Struggling with Nissan 18hp 4-stroke

oncebitten

Petty Officer 2nd Class
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104
Hi,

First post. I've got a Nissan 18hp 4-stroke remote steering 2003 model year. It's been running progressively worse over the last two seasons. Here's the whole story.

First, let me say, this started after I foolishly tilted the motor up while idling to get at a bunch of nasty mill foil wrapped around my prop. I realized my mistake within seconds and killed the motor, but perhaps some damage was already done. Here's the sypmtoms.

Motor idles fine, runs fine then, suddenly, it will drop rpms, power, speed and almost seems like the prop has stopped spinning. Then, after a few seconds, it picks back up, then randomly, it will happen again, and again. It happens at almost all speeds and durring accelleration. Any time.

It got worse over the course of the summer and this year, after changing gas and heading out with clean lines, drained bowl, fresh gas, it's so bad it won't even get past 3-4mph. Now it's really chugging. My friend says, clean the carbs. Does that sound like the best first step? On another similar thread it was related to the fuel pick up and tempermental carbs. Any suggestions. Thanks.
 
Joined
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Re: Struggling with Nissan 18hp 4-stroke

Your friend was right, I would start off by cleaning the carbs. Let me know if it works.
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

Well, I've taken apart the carb and it looks perfect, brand new, no gleep, no build up, I don't see any clogging of any kind. I'm still going to clean it and rebuild it, but I'm wondering what's next?

Should I replace all my fuel lines, my tank and my filters? Could these kinds of symptoms be caused by a torn up impeller?
 

TOHATSU GURU

Admiral
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Messages
6,164
Re: Struggling with Nissan 18hp 4-stroke

Check the engine compression and check for fire while the engine is on the water. If they are all okay, then clean the carb by soaking it in carburetor cleaner. You probably have a port that's restricted.
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

Thanks. I've got the carb in pieces now, so I'll clean and rebuild, get all new lines and then get her on the water and check things out. I noticed a nick in a wire, I wonder if that has anything to do with my problems.
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

It's a white wire going to the heat sink on top of the intake manifold. When I removed the carb I noticed there is some of the sheating missing- a nick about 1/2 cm long by 1/4 cm wide on the engine side of the connector.
 

TOHATSU GURU

Admiral
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Re: Struggling with Nissan 18hp 4-stroke

Sounds like it is grounding out. Wrap it and try the engine before you do anything else.
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

Is it okay to just put the carb back together using the original gaskets to test whether or not it is the nick in the wire causing problems? Or should I wait until the new gaskets come and I rebuild the carb?
 

TOHATSU GURU

Admiral
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Re: Struggling with Nissan 18hp 4-stroke

The old gaskets are fine...Unless you ripped one:)
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

Alright, after struggling with this issue awhile, here's what happened. I put the carb back together, the nick was not a nick, it turned out after even closer inspection, it was just a strange paint dob from the motor block paint I think. It looked just like a piece of missing insulation on the wire. I did however find a break in my fuel line. I bought more and replaced all the fuel line. I also blew out my carb with air and made sure it was clean- it looked brand new, but I blew it out anyway. I then drained and blew out my line from tank to engine. I put it all back together and took it for a run. After about ten minutes screwing around with the idle screw, I finally got it to level out and run great. She ran perfect for the rest of the day. No more chugging and coughing. I'll have to take her out again soon to see if I fixed the problem and it was in fact just bad gas and then a hole in my fuel line which made it even worse.
 

ziemann

Chief Petty Officer
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Re: Struggling with Nissan 18hp 4-stroke

Outstanding. Treat her well, and she will give you many many years of enjoyment.
 

oncebitten

Petty Officer 2nd Class
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Messages
104
Re: Struggling with Nissan 18hp 4-stroke

Yes, she's a good engine and seemingly very tolerent of my misuse. I'll try to do better by her in the future.

One more question. I can't remember the sequence of gaskets when I took the carb off the intake manifold. There's one thick black gasket/spacer and two thin rubbery gaskets. I thought the thin rubbery ones were stacked up on the manifold side with the thick black one against the carb. Am I wrong about this? Should it be thin-thick-thin? Like a sandwich with the two thin gaskets sandwiching the thick black one? Thanks for any input, my new service manual doesn't address this.
 

oncebitten

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Re: Struggling with Nissan 18hp 4-stroke

Thanks. I guess I've got to take it apart one more time. :|
 

oncebitten

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104
Re: Struggling with Nissan 18hp 4-stroke

Hi again,

While the engine is running better, I'm still getting a mushy bulb after about five minutes of run time. I think I'm still getting air into the system somewhere. Is the bulb supposed to stay firm after you've pumped it up initially? Can the air be coming in anywhere on the system, or does a soft bulb mean it's between the tank and the motor?

I also think I'm going to completely clean my carb (do a full soak) and reasemble because I'm having difficulty getting it running well until it's really well warmed up. I think it could be a sticky slow speed jet problem.

Thanks for help you can give me with the air problem.
 

TOHATSU GURU

Admiral
Joined
Jul 22, 2004
Messages
6,164
Re: Struggling with Nissan 18hp 4-stroke

The soft bulb means that there is a leak somewhere from the fuel pump to the bulb. The bulb itself has a check valve so take a hard look at it too.
 

oncebitten

Petty Officer 2nd Class
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104
Re: Struggling with Nissan 18hp 4-stroke

Thanks once more Elvin. I'll check it all out.
 

fishingdan

Lieutenant Junior Grade
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Feb 12, 2005
Messages
1,045
Re: Struggling with Nissan 18hp 4-stroke

I think you should put a Etec 200 H.O. engine on that GV13 and use the 18 for a kicker. 8) I think Evan would be ok with that.
 

oncebitten

Petty Officer 2nd Class
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Re: Struggling with Nissan 18hp 4-stroke

Ha! 8) You tracked me down. What's up buddy? Now, which site am I supposed to watch? :%

200 H.O. huh? Hmm... I'll take it under advisement.
 
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