Excellent report, very well described result.
I'm not surprised by your findings, but wondering what are the differences between
the OEM and Chinese slide/needle unit.
The typical report is as you said, when Chinese carb installed just as it came,
the engine is hard to start, won't idle, impossible to tune, among other issues.
I pose this question to you: Will the bystarter fit properly into your OEM carb ?
If yes, I would give that a try on the engine, see if it changes the rich condition.
Running rich
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Re: Running rich
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Re: Running rich
Tried new carb bystarter on old carb, no help. Still too rich. Measured bystarter slide/needle lengths and diameters, all the same.
Removed main jets and found old carb has a number on it but I can't read it. New carb main jet appears to have no numbers on it. Used a set of tiny round files used for cleaning gas torch tip holes as go/no-go gauges. Also used a digital caliper to measure the file diameters. Compared main jets and holes appear to be the same. Compared idle jets and found the old carb would pass a 0.73mm file where-as the new carb would only pass a 0.46mm file. Appears someone did drill out the idle jet.
Filled float bowls then drained fuel into a container. The new carb holds slightly more fuel than the old carb so fuel level does not appear to be the issue. (new carb=15.39 grams VS old carb=15.06 grams).
In regards to why old slide/needle assy work better; slide diameters were identical. Didn't see anything obviously different other than the color. Measured needle dia near slide and they were identical. Getting repeatable measurements of the diameter near tip of needle it tough since the needle is tapered but doing the best I could I measured new needle at 1.19mm VS 1.52mm for the old needle. So using the new needle would make mixture too rich.
Another thing I noticed was that the clear vac hose that runs from the intake to the fuel petcock has fuel bouncing around in it abt 1/2 way up the hose with the old carb. With new carb, I can see just a tiny amount of fuel near the intake nipple bouncing around. Seems like this may be a good indicator that fuel is not atomizing properly with the mixture being too rich.
Looks like I'll be running the new carb with the old slide/needle assy.
Removed main jets and found old carb has a number on it but I can't read it. New carb main jet appears to have no numbers on it. Used a set of tiny round files used for cleaning gas torch tip holes as go/no-go gauges. Also used a digital caliper to measure the file diameters. Compared main jets and holes appear to be the same. Compared idle jets and found the old carb would pass a 0.73mm file where-as the new carb would only pass a 0.46mm file. Appears someone did drill out the idle jet.
Filled float bowls then drained fuel into a container. The new carb holds slightly more fuel than the old carb so fuel level does not appear to be the issue. (new carb=15.39 grams VS old carb=15.06 grams).
In regards to why old slide/needle assy work better; slide diameters were identical. Didn't see anything obviously different other than the color. Measured needle dia near slide and they were identical. Getting repeatable measurements of the diameter near tip of needle it tough since the needle is tapered but doing the best I could I measured new needle at 1.19mm VS 1.52mm for the old needle. So using the new needle would make mixture too rich.
Another thing I noticed was that the clear vac hose that runs from the intake to the fuel petcock has fuel bouncing around in it abt 1/2 way up the hose with the old carb. With new carb, I can see just a tiny amount of fuel near the intake nipple bouncing around. Seems like this may be a good indicator that fuel is not atomizing properly with the mixture being too rich.
Looks like I'll be running the new carb with the old slide/needle assy.
Re: Chiness POS carbs
I brought an el cheapo Chinese carb for my Honda Nifty 50 1984-5 just to try but the throttle would stick inside the carb. Maybe was stuck inside the carb, can't remember now. I messed around for ages checking the needle setting until I noticed it was sticking. Not sure whether it was a machining fault or what but rather than toss it I used a dremel in the carb until the throttle barrel would slide freely. I couldn't believe how incredible the acceleration was . Two years later and going well. It probably depends on the factory. Some buyer feedback is brilliant. Should probably publish here which sellers are best for Sprees. Mine required aluminium whittling but was worth the effort.