Encarwi Carburetors

October 25, 2014

encarwiContents:   1. Encarwi “Tomos”   2. Encarwi “Batavus”   3. Encarwi “Trac”

               4. Encarwi Jets   5. Encarwi “Early”  6. Bing Jets

1971-1977 Tomos Automatic N had a Laura M48 engine with an Encarwi carb

Before 1973, Tomos had Puch and Laura engines. The 1971 Tomos Automatic N had a Laura M48 engine with Encarwi carburetor. Tomos continued to use Encarwi on their A3 engine, until 1983.

1977 Flandria Bermuda with Encarwi

1977 Flandria Bermuda
Encarwi A-type carb

Welcome. Encarwi (made in Holland, now the Netherlands) was a division of Bing (Germany). On US models, Bing-Encarwi carburetors were used on mopeds by Batavus and Badger, with Laura (Holland) engines, Flandria (Belguim), and pre-1986 Tomos (Yugoslavia). 



Encarwi Carbs

Encarwi carbs on US models of Batavus and Tomos.
Top, S-series. Bottom, A-series (no idle screw).

 bing crown
Encarwi “A” series carbs had an “automatic” choke, controlled by a special twist throttle with thumb button. The choke button lets the throttle twist opposite, below “zero”. This exposes a hole in the slide valve, in front of the fuel nozzle. After starting, twist throttle and choke clicks off automatically.  
A11            (8mm, Ø14 slide 408, jet 52-54), for 20kmh Laura M48 engine (Euro model)
A22            (8mm, Ø14 slide 108, jet 50-52), for 25kmh Laura M48 engine (Euro model)
A21          (12mm, Ø14 slide 202, jet 56-58), for 40kmh Laura M48 engine (Euro model)
A83          (12mm, Ø14 slide 426, jet 46), for 20, 25, 30mph Tomos A3 engine 1974-80+
88A85/102 (Ø12, Ø14 slide 426, jet 46) for 20, 25, 30mph Tomos A3 engine 1980-83+
88A85/103 (Ø12, Ø14 slide 426, jet 56, no jet access from side) for Tomos A3 1983-85
Encarwi “S” series carburetors had a “standard” choke, controlled by a small lever on the handlebar via a cable.
88S23A      (8mm, Ø14 slide 190, jet 54),    for 20kmh Laura M48 engine (Euro model)
S23B          (8mm, Ø14 slide 190, jet 52-54), for 25kmh Laura M48 engine (Euro model) 
S23A          (8mm, Ø14 slide 190, jet 50-52), for 20mph Laura M48 Batavus 1976-77
S8A            (8mm, Ø14 slide 190, jet 52-54), for 25mph Laura M48 Batavus 1976-77
S22          (12mm, Ø14 slide 405, jet 54-58), for 30mph Laura M48 Batavus 1976-77
S25          (12mm, Ø14 slide 167, jet 56-58), for 30mph Laura M48 Batavus 1977-78
88S25/101 (Ø12, Ø14 slide 188, jet 56-58), for 30mph Laura M48 Batavus 1978-80
Encarwi “H” series carburetors were designed specifically for the Laura M56 engine, later made by Trac (Daelim).
H8           (8mm, Ø12 slide ???,  jet 46), for 20mph Laura M56 eng Batavus 1978-80
H12/102 (12mm, Ø14 slide 3,  jet 56), for 25 & 30mph Laura M56 Batavus 1978-80
unmarked (12mm, Ø14 slide 3?, jet 56), 25 & 30mph M56 remake Trac 1982-85 
Encarwi carbs and slides

Top, Encarwi carburetors, engine view, with slides slightly open, showing the idle air channels or slots or holes.
Bottom, the corresponding throttle slides, all 14mm diameter, bottom view. The pair of large holes is for the cable.
Substitutions or conversions: Any S-type slide can be drilled and machined to be made for an A83 or H12 carb.
The S-type slides (190, 405, 188, 167, 2) all interchange, but have different idle mixture idling behaviors.
The Tomos A3 slide 426 fits a Trac M56 with H12 carb, with only minor widening (drilling) of the sprayer hole.



