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  1. #1
    Join Date
    Jan 2015
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    Hernando, Mississippi
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    170

    Default Nissan NSF 9.8A3 Oil Question

    I installed a new fuel pump and cleaned/stalled gaskets and low speed jet in a fellows 9.8 Nissan 4 stroke yesterday. The motor is on his pontoon boat and was running pretty good. I mentioned to him that his oil level was low and he should check it. He called me back later and said it ran well at low speed but was a little rough at higher rpms. He decided to check the oil, found it low and added most of a quart of oil. Then he said it wouldn't restart. I have enough sense to rebuild the carb but I don't pretend to know much about 4 strokes. Could adding too much oil keep it from starting? I went through 8-10 start cycles before I left and the owner hooked up the controls and drove all over the lake before adding the oil so, it was starting well before.

    If it can be overfilled, what should I do to help him out?

  2. #2
    Join Date
    Mar 2010
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    Buffalo, NY, USA
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Assuming your model is NSF9.8A3. It only holds about 3/4 quart from dead empty. It's likely way way way overfilled, causing oil fouling of the plugs, extremely high crankcase pressures when running, and way too much sloshing friction in the crankcase when trying to start. You Must always check on the dipstick (after several minutes to allow the oil to flow down from the rocker cover). Don't guess. Best to keep the oil about 1/2 to 3/4 on the stick until the rings are well-seated, say 20 hours of very hard running from new, then maybe 3/4 or so thereafter. Never ever even a drop over full. Use non-synthetic type FC-W 10w-30 oil. Heavier oil or synthetics will cause a lot of oil gain.
    Last edited by pvanv; 04-25-2017 at 09:18 AM. Reason: sp
    Paul
    Buffalo NY USA

  3. #3
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Thank you pvanv. I will give the owner your instructions.

  4. #4
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    Hernando, Mississippi
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Same motor. More issues. Currently the motor is not running. It ran for about 3 weeks after my post above. Since then I have removed and cleaned the carb 5 or 6 times. Only once have I gotten it to run at idle. If you open the throttle it will start and run roughly. If the choke is engaged it will run more smoothly and the revs increase a good deal.

    Learned some history on the motor. According to several people in this lake community the motor did not run well even when new. More than one person has told me that mechanics from the dealership came out several times to work on the motor and stated it had carburetor issues but nothing was ever resolved and eventually the motor was put into storage. The motor changed hands this spring and the current owner asked me to take a look.

    I know what this sounds like but, is a carb ever just bad for some reason? I have cleaned it meticulously but I still cannot get it to run. If I put a little gas in the cylinders it starts right up. It will start and run with the throttle advanced and runs better with the choke also engaged. Am I missing something?

  5. #5
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    Mar 2010
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Definitely sounds way too lean.

    Yes, there are occasionally bad carbs. Not likely on a Tohatsu (Nissan was made by them), since all those motors get a test run at the factory. However...
    What method did you use to clean the carb? If there was visible gunk in the low speed jet, odds are the whole low-speed passage system is gunked. I have never had a 9.8 carb that I could not eventually get clean enough to run, but that was when the motors did run well at one time.

    These EPA-rated 4-strokes (from all manufacturers) will definitely varnish up (with cheap US gas) if they are allowed to sit for a week or two with gas in them. They Must be idled out or drained if they will be unused for a few days.

    We completely disassemble them (jets, emulsion tube nozzle, the works), do a 4-plus-hour soak in real carb dip, and then use a whole can of generic carb spray to blow them out... then reassemble and check float height in the process.
    Paul
    Buffalo NY USA

  6. #6
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    Default Re: Nissan NSF 9.8A3 Oil Question

    I disassemble and use carb cleaner followed by compressed air. I haven't tried soaking it.

    It does seem to have some white gunk in it after a week or so.

  7. #7
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Spray carb cleaner is not aggressive enough. You need real carb dip, in a 1-gallon can. White gunk could be oxidation from ethanol and water in the fuel. If the passages are water/ethanol corroded, it will be time for a new carb.
    Paul
    Buffalo NY USA

  8. #8
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    Hernando, Mississippi
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    Default Re: Nissan NSF 9.8A3 Oil Question

    I discovered water in his fuel last time I was out and had him dispose of the fuel and refill the tank. I had to scrape the white gunk out of the carb on a couple of occasions. The inside of the bowl has a mottled appearance. Could this be from the water/ethanol corrosion?

    I did some reading last night on carb dip. I think I can get a can today at Napa or Auto Zone. I don't normally remove the choke and throttle butterflies. Will it be necessary to remove those before soaking?

  9. #9
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Quote Originally Posted by Bullie View Post
    I discovered water in his fuel last time I was out and had him dispose of the fuel and refill the tank. I had to scrape the white gunk out of the carb on a couple of occasions. The inside of the bowl has a mottled appearance. Could this be from the water/ethanol corrosion?

    I did some reading last night on carb dip. I think I can get a can today at Napa or Auto Zone. I don't normally remove the choke and throttle butterflies. Will it be necessary to remove those before soaking?
    No need to remove the plates. Do pull the emulsion tube nozzle, and the jets.
    If the bowl has white corrosion (aluminum oxide), order a new one.
    Paul
    Buffalo NY USA

  10. #10
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    Default Re: Nissan NSF 9.8A3 Oil Question

    I ended up completely disassembling the carb. I didn't think the little plastic bits would fare well in the dip. No change after reinstall. It still will only run with the throttle advanced and then much better with the choke engaged.

