NC50 stutters at top speeds

Just got a new float, cleaned my carb, and in the process of cleaning my exhaust...

question: why does my express (1981 NC50) slow down at top speeds?

I've adjusted the air mixture numerous times, with no success.

It seams that when I reach my top speed (25 mph with a VERY strong wind on my back, in my case), my bike stutters and slows down, then resumes speed.

Re: NC50 stutters at top speeds

the air mixture screws only afect the bike when you are running at idle speed..

you shouldnt adjust it for full speed... only idle...

clean the exhaust, it offen makes a big difference


Re: NC50 stutters at top speeds

Jonas Quimby /

I'd say you want to do a few things. Cleaning the muffler will be a huge improvement all around, even if you can already blow through it fairly easilly.

I'd also make sure your spark plug is the correct one and gapped at 0.026"

After that, check the needle on the end of the throttle cable. It's keeper C-Clip should be in the middle notch for most engines. Anything else will effect your mixture at higher speeds.

My Express would often stutter pretty badly when the carb was dirty or when I had a leaky O-Ring in the carb, but it does something similar now that my muffler is clogged. It also likes to act strangly if the spark plug gap is too narrow.

Re: NC50 stutters at top speeds

Leon Swarmer /

make sure you are getting a good fuel supply to the carby too. I gained 1 mph when I put on a new petcock.


Re: NC50 stutters at top speeds

Thanks for the info.. i'll check my plug again, I gunked up one trying ot get the bike started. I'll make sure. I know the c clip is in the right position, I checked that during my cleaning.

I should try to find a gasket kit as the ones I have are pretty flat...

Re: NC50 stutters at top speeds

Jonas Quimby /

You can still get a surprising number of parts out of local Honda shops if they've been around for awhile.

I was able to buy single gaskets, cables, rings, etc.

Re: NC50 stutters at top speeds

Matthew Scholtens /

I love it. We do anything to squeak out an 1 mph! Thanks for the tip Leon.


Re: NC50 stutters at top speeds

Could be 4-stroking for LACK of sufficient air. Remove or loosen the airbox and see if it goes away. don-ohio

Re: NC50 stutters at top speeds

Hi all,

Don, I tried the removing the air box, presto it stopped. However, the bike dies at a stop now (to lean?)

So that means not enough air at high RPMs right...

The air filter is brand new, => shoudn't be causing much restriction to speak of.

That being said my next step was to adjust the needle setting to allow more air in the higher RPMs, I raised the needle 1 position. This appears to have worked to some degree, I don't "bog" as much at top speed, BUT now my low end is wrecked. I have no acceleration AND I die coming out of a rolling stop.

I keep playing with the settings, and it's at a point where I've completely lost track of them ...

Any suggestions?

Re: NC50 stutters at top speeds

Jonas Quimby /

If you change the needle position you would also probably need to adjust the idle mix to compensate at the low end.

I would Suggest that you restore the carb to where it was - needle in the middle and use my guide to express repair to adjust the idle and throttle screws WITH the air filter on.

And then get that muffler spotless. I say this because the Express engine almost always runs fine with the needle in the middle spot, a fresh air cleaner and a clean muffler.

My best guess is that the clogged muffler isnt allowing enough air to be sent into the cylinder.

So once more, Clean Your Muffler!

You'll be going in circles with adjusting screws otherwise.

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