Identified two more issues to resolve now to get it all sorted correctly.
One is the cold start choke unit when engaged halfway causes the mixture to fatten to less then a 10:1 mixture but it does not raise the idle speed. If pulled on fully it will not assist the starting and it will not sustain the running after it does start. Since this unit supplies both additional air and fuel this should not be the correct result. It should rev the engine up to about 2k rpm and help not hinder the cold running performance. Suspect the stock setup is jetted way to fat.
Secondly, I’ve got a mixture leaning situation at high revs now. None of the tuning books properly address how to correct this condition BTW. By jetting the mains (100 w/Shell 91 fuel) for a mixture of 13:1 at ~3K rpms w/no load by the time it gets to 6k at WOT and at maximum load it’s at 17:1. This is not okay and I’ve already got tiny 140 air corrector jets installed with little affect on this situation. Appears the best adjustment to try first is to install larger main venturis. The stock 30mm ones are undersized according to the graph (pg22, fig32) in the Weber Tuning Manual. This is assuming that the one labeled ‘4-stroke sport engines’ is the correct one to apply for the twincam. By this graph a 36mm size is required which just so happens to be the largest size which fits and is available for the 40DCOE. So what I think is happening is the undersized venturi is generating to much low pressure at to low a rpm. This causes a very fat mixture at the intial rpm point of mixture’s introduction. When it reaches the high revs it then is restricting the airflow so much it impedes the auxillary venturi from reacting to a high enough vacuum to keep the mixture constant. By enlarging the main venturi it should reduce the vacuum level and delay it a low revs and at the high end it should allow more air to pass through so according to Bernoulli’s principle it could actually increase the vacuum level in theory. Have to test this theory. Just hope it’s this simple to solve. Can’t believe how lame the advised criteria on which the tuning books use to size the the main venturis. My engineering intuition tells me it’s generally true but for a different reason then what’s described.
Keith
p.s. Hoping at this point the stock exhaust system does not impede the induction system at higher flow rates. Going to attempt to measure the pressure drop at the downstream point the auxilary venturi protrudes into the main venturi at least for the no load condition. It may be possible to establish a correlation between the pressure drop and the mixture strength. These two effects should be slaved together ideally.