hose and bulb, no change. I found that the engine will keep running by continously pushing in an out on the choke and revving the engine. Could a flakey fuel pump do this? The carb looked very clean when I took it apart.
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Old 17-08-2010, 16:25   #19
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Aloha Zippy,

Have you tried a new or borrowed tank, hose and fittings? You might also try (as an experiment) a section of hose with the engine side fitting directly to a can of clean mixed 2 cycle fuel and set it higher than your engine so it is gravity feed. What you are describing as symtoms definitely is a fuel starvation problem. For some reason clean fuel is not flowing freely to your carb. Does the float in the carb work easily and properly? When I had to use the choke to keep my old gas IH tractor running I knew it was time to clean out the fuel tank. Used to happen on my old '57 Beetle too.

kind regards,
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Old 17-08-2010, 16:47   #20
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...I found that the engine will keep running by continously pushing in an out on the choke and revving the engine....
That's usually a clogged main jet, and/or a leaky float, and/or a misadjusted float level, and/or otheriwse float/needle-valve related, and/or a dirty emulsion tube.

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...Could a flakey fuel pump do this?...
Remotely possible, but if there is fuel enough in the bowl to run it when the choke is on, its not likely a fuel pump issue. Besides, you ruled that out before when you squeezed the bulb when it was acting up and it didn't help...

You may want to go ahead and buy the carb kit and rebuild the carb according to instructions linked below - its a thing we have to do WAY more often now that we're turning some our our food into high-priced, low-grade fuel (the process is heavily taxpayer subsidized), and then using that product to degrade our lower-priced, higher-grade fuel .

Read all these 4 threads, then just GO DO IT:

~~~~~~~~~~~~~~~~~~~~~~~~~~~
CARB NOTES AND REBUILD LINKS

ALCOHOL, FUEL LINES AND CARBS:

http://forums.iboats.com/showthread.php?t=330129

http://forums.iboats.com/showthread.php?t=244013

http://forums.iboats.com/showthread.php?t=258536

http://forums.iboats.com/showthread.php?t=338495
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Old 17-08-2010, 16:47   #21
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Even though you looked at the carb, and it "looked" clean, it may still have clogged jets. Only a complete disassembly and through cleaning can eliminate the carb as the problem. Expensive, but an easy way would be to replace the carb with a new one. I do agree that the problem is in the fuel system.
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Old 17-08-2010, 17:46   #22
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Couldn't agree more with Whimsey.

I've been selling and servicing Evinrude & Johnson motors since 1971. And have seen way to many people pop a float bowl and call all is well. Buy a kit and take her down all the way so you can see all the small passages. Really take a look at the plastic top. If it's that new I've seen them crack.

Hope it helps

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Old 17-08-2010, 18:35   #23
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Another vote for a carb problem from someone who owns a 2004 Johnson 8 HP. Possibly a sticking float and/or needle valve. Could be just crud in there somewhere. Your fuel is gradually being cut off. If it was a low speed or high speed jet problem it wouldn't run well in the first place. In any case, for many more years than I want to count I have added StaBil to every can of gas, along with the 2-stroke oil. The StaBil seems to keep everything working well.
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Old 17-08-2010, 19:36   #24
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change the fuel filter first
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Old 18-08-2010, 01:59   #25
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Oftentimes when an engine will only run on choke or at high revs, it is sucking air between the carb and the head/block. Make sure that connection is sound. If it is a 2 stroke, overheating is still a good guess. The piston siezes in the barrel till it cools a bit.
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Old 18-08-2010, 02:06   #26
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I haven't read this thread fully, basically I know nothing about outboards...
but isn't that Johnson 8ph one that you can fiddle with the carb (or something) and turn it into a 15 hp?

May the previous ower done that and now you need to correct it?

Just a thought Please disregard if I am a goose


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Old 18-08-2010, 02:28   #27
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Just a thought Please disregard if I am a goose

If?

Couldn't resist.

I have one of these. Asked the conversion question at the shop and get no satisfiying answer.

Thanks for asking goo... Mark. Maybe now someone will bring me peace on the subject.
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Old 18-08-2010, 06:00   #28
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but isn't that Johnson 8ph one that you can fiddle with the carb (or something) and turn it into a 15 hp?
Nope - The 8 is in the same family as the 6. The 15 is in the same family as 9.9.

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Old 19-07-2011, 17:24   #29
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Re: Problem Solved

I felt that that this problem was caused by overheating of something, so even though there was a return of cooling water, I replaced the raw cooling water impellor and my problem has been solved. The impellor was not broken but it was a bit out of shape. It must have been deformed enough to provide an insufficient volume of cooling water to the engine. I have been out for 2 long runs now, and no stalling .
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Old 19-07-2011, 22:58   #30
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Re: Help ! . . . Johnson 8hp Dies After 20 Minutes !

Congratulations! Your answer went a totally different direction than the information I provided but I'm glad you got it sorted out.
kind regards,
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