This Modification is all the work of Alan Dean. The information has been published in the RSSOC Magazine "Slice. The first part of the Text is an explanation from Alan. There are pictures at the bottom of the page showing the Gauzes and a diagram for fitting.
The gauzes have a flange around the top so that when fitted into the bakelite block, with the W piece removed and the screws, they fit in on to the existing gasket and are just above the bottom of the manifold. The flats on the flange must come together. Put a small bead of silicone (about 3mm diam) around the outside edge of the flange and put another thin gasket on top. Then fit the Carb. The silicone is squeezed out flat some going into thee gauze and the remainder flattening out around the gasket surfaces thus forming a good air tight seal. The silicone is, in most cases not resistant to petrol (some are) so you do not want the silicone to come to the inner edge of the gasket where it will be attacked by the petrol. It works for me. The auto choke. Either lock it open or remove it all together. I would suggest that until you gain confidence and depending on the tune of your engine that you leave the choke connected but locked open. You can tune the engine, on the jet settings or the idle mixture screws, to be slightly rich or weak either side of stoichiometric. My engine has never seemed short of power yet the recommended plugs are almost white. Normally I would change them for a colder plug but I have never bothered because it goes very well as is so according to the good old engineers rule – if it ain’t broke don’t fix it. Make sure that your engine is set up reasonably first, i.e. it starts OK and runs OK. Then when cold put the gauzes in. Pump the pedal twice and hit the starter and it should fire up immediately. Drive away. For the first few minutes, in very cold weather, it might try to hesitate but that will pass.
This part of the Text is my findings after I fitted the Gauzes.
Whenever I change or modify something I like to get a before and after comparison because if I am expecting an improvement I “Think” it must be better. If some of the numbers quoted seem too exact it is because one of my Jobs is Management of a Calibration Lab and I have access to Test Equipment that is Very Accurate and has the ability of “Averaging” readings, helpful for example with Vacuum Measurement. There was repeatability with measurements and readings, i.e. Tests were done a number of times to eliminate, as far as possible any errors.
All tests were done with the Engine at 95Deg.C. External Air Temperature and Humidity were the same throughout the tests.
Tests were done before fitting the Gauzes, After fitting with no adjustments and after fitting with adjustments made to the Carburetor.
Engine Idle Speed before: 650 rpm.
Engine Idle Speed after, no adjustment: 640 rpm.
Engine Idle Speed after, with adjustment: 680 rpm.
Vacuum Reading , Inlet Manifold before: 46 cm hg of Vacuum.
Vacuum Reading , Inlet Manifold after, no adjustment: 48 cm hg of Vacuum.
Vacuum Reading , Inlet Manifold after, with adjustment: 50 cm hg of Vacuum.
After fitting Gauzes the Test Equipment was able to Average the readings much quicker which would confirm a much smother running Engine.
The following Test was not so “Scientific” but have some validity, the Speed and Distance covered were not important, the Time differential is. I would drive past a “Marker” in the road. I would then accelerate (Pedal to the Floor) until another “Marker”; I would measure the time taken.
20mph, Third Gear.
Before fitting. 15 Seconds.
After fitting, no adjustment 14 Seconds.
After fitting with adjustment. 13 Seconds.
One of my concerns was the Instructions to disconnect the Choke. The first start of the Morning was always first turn of the Key, Engine started, No change after Gauzes fitted. The only difference was from my house it is about 500 yards to a Main Road where I turn onto. It is one of those roads that you need to make the most of a gap in traffic or you could be there a while, when the Choke was fitted there was never a worry, after Gauzes fitted if I pulled out the same as before the Engine hesitates for a second or two. This is not a problem as increasing the Engine speed slightly eliminates the hesitation. All is then OK unless you try to get sudden acceleration then there is a slight hesitation, this only lasts for about 3 to 5 minutes. After that all OK.
This part in italics added March 2005.
I have fitted a Manual Choke. Although as explained not having a Choke was not a major problem I felt having the ability of Manually applying Choke when cold gave me more control when required. This has made pulling out from Junctions and in Traffic easier when cold. I did not like having to give more revs than necessary when cold. I like to keep the revs down until Engine warm. A personal choice.
Conclusion, I have no doubt that the Gauzes have improved the Power of the Engine, especially the Torque, My only comment is Carburetor adjustment must be made to make the most of the modification. The hesitation when cold is not a problem, only needs a slight change to driving style when Engine Cold. I did not do an MPG comparison as any increase in Engine Power with a Modification like this would give an improvement in MPG, unless of course you “Use” the increase in Power.
Pictures and following Text courtesy of Alan Dean.
Click on Picture for Larger Image.
The gauze I am using (Alan Dean) is 20 mesh i.e. 20 wires per inch. The material is Stainless Steel and it MUST be SS. The wire is 0.014” diam or 0.3556mm diam. This may differ slightly from the article in Slice 183 but not by much. If you cannot get that gauge use a smaller wire diameter rather than a larger one. If you cannot get 20 mesh (and I cannot imagine why not) then go 2 meshes either way – 18 – 22 – no more. The flange you create on the top of the gauze must fit above the bakelite heat barrier to get the longest length of gauze possible. However it is not a good idea to have the gauze touch the manifold at its bottom end. The whole idea is to get the fuel, most of which is still on the choke tube wall, to flow onto and down the gauze so that it is exposed to a significantly larger surface area from which to evaporate. Liquids can only evaporate from their surface – give the petrol oodles of surface area. This is a zone of high air speed and the evaporation rate will be at a maximum and consequently the air temperature will drop the most. All this happens before the air splits to the three cylinders so that each cylinder is getting the same mixture strength and consequently each cylinder will be firing the same stoichiometric ratio and will be more balanced.
On damp cold mornings ice will form on the gauze instead of on the butterfly. As the manifold heats up the ice will disappear sometimes in a lump into one of the cylinders and the engine may just miss a beat but it will carry one at full power after it. The chances are that you will never notice it. This all happens in the first few minutes of driving.
Scanned copies of the Manual choke conversion can be found by clicking on images below.