Hello! New to the forums and mopeds in general so please bear with me.
About two months ago I got a 1983 Suzuki FA50 out of my grandfathers barn. It has been sitting for about 20 years. Changing the spark plug got it to start up, a new clone carb from Ebay ( https://www.ebay.com/itm/201950969646?ul_noapp=true ) got it to start up easily.
(I still have the original carburetor, but being new to this sort of thing, I figured for the price, a new carb was better than taking apart the original and potentially screwing it up.)
The guy who sold me the carburetor said it is completely stock including jets. It idles great and runs great until I open the throttle all the way. When I take it on a good stretch of road to test top speed, it tops at about 20.
BUT: when I let off the throttle just a little hair, it will inch its way up to 25. What gives?
Well I thought maybe the exhaust was clogged so I took it off and threw it in a charcoal grill for a while. I shook out some black flakes for a while, but maybe not as much as I expected, and I scraped out some carbon crap from the exhaust port on the engine. No luck though, but maybe I just didn't clean it well.
A look at Fred's Guide suggests it might be four stroking?
Specifically where he says "and the engine acts like it is choking, like it would like to go faster... and sometimes it WILL go faster if you close the throttle a little bit."
So, my questions are:
Is it my air filter? I bought the foam element brand new from treatland, but maybe I used too much oil... I soaked it and made sure to squeeze it out real good until nothing else came out. Also worth noting is I lost the slider bar that holds the box together on a bumpy driveway and have it held quite tightly with duct tape, but I don't think that would affect much.
Is it the carburetor/jetting? It's supposed to be stock, and I even asked the seller after I bought it about the jetting. He claims its completely stock.
There's a little clip that adjusts how deep the needle can go, should I try adjusting it? The service manual tells me I can make the mix richer or leaner this way. This shouldn't affect WOF, should it? Wouldn't that be the main jet?
What about adjusting the throttle? Is it possible that a wrong throttle adjustment at the handle would cause this issue?
Thank you all, I'm new to this so I'm not sure what to look for and I've tried scouring the internet for answers. It's frustrating because I'm sure that once I sort this issue out I'll finally have it up to stock speed, and I'm too stubborn to take it to a mechanic like my dad suggests. (edited)