Carby NT Carb Tuning Basics



crassius

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that's 21mm with gasket on
I usually use my finger to gently bend tabs and sight across top of float to get the main jet barely peeking thru the hole in the float
 

gary55

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Nonsense. I'm showing 21mm with no gasket and the jet is still not peeking out of the float. If you ad the gasket the jet would be even lower. This is a cdh kit with the same carbs you are currently using so what are you talking about. You can have 21mm or you can have the jet peeking abv. the float. You can't have both.
 

crassius

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I have a stick on a key ring that I used to use to measure at exactly 21mm - maybe just because there are so many hills here or that I prefer a bit rich over a bit lean for safety with noob riders, but for many years I've measured by the main since it is easy to understand by noobs and works well - next time I have one apart, I'll see what the measurement is at the main. That 21mm figure is from a diagram from about 10 years ago of the first delorto clones and may not be right (but close enough) for the NT clones.
 

gary55

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I have a stick on a key ring that I used to use to measure at exactly 21mm - maybe just because there are so many hills here or that I prefer a bit rich over a bit lean for safety with noob riders, but for many years I've measured by the main since it is easy to understand by noobs and works well - next time I have one apart, I'll see what the measurement is at the main. That 21mm figure is from a diagram from about 10 years ago of the first delorto clones and may not be right (but close enough) for the NT clones.
Now I get it. The main on the cdh one's I'm getting are 20.3mm abv. metal. I guess +- 1 mm probably ain't gona be noticed much anyway. Lately these carbs have been a real consistent 21mm at the float. Kinda nice for a change.
 

crassius

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It occurs to me that some of my methods might seem peculiar, but with customers living 40 to 60 miles from the shop, I often have to fix things over the phone. I try to use easily understandable fixes that can be remembered for future problems, and always try to recommend troubleshooting methods and fixes that can be easily reversed if they fail to address the problem.

I rarely replace jets or solder and drill them now. Instead, I have a dead mag coil that I unwind some very thin copper wire from and tie a piece to the jet tube of the carb and run it down the tube thru the float and then stick the end into the main jet to see how it runs, still too rich? add one more wire, and more if needed.

If porting or high-flow muffler is later added, then wires come out to re-tune the carb.

I know these methods are not common (or maybe not even best for a hobbyist) but they work for me and save my customers some long rides to the shop.
 

beetleman

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My engine was four stroking at about half throttle with the needle all the way down (upper notch), so after reading this thread I went ahead and got different jets. Someone wrote that the NT carbs come with a 0.7 mm jet, so I replaced mine with a 0.61 jet. No more 4 stroking! That hit the nail on the head. However, now I'm concerned about overheating. Lean mixture = high temps. Should I be worried? Or just assume the engine was build to run 2 stroking so I have nothing to worry about? Yes, the engine is too hot to touch after a short run.
 

crassius

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if you have one on hand, see if a slightly larger jet still 2-strokes OK, else, try a richer float setting
 

HeadSmess

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the thin wire in the jets works...
just keep sticking them in there until it hits a wall, then remove one or two and do a plug chop...

its really hard to get a china girl to sieze from being too lean... a chainsaw, yes, a motorbike, yes, a happytime engine? no. it will be other things that bring you undone before a lean/heat siezure occurs...

i was getting down to a 0.5 on some engines...
 

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