Encarwi Slides

The amazing Encarwi 426 auto-choke throttle slide (Tomos A3) is explained in four steps:
1. Full power   – throttle cable is pulled all the way. The slide does not have to be there. Main jet controls the mixture.
2. Partial power -throttle cable is pulled part way. The slide limits the amount of air. The main jet controls the mixture.
3. No power (idle) -throttle cable is pulled slightly. The slide blocks most of the air. Idle slot size controls the mixture. 
4. Cold start  – throttle cable is not pulled at all. The choke jet hole and choke air hole in slide 426 control the mixture.
Substitutions or conversions: The S25 and A83 Ø12 carbs are the same, except for the throttle slide and idle screw.
The Ø14 throttle slides 167 and 426 are nearly the same, except the Auto type 426 has extra choke holes and cut outs.



Encarwi Tomos1. ENCARWI A83, 88A85/102, 88A85/103

– Used on 1976-83 Tomos A3 mopeds.
– Located above engine, difficult to remove.
– Serviceable from sides.
– No choke cable. Choke is part of throttle.
Pic  Number   Description            Price   Remarks 
a   209070  carburetor A83          N/A  Ø12 1976-83
b               carburetor 88A85/102   N/A  Ø12 1980-83
c               carburetor 88A85/103   N/A  Ø12 1984-85
1   209116  main jet see below Bing Jets M3.5-46
1a             long jet see below Encarwi Jets long-46
2   206765  long holder for short jet see Encarwi Jets
2a 481731  long holder for long jet  see Encarwi Jets
3   209118  slide Ø14 #426 w/hole $18 for auto-choke
4   209003  spring Ø9.5 x 42        $5
5   206763  carb top screw-on     $15 M18x1 thread
11  206770  float with needle        $25 can repair this
12  206772  float top with seat      $25 can polish this
13  206771  gasket for float top      $10
14  206773  banjo black plastic     $15 breaks easy
14  gmbanjo banjo metal upgrade $12 w/ 2 washers 
16  206775  banjo bolt                  $7
17  206774  fuel filter all metal      $15 clean & reuse
18  027053  see hardware M4 x 10 slot head
20  027079  clamp bolt                 $5
24  200384  air filter metal mesh  N/A
25  209215  air box (silencer)       $20
26  209216  junction sleeve rubber $30 gets hard
27  209217  inlet tube connector    $3
28  209579  inlet tube (not shown) $3
30  200382  intake gasket thick     N/A
32  217315  intake manifold oil inj.  N/A w/M6x1 hole
33  209085  intake manifold          $22 OD 16, ID 12
34  031932  see hardware M6 lock washer
35  044284  see hardware M6 x 22 hex bolt
Encarwi Tomos Carbs

Left, 1974-83 Tomos carb, Encarwi A83, bare.
The jet and jet holder unscrew from the side hole.
The jet can be cleaned out easy, on the roadside.
Right, 84-86 Tomos, Encarwi 88A85/103, complete.
The side hole is blocked. Jet access is from bottom.
The engine must be lowered to access the jet.
Jetting/servicing is ten times more difficult.



Encarwi Batavus2. ENCARWI  S8A, S23, S22, S25, 88S25/101

– Original on Laura M48 engine
– Used on 1976-79 Batavus, 1977-78 Badger.
– Located behind and below engine
– Needs longer throttle and choke cables.
Pic# Number   Description             Price   Version
a   487180  carburetor S22 (Ø12)     n.a. 30mph
      56 jet, Ø14 slide 405, Ø16 air inlet
b   541780  carburetor S25 (Ø12)     n.a. 30mph
      56 jet, Ø14 slide 167, Ø16 air inlet
c   481790  carburetor S8A (Ø8 )     n.a. 25mph
      52 jet, Ø14 slide 190, Ø14 air inlet
d   486795  carburetor S23A (Ø8)       n.a. 20mph
      50 jet, Ø14 slide 190, Ø14 air inlet
e   5417xx  carb 88S25/101 (Ø12)     n.a. 30mph
      56 jet, Ø14 slide 188, Ø16 air inlet
1a  541729  see below Bing Jets M3.5-56 30mph
1b  481727  see below Bing Jets M3.5-52 25mph
1c  481726  see below Bing Jets M3.5-50 20mph
2    206765  long holder for short jet see Encarwi Jets
2a  481731  long holder for long jet   see Encarwi Jets
3    481758  throttle slide #405       n.a. S22 30mph
3a  561742  throttle slide #167       $35 S25 30mph
3b  5617xx  throttle slide #188       n.a. 88S25/101 
3c  486723  throttle slide #190       $25 25 & 20mph
4   209003 spring Ø9.5 x 42          $5
5   206763  carb top screw-on     $15 M18x1 thread
  481746  idle screw M4-0.7×15 $12 can use M4
10  481747  spring Ø4.6,Ø6.6 x 9    $3
11  206770  float with needle          $25
12  206772  float top with seat       $25
13  206771  gasket for float top       $10
14  206773  banjo black plastic      $15
14  gmbanjo  banjo metal upgrade $12 w/2 washers 
16  206775  banjo bolt                   $7
17  206774  fuel filter                   $15
18  027053  see hardware M4 x 10 slot head

