Honda Express only runs well without air filter.

I have a 1981 Honda Express NC50 that runs great as long as the air filter is off. But with the air filter in place, it bogs down at about 18 mph as if not getting sufficient air. I've tried several different types of filter (cuz the stock Honda filters are no longer available), but none seems to work. Suggestions? Thanks!

Re: Honda Express only runs well without air filter.

Moped Lar (OFMC) /

Sounds like your jet is too large. Get a smaller jet and try that with the stock air box.

Re: Honda Express only runs well without air filter.

Okay, thanks. Two things: The stock airbox has no filter inside, and apparently they are no longer available. Also, it's the original stock carb, so I'm assuming it's got the original jet. What specifically am I looking for? What size jet? Forgive me for being so uninformed. I'm new to all this.

Re: Honda Express only runs well without air filter.

Moped Lar (OFMC) /

If a bike requires more air to run properly, then that means it’s getting too much fuel. That’s why when you take the air box off it runs better. I would pull the carb bowl off and check the number scribed on the main jet, and then get a jet one number smaller. Put the air box back on and see if that fixes it. Also, you may want to do a plug chop. That will tell you whether you’re running too rich, too lean or just right. You want a nice brown color. Search the wiki for “plug chop” to see how to properly do it.

Re: Honda Express only runs well without air filter.

Here's another dumb question: How do I remove the jet to check what size it is?

Re: Honda Express only runs well without air filter.

Moped Lar (OFMC) /

I think the jet number is inscribed right on the "head" of the jet, so you don't need to remove it. You may have the polish the head up a bit to read the number.

Re: Honda Express only runs well without air filter.

Most likely a problem with the choke being on. If this has auto choke then thats where i would start looking.

Re: Honda Express only runs well without air filter.

Can you be more specific? What should I check with regard to the auto choke?

Re: Honda Express only runs well without air filter.

Moped Lar (OFMC) /

> live ɘvil Wrote:

> -------------------------------------------------------

> Most likely a problem with the choke being on. If this has auto choke

> then thats where i would start looking.

Good point! I forgot these nopeds have electric chokes.

Re: Honda Express only runs well without air filter.

How do I fix it? What should I check on the auto choke?

Re: Honda Express only runs well without air filter.

> Dan Church Wrote:

> -------------------------------------------------------

> The stock airbox has no filter inside, and

> apparently they are no longer available.

On that air box assembly, should there be anything else inside the box other than the foam filter? I had an Express with the same symptoms. Turns out there was supposed to be little frame in the airbox holding the filter a short distance from the carb intake. Air was to pass over the entire rear side of the filter, exit the entire front side of the filter and then be drawn into the carb. (there is a short distance from the filter to the carb - 1/2", 1", ?, I don't remember). Without this little frame to maintain that space between the exit side of the filter and the carb, the increase in air velocity as engine speed increased would draw the filter up tightly against the carb. At this point, instead of air coming across the full face of the filter (what, 3" X 4"?), you had air coming across only at the opening of the carb (what, 1-1/4"?) - not enough air. I made a little frame device out of a coat hanger and solved my problem. p.s. look up the airbox assembly online and see if you are missing anything. (edited)

Re: Honda Express only runs well without air filter.

^ This is good to know, thanks.

Re: Honda Express only runs well without air filter.

Thanks!

Re: Honda Express only runs well without air filter.

Re: Honda Express only runs well without air filter.

1977-1980 looks like this. I bought my brand new foam filter off of eBay 3 years ago. Was still in original Honda packaging with part numbers. The other parts are gold and very difficult to find.

This is from my 79....

20160825_152211.jpg

. (edited)

Re: Honda Express only runs well without air filter.

^Yep, I got all that stuff, just had to open mine up to see if I had the cage for filter..could he not just put a cone filter on it and call it good, maybe block portions of it until it is mixed right...or it's just mopeds, run it!

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