evil carburetor

[edmo]

I've been messing with the carb on a 86-88 Nissan NS40C off and on for a year. When it runs it idles, accelerates and runs full throttle fine. when it doesn't run it just won't start.

I found one problem the other day, the float valve had stuck shut. Took the carb apart, carb cleanered all the jets and other orifices and replaced the needle/seat.

took it to lake and ran and started great several times during the morning. then decided to be stubborn and wouldn't start choke or not. pulled the line from the carb and bulb squirted fuel. then turned the motor over to check fuel pump. it pumped gas. then as I was checking fuel pump with the hose disconnected, the motor fired and started. I slid the hose back on and it ran fine back to launch. Any ideas where to check next would be appreciated.

don't know if it might be a factor, but is on a pontoon with ~ 8 foot hose from portable tank to motor. hose goes down a bit then up and over railing and back down to motor. somebody said they thought hose routing might matter.

 

[Sea Rider]

Re: evil carburetor

Open air vent on tank if forgot to do so. Try a new fuel hose, could be air entering through worn connector o'rings on tank or engine.

Happy Boating

 

[edmo]

Re: evil carburetor

Thanks for the response. I have indeed forgot to open the vent in the past on this thing, but not lately. Also put on a new hose and bulb recently. after I start it first time it restarts within the next hour or two at least in idle position(no choke and no throttle). Then when it decides not to start it won't start in idle position, so I try throttle, nothing, and then choke, nothing. I'm kind of thinking that since it eventually started after I disconnected the fuel line that it may be flooding a bit when its warm with no throttle or choke. I'm ordering a new needle valve and seat in case it may be sticking a bit both open and closed. Never known one to do that, but I always get the weird ones.

 

[pvanv]

Re: evil carburetor

A warm motor will want some throttle in order to get enough air to compensate for the "extra" vaporized fuel that accumulates when the hot carb "soaks" in the heat.

 

[gm280]

Re: evil carburetor

If you seriously think that it could be flooding, reset the float level a little lower and it should take care of that issue...

 

[edmo]

Re: evil carburetor

Thanks guys for the suggestions. I've ordered a new needle and seat and will see what that does, if anything. and will try lower float set. The reason it's so perplexing is that I can get it running great here at home. Then take it the lake it starts and runs fine. For four or five fishing stops it starts and runs as soon as the key hits the start position and with throttle lever down. THEN, it decides it's time to quit fishing so the next attempt to start it as I have been doing it just turns over, so after a bit I try some throttle. Still nothing. Try a little choke. Nothing.

Weird that it finally started as I was cranking motor with fuel line unhooked at carb to see if fuel pump was working. I'll keep at it. I expect it's something simple I have overlooked. Usually is.

 

[Sea Rider]

Re: evil carburetor

Some important points to look after:

Edmo,

So you have an electric start engine, right. Probably you are experimenting a stuck closed position butterfly. When key is pushed, butterfly shuts, when key is released after strating procedure is completed, butterfly should remain at open position, but could remain closed.

Remove carb silencer and check electric choke operation. Sometimes butterfly's solonoid due to parelell miss aligment with respect to plunger, could stuck plunger inside solenoid, check correct solenoid free movement when key is pushed in and released or with finger while engine is not cranked. Lube with thin oil all related sliding parts including butterfly's horizontal shaft for proper lubrication to slide well. Have had 2 MC40 with described issues and owners about to pay a visit to Bellevue insane facility.

2 stroke 25/30/40 are sometimes a real pain, you know where to correctly start , there are staring procedures that deal with external temperature. Check and try which matches your boating temperature. Just replace needle and seat, don't play with float height unless you have tampered float height and needs to be seated as factory delivered.

With respect to bulb priming, just squeeze bulb untill slight hard, not rock hard. Sometimes when you exesivelly prime hard on bulb will create excessive fuel pressure inside carb's bowl and engine flood specially if having needle/float/float height issues, that is not seating well and releasing fuel inside cylinders. Just prime enough, fuel pump & carb will take care of it. That's why when you release engine fuel connector fuel is squirted back, too much fuel pressure accumulation.

Happy Boating

 

[edmo]

Re: evil carburetor

Yep, it's electric start and the choke is working as best as I can tell. I hear it when I push the key in and it pops open when released. Something to watch though as the switch is old and dilapidated looking. Guess there is a chance it could be throwing the choke closed on the restart attempt that fails even though I'm not pushing in on the key.

Next time I go to the lake, I'm taking my shop supplies and will set up shop in a shallow cove.

If I don't get it figured out before long I'll be contacting you for directions to that Bellevue place.

 

[Sea Rider]

Re: evil carburetor

Edno,

Have you tried any of the 3 mentiioned starting procedures ? Try starting with the one that matches your outdoor temp, follow procedures. Sorry, Bellevue is already full, was the last one to be admitted...

Happy Boating

 

[TOHATSU GURU]

Re: evil carburetor

Do a compression check when the engine is hot and see if you have a difference.

 

[edmo]

Re: evil carburetor

Appreciate all the help. Have C-kit, and pump diaphragm kit coming. Also am going to replace all lines under cowling and swap out the sediment bulb for an inline filter. And will check cold and hot compression.

First though have to go to gulf for week and half vacation. Maybe epighany will occur there.

 

[MattFL]

Re: evil carburetor

Do you have spark at the times it wont start? Could be a flaky ignition or kill switch, loose wire, etc..

 

[edmo]

Re: evil carburetor

Thanks Matt, for the suggestion. I'm open to all possibilities. Haven't check spark yet, but have been in the middle of the lake when it quits. I'll check that after I do some more work on the fuel system. I know what you mean though. I had a old homelite saw one time that quit on me. On testing for spark one time it would have spark, the next not. Turned out to be the pigtail from the coil had a crack on one side.

 

[KFarmer]

Re: evil carburetor

Brand new here on this forum.
I too have the exact problem on my 88 NS40c.
I was wondering if the fuel can pass throught the fuel pump with the engine off?

 

[pvanv]

Re: evil carburetor

Brand new here on this forum.
I too have the exact problem on my 88 NS40c.
I was wondering if the fuel can pass throught the fuel pump with the engine off?

This is actually material for a new thread. But, yes... The primer hose pushes fuel past the pump to fill the carb bowl. Also, if the tank is higher than the motor, fuel could pass through the pump when the motor is off. However, if the carb float/needle/seat is working, the worst that would happen is that the carb would be full. Since you want to disconnect the fuel hose and run the motor out at the end of every day, that should not be an issue.

 

[edmo]

Re: evil carburetor

Paul gets the chicken dinner. It was indeed a throttle issue. After a failed starting attempt at the lake, I got off an saw it had flooded. Raised the throttle lever up about 3/4 and tried again and nothing. Pulled the cowling and looked down the carb throat and the throttle plate was completely closed. Didn't open any until throttle was pushed to max. Until I could get home to make the needed adjustments a little duct tape around the throttle rod that contacts the throttle cam did the trick. Caught three walleye and motor started flawlessly. Thanks to Paul and the rest for help.

 

[MH Hawker]

Re: evil carburetor

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