Left 1970’s original float, right 90’s replacement

20  481724  clamp bolt                  $5
21  481743  choke plate                 $7
22  481745  bolt choke pivot           $3
23  481744  spring choke                $3
24  200384  air filter metal mesh   N/A
25a 481713  air box (inlet 16mm)   N/A 30mph
25b 481734  air box (inlet 14mm)  $35 25 & 20mph
26  481733  rubber band              $5
27  481735  wire clip                    $10



– Made special for Laura M56 engine.
– Serviceable without removal.
– Used on 1978-80 Batavus Regency (M56)
– 1981-85 Trac Clipper, Eagle, Hawk (M56)
 56xxxx  carburetor H12 (30 and 25mph)     $220
      Ø12  56 jet
 56xxxx  carburetor H8 (20mph version)       N/A
       Ø8 46 jet
1   see Bing Jets M3.5 #56  
1a see Bing Jets M3.5 #46
2   491722  short holder for short jet  see Enc. Jets
2a 49xxxx  short holder for medium jet see Enc. Jets
3   561748  slide throttle Ø14 (H12) #3          $25
3a 561742  slide throttle Ø12? (H8)               N/A
4   481759   spring throttle Ø9.5 x 44           $10
  561721  carb top white plastic                 $25
6   5617xx  rubber cover over carb top           $7
  481739  see hardware M5 x 15 slot head
9   206770  float with needle                         $25
10  206772  float top with seat                     $25
11  206771  gasket for float top                     $10
12  206773  banjo fuel inlet                          $12
14  206775  banjo bolt                                  $7
15  206774  fuel filter                                  $15
16  027053  see hardware M4 x 10 slot head
18  561740  idle screw M5-0.80 x 16             $5
19  481747  spring idle screw Ø5,Ø7 x 10     $2
20  561743  choke slide                                N/A
21  561745  o-ring for choke 1 x 4.5, qty 2    $3
22  5617xx  see cables W2 univ throttle wire
23  491724  spring choke return                     $8
25  5617xx  air box with filter                       $65
26  5617xx  see hardware M5 x 30 phillips
27  5617xx  air filter – screen-foam-screen     N/A 


Encarwi H12 carb on Trac M56 engine

Encarwi H12, with no top, on Trac M56 engine




Encarwi Jets: Most Encarwi carburetors use standard Bing 3.5mm jets. Those jets have a “short” head that is only 3mm long. To use a short jet, the jet holder must be for a short jet. But some Encarwi carburetors have longer 3.5mm jets with 8mm “medium” or 12mm “long” heads.

Encarwi “medium” jets for Laura M56
size 56     $12  threads 3.5mm, head 8mm
Encarwi “long” jets Laura M48, Tomos A3  
size 45     $12  threads 3.5mm, head 12mm
size 46     $15  threads 3.5mm, head 12mm
size 52     $12  threads 3.5mm, head 12mm
size 56     $12  threads 3.5mm, head 12mm
size 58      $7  threads 3.5mm, head 12mm
Encarwi jet holders
long jet holder for short (Bing) jet          $25
2  long jet holder for long Encarwi jet         $20 can be a substitute for 3
 short jet holder for medium Encarwi jet  $30 
4  short jet holder for short (Bing) jet         $40

Encarwi Karburator from 1960's

Encarwi Carburator, from 1960’s or 70’s


Carwi Karburator

Carwi Carburator, from the 1950’s




















Encarwi A30 carb

Encarwi A30 carburetor

Encarwi A30 on 1960's Flandria moped

Encarwi A30 on
1960’s Flandria

You can see that these early Encarwi carbs have many things in common with the later ones. The most obvious thing is the angle of the throttle slide with the venturi. Most carburetors have the slide valve 90 degrees to the air flow, but Encarwi carbs are more like 60 degrees. The other thing unique to Encarwi is the “automatic” choke, indicated by the absence of an idle speed adjustment screw, the choke holes and cut-away in the slide, and an extra thumb button on the throttle control that lets the throttle cable go completely slack, below normal idle or “zero”.  



