AMAL JETS/SMALL DIAMETER HOLES

[CHARLES lipscombeParticipant @charleslipscombe16059]

Hopper, what you say about electrical problems is absolutely correct, personally I don't contemplate doing a restoration without getting the electricals renovated. Seen too many people on rallies with phoney carb problems

In this case however there is a genuine problem. Amal literature on lightweight carbs is very poor, often misleading and in this case just plain wrong. The carbs are extremely simple (no needle. Binks style) so tuning problems usually boil down to the fitting of incorrect parts or bodging, since the time they were made in the 1930's.

At this point in time the only aspect we are completely sure of is jet aperture, we are not even sure what overall lengths the jets should be. Reason is that AMAL made many types of small carb and parts often interchange but don't work properly in their new home. The literature is absolutely u/s in this regard so the first stage is getting owners to measure the jet lengths, protrusion into the inlet tract,etc. Only then will we be able to work out what should be fitted.

My original query was thinking ahead, that at some time, the owners association may be faced with getting new jets made of the correct height to replace the (non-existent) current stocks. I had no idea how these could be bored to the correct orifice.

Chas

[JAParticipant @ja]

It has been said over the years, having bought an old bike get the carb and mag refurbished and you will get rid of most of the problems.

It is quite probable that jets were first drilled, then calibrated by flowing and finally stamped with a size. A flow test is very simple. Paraffin would probably have been used. All one has to do is to measure the flow rate (stop watch and measuring cylinder) for a given pressure drop (gravitational head). It would be interesting to know what the number on the jet actually meant.

It would be very easy to increase the flow by putting a chamfer on the jet entry. The result could be checked against the original by flow tests.

JA

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JA on 17/01/2017 07:59:57:

It would be interesting to know what the number on the jet actually meant.

.

Interesting, and simple enough … [for modern specifications]

MichaelG.

.

http://amalcarb.co.uk/main-jet-size-180.html

 

Details for Main Jet – Size 180

All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head. Beware of imitations as they are just drilled to a size. All our jets are branded and packaged with the official AMAL logo.

Edited By Michael Gilligan on 17/01/2017 08:45:06

[Michael GilliganParticipant @michaelgilligan61133]

AMAL's note on Ethanol may be useful … especially the comment at the end, about materials.

**LINK**

http://amalcarb.co.uk/ethanol-fuels

MichaelG.

[HopperParticipant @hopper]

Posted by CHARLES lipscombe on 17/01/2017 06:32:15:

Hopper, what you say about electrical problems is absolutely correct, personally I don't contemplate doing a restoration without getting the electricals renovated. Seen too many people on rallies with phoney carb problems

In this case however there is a genuine problem. Amal literature on lightweight carbs is very poor, often misleading and in this case just plain wrong. The carbs are extremely simple (no needle. Binks style) so tuning problems usually boil down to the fitting of incorrect parts or bodging, since the time they were made in the 1930's.

At this point in time the only aspect we are completely sure of is jet aperture, we are not even sure what overall lengths the jets should be. Reason is that AMAL made many types of small carb and parts often interchange but don't work properly in their new home. The literature is absolutely u/s in this regard so the first stage is getting owners to measure the jet lengths, protrusion into the inlet tract,etc. Only then will we be able to work out what should be fitted.

My original query was thinking ahead, that at some time, the owners association may be faced with getting new jets made of the correct height to replace the (non-existent) current stocks. I had no idea how these could be bored to the correct orifice.

Chas

Interesting stuff. Yes, who knows what 80+ years of previous owners have done to the carbs mixing and matching parts etc etc.

[Michael GilliganParticipant @michaelgilligan61133]

Charles,

Hopeflly it was self-evident from the AMAL quote that I posted, but [just in case]:

If, as stated, the current AMAL jets are individually calibrated; then they could be used as 'transfer standard' for your own calibration rig. … You don't need to know the full details of their test; you simply need to work backwards from their answer.

Use whatever test fluid is convenient for you, and set the 'head' [pressure] to achieve the right result for your 'standard' … then use that fluid, and that head, to test your own manufactured items.

MichaelG.

[Chris Evans 6Participant @chrisevans6]

Agreed, lots of carburation problems are electrical. Whilst I restore the brass bodied carb on my 1929 bike (Bored the body and made a new slide) I am running it on an Amal monoblock. First kick starting comes by using electronic ignition.

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