NT Carb One Piece Main Jet Blues

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Quanah

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I would have thought this had been covered here, but I can't seem to find anything about it. I recently got a 66cc china motor kit and the main jet is one piece. Seems like I read that the old carbs had a slide needle with 4 grooves, and the newer ones have 5. Mine has 4. So I guess mines the older one? I have never seen a carb that didn't have the main jet that unscrewed from the slide needle jet tube. I haven't started this motor yet, but I am sure I will want to play with this main jets sizes when I do. I would also think that the type I have seen before would interchange, but can't seem to find the slide needle jet tube I need, jets aren't hard to find...checked all the major sellers of these china girls. Anyone with same problem?
 
yes, that's the old style metering tube & jet

that jet unscrews, but sometimes it can corrode so much that it is stuck pretty tight

no need to take it off if you use the solder & drill method of changing jet size
 
agreed, thats the plain old jet and tube.

and i hate it when the jet wont release!

usually end up cranking the tube in hard then just tweaking the jet in with needle nose pliers, and then next time...the tube releases first again!!!!!


AAAAAARRRRRGGGGHHHHH!!!!!!!!
 
I'll look at it again, but I swear it is all one piece. Thanks for the input, I'll let you know what I find out.
 
think about it like this...

why would they manufacture it with two hex's of two different diameters, that are slightly out of line with each other?

simple. they dont ;) they use two separate pieces of hex bar in auto feed lathes that spit them out at a rate of ten a minute or so...

(first hex tube ive seen now i think of it...mine are always round with two flats at the end... anyway. same thing.)


that jet hole does like slightly large, so kudos for wanting to get a smaller one.

^^^crassius' suggestion^^^^ solder and drill it, the drills can be re-used, so a better purchase than new jets ;) other way is to use bits of fine copper wire but that can take some skill with a soldering iron...
 
Well they did come apart. hard to believe how tight they were. I'll more than likely go for jets, because I don't have a set of numbered drills...although I have been wanting a set for some time now... we'll see.
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Oh yeah, this jet doesn't have a number on it, another reason to get a set of numbered drills, I could use them to find out what size the existing hole is.
 
The jet is designed to be a tight fit into the tube so that fuel can't leak down the jet threads and artificially richen the mixture over the set jetting size.

After you've spent time running different sized jets in and out of the tube, it pays to buy a new tube so that the jets are once again a tight fit.

Drilling out the jets to larger sizes is fraught with danger because a home drill press doesn't have the required accuracy of precision machinery.
For the NT carburettor, i have a selection of 26 jet sizes from #68 to #90, though the widest extremes for accurate jetting on different 2-stroke Chinese engines has been between #70 and #86 with the average mostly hovering around #76 - #78, using ethanol free Australian lower south eastern 98 octane fuel. Someone on here said that Australian 98 octane works out to American 93 or 95 octane - can't remember exactly which one.
 
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