80 NC50 not running good

I am trying to help a friend of our boys get his 80 NC50 running and it does not want to run above 15 mph. I took the pipe off and that did not help very much. The carb is clean throughout, the air screw is set at 1 1/2 turns out and it has a new air cleaner element. It also has a new plug. Does anyone know what the compression is supposed to be. Perhaps it may new a new ring job?

Re: 80 NC50 not running good

Symptoms sure do sound like a clogged exhaust.. Aside from the muffler, the exhaust port on the cylinder could be clogged but you probably would have noticed.

If it's belt driven, a loose belt can do it. If the belt or pulleys are hot, thats a good indication it's slipping..

Air screw has minimal influence on top speed..

An ignition problem would be evident by severe misfiring.

Compression? First i would make sure the head is torqued down before suspecting bad rings. May as well pull the head and look for a blown head gasket. Also the decompression valve sometimes get stuck open. Check that too.

Re: 80 NC50 not running good

Mark Youngs /

We cleaned the carbon off the top of the piston and the exhaust port as well. Also a new head gasket was installed before running the machine. It revs out fine on the center-stand (although it does sound like it gets into the rev-limiter), but as soon as he tries to drive the moped it will not rev out very good.

Re: 80 NC50 not running good

brakes aren't dragging.. clutch is not slipping.. drive belt (?) is tight.

There are only so many things that can cause the bike to run fine on the centerstand but not on the ground.

Perhaps you have a serious vacuum leak somewhere between the carb and engine. Gaskets and O-rings on old bikes that sit for years shrink and crack..

Whats the history behind this bike? Whens the last time it ran OK?

Re: 80 NC50 not running good

Mark Youngs /

The bike sat around for years. When he got it, he had to get another motor for it from e-bay. We put it together with the new head gasket and ran it. I thought it might be compression because it runs fine on the center-stand, but under load it will not rev out. I am thinking of pulling the head and cylinder tonight and checking out the piston and rings, although when we put the new head gasket on it, the cylinder walls appeared in very good shape. We have a new base gasket we will put on it also.

Re: 80 NC50 not running good

i think that if, due to worn rings, compression is so poor that it barely reaches half speed, the cylinder walls are gonna show some evidence of it.. At least there will be a deep ridge worn around the top of the cylinder wall. You can look in the exhaust port and examine the rings (see if it still has rings :)

Whatever would cut road speed in half is a major thing. The cause should be very obvious once it's discovered.

Re: 80 NC50 not running good

Mark Youngs /

Well, last night I changed the piston, cylinder, and head from the other motor we had for the bike. There was a fair ammount of blowby on the piston that I removed. After taking it out it seemed to run a little better, but we noticed that it runs better at 3/4 throttle (nearly 25 mph) and when you open it up it actually slows down to 17-18 mph. Doesn't that seem to be a lean condition? As soon are you rool the throttle back to around 3/4 open it speeds back up.

Re: 80 NC50 not running good

could be leaning out.. could be too rich. Do plug chops to find out which. Search 'plug chops' for directions on how-to.

A clogged air filter can make it run rich. A improper float level can make it do either.

Re: 80 NC50 not running good

Mark Youngs /

The plug is a little rich looking. I will check the float and clean the carb. a little bit more tonight. Thanks for the help.

Re: 80 NC50 not running good

Leon Swarmer /

Gotta tell you 27 mph is top end on my '80 NC50.

Joew, it is chain driven shaft drive to the rear wheel.

Does sound like fuel mix now though.

Leon

Re: 80 NC50 not running good

thanks..

chain driven shaft drive? I can't picture that in my head.. I was tempted to grab a basket case scooter at the salvage yard just to take that drive line apart and see how the average one works.

As far as the almost universal carb problems on all these bikes, someone might become rich if they could build and sell a fuel injection retrofit-kit or something.. any substitute for these primative, crappy little carbs..

Re: 80 NC50 not running good

Did you ever get your bike running better? I have an 82 express that is doing the same exact thing. I have cleaned the carb out and checked it 3x now and still it will only get up to about 19. It will slow down if I give it full throttle, but do better at 1/2 throttle. It kind of sputters along. I have a new air cleaner, new spark plug, new oil, new gas, clean carb.

I'm thinking maybe spark plug gap? I haven't checked that yet. Also, I haven't checked the muffler for carbon, but I don't know how to do that. the manual is too basic. Do you know how I should go about cleaning out the muffler?

Did you ever figure out if it is your carb, like the float level? If so, how did you measure it?

later,

Bill

Re: 80 NC50 not running good

Will Percival /

Hey 50plus... how many miles you got on that thing? Mine revs out at about 33 MPH with just over 4k miles on it... but on the other hand, i weigh 150 so that may be it...

Re: 80 NC50 not running good

Leon Swarmer /

Will,

My 80 has about 2.5K

81 has somewhere over 4k

I weigh 195 (yea, Overload for a NC50)

Maybe the express II's are faster?? They cost more orignally.

Never ridded one.

Leon

Re: 80 NC50 not running good

Will Percival /

Both of the Expresses I have are Express 1's as far as I can tell... Hope the '78 I'm rebuilding will haul like the '80 =). The '78 will be a rope start... can't find the parts i need for the winder, so I'm gunna plug it off and fill it up wit oil. I did this for a friend of mine on 3 of the '78's he aquired and it works great!

Re: 80 NC50 not running good

Leon Swarmer /

Take pics of the process. I think a lot of riders would appreciate a way to start it that doesn't invovle a lot of money.

Your profile shows a NU???

Leon

Re: 80 NC50 not running good

yeah, I could use a walkthrough to convert to a rope start, I've got a 78 with a broken tap spring.

Re: 80 NC50 not running good

Will Percival /

My profile shows an NU? Should be an Nc... anywho, the conversion isn't too tough... But I will try to get some pics for you guys. The conversion itself is a matter of 5 minutes if your L case is intact with maybe 20 - 30 mins of prep work. Prep may be as much as 3 hours if you want it to look great =)

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