Issue with my 150cc "NST" scooter

[ajbell78]

Hey guys,

I have a NST 150cc Scooter. I've done a ton of homework, and I'm still baffled as to what is causing the problem.

My scooter has a very hard time starting when it's cold. Once it's warmed up, it runs like a champ.
I've replaced the "auto choke".
Adjusted the valves. Replaced the spark plug. Checked the coil wire. Checked all my lines.
 It's getting good fuel. Tinkered with the idle & air/fuel settings. Cleaned the carb (and ports)


My only thought is maybe the new Auto choke I bought is bad?
This problem is driving me nuts.

Any suggestions would be very very helpful!

Thanks guys

      

[scooter 49]

It certainly does sound like that NEW choke is bad. Your engine should idle high at first startup and slowly idle down if the choke is working properly. You said you have adjusted valves and cleaned the carb thoroughly. Either the choke is bad or perhaps it is not getting power to the electric choke because of faulty wiring. You say it runs good once it warms up so again that points to the choke not working like it should. I guess I would double check the wiring to the choke or get another one.

[ajbell78]

The idle doesn't go up at all once it starts. I will go check all the wiring. I'm planning on buying a few new toys for it. Which included a new high performance carb ( http://www.monsterscooterparts.com/125cc-150cc-electric-choke-carburetor.html) and a new CDI ( http://www.monsterscooterparts.com/racingcdi.html )

Wasn't wanting to buy them until I figured out the problem (nothing worse then spending money on something that just sits there) but I'm thinking maybe they might help me fix the problem?..

Is there a way to test the auto choke? Like hooking it up to a external battery and watching to see if the needle moves?

[scooter 49]

Yes . I have'nt ever had to do it myself but I think if you do like you said that would be the way to test it.
You should see the needle move slowly after the wiring ends are placed on the battery terminals.
You certainly have nothing to lose by testing it so I say go for it. Exactly which wire goes on the positive terminal and which one on the negative I could not say. I would say try it and see what happens.

[ajbell78]

I was on another forum and figured out how to test the auto choke.

To test if that is it, take the Enricher Off only two screws and then cover the hole with your hand or thumb and try starting it. What you are doing is acting like the Enricher allowing extra gas when cold. The Enricher must be stuck in the Extended Position which closes off the extra fuel when cold or the fuel passage from the Enricher is clogged.


   

[Fox]

The carb has a separate passage that allows extra fuel into the engine when it's cold. After a minute or so the needle on the enricher extends out and cuts off the extra fuel effectively leaning out the mixture. If the needle extends and the unit feels warm to the touch after a couple of minutes when hooked to a battery then it's good.

I have worked on a hundred or more scooters and I have run into a few scooters that act just like yours. I try all the things you mentioned and the darn things just don't want to run cold but they run excellent once warmed up. Short of replacing the carburetor I'm not sure what else you can try to fix the issue. Maybe try some different valve clearance settings.

[rcockrum]

I have the same exact problem with a "Longbo" 150cc scooter.  I put in a new spark plug, new carburator complete with the chocke setup, and a new fuel valve.  Runs perfect once warmed up.  Will not start cold at all.  Have to crank it forever, then it will come to life and idle normal (not fast at first).  When warm, it restarts just fine.  Let it cool down....and I'm back to square one.  This scooter has 3,090 miles on it.  What else should I test or check?  Any help would be appreciated.

[Sparky]

Most of the time, the only thing needed to start when cold, is an increase in idle speed.
Be sure your scooter's idle is set at 1500 rpm (+/- 100)
I know this sounds high, but this is what is required to get these engines to run right.
The idle is set low at the factory so it will pass emission standards during testing.

[rcockrum]

Ok......I'll admit it.  I have participated in many mechanically related online forums....Dodge trucks, Saturns, GM 3800s what have you.  I made the typical newbie mistake.....started asking questions before searching the forums.  After  posting....I got to searching and reading and came across the valve adjustment topic.  This evening, I adjusted the valves as per info I found here and wa-la....this scooter colds starts like new!!!!  Thanks to the forum and members!!!!!  Sorry for being that newbie!  Rob

[frostyman]

Although I can usually get away with it, I seem to tweak my idle every 25 or so degrees F of temperature change. Like this time of year where I live, where it can be 82 in the daytime, and then 50 degrees at night. I've gotten away with it so far. The winter time I fine tune it more often.