Bing Jets

October 26, 2011

Bing jets for Puch, Encarwi (Batavus M48, Tomos A3, Trac M56), Solo, Kreidler are M3.5 x 0.6 threads.

Bing jets for Sachs square Bing are bigger, size M4.0 x 0.7 threads. This is also a Dellorto pilot jet thread.

  • bing crown

    Bing crown logo
    on original jets

    The meaning of “jet size” depends on the jet maker. This has caused much confusion.

  •       For Bing originals, a size 50 jet has a 0.478 mm hole, not 0.500.
  •       For Bing generics, a size 50 jet has a 0.500 mm hole.
  •       For Dellorto originals,   a 50 jet has a 0.533 mm hole, not 0.500.
  • So Bing jets are smaller than they say, and Dellorto jets are bigger than they say.
  • Many or most aftermarket jets are what they say. The graph shows the true sizes. 


           Bing Jets (3.5 mm) 

Part No.    Maker    Jet Number   Actual Hole Size    Price     Applications

209116     Bing orig #46 original  0.0175″=0.445mm    N/A   76-83 Tomos early A3 models (30, 25, and 20mph)
209116     modified #xx =Bing46  0.0175″=0.445mm   $18   (made from a 52 soldered or smashed and redrilled)
44021/48  Bing orig #48 original  0.0182″=0.462mm    N/A   78-80 Puch (2-spd hi torque Ø12 carb 20mph)
44021/50  Bing orig #50 original  0.0188″=0.478mm    N/A   76-78 Batavus (Laura M48 Ø8 carb 20mph)
44021/52  Bing orig #52 original  0.0194″=0.493mm     $7   76-78 Batavus (Laura M48 Ø8 carb 25 mph)
335000     generic  #50 =Bing53 0.0195″=0.495mm     $7
44021/54  Bing orig #54 original  0.0200″=0.508mm     $7   74-83 Puch (1-spd alum. cylinder, Ø14 carb 2.22, 20mph)
335200     generic  #52 =Bing55 0.0204″=0.518mm     $7
44021/56  Bing orig #56 original  0.0206″=0.523mm    N/A   77-80 Batavus M48 and M56 (30), 80-83 Trac M56 models
44021/58  Bing orig #58 original  0.0213″=0.541mm    N/A   78-83 Puch (2-spd hi torque cyl. Ø12 carb 2.22 30mph)
335600     generic  #56 =Bing59 0.0217″=0.551mm     $7
44021/60  Bing orig #60 original  0.0222″=0.564mm    N/A   78-83 Puch (1-spd hi torque cyl. Ø12 carb 2.22 30mph)
335800     generic  #58 =Bing62 0.0228″=0.579mm     $7
44021/62  Bing orig #62 original  0.0229″=0.582mm     $7
44021/64  Bing orig #64 original  0.0234″=0.594mm    N/A   74-83 Puch (1-spd al cyl Ø14 carb 2.22 needle jet 30mph)
336000     generic  #60 =Bing64 0.0235″=0.597mm     $7
44021/66  Bing orig #66 original  0.0239″=0.607mm    N/A
336200     generic  #62 =Bing67 0.0242″=0.615mm     $7
44021/68  Bing orig #68 original  0.0248″=0.630mm    N/A   78 Sears (1s al cyl Ø14 carb 30mph), Kreidler Flory (30mph)
336400     generic  #64 =Bing68 0.0248″=0.630mm     $7
44021/70  Bing orig #70 original  0.0254″=0.645mm    N/A   84-86 Puch Cobra (Ø14 carb, 2.17 needle jet 25mph)
336600     generic  #66 =Bing71 0.0258″=0.655mm     $7
44021/72  Bing orig #72 original  0.0260″=0.660mm    N/A   84-86 Puchs had bigger main jets, but smaller needle jets.
44021/74  Bing orig #74 original  0.0267″=0.678mm    N/A   1990’s Puch remakes also had 70’s jets, 2.17 needle jets.
336800     generic  #68 =Bing74 0.0268″=0.681mm     $7
44021/76  Bing orig #76 original  0.0273″=0.693mm    N/A
337000     generic  #70 =Bing77 0.0278″=0.706mm     $7
44021/78  Bing orig #78 original  0.0280″=0.711mm    N/A
44021/80  Bing orig #80 original  0.0287″=0.729mm    N/A
44021/82  Bing orig #82 original  0.0294″=0.747mm     $7  2000’s Bing Ø15 carb with smaller 2.17 needle jet

