NU50 idle and throttle issues.

Hi everyone,

I have read a lot into these issues on here already but am yet to see one specific thing mentioned that pertains to my problem. To get to the point, my 83 nu50 will not seem to idle properly and could just need some adjustment. But my main concern is that the bike will be working fine and while I am riding it will continue riding at whatever speed I'm doing even after I let off the throttle. Now I checked time and again and the throttle and cable themselves do not seem to be sticking. Additionally as it is continuing to ride without giving it any throttle but when i finally do it will act as a kill switch and the bike conpletely dies. I wait a minute or so and it will start but problem occurs shortly after.

I have completely cleaned out the carb and reassembled properly

Fuel is flowing nicely.

Played with the idle and fuel or air screw( not sure what it is sorry)

It will also rev very high everymorning when I start it up but once I turn it off and back on its fine.

Any advice or help would be appreciated.

Thanks

Re: NU50 idle and throttle issues.

Maybe air leak between carb-intake,intake-reeds, or carb issue.Could have missed something in the carb.Those stock carbs suck cuz it doesn't take much to clog them or make them act funny.Check evrything again with a tiny piece of wire,carb cleaner, and air to blow everything out.Use the cleaner to check for air leaks too

Re: NU50 idle and throttle issues.

That's my plan for tomorrow, to clean thoroughly again (4th time) my fear is that nothing will change. My biggest confusion is that giving it throttle kills it even though things appear to be cleaned out. I've read about the autochoke causing somewhat similar problems so maybe something to look into as well. Also was told that running too rich of a mixture would mess with the performance but not sure how to adjust this.

Thanks for the timely reply!

Re: NU50 idle and throttle issues.

If it was staying choked after being warmed up it would just flood out and die but it is worth a shot to unhook the vacuum lines on the auto choke and plug them off to see if that helps

Re: NU50 idle and throttle issues.

Alright I think I will do that then. Also wasn't able to find the starting adjustments for the idle and air screw. Any idea of a thread mentioning this?

Re: NU50 idle and throttle issues.

Air screw out 1.5 to 2 turns and I would leave the idle screw loose til its running then screw it in little bit at a time til it hits the slide and idle up to where you want it.I had a stock carb with a sticky cable and slightly bent needle that felt like it had cruise control for a few seconds when you let off the throttle kinda what your describing

Re: NU50 idle and throttle issues.

Downhill Harvey (OFMC) /

Re: NU50 idle and throttle issues.

Appreciate the manual and the help with the screws. Cruise control is exactly what it feels like but i know the needle is straight. I wouldn't mind it so much if it didn't eventually kill the engine. I'll mess with it tomorrow and post. Thanks for the help

Re: NU50 idle and throttle issues.

Gruff "(OFMC)" - /

maybe your needle is slightly bent or scarred and is geting stuck open. To check if your throttle assembly is working correctly, take your aircleaner off and look down the carb throat and work the throttle to see if the needle/throttle valve is going up and down smoothly. with it not running of course!

Re: NU50 idle and throttle issues.

Adam Kollipara /

My 1981 NC50 does the same cruise control thing but only when it's cold. I have to turn in the gas/air screw in all the way to act as a choke. I have a problem with my auto choke but it's just staying open as if the engine is always hot. It sounds as if yours might be stuck closed as if the engine is always cold. What you can try is put an inline plastic fuel petcock in line 2 (middle tube) going to the auto choke. It should have a spring over it. When the engine is hot, close it to see if the cruise control will stop and the throttle stops acting as a kill switch.

~Adam

Re: NU50 idle and throttle issues.

I did that and it seems to be working fine. Put 30 miles on it the other day with no issue. Idle was still bad so I played with it and have since had this problem but I'm not sure that is the direct cause. I'll take a closer look at the needle for scratches or a bend.

Thanks

Re: NU50 idle and throttle issues.

Replace your oil seals . Bad seals cause an sip leak and prevent proper mixture threw out the rpm range . More leak at higher rpm and less at idle . But it will prevent accurate tuning in any case . If they are 30 years.old then they are bad ...

Re: NU50 idle and throttle issues.

Thanks Adam, that's something I havent read about yet and ill definitely give that a try.

Re: NU50 idle and throttle issues.

Yeah I have to agree with that. I was told to spray carb cleaner anywhere there is an attachment to the motor while it is running to check for air leaks. If it hits a leak it will affect the rpms. I'm leaning towards an air leak as the problem.

Re: NU50 idle and throttle issues.

An update to my issue is that I found that I don't need to give it any throttle or Rpms for it to stick or accelerate on it own. I turned it on today to check for leaks and i let it idle for about 2 minutes. It then started to accelerate on its own until max rpms and then died. This seems to rule out any throttle or needle issues in my mind but an air leak or oil seal issue may still be the problem. Not positive though.

Re: NU50 idle and throttle issues.

Gruff "(OFMC)" - /

crank seals! if you did air leak testing on the outside already and nothing showed up/ I found with all mine, if its not tunable and everything else is good its the seals. Replace them and all the little issues just disappear.

Re: NU50 idle and throttle issues.

I did spray some carb cleaner around different areas and found nothing. Are the seals a Honda specific product? Or are they pretty generic. I'm already becoming best friends with the Honda guy so just wondering if I have to pay him another visit!

Re: NU50 idle and throttle issues.

Yeah carb cleaner won't be able to check the seals behind stator or on the other side with the motor running.There is a more in depth way to check for leaks by checking vacuum in the motor but I'v never done it.If you search the threads you could find it somewhere

Re: NU50 idle and throttle issues.

Whatever . To check for leaks at the oil seals on the variator side simply remove all the kick start gears and the kicker cover , then start the bike with a drill . After its running , spray carb cleaner on the crankshaft / oil seal area . If it affects the idle , replace it, its leaking .

To check for an oil.seal leak on the magnito side , start the bike and remove the plastic timing cap with a big flathead screwdriver and spray carb cleaner in there . If your idle changes , change the oil seal as it is leaking and is your problemo just like I said earlier ^^^

You Will need a pulled to remove the flywheel , treats sells them for 26 bucks .

You Will need a welded up three jaw or a Harbor Freight two jaw for 16 bucks .

Buy oil seals from bike bandit .com . The right and left are different sizes !

Really clean the case and crank @ seals . Epoch or crumpled the seals in place . Or do both . I apply a thin layer of jb weld to the seal ans case before I carefully and evenly press/ tap them in place with a socket . Use a punch or nail set to make a slight indention .in 3-4 places around the lip of the case that the seal rests in .

Let it dry 24-48 hours . And done . (edited)

Re: NU50 idle and throttle issues.

Cosmo nPuch Stillstolen /

My wife's 82 has similar issues. Once in a while it has the accelerating thing and high idle. It will also stay at whatever RPM I was going after I brake, but still rolling, then suddenly drop down to the correct idle. The staying at high idle seems to be associated with the variator, or at least it feels that way.

No effect when sprayed with stuff, but I heven't yet removed the covers to check the crank seals.

Re: NU50 idle and throttle issues.

Downhill Harvey (OFMC) /

@ Rick Ems, jb weld on the seals? I disagree with that.

Re: NU50 idle and throttle issues.

I recently replaced my old belt with a bx31. Maybe this change is having an affect on the variator

Re: NU50 idle and throttle issues.

I have and will use jb weld. It's no big deal , you can use bearing retainer . I've just had too many seals pop out at high rpm / high compression . So now they get jb welded and they stay there until I knock.then out with..a mallet .

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