I happen to have read enough of Carbking’s posts to know that he recommends mechanical power systems for multi-carb setups vs carbs with vacuum power systems. For purposes of this conversation, that means something like Carter W1s over Carter YFs.
I’d like to know more about WHY that is……
1) I’m assuming that multiple throttle openings screws with the vacuum signal and requires some major recalibration to respond to a different signal. No such signal problem in a mechanical system. Your adjustment is the movement of a lever or such. Is that reasoning more or less right?
2) Let’s say one has unlimited tinker time, and even unlimited funds. How much more difficult would tuning be with two YFs (let’s just use the two Tuts59 has on the way for discussion purposes) vs a pair of W1s? Let’s use a good running 235 6 cyl as the hypothetical engine for that question.
In general, the reason for my comments about mechanical power system carb being preferable to vacuum power system carbs boils down to two issues: Time (ease of calibration modifications, and adjustment), and cost (time is not free, and often there are special parts required that must be fabricated).
The YF is a special case, as the design of the YF allows a PARTIAL manual override of the vacuum system. Parts of this post would apply to other vacuum power system carbs, but not all. As an example the Rochester B has a power piston that can wear, a piston spring that can fatigue, and a vacuum chamber that can warp.
Keeping the exact calbration in all carburetors can be both challenging and time consuming.
It is important to keep the movement of the calibration parts, in the case of the YF, the diaphragm and metering rod, exactly the same on all carbs.
There are two issues with the YF in accomplishing the above: (1) fatigue of the lower diaphragm spring, and (2) warpage of the diaphragm housing (read Jon G.'s excellent posts on machining the diaphragm housing). The tension of the lower diaphragm spring is important, as its position is counteracted by the vacuum below the diaphragm. As Jon G. has posted, the YF pump circuit works opposite to what most would think, as the pump RISES as vacuum is lowered; activating flow through the pump jet, and raising the metering rod's position in the main metering jet.
New springs should be installed when the carburetor is rebuilt. And the diaphragm housing should be inspected and repaired if necessary.
The mechanical override of the power system is a "failsafe", and does not create the range of movement created by the vacuum system; thus the YF may be considered as a vacuum power system carburetor.
Once all of the carburetors have the vacuum systems in good working order, the next issue is the lower pump spring, which doubles as a vacuum spring. What does one do if one needs a set of springs with a different tension? How do you feel about hand-winding small precision springs?
I have done a lot of work with the Carter AFB springs, which may also be used in some of the Carter WCD and WGD carbs, and I have also done some work with the WCFB springs. I have never seen the need to do the research on YF springs (and, no offense meant, I still don't). And forget about the old wives tail of clipping coils (actually this is an old husbands tail, old wives are smarter than this!).
So, to answer JW's question within his parameters: If one has unlimited time and unlimited finances, then YES, it is possible to make the YF's work as multiples.
Would I personally do it? Maybe, if I were 60 years younger, and had ample free-time as I did then. Shoot, I actually once participated in a bowling league.
Nah, I still wouldn't do it. The W-1's are common as dirt, and so much easier to work with........
But if this post hasn't convinced those interested in doing this, I have a LOT of the 216 sized YF's that are just begging for a new home.
Jon