           Bing Jets (4.0 mm) 

Part No.      Maker    Jet Number    Actual Hole Size    Price     Applications

243222      Dellorto  #25 =Bing27 0.0107″=0.272mm     $8  Tomos A55 pilot (idle) jet
243110      Dellorto  #29 =Bing31 0.0124″=0.314mm     $8   same as Tomos #25 idle jet “cleaned” with #80 drill
D1486-030 Dellorto  #30 =Bing33 0.0128″=0.325mm     $8
D1486-032 Dellorto  #32 =Bing35 0.014″ = 0.355 mm    $8
D1486-035 Dellorto  #35 =Bing39 0.0149″=0.378mm    N/A
D1486-040 Dellorto  #40 =Bing45 0.0170″=0.431mm     $8
44031/45   Bing orig #45 original  0.0171″=0.434mm    N/A   Sachs 504/1A DK (19mph)
44031/48   Bing orig #48 original  0.018″ = 0.46mm      $8
D1486-043 Dellorto  #43 =Bing49 0.0182″=0.462mm    N/A
44031/50   Bing orig #50 original  0.0183″=0.465mm     $8  Sachs 504/1B and 505/1B (Ø10 carb 20mph)
D1486-044 Dellorto  #44 =Bing51 0.0187″=0.475mm    N/A
D1486-045 Dellorto  #45 =Bing52 0.0190″=0.483mm     $8
44031/52   Bing orig #52 original  0.0190″=0.483mm    N/A   Sachs 504/1A and 505/1A (Ø12 carb 30mph)
D1486-046 Dellorto  #46 =Bing53 0.0194″=0.493mm    N/A
D1486-047 Dellorto  #47 =Bing54 0.0198″=0.503mm    N/A
D1486-048 Dellorto  #48 =Bing55 0.0202″=0.513mm     $8  Sachs 504/1A and 505/1A (without air filter box)
D1486-049 Dellorto  #49 =Bing56 0.0207″=0.526mm    N/A
D1486-050 Dellorto  #50 =Bing57 0.0210″=0.533mm    N/A
44031/58   Bing orig #58 original  0.0213″=0.541mm     $8 Sachs 504/1D and 505/1D (Ø12 D-carb 30mph)
D1486-051  Dellorto  #51 =Bing59 0.0215″=0.546mm    N/A
D1486-055 Dellorto  #55 =Bing63 0.023″ = 0.58 mm      $8
D1486-060 Dellorto  #60 =Bing69 0.025″ =0.635mm      $8




Encarwi Carburetor Service

May 4, 2008

Encarwi A83 carburetor on Tomos A3 engine

Encarwi Carb Service for Tomos A3 1974-83

This very simple, early Tomos carb is designed to be serviced without removal. After 1985, Tomos A3 & A35 models came with Dellorto SHA14/12 carburetors. The Tomos A3 carburetor is in a confined area above the engine and below the sheet metal gas tank/frame. It is difficult to remove.

 Two super usfeul and easy checks:

1) Check the jet. With a large flat head screwdriver or a 9mm wrench, remove the jet holder #2. Remove the jet #2 with a medium-thin flat head screwdriver. Hold the jet up to a light source, such as a sunny white wall. Look through the tiny hole to see if light gets through. If it’s pitch black it’s completely blocked. If it’s not circular then it’s partially blocked, like by a fiber.

2) Check everything else. When the jet holder is removed, and the gas valve is turned on, gasoline should flow out of the gas tank, through the banjo bolt #16 at the float top #12, and then dribble out the hole where the jet holder was. This is a way to quickly test the fuel system, tank, valve, line, filter, and float, all at once.

If gas does not spill out with the jet holder removed, then gas is not getting to the jet. Check if gas comes out of the tank. If gas is getting to the carburetor, but not getting to the jet, then either the inlet banjo #14 or banjo bolt #16 is clogged, or the float top #12 is clogged, or the float #11 is in upside down, or the float is stuck in the up position. Several things can cause this kind of float to stay up and not drop down and let gas come into the float bowl reservoir: being installed upside down (pointy end goes up), rust powder filling up the guide hole at the bottom of the float chamber, the float bulb being pushed too far down the rod, the wrong float, or a dented float chamber wall.



Encarwi Batavus

Encarwi S25 carburetor on Batavus M48 engine


The jet holder #2 unscrews from the left side. It holds the jet #1, Bing 3.5mm size 46.

