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Old 02-09-2013, 16:14   #1
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4hp Nissan OB Won't Start

The 4-stroke 4hp Nissan (2003, I think) that came with the boat/dinghy won't start. I'm happy to be this far down on the "to do" list, but I'm out of my depth on this one. I have drained the fuel, blown out the fuel lines, and taken apart and cleaned the carb a couple of times. I changed the spark plug (old one was pretty black) and checked that I have a spark with the new plug out and grounded. I have good fuel up to the carb when I pull the cord. The engine arrived (after winter storage) with a half tank of fuel, and I know I laid it down the wrong way in the back of the car until I learned better. The engine appears very clean--low hours despite the age. Any suggestions to try next?
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Old 03-09-2013, 14:06   #2
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Re: 4hp Nissan OB Won't Start

No bites yet, I see. OK, maybe I just need to be patient...but maybe I need to mention anchors, guns, or multihulls to get some quick replies. So here goes: What sort of gun should I use to shoot my (currently useless) Nissan 4hp outboard to (a) work out my aggression, and (b) turn it into an anchor for a friend's trimaran?
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Old 03-09-2013, 14:51   #3
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Re: 4hp Nissan OB Won't Start

It sounds like a carb problem. Are you sure you got the carb fully clean?
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Old 03-09-2013, 14:53   #4
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Re: 4hp Nissan OB Won't Start

Will it start if you use starting fluid?
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Old 03-09-2013, 15:05   #5
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Re: 4hp Nissan OB Won't Start

How did you "clean the carb"? Did you clean the jets? This is usually the problem especially with ethanol fuel. When you pulled the start cord a few times did you pull the plug and check that there was fuel on it? Was the plug wet? If you are getting a spark and the engine doesn't fire then in all probability, it's not getting fuel.
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Old 03-09-2013, 15:16   #6
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Re: 4hp Nissan OB Won't Start

My standard approach with O/Bs today that won't start is to first check for spark. If spark is there (and you confirmed that in your first post), then it is almost certainly fuel. If there is no spark then it might be the shut off wire or switch or it may be a bad electric module.

The if spark is present then disconnect the fuel supply line to the carb and then dump all of the fuel through that hose. If fuel won't flow through the hose, then it is plugged with junk. Clean.

Wash the tank out with clean fuel after draining it and make sure that fuel flows easily out of the hose.

Then take off the carburetor and disassemble it down to its smallest components. Put them all in the basket of a container of carburetor cleaner and let sit overnight. Reassemble and reinstall.

Reconnect the fuel line, set the choke and throttle, pull the cord, and pray!!!

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Old 03-09-2013, 15:46   #7
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Re: 4hp Nissan OB Won't Start

2 stroke or 4 stroke?

I go with the coked up fuel in the carb, the new fuel is deadly for small engines.

Take out the tiny jets, let them soak in strong stuff, the longer the better.
Clean out with tiny needles or high pressure air, rinse and repeat...
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Old 03-09-2013, 16:43   #8
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Thanks for all the replies. No, I'm not positive I got the carb all the way clean. I followed a YouTube video and took it apart, including the jets (everything I know about 4-stroke outboards I learned on YouTube). I sprayed carb cleaner through everything liberally, then reassembled. I did not soak overnight--I'll try that tonight. Actually, it will be a few days before I can get back to it, so I'll soak the parts for a few days. It'll be the weekend before I can check back in with results.
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Old 03-09-2013, 17:02   #9
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Re: 4hp Nissan OB Won't Start

Cowboy Sailor already came up with the best test to see if it's a carb problem or not. Try some starting fluid. If it runs for a few seconds on starting fluid, then dies, it's the carb.

When cleaning carbs, my tool of choice is electric guitar strings. They come in lots of different sizes. When you buy a set, the set is specified by the smallest string in the set. A 008 set would have strings that start at 0.008" diameter & go up from there. A 011 set would start at 0.011" diameter. If you know the size of your jets, then you can choose a guitar string that is a close fit & guarantee that the jet is full open by passing the appropriate size string through it.

I have also found that 100LL grade aircraft fuel is great for cleaning out carbs. The only thing is, if you run the engine on that stuff, be sure to change the oil pretty darn soon. Standard oils get eaten up by aircraft fuel.

If the motor does not start on starting fluid, then check your spark timing.

I'll assume that you have already checked to be sure that you have enough compression. Rule of thumb is that 100psi is enough to run, despite what the book might say is actually correct or desirable. The farmer's test is to remove the spark plug, stick your thumb over the hole & see if the motor blows your thumb off of the hole when you crank the motor over.

If all that looks good, then check to see if your exhaust is plugged. That can stop a motor from running too.

The basics of any 4-stroke gas motor are: suck, squeeze, bang, blow. That is: air & fuel in, compress them, spark at the appropriate time, & exhaust. All are required.
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Old 03-09-2013, 17:17   #10
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Re: 4hp Nissan OB Won't Start

I don't know if it will work but when I left unleaded (no ethanol!) fuel in my 4 stroke generator for a few days longer than I should have I could not find a repair manual and the owners' manual just said to return the generator to the dealer so I took off the air cleaner and sprayed a generous dose of carb cleaner into the carburetor.

Sort of worked so I repeated the dose and now the generator runs tolerably well.
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Old 03-09-2013, 17:27   #11
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Re: 4hp Nissan OB Won't Start

After you get it to run check inside the fuel tank at the fuel hose they like to put a filter there. Usually some dish soap will clean it.
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Old 03-09-2013, 17:43   #12
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Re: 4hp Nissan OB Won't Start

If you have spark pour a bit of raw fuel down the spark plug hole. The engine should run for a second or two and repeat this a few times as it may dislodge any fine particles stuck in the jet and idle ports.
If nothing else it will confirm a fuel problem and you will have to disassemble and clean the carb.
P.S. My personal preference is to not use staring fluid on a gas engine.
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Old 03-09-2013, 19:38   #13
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Thank you all for taking the time to reply. I still have time to check CF; I just won't be able to get back to the outboard until the weekend. The carb is apart, jets soaking in carb cleaner (not enough left in the can to soak the whole thing), and the fuel drained down as far as it would go through the lines. When I get back to it I'll try the rest of the ideas here. It feels good to at least have a plan.
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Old 04-09-2013, 06:19   #14
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Re: 4hp Nissan OB Won't Start

Get a carb rebuild kit. Should be about 20 bucks and replace all the o rings while your in there. I do this every 5 or so years. Use a fuel additive also.
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Old 04-09-2013, 15:12   #15
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Re: 4hp Nissan OB Won't Start

There is a 3rd set of jets that is the air bleed which controls idle also. the EPA has mandated that they be hidden behind a brass cap. you have to drill it out to get at the screw. screw it all the way in counting how many turns then take it out and clean the very small holes.
Just had the same problem with a Nissan 6hp.
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