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Old 2 stroke Nissan 9.9 wont stay running

CYoung2970

New member
Hey I own an old 2 stroke Nissan 9.9 and it had been working great and then one day it wouldn’t start anymore where I found that the fuel filter had a crack in it and was squirting the fuel out when gas was pumped into it. So I replaced the piece with a brand new one and upon starting the motor it started up beautifully on the second crank but then after about 20 seconds it died. Which upon further testing I found that it would only stay running from anywhere between 10sec to sometimes 25 or so seconds. Any advice is highly appreciated thank you.
 
Sounds like it is running out of fuel.----So try operating the manual pump.----Or inspect fuel pump diaphragm.----Or test run with another hose and tank.
 
It is an old tank and hose. You think it could be something as simple as needing a new fuel tank and hose? What do you mean by the manual pump? Sorry if that’s a dumb question I’m by no means an expert on this stuff
 
Sounds like it is running out of fuel.----So try operating the manual pump.----Or inspect fuel pump diaphragm.----Or test run with another hose and tank.
By manual pump are you saying continue to pump the bulb on the fuel line while the motor is running? And the tank is old so could an old tank cause it to not get good fuel?
 
What is your actual model? Not year. Yes, it could be a fuel problem. Keep pumping the primer to see if that helps. Yes, a tank or hose that leaks air could cause this issue.
 
The model is NS9.9B 355A-1. Tested it out with muffs yesterday and continued to squeeze primer bulb while it was running. This worked well and after probably 45-60 seconds of manual squeezing it it was able to continue to run and run well on its own. So I would assume that maybe the tank or hose needs to be replaced then? Thank you so much for the help
 
The 9.9B2 dates back from the 1980's. Many parts are NLA.
Check the o-rings on the primer hose. One leaker could cause your problem.
 
Definitely sounds like air leak issue which I have had before and gave the symptoms. As you say the issue started after replacing the fuel filter I would check this is sealed up correctly, both on the inlet/outlet barbs and also that the filter has an o ring installed and is sealing.

If you pump the primer bulb you will likely see/hear bubbling or hissing from around the fuel filter.

I also had an issue where the plastic barb on the carb had cracked and air was leaking from there.
 
So Incase anybody wanted to know could never get it running so I took it to a Nissan technician and he said it’s burnt up and probably won’t run again sadly. So I’m on the look for a new motor if anyone has any suggestions. I have a 14ft Jon boat and I was wondering would a 5hp be strong enough to get me around well on lakes and possibly slow moving rivers? I’m downgrading from a 1989 Nissan 9.9 so not sure how much of difference that would be and I doubt the 9.9 was even getting even that much hp anyways due to its age. Anyways just wondering where I should go from here in terms of what motor to look out for.
 
I never diagnosed a motor as "burnt up". Not sure of the specifics. Is the compression OK? Is it getting fuel and spark? If so, it should run.

What does the USCG placard on the boat say is the maximum HP motor? If you get near 80% of that, everyone will be happy. Below 70%, only some folks will find it acceptable.
 
Yes it gets spark and fuel. I’m still in high school so my dad took it to the guy and he said that he put a scope inside it and said that the cylinders were burnt up. So I guess that would mean it’s not getting the compression to start?
 
It could have scored cylinders from overheating, or if there wasn't enough oil in the fuel mix. While that could be repaired, it's not cost effective. What is the actual compression?
 
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