Dellorto Jets

 

4, 5, or 6 millimeter

 

Thread Size: Dellorto jets in mopeds come in three thread sizes 4, 5, and 6 millimeter. Each thread size has maybe a hundred different jet sizes. They all fit and look the same but have different size pin holes. 

 

 

Left, genuine (with “diamond INC” logo)
Right generic (with different or no logo)

Jet Number: Jets have a number stamped on them indicating the hole size. The number can have different meanings for different jet makers.

For generic Dellorto jets the jet number is the mm size.
A generic Dellorto 60 is 0.600 mm.

For genuine Dellorto jets the jet number is less than the mm.
A genuine Dellorto 60 is 0.627 mm.

So a genuine 60 is in-between a generic 62 and 63.
This sounds wrong but is true!

 

How this was determined: Below is a graph of 17 genuine Dellorto 5mm jets actual sizes. The direct measurement was done with a set of machinists wire gauges, in increments of 0.001″. You can see how the measured sizes fall nicely on two lines. The line for over-56 has less slope than the line for under-56. You can also see what drill sizes correspond to what jet sizes. This study was done in 2002 before there were generic jets. It was surprising to learn that the stamped number did not mean the millimeter size.

Dellorto Jet Sizes Graph, drawn in 2002

Genuine 6413 (6 mm) Jets (M6-0.75 thread)
genuine       closest generic

##  inch size mm   ##     price
    applications
51 0.0215″=0.550  55  $4.00 generic 55 (= Dellorto 51)
52 0.0219″=0.556  56  $6.00 A55 smaller for high altitude
54 0.0228″=0.580  58  $4.00 generic 58 (= Dellorto 54)
55
 0.0231″=0.587  59  $8.00 Tomos A55 243160 original
56 0.0236″=0.600  60  $4.00 generic 60 (= Dellorto 56)
58 0.0242″=0.615  61  none  
59 0.0244″=0.620  62  $4.00 generic 62 (= Dellorto 59)

60 0.0247″=0.627  63  $6.00

Genuine 1486 (5 mm) Jets (M5-0.75 thread)
genuine       closest generic
##  inch size mm   ##    price
    applications
42 0.0178″=0.451  45   $5.00
43
0.0182″=0.462  46   none   pre-78 Ciao & Bravo
44 0.0186″=0.472  47   $5.00
45 0.0190″=0.483  48   none   78-on Ciao & Bravo
46 0.0194″=0.493  49   $5.00
47 0.0198″=0.503  50   $7.00
48 0.0202″=0.513  51   $5.00 most 20mph mopeds
49 0.0207″=0.525  52   $7.00 78-83 Vespa Grande

Dellorto Jet Sizes Graph, improved in 2019

50 0.0210″=0.533  53   $5.00 76-80 Garelli (some)
51 0.0215″=0.546  55   $7.00 85-91 Tomos A3
52 0.0219″=0.556  56   $5.00 almost all 30mph mopeds
53 0.0223″=0.566  57   none   92-06 Tomos A35
54 0.0227″=0.577  58   $5.00 86-90 Derbi (flat reed)
55 0.0231″=0.587  59   none  
56 0.0235″=0.597  60   $5.00
58 0.0242″=0.615  62   $5.00
60 0.0247″=0.627  63   $5.00
62 0.0255″=0.648  65   none  
64 0.0262″=0.665  66   none  
66 0.0268″=0.681  68   none  
68 0.0274″=0.696  70   none  
70 0.0280″=0.711  71   none  

Genuine 11600 (4 mm) Jets (M4-0.70 thread)
genuine       closest generic

##  inch size mm   ##   price
    applications
25
0.0107″=0.272  27  $8.00  Tomos A55 pilot jet
29 0.0124″=0.314  31  $8.00
30 0.0128″=0.325  33  $8.00  good for A55 pilot jet
32 0.0140″=0.355  35  $8.00  same as #80 drill
35 0.0149″=0.378  38  N/A
40 0.0170″=0.431  43  $8.00
42 0.0178″=0.451  45  N/A
44 0.0187″=0.475  47  N/A
45 0.0190″=0.483  48  $8.00
48 0.0202″=0.513  51  $8.00  Sachs 504/1A and 505/1A
50 0.0210″=0.533  53  N/A
55 0.0230″=0.580  58  $8.00
60
 0.0250″=0.635  63  $8.00

 

Clone Carbs: Some Dellorto SHA clone carburetors have a different jet thread, M5-0.8. But the Runtong (China) SHA clone has the same thread M6-0.75.