The Bubble Engine
Created | Updated Jan 7, 2003
With the cost of petrol forever going up I think that it's time to reintroduce an engine system that was last used some years ago during the last fuel crisis. I am told that the idea was so simple and cheap that the oil companies bought the silence of the 'back street' inventor. The beauty of the modification is that almost no cost is involved other than the purchase of a pencil H or 2H, and some washing powder (Tide or Daz is best).
1. First remove the plug and the ignition leads, now use an old plug and remove the centre electrode. Into the hole left by the removed electrode place the pencil (NB you must ensure that the pencil is sharp. Do not push the pencil in too far yet as the distance (timing) will be set once the modification is complete.
2. Now check that the fuel tank is clean and empty. If it is empty, but a little dirty do not worry, it will be cleaned by the new fuel. Now mix the washing powder with water in the ratio of 2 handfuls to the gallon and ensure that it is well mixed, a very good check of its strength is to drop a pair of underpants (the pants should not have been worn for more than two weeks) into the mixture. Any staining should dissolve in about 15 minutes.
3. Place the mixture into the fuel tank, remembering to remove the test underpants. Now with the rear wheel clear of the ground and the bike in 2nd gear slowly turn the engine onto compression taking care not to go over TDC. The pencil that was fitted in stage 1 should now be gently pushed into the cylinder until a loud pop is heard. The timing is now complete.
4. For the technically minded I will include a description of how the new system works. On the inlet stroke the water/washing powder mixture is drawn through the carb forming a bubble inside the cylinder. On compression the bubble is squeezed towards the cylinder head. Just before TDC the bubble will contact the sharp end of the pencil. This will cause the bubble to burst, forcing the piston back down. The spent bubble is expelled through the exhaust in the usual manner and then back to inlet and a fresh bubble.
5. Some frequently asked Questions and Answers
(a) I have run out of washing powder. Can I use a low temperature modern equivalent?
Answer: No. The 40-degree stuff will not cope with the high exhaust temperatures involved.
(b) After about 5000 miles there was a loud knocking, also the bike was very hard to get over compression.
Answer: A common problem. The mixture is too rich, usually caused by too much powder or you are not letting the powder dissolve fully. The difficulty in starting is caused by a build up of soap powder on the piston crown. This will effectively raise the compression ratio until the starter motor struggles to get over compression.
(c) The pencil requires regular re-sharpening and adjusting.
Answer: Check that you have not used a B or even worse 2B. The lead is too soft to stand the pressure of detonation.
1. First remove the plug and the ignition leads, now use an old plug and remove the centre electrode. Into the hole left by the removed electrode place the pencil (NB you must ensure that the pencil is sharp. Do not push the pencil in too far yet as the distance (timing) will be set once the modification is complete.
2. Now check that the fuel tank is clean and empty. If it is empty, but a little dirty do not worry, it will be cleaned by the new fuel. Now mix the washing powder with water in the ratio of 2 handfuls to the gallon and ensure that it is well mixed, a very good check of its strength is to drop a pair of underpants (the pants should not have been worn for more than two weeks) into the mixture. Any staining should dissolve in about 15 minutes.
3. Place the mixture into the fuel tank, remembering to remove the test underpants. Now with the rear wheel clear of the ground and the bike in 2nd gear slowly turn the engine onto compression taking care not to go over TDC. The pencil that was fitted in stage 1 should now be gently pushed into the cylinder until a loud pop is heard. The timing is now complete.
4. For the technically minded I will include a description of how the new system works. On the inlet stroke the water/washing powder mixture is drawn through the carb forming a bubble inside the cylinder. On compression the bubble is squeezed towards the cylinder head. Just before TDC the bubble will contact the sharp end of the pencil. This will cause the bubble to burst, forcing the piston back down. The spent bubble is expelled through the exhaust in the usual manner and then back to inlet and a fresh bubble.
5. Some frequently asked Questions and Answers
(a) I have run out of washing powder. Can I use a low temperature modern equivalent?
Answer: No. The 40-degree stuff will not cope with the high exhaust temperatures involved.
(b) After about 5000 miles there was a loud knocking, also the bike was very hard to get over compression.
Answer: A common problem. The mixture is too rich, usually caused by too much powder or you are not letting the powder dissolve fully. The difficulty in starting is caused by a build up of soap powder on the piston crown. This will effectively raise the compression ratio until the starter motor struggles to get over compression.
(c) The pencil requires regular re-sharpening and adjusting.
Answer: Check that you have not used a B or even worse 2B. The lead is too soft to stand the pressure of detonation.
