Nissan NSF 9.8A3 Oil Question

[Bullie]

I installed a new fuel pump and cleaned the carb and installed 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 after my work. 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 then 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? I will be going out there soon to check the motor out. Is there some damage I should look for or will just draining the oil to the correct level help things out?

 

[TOHATSU GURU]

Yes. Too much oil pressure will keep the engine from running correctly. Drain the oil back down to where it should be and all will be well.

 

[pvanv]

Yes. Too much oil pressure will keep the engine from running correctly. Drain the oil back down to where it should be and all will be well.

Elvin is (as usual) exactly correct. 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 and foaming 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.

 

[Bullie]

Thanks for the information. I will pass it on to the owner.

 

[Bullie]

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?

 

[ondarvr]

It's not uncommon for shops to put forth very little effort in cleaning the carbs on small 4 strokes, they just replace them. The cost and hassle of repeated attempts to clean them make for unhappy customers, and costs more than a new one.

 

[Bullie]

Makes sense to me. I just hate failing at getting it going for him. But, I don't want to keep wasting my time either. We have discussed him purchasing a new carb for it but I keep trying because it should run.

 

[pvanv]

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.

 

[ondarvr]

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.

​I haven't had a carb I couldn't get to work either, but I wasn't charging $100.00 per hour to a customer that wants to be back on the water right away, Shops around here, including many of the ones that have motors made by Tohatsu, won't try very hard to get a gunked up carb working, some have almost an automatic response of, "a new carb will cost $xxx.xx and you can have it back in two days". They get tired of customers coming back or needing to take the carb apart again, and then the final cost coming out higher than the new carb.

 

[pvanv]

​I haven't had a carb I couldn't get to work either, but I wasn't charging $100.00 per hour to a customer that wants to be back on the water right away, Shops around here, including many of the ones that have motors made by Tohatsu, won't try very hard to get a gunked up carb working, some have almost an automatic response of, "a new carb will cost $xxx.xx and you can have it back in two days". They get tired of customers coming back or needing to take the carb apart again, and then the final cost coming out higher than the new carb.

Yep. Many here do the same. I'm olde-tymey, and always see whether a hour of labor (the new carb costs 2x that) can fix it.

 

[Bullie]

I bought a can of carb dip from Napa, took the carb completely apart and soaked it per the directions. Waiting on a rain shower to pass over to reinstall.

On a different note. When you drop a good screwdriver overboard and the water is fairly shallow you can put a magnetic screw cup in a latex glove, poke a hole in the glove to flood it (yeah, it floated), and tie some fishing line to the glove and a suitable pole then fish for your screwdriver. I hated to lose it. My reading glasses are still down there somewhere.

 

[Bullie]

Results were very much the same. It will start with the throttle advanced and run roughly. It will smooth out and greatly increase revs with some choke applied.

 

[pvanv]

PM me if you need a carb.