Thanks very much to TLC for article on cleaning carbie.

I cleaned it out and bike is going fairly well, but I was reading the article per:


"There are 3 main adjustments on a carburetor for air-to-fuel ratio. These are the pilot system (pilot air jet and pilot jet) for idle to 1/4 throttle. The jet needle system for 1/4 to 3/4 throttle. And the main jet system for 3/4 to full throttle."

It seems the bike has a "happy speed" of 30 mph or more, when it just sings along [1/4 to 3/4?] , but we have speed limit of 20 mph on our beach and at 20 it seems I am on the point of going from "idle to 1/4 throttle" to step 2, and there is a slight dead spot.

I am thinking the pilot air jet needs adjustment. I counted 2 1/2 turns and reset it to that but I feel sure the previous owner would have changed that from any factory setting.

So could someone either give me a suitable setting [sea level in tropics] or explain how to tune it "by ear".

 

I cleaned mine on my snowmobile which is the same carb, 2 1/2 on the pilot air jet sounds high, I can,t remember but I thought it was more like 1-1/2. If the previous owner fooled with it, it will be trial and error to get it back.

 

yes, someone yesterday in another post mentioned 1 1/2 turns as well.

But I would like to better understand the function of this screw. I am thinking that it acts to reduce the vacuum effect on the fuel in float chamber, correct? ie for the same amount of air via the throttle slide [which is say 1/2 inch raised] it controls how much fuel gets mixed in via the pilot jet [I am assuming the main jet needle at same time is totally blocking main jet]. Hence I am thinking that screwing it IN will therefore richen the mixture in this "idle to 1/4" part of the operation.

Is that correct?

 

The guy on this video can explain it much better than I can.YouTube - how motorcycle and atv carbs work

 

thanks again TLC

I ended up with pilot air screwed out 1 turn and it all seems to run OK at the 1/4 throttle setting without any spluttering. Not perfect but I guess 1 cylinder 2 stroke w/carbie was never meant to be totally smooth.

My car is an old 1976 Volvo with Bosch KJet Injection. It is also called "mechanical Injection" or "Continuous" and I now understand why it is called continuous because it has one single SMOOTH mode of operation from idle to full speed and once setup correctly is a joy to drive.