dell'orto jetting

The PHBH range seems to be a popular choice. With plenty of other people using these carbs there is plenty of help around and the ability to swap jets and needles with others to save buying loads to get your set-up correct.  

If you don't know where to start when it comes to jetting, here is a basic guide to help you identify and locate the different jets in your carb. 

Getting the jetting just right is possibly the single most difficult thing you will have to do when working on your scooter. This can be for a number of reasons, but chief among which is, there are no hard and fast rules.

Once the main jet is out (see instructions below) the float bowl can be removed by simply pulling it away from the carb body. This will reveal the other three jets, the pilot, the choke and the atomiser (see below). The atomiser and needle jet combo kinda act as one jet really and certain pairs work better than others on Lambretta engines. The two most common pairs are an AV266 atomiser with a X7 needle, or an AV264 atomiser with a X13 needle. Really the only three atomisers you are likely to need are the AV264, AV266 and AV268 the 268 being the richest and 264 being weaker.

For more on Dellorto carb Atomisers and needles click here.

 

To remove these jets its simply a case of using a screwdriver to unscrew them. The needle jet can get in the way of removing the atomiser, so a good tip is to tape the throttle open to lift the needle out of the way. (see photo) Whilst you have the carb apart it's worth checking all is good and clean inside. Check the condition and operation of the floats and clean out any gunk in the floatbowl with some neat petrol.

For information on setting the mixture on Dell'orto carbs click here 

For a full understanding of how these carbs work click here for the Dellorto Manual.

main jet removal

 

The main jet can be found within the large nut that is on the bottom of the carb (pic 1). The main jet primarily affects full throttle mixture, however it comes into play from around half throttle upwards. To change it, first turn off the fuel tap. You may also need to unbolt you carb if to gain better access. Then simply undo the large nut on the bottom of the carb with a 14mm spanner and remove it from the float bowl. (pic2)

Within this large nut is the main jet. Just hold the nut in the spanner and now the main jet can be removed by unscrewing it with a flathead screwdriver. There is a small number engraved on the top of the jet to identify it. (pic 3)

  

 

Click here for some 26mm PHBH Ballpark Jetting 

Click here for some 28mm PHBH Ballpark Jetting 

Click here for some 30mm PHBH Ballpark Jetting  

For information on setting the mixture on Dell'orto carbs click here  

For a full understanding of how these carbs work click here for the Dellorto Manual.

 

needles and atomisers

 

Here you can find info to help you choose needles and jets for any Dellorto PHBH carb.   

The two most popular carb sizes used seem to be the 26mm and the 30mm, with the 28mm being overlooked somewhat. The good news is they all share the same parts. For a full understanding of how these carbs work click here for the Dellorto Manual.

 

PHBH Atomisers

The two main atomisers we are interested in for these carbs are the AS and the AV. 

Code NumberTypeX value measured in hundredths of a millimeter
  9695 x 28  AV  264-266-268-270
  9423 x 28  AS  260-268-270

 

As you can see the AS is slightly taller than the AV, apart from that they are the same. So by using the AV you will get richer sooner in the rev range compared to a similar needle setup using an AS atomiser. The lower the number the smaller the hole, so lower means leaner and high numbers are richer. This is over simplifying things a little but lets just ignore that for now.

The needle / atomiser combo is possibly the hardest to get right on your new setup and will take a bit of trial and error to get just so. The more popular needles for Lambretta applications are highlighted green in the chart below. When jetting a carburettor always start rich and slowly go weaker.

Click here for some 26mm PHBH Ballpark Jetting  

Click here for some 28mm PHBH Ballpark Jetting  

Click here for some 30mm PHBH Ballpark Jetting  

dell'orto Needles

 

 

PHBH carburetor slide needle above

This chart shows the dimensions for Dellorto needles, the main ones used with Lambrettas have been highlighted 

TypeValue XCharacteristic expressed in millimeters
ØAØBCØDE
X112.481.2026--
X222.501.8024--
X332.461.6022--
X442.481.8020--
X552.461.8024--
X662.501.2026--
X772.501.8020--
X882.501.4026--
X992.501.4018--
X10102.501.4020--
X11112.501.4022--
X12122.501.8018--
X13132.501.8022--
X14142.500.8024--
X15152.500.8026--
X16162.500.8028--
X17172.501.2024--
X18182.501.2028--
X19192.451.0028--
X20202.421.0022--
X21212.501.0020--
X22222.481.2025.5--
X23232.481.2026--
X24242.501.0030--
X25252.501.8025--
X27272.481.4020--
X28282.501.20262.3820
X29292.500.6030--
X30302.501.00282.3020
X31312.481.2028--
X32322.481.5024--
X33332.501.0032--
X34342.481.20292.3415
X35352.480.80252.3220
X36362.530.6030--
X37~372.530.6030--
X38382.481.20282.2820
X39392.500.80262.3320
X40402.500.80272.3324
X41412.481.00292.4327
X42422.530.6529.25--
X43432.500.80242.3818
X44442.461.8022--
X45452.480.8024.52.3018
X46462.501.2023--
X47472.501.80302.3515
X48482.471.8029--
X49492.501.2022--
X50502.501.2025--
X51512.501.20242.3718
X52522.520.9829.46--
X53532.530.60282.4024
X54542.501.30202.3520
X55552.510.9829.25--
X56562.500.80262.3622
X57572.500.9820.05--
X58*582.500.6030--
X59592.501.0021--
X60602.541.0028--
X61612.461.5020--
X62622.501.00302.3122
X63632.501.2027--
X64642.501.50302.3122
X65652.521.0034--
X66662.530.9829.65--
X67672.521.0032--
X68682.451.8028.14--
X69*692.520.9829.45--
X70702.520.6529.09--
X71712.481.0029--
X72*722.521.0229.55--
X73732.521.0229.55--
X74742.521.0030--
X75752.521.6029--
X76762.521.6029.36--
X77772.480.8026--
X78782.521.5529.22--
X79792.511.0128.17--
X80802.501.2026--
X81812.481.0024--
X82822.530.9829.45--
X83832.530.9828.85--
X84842.520.9829.45--
X85852.481.0032--
X86862.501.6029--
X87872.541.4030--
X88882.501.2028--
* Constructed of anodized aluminum
~ Differs from X3

 

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