My 750 is finally finished now aside from the weber tuning.I'm currently studying any information I can get my hands on as to how to tune emulsion tubes and their effects on various rev ranges.After reading Higgy and Romus's Weber mods pdf. I decided to test the float level of my carby vs the holes in the emulsion tube (f21) to see what holes were above float level,at float level and below float level,and the total volumes of air that these holes allowed to pass.I compared these to the 906 f27 and 750 f36 tubes and found that the vertical heights of holes are basically the same in the lower rev ranges,when float levels were taken into account.They all have a row of holes sitting about 1 mm above float level,these would be the first to start emulsifying as the main circuit cuts in.and they all have a row of holes well above the float level to delay the onset of emulsification,I'm unsure of the other effects of these upper holes on the transition,maybe someone could enlighten me ?.The f21 tubes that I'm currently running have no more air bleed holes below float level,and seem to bog down a bit toward the top end,I would say they are leaning out too much ?.The f36 and f27 tubes are essentially the same ,with a slightly different outside diameter(what effect would this have ?).The f36 lacking the upper row of holes ,but having its float level set 4-5 mm lower which corresponds to the next row of holes down the tube.Almost Identical spacing to the 906 but different no. and diameter of holes for the smaller capacity.The F36 has one more set of holes further down the tube and the F27 two more sets plus a third set on the customised tubes of Higgy and Romus.
I was wondering what other effect float level would have on the carby other than raising and lowering fuel to match holes on the et's,would it effect the progression or idle circuits ?
I have noticed that Geomac has posted again recently and seem to recall him saying in an earlier post that he would post a picture or diagram of his emulsion tube spacings one day,they would be really handy to compare with the information I currently have ,before I start turning my f21's into a block of swiss cheese.
I know that the 750 is over carbed with the 36 chokes ,but smaller chokes are getting hard to come by and I would like to have a good crack at sorting the tuning without swapping them .I'm running a K&N and Contis so this should help.
So heres the plan so far:
fit 60 idle jets,160-165 main jets
raise the float level to bring on earlier emulsification
Block at least one of the four 120 bleeds above float level (the 906 only has 4 x 115 and the f36 2 x 110) to bring on earlier emulsification
hopefully these mods will cover the lean hole at transition.
Try and get diagrams or pictures of others modified et's that are working
drill several more holes at a yet to be determined diameter and height below float level.
It all sounds easy but I've no doubt that I'll be tearing my hair out before I finish.
Any help would be appreciated.
PS. I don't consider 'throw the weber in the bin' to be helpful

Thanks Higgy, There's a lot of information out there with much of it conflicting .It makes it extremely challenging to get to the bottom of the problem.

Most of it is fairly straight forward, The emulsion tube unfortunately is largely a matter of trial,and error, due to the nature of its function. Add to that the fact that parts are not easy to find and it can be a challenge to get it correct. The very first thing you need to do is get your fuel pressure under control. Weber DCNF's require a pressure of around 3psi. Having the ability to vary it between 2.5 and 3.5 can largely make up for the DCNF's lack of a power valve. Romus and I also found a good filter and a Grose jet worked best.

Got the holley reg fitted.Grose Jet ?

Want to get a Grose Jet?
Send an email to johndtitus@q.com
$18 each plus $5.99 for shipping priority mail if you are in the US (a bit more for overseas)
A Grose jet uses a ball bearing to control fuel flow rather than a rubber nipple