To remove an old, hard, shrunken and very stuck on, fuel hose, be careful not to break off the “neck of the banjo”. That means you only pull straight out and rotate, never pull or twist sideways. If that fails, a diagonal pliers aka dikes aka wire cutters, can be used to cut the old fuel line, parallel to the hose, without cutting the banjo underneath. The cut does not need to go all the way through the old fuel hose, but far enough to weaken it.   

To service the float, loosen the clamp screw #20 and rotate the carb so it is tipped to the right. Remove the 11mm hex head banjo bolt. Remove the two slot head screws #18. Lift off the float top. Lift out the float with your fingers. It should lift out freely and not feel stuck.

Float versions, left 70’s bulb, right 90’s solid












Encarwi S12 carburetor on Trac M56 engine

Things that cause not enough gas:

Rust powder filling up the guide hole at the bottom of the float chamber. Remedy is twisting a correct size drill bit with your fingers, to pull the powder up and out of the hole. With the jet holder removed and the gas valve turned on, gasoline should flow out of the tank, through the float valve, and spill out the jet holder hole. The amount should be enough to fill the float reservoir in a few seconds, which is roughly a spoonful every 4 seconds.

The bulb being pushed too far down the rod. Remedy is to push it back up. See the above photo with measurements.

Dented float chamber wall. Remedy is to grind or sand down the high spot.

Blocked float reservoir air vent. Gasoline cannot come in unless air can get out. Remedy is to find where it is blocked at, and remove the blockage. The vent follows a channel in the back mounting surface. An empty float reservoir should fill up in a few seconds after the gas valve is turned on. To test for a blocked air vent, first empty the reservoir, then turn the gas valve on for 8 seconds and then off. Then remove the jet holder, allowing gas to dribble out, to see how much gasoline there was in the reservoir.

Blocked gas tank air vent. Gasoline cannot leave the gas tank unless air comes in. So there is a pin hole in the gas cap. When the tank is full, and the vent hole is blocked, the bike will seem to run out of gas. To test for a blocked gas cap vent hole, first fill the gas tank, then close the gas valve, then remove the fuel hose. Place a clean container under it (to check for purity and to put the gas back in the tank). Turn on the gas and observe the flow. It will flow normal at first. But in a few seconds, as negative pressure builds up, the flow will slow down and stop, if the vent is blocked. If the flow continues for 20-30 seconds (or indefinitely) then the gas tank is vented.

Things that cause too much gas:

Worn float needle tip. Remedy is to sharpen it. Examine the tip with a magnifier. Spin the float with a drill while pressing the tip gently against a sheet of emery cloth or very fine sandpaper, at the same angle, and move it slowly around to fresh parts of the sandpaper. The needle rod must be straight first. Examine the tip with a magnifier. There should be, everywhere on the cone tip, circular sanding marks, and no more circular “potholes”.

The needle is bent. Remedy is to straighten it. Normally the bend is just above the top of the bulb. It is done with just fingers and eyes. Rotate to see which way it needs to go. Bend a little. Repeat. 

The bulb being pushed too far up the rod. Remedy is to push it back down. See the above photo with measurements.

Worn float seat hole. The float valve seat is part of the float top. It is the tiny hole at the bottom of the small hole. Examine the hole with a magnifier. It should be perfectly circular and free of nicks and scratches. Polish it with a spinning tooth pick, or the stalk of a Q-tip. 

Float bulb has gasoline inside it. If the float too heavy, it won’t have enough buoyancy to stop the gasoline from getting in. Remedy is to evacuate the fuel with compressed air, locate the leak hole, and apply a minimal amount of fuel tank sealant. 


Servicing the M56 engine’s H12 or H8 Carburetor:

One problem unique to this carb is warping of the engine side surface. This is caused by over tightening the two mount bolts, and maybe also because the heat block behind it is semi-soft. The back side must seal not just air, for good idling, but also there is a fuel passage that can leak because of a warped carburetor body. The remedy is to grind the back side flat again, without taking too much off. In the body, there is a narrow fuel hole at the bottom of another hole, that is impossible to see directly. That hole must be checked and cleaned with carb spray and compressed air. 

The float is the same as the other carbs. The float top is the same except it has no air vent pin hole. The idea was to not let gas spill out the vent hole. Instead the vent goes to the mounting gasket, where there is a small opening to the atmosphere, higher up.




