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| Joined: | 04-01-2008 |
| Location: | Sandefjord, Norway |
| Posts: | 617 |
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If I may, I would like to ask for clarification on one point. As I understand the text of Des Hammil's book, when an emulsion tube is referred to as "richer", it will have either fewer, or smaller, emulsion holes than a tube which is labelled "leaner". Am I correct in that assumption?
I have Des Hammill's book, and IMNSHO it is a piece of c%&#, its only justification is that it gives a good stripdown and rebuild procedure. Since I am curious by nature, I have tried to piece together some kind of mental image of how the emulsion tube works, but that book was not any help whatsoever. John Connolly at aircooled.net has written a few bits and bobs about the subject spread around the net, the best one was at the Innovate forums - AFAICT those are gone.
So here we go:
The emulsion tube controls the fueling curve from vacuum begins to build in the main venturies and until the vacuum (somewhat proportional to airflow) is high enough to completely drain the emulsion tube well. At that point fueling is controlled by the main jets and air correctors only.
Three main factors control the shape of the curve while the emulsion tube is active;
1. Fuel level in the float chamber, controlled by the float and needle valve. I believe a higher fuel level will richen the mixture across the board, but I am not positive. A change might add or it might multiply fuel flow, I don't know.
2. Placement, size and angle of the holes in the emulsion tube. If my thinking isn't completely off, larger hole area means less fuel and more air, i.e. leaner mixture. Holes high up probably affect the whole curve, low down it will affect the curve only when the well is almost dry (at close to max airflow).
3. Diameter of the emulsion tube. This controls the amount of fuel in the well, but how exactly this translates in tuning is still beyond me.
Most likely, all of these three parameters have interactions with the main and air corrector jets, and possibly even with the idle circuit.
Since I have been spending a lot more time tweaking EFI than trying to figure out carbs, I'm not able to give a better explanation and caveat emptor; this is my perception of it from trying to wrap my head around the concept - I may be mistaken.
--
Joachim