Jetting hp carb

seanbbolson7878

New Member
Aug 21, 2019
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Just broke in my 66cc china girl. It's got a bike berry hp carb and I'm wondering what size jet to get. I dont know if the bigger number the jet the smaller hole or the other way around. Its 4 stroking at 1/2 to WOT and getting wayyyyy to much fuel. The plug is black. Half throttle is faster than WOT right now. I think the stock jet size in the hp carb is .70 and just wondering what size jet I should get. My altitude is around 400ft and average temp is usually around 70-80. People are saying to run a .90 size jet? I dont know if that is a bigger or smaller hole.
 

FOG

Well-Known Member
Mar 3, 2019
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Bigger number means bigger hole. More fuel. From your description it sounds like you need a smaller main jet.
 

Warphones

New Member
Mar 23, 2020
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Albuquerque
I'm running stock exhaust with no cap. Should I be trying a 60?
all motors run a bit different in their own way I was shocked when I had to run a .60 on the dellorto.
it was funny though because on the NT carburetor I got away with a .70 just fine.
I highly recommend getting the 20 piece jet kit from .60 all the way to .80 that way you can get a full tune exactly where you want it and in the end it pays itself off I know it's like 20 bucks or something.
 

Tyler6357

Well-Known Member
Mar 15, 2012
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Santa Barbara, CA
The correct jet is usually somewhere between 60 and 70. It's best to start high and work your way down until you find the right one. Also, it's best to let the engine get hot before making your analysis, it might run slightly different when warmed up.

https://www.ebay.com/itm/Dusensatz-...-69-Jet-set-Puch-Maxi-E50-Tuning/182901922538

https://www.ebay.com/itm/5mm-NT-Carburetor-Jet-Kit-80CC-Gas-Motorized-Bicycle/262277794930

If you don't want to buy jets you can make your own. Just take a jet and solder over the hole, then drill out the new hole to the size you want with micro bits.

https://www.ebay.com/itm/New-Set-21...826356?hash=item3f1a93b0f4:g:1FgAAOSwbqpTxXxp
 
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Tron mobile

New Member
Mar 30, 2020
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So I need to jet somewhere between the hp jet and the nt carb jet the hp jet doesn't work on the nt carb
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,142
170
63
Santa Barbara, CA
My guess is that they are not exactly very accurate. One #70 will sometimes be smaller than another #70. Stock size for both carbs is supposed to be #70. For the HT Carb, most of the time #70 is too rich, and you need to jet down, usually in the 60's.