Jet Drills

January 27, 2007

Above, a Tomos A55 idle jet (M4 thread) is physically bigger than a Puch Maxi main jet (M3.5 thread), but the hole size is much smaller. The photo shows how the #25 jet, 0.010" (ten thousandths of an inch), will allow the thinner wire of the wire wheel to pass through the hole, but not the thicker wire of the wire brush. This is a useful cleaning technique.

Above, a Tomos A55 idle jet (M4 thread) is physically bigger than a Puch Maxi main jet (M3.5 thread), but the hole size is much smaller. The photo shows how the #25 jet, 0.011″ (eleven thousandths of an inch), will allow the thinner wire of the wire wheel to pass through the hole, but not the thicker wire of the wire brush. This is a useful cleaning technique.

This will help you visualize how small these drills and jets are!

Moped main jets range from 0.018″ (#77 drill) to 0.026″ (#71 drill). 

Moped idle jets, like Tomos A55, are 0.011″ (smaller than #80).

An average human hair is 0.003″ (three thousandths of an inch).

So moped jet holes are 4 to 9 hairs wide!

Shauns well used jet drill container from the 1980's

Shaun’s well used drill container from 1987


Jet Drills: All through the late 1980’s and 1990’s, Shaun (at Royal Cyclery and later at Myrons Mopeds) used the USA-made jet drills to service carburetors. The drill sizes are an American wire gauge. They did not vary in size. Those 20-piece Drill Sets 61 to 80, cost $40 in 2015, $33 in 1998. and $29 in 1987. Some are in clear plastic round dome containers, and some are in conventional metal drill set boxes.


Drill Set 61-80 USA-made

Drill Set USA-made

Jet Drills made in China

Set 1 China-made

China-made Drills: In the 2000’s there were many China made tools sold in “surplus” tool stores. The China made 20-piece Drill Sets 61 to 80, sell for $7 to $10, or one fourth as much. They have an excellent blue plastic container, that only lets out one at a time. But the drill sizes are all wrong. From about 2010 to 2014, Myrons Mopeds sold these inexpensive drill sets, not knowing that the drill sizes were inexact, to say the least.

So although the China sets cost one forth as much, they only have about seven or eight different sizes, and they lack the smaller sizes below 0.4 (or sometimes 0.6) mm. Each set is different.


Jet Drills made in USA

Jet Drills made in USA

Set 2 China-made

Some have poorly made drills, twisted funny, bigger at the cutting end, or lumpy, varying in thickness. Some have poorly made cutting tips, so they might wander, grab and break, or not cut well.

Despite the poor quality and inexactness, the inexpensive drills are still useful for cleaning purposes, but not for measuring and maybe not for drilling. Fortunately, brass carburetor jets are the easiest thing to drill, with a drop of oil and a pilot hole already there.



Micro Drills and Wires for Sale Individually

These drills are measured at the shank (the smooth part). At the cutting edge they are 1 or 2% bigger.

These wires are steel guitar strings, cut into 5 inch lengths. 

“Metric” jets have a number that literally means hundredths of a millimeter, so a 64 jet is 0.64 mm.

