Nissan NS5B carburetor problem

I have a 2003 Nissan NS5B 2-stroke. Symptom is that after starting, the carb overflows fuel and the engine chokes out.

I have replaced the float valve and am confident it is installed correctly. After removing the carb, when blowing through the fuel inlet on the pump, air passes through the carb both right side up (float valve open) and upside down (float valve closed). The float is level when turning carb upside down, and the float valve appears fully closed, suggesting it is properly adjusted.

It appears that it's something simple, but I'm stumped.

Would appreciate suggestions on the fix.

Many thanks,

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Re: Nissan NS5B carburetor problem

Probably internal valve where float tip valve sits has still debris inside, is worn out, scratched, not round for a perfect seal fit, have you changed float for a new one too ? Remove float and float valve, with a lantern check bottom valve's inside to see it's working condition. This part does not comes as spare, needs fix , if not operative, will need to buy a new carb

Happy Boating

Re: Nissan NS5B carburetor problem

Luis is correct. The float valve is NOT working at all, or it would shut off the fuel when the float rises.

Re: Nissan NS5B carburetor problem

Gents,

Thanks for your input.

As info, I had run the carb dry, drained the float bowl and completely emptied the fuel tank at the end of last season, so no visible sign of any shellacing.

As suggested, I did shine a light into the valve seat and could not see any debris or damage. Sprayed it with carb cleaner and it improved the air flow leakage, but not completely. I didn't buy a new float, but can't find anything wrong with the old one.

After reassembly, and attempting to start the engine, couldn't get it to fire and carb overflowed, couldn't tell whether it was due to excessive use of choke or continuing float valve leakage.

After pulling the plug to dry it and getting a blister from the pull handle, called it a day.

Will try again tomorrow, but it appears that float valve orifice isn't mating cleanly with the rubber valve tip, hence may be in for a new carb.

Thanks again.

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Re: Nissan NS5B carburetor problem

Are you sure you have specified and received a new valve for that model, compare against old one, check float chamber black o 'ring, if completely plain flat and dried out, will be a cause of gas leakage, is float spring correctly seated bolted on carb body ? if found ok, probably rear plastic portion or yellow metal support, where valve spring hangs is /are bent and out of proper float height ? check, if defective, buy a new float and test, at the moment cheaper than buying a new carb.

Happy Boating

Re: Nissan NS5B carburetor problem

Great additional suggestions!

I have carefully checked the position of the float shaft, and the screw which secures it, and it operates smoothly and appears correct.

Coincidentally I did receive the wrong float valve earlier and had to return it for the right one, which is an exact match for the old one, as well as exact match for the part number on the exploded parts diagram for this model. So I'm confident I have the right valve.

The "O" ring appears flat and dry, so will replace. Will also re-check the metal tab on the float for position on the valve spring and/or replace the float.

And you're abosutely right - any and all of these are much better than buying a new carb.

Thanks again!

Re: Nissan NS5B carburetor problem

Is the float height correct?

Re: Nissan NS5B carburetor problem

Gentlemen,

It's time for me to report the OUTCOME of my work on your suggestions:

Received the new "O" ring today and installed it on the float bowl, as well as taking another look at the position of the float tab on the valve and spring (thank you Paul). Bent the metal tab slightly to make a firmer push on the valve spring before reassembling.

Re-installed the carb and linkage, and VOILA!!! The engine started immediately. Just finished running it for 20 minutes at various RPM's while watching for any leaks. It runs perfectly, idles down as new, is not leaking a drop of fuel, and in short is operating exactly as it should.

Couldn't have done it without your excellent suggestions!

So a hearty THANK YOU and kudos to this forum!!

I'm off to do give it an extended sea trial and will be thinking of my good fortune at posting on this forum.

Happy boating to all!

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