  11. #11
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    Default Re: Nissan NSF 9.8A3 Oil Question

    The hard plascit is OK to dip. As long as you have verified that timing is OK and ignition is working properly, it's probably best to go with a new carb. I would be happy to supply it, if you don't have a local dealer you like.
    Paul
    Buffalo NY USA

  12. #12
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    Default Re: Nissan NSF 9.8A3 Oil Question

    I fully disassembled the carb and had no change after reinstall. I ordered a new carb shortly afterward, before I saw your response. I have checked for spark but not timing.

  13. #13
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Still no joy. New carb same result. How do I check the timing? Can't figure this one out.

  14. #14
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    Default Re: Nissan NSF 9.8A3 Oil Question

    You can use a timing light. There is a window in the flywheel/recoil cover that will let you see the timing mark. Verify oil level again. Make sure the intake manifold gasket is there (could cause a vacuum leak. Make sure the plastic spacer is there where the carb attaches, along with a gasket on each side. You can also do a compression test and a leak-down test. As a last resort, you could also check valve lash, but that typically only limits power.
    Paul
    Buffalo NY USA

  15. #15
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Ok. The spacer is there. I have taken that carb off 10 times and this morning I dropped the spacer in the lake. The water was surprisingly cold but luckily only about chest deep. I bought new gaskets when I got the carb so those are also there and in good shape. I will take my timing light back over this evening. After going swimming I found I was no longer in the mood to work on the motor.

  16. #16
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    Default Re: Nissan NSF 9.8A3 Oil Question

    An update. I checked the flywheel key as the owner stated he had hit an obstruction in the water prior to the motor konking out the last time. It was not immediately after hitting the obstruction but I thought I would check anyway. It had bad creases but was still intact. I replaced it this evening.

    Anyway, I had the owner crank the engine while I sprayed carb cleaner around the intake manifold and carb as it had been suggested that it may be sucking some air somewhere. When I got to the junction between the carb and intake manifold with the carb spray it would start and idle as long as I kept a light mist going. The gaskets on either side of the insulator are new. What should I try?

  17. #17
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    Default Re: Nissan NSF 9.8A3 Oil Question

    I would check the manifold flange for flatness. You can file it flat if needed. Then get a new pair of gaskets, and a spacer, and torque the carb correctly.
    Paul
    Buffalo NY USA

  18. #18
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    Default Re: Nissan NSF 9.8A3 Oil Question

    Paul, what I decided to try was a slightly thicker gasket. The reason I did this is that, to work on this motor I have hang out over the water on the back of pontoon boat like a circus monkey. I took my file as you suggested but I really couldn't get the angle right with the intake on the motor and I was afraid I might do some damage to the flange if I had the file canted. To remove the intake I would have to get in another boat and tie up to the back of this one. A big mess.

    Anyway, I made two gaskets up but was only able to get one in due to the restricted amount of space. I decided to put the gasket I made against the intake manifold. So, there is a new stock gasket on the carb side of the spacer. I put everything back together, bumped the starter, and she purred. I tested FNR for 15 min or so as best I could with it tied to the dock. The owner sleeps til about noon so it didn't get a lake run.

    Do you think what I have done may be enough or should I try to file down the flange as you originally suggested and go back with new gaskets and spacer?

    Paul, thanks for sticking with me through this thing. I know I am not the easiest person in the world to direct, especially long distance. I have learned a good deal about this motor in the process but, I have put about 20 hrs and lots of road miles into it and I just want it to go away...running, but go away.

    The owner says this motor has been a "lemon" since new (2008 I think). It is sort of funny that a real mechanic and I have spent lots of hours on it and all it may have needed was a flange cleaned up or 25 cents worth of gasket material.

    I hate I had him buy the carb. Feel bad about that.

  19. #19
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    Default Re: Nissan NSF 9.8A3 Oil Question

    It's so unusual to have an intake that isn't flat, that I would have probably done the same as you. As for a hand-cut gasket... should work OK. Just so weird that the problem was there at all. As for having a spare carb, never a bad investment. If the one on the motor gets corroded from water, etc., the spare is right there at hand. When the boat hauls in the fall, that might be a good time to check the intake for flatness, and if needed, flaten the flange. Then you can install a factory gasket, and all will be as original.
    Paul
    Buffalo NY USA

  20. #20
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    Default Re: Nissan NSF 9.8A3 Oil Question

    The owner and his dog took a lake run yesterday. He is happy again. I am not going to really relax about it until the motor has run awhile.

    Like I mentioned above, this motor has NEVER ran correctly according to several people in that neighborhood that discussed it with me. Maybe the intake isn't flat or maybe the choke bracket is somehow twisting things out of alignment. I guess the spacer could also be misshapen. I don't know for sure.

    Down here the pontoon boats in lake communities can stay in the water all year. I doubt the guy even has a trailer. It gets too hot here to go out on the boat for weeks at a time but seldom does the water stay frozen for more than a day or two.

    I will inform the owner what the repair to original requires. Since that will only get him to where he already is I am hoping he calls the matter resolved. If he ever has any further trouble I will flatten the flanges and replace the other pieces.

    Thanks again pvanv!

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