Micro Drills for sale

inch   mm/#  price     moped jets that it cleans
0.011   wire     N/A Gurtner Motobecane diffuser – two idle holes (.013)
0.0135 #80  $3.50
0.0145 #79  $3.50
0.0157 0.40  $2.00 Dellorto 38 (.0162), Bing 42 (.0162)
0.016   #78  $3.00 Dellorto 40 (.0168), Bing 44 (.0167)
0.017   wire  $0.50 Dellorto 42 (.0177), Bing 46 (.0175)
0.018   #77  $3.00 Dellorto 44 (.0186), Bing 50 (.0188)
0.019   ——  $1.50 Dellorto 46 (.0194), Bing 52 (.0194)
0.0197 0.50  $1.50 Dellorto 48 (.0202), Bing 54 (.0200), “Metric” 51 (.0201)
0.0200 #76  $1.50 Dellorto 49 (.0207), Bing 56 (.0206), Gurtner 210=52 (.0210)
0.021   #75  $3.00 Dellorto 51 (.0215), Bing 58 (.0213), Gurtner 220=54 (.0220)
0.0225 #74  $1.50 Dellorto 55 (.0231), Bing 62 (.0229), Gurtner 230=56 (.0230)
0.023   ——  $1.50 Dellorto 56 (.0235), Bing 64 (.0234), Gurtner 240=58 (.0236)
0.0235 0.60  $1.50 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 250=60 (.0242)
0.024   #73  $1.50 Dellorto 60 (.0247), Bing 68 (.0248), “Metric” 63 (.0248)
0.025   #72  $3.00 Dellorto 62 (.0255), Bing 70 (.0254), “Metric” 65 (.0256)
0.026   #71  $3.00 Dellorto 66 (.0268), Bing 74 (.0267), “Metric” 68 (.0268)
0.0275 0.70  $1.50 Dellorto 70 (.0280), Bing 78 (.0280), “Metric” 71 (.0280)
0.028   #70  $1.00 Dellorto 72 (.0287), Bing 80 (.0287), “Metric” 73 (.0287)
0.0292 #69  $2.50 Dellorto 78 (.0306), Bing 84 (.0301), “Metric” 77 (.0303)
0.030   wire     N/A Dellorto 80 (.0312), “Metric” 79 (.0311), Gurtner K80 (.0311)
0.031   #68  $1.00 Dellorto 82 (.0318), “Metric” 81 (.0319)
0.0315 0.80  $1.00 Dellorto 84 (.0324), “Metric” 82 (.0323)
0.032   #67  $0.75 Dellorto 86 (.0331), “Metric” 84 (.0331)
0.0325  —— $1.00 Dellorto 88 (.0337), “Metric” 86 (.0339)
0.033   #66  $2.50 Dellorto 90 (.0343), “Metric” 88 (.0346)
0.034   wire     N/A “Metric” 90 (.0354)
0.035   #65  $1.00 “Metric” 92 (.0362), Gurtner MB (side mount) diffuser (.0358)
0.0354 0.90  $1.00 “Metric” 94 (.0370)
0.036   #64  $2.50
0.037   #63  $2.50
0.038   #62  $1.00
0.039   #61  $0.75
0.0394 1.00  $0.75


Deluxe 40-piece Micro Drill Set

Jet Drills 80-72 and 71-60

Myron’s Mopeds two case deluxe micro drill set, 80 to 72 (small) and 71 to 60 (large) plus many in-between sizes.
Price $45

Slide clear top plastic until hole is over drill (and pointer is on desired drill number). Only lets one drill out at a time. Never take out more than one at a time, or they can get mixed. The case keeps them organized. If any get lost, dull, or broken, individual drills can be bought at some hardware stores for $2-$4 each.

Useful for sizing to tell how big a jet really is (sometimes they’re drilled out or labeled wrong).

Useful for cleaning varnish or corrosion coating the inside of an old jet. It doesn’t really clean out any other way. The drill is used as a file, held with a needlenose pliers.

Useful for drilling jets to make a new size, as an alternative to buying ones. The drill is held with a needlenose pliers, and the jet is rotated with your fingers, with a drop of oil. To go down in size, fill the hole with solder and re-drill it smaller.




Other Tools for Cleaning Jets

Using a micrometer to measure a 0.017 wire

Using a micrometer to measure a 0.017″ wire

Guitar steel string 17 thousandths of an inch

Guitar string

Guitar Steel Strings in the smaller sizes are excellent tools for cleaning small holes. Here is a 0.0170 inch steel wire guitar string, perfect for cleaning out a 1974-85 Tomos stock jet size 46 that has a 0.0175 inch hole. A Honda Express NC50 (Keihin) carburetor, has a long brass idle jet tube with a tiny jet hole at the far end, too far for a drill to reach. For that, only a 2 or 3 inch piece of 0.010″ steel guitar string will reach to clean it. Ultrasonic cleaners, carb spray, or soaking are not effective for that. Other examples are a Sachs 52 jet 0.0190 would be cleaned by a 0.018″ wire, or a Motobecane 230 jet 0.023″ would be cleaned by a 0.022″ wire. The wire has to be a little smaller than the hole. Plain steel strings range from 0.008″  to 0.017″ in steps of 0.001″. Wound strings range from 0.017″ to 0.065″. 


Torch Tip Cleaner Set

Torch Tip Cleaner Set

Root Canal Files

Root Canal Files (say ahhh)

Welding Torch Tip Cleaners are another excellent tool for cleaning small holes. The tip has a cutting surface but not the sides. So it is made to clean the hole without widening it.

Wire Feeler Gauge Sets: There are also wire gauge measuring sets that look the same as the torch cleaner set shown.

Dentist’s Root Canal Files are also good for cleaning small holes. Color coded files range from 0.06 to 1.10 mm (0.0024 to 0.0433 inch).