Wow - Jet size really does matter !!! RT carb 70 main

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abefroman

New Member
Sep 13, 2013
103
0
0
new orleans
I bought a motor from Dax and it came with an RT carb and a jet kit. the stock jet in the carb is NOT marked !!! does anyone know the size ? The jet kit had 65, 70,75,80, and 85. my motor is ported and polished. With the stock jet it ran great at low rpm but not at WOT. so, I started with the 65. it sucked. then I tried the 85. it sucked even more ! Then I tried the 70 and it ran really well !!! I'll probably also try the 75 when I get a chance, but I think I'm' going to break the motor in using the 70 since it is running so well. Using a magnifying glass and comparing the hole sizes, it's really hard to tell a difference, but it SURE DOES make a BIG difference !!!!

cheers
 
Davezilla

Davezilla

New Member
Mar 15, 2014
2,705
10
0
San Antonio Texas
Yup... something you can't even see the difference between a 65 and an 85 but can make a huge difference... and if you want to really fine tune one you can even get them in split sizes like 62.5 or 67.5... not for these engines, but for motorcycle carbs like mikuni or keihin. You can usually find a jet from another carb with the right dimensions and as long as their numbering system is the same or at least understandable they can be used. I've used genuine Dellorto jets in the nt and speed c abs without any issues before as their numbering and sizing is light years more accurate than the Chinese jets where you can get 5 #70 jets and each one will be a different size... even then, it's not the number stamped on the side of the jet or who makes the jet that will make your engine run the best, but which one will give it the proper air/fuel mix.
 
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