Nissan 6 HP runs for 5 seconds

I have a Nissan 6 hp that is giving me fits. It will start easily but only run for about 5 seconds. Then it will not start under any combination of choke/throttle.
If I let it "rest for 20 minutes it will start easily and run for another 5 seconds. I took the carb apart and soaked in carb cleaner for 4 hours and it made no difference. New fuel. Plenty of spark. Seems like the problem is getting worse, that it is running for less and less time. Last time I tried it, it seemed to run for about 15 seconds. Would appreciate any help. Thanks

You did not mention model; I assume you have something like an NSF6B, right? Could be a number of things, but most commonly sounds like you are running out of gas. When the motor will not start, is the plug wet or is it dry? If dry, no fuel. Do you have dual tanks, or onboard only, or external tank only? If no fuel, what is the setting of the fuel cock (if setup for dual-tank)? When it won't start, are you still seeing the low oil LED when pulling?

Thank you so much for responding to my question.
It is a Nissan NSF6A2S 2, 6 HP. The plug is dry. The red led goes off when it's running and flickers on just at the end of a pull that does not result in starting. It ran for a good 20 seconds after "resting" all night. When it does run throttle response seems poor. Like when the motor is cold. At times it back fires through the intake when pulling and it won't start. At times today I could get it to start without waiting 10 -2 minutes between attempts, but it would only run for less than 5 seconds. Trying to slowly increase throttle during these 5 seconds killed the motor.

Any other trouble shooting tips?

Thanks again

Check the needle valve and float height in the carb, with the aid of your trusty Factory service manual. Also verify fuel flow to the carb. You could possibly have a stopped-up fuel filter.

Hi Paul,

Thank you so much for your expertise and advice. I think you hit it with the needle valve. Another 12 hour soak in Berrymans carb cleaner with special attention to the needle valve did the trick. (although the throttle response seems a bit sluggish. Is that the main jet?) The needle valve must have been sticking closed.

I did check fuel flow to carb by replacing fuel line with a clear one. That was fine. Don't have the shop manual to find the details of the float height adjustment.

Thank you again. I owe you a couple cold ones.
Pete

The float height is correct if, when the carb is inverted, the float is parallel to the carb casting. The Factory service manual is Part# 003N210341, $27.58. The carb kit (if you need a new needle) is Part# 3H6871220M, $28.97. These are available from any dealer, including me.