yes, that is the best thing about weber idf's. they are very well thought out and engineered. your idle jets, which deliver fuel to the progressive circuit, can be real lean. especially when complimented with the svda. the svda will advance up 42 degrees. idle/progressive circuit will be used for part throttle and cruise situations. this is where you get your killer m.p.g. and lower cylinder head and exhaust gas temps.

then, when you jet your mains rich, (12.75-13.25) you dont run the risk of being lean at WOT. the svda will run out of vacuum and retard back to 28 degrees. so when your giving your 250 lbs buddy i ride (high load), or cranking it up thru the twisties, you wont run the risk of running lean because you will be on the mains anyways. this time you will be on the other side of the curve (rich of peek) running cooler.

stoich (14.7) is the death zone. this is where your cylinder head temps and exhaust gas temps are highest. and should be avoided at all times.

NOW, i dont have actual proof of this. this is 80 year old information. these tests where done years ago. the aircraft guys are masters of this. aircooled or watercooled. it dosent matter. it is what it is. the aircraft guys have alot more riding on this information. higher fuel costs, higher engine overhaul costs, but most important, they cant look for the nearest off ramp if there motor blows chunks. literally.

and no, he dosnt need to invest in a bunch of hidollar instrumentation. i think ac.net rents a portable wideband instrument. just install it, do your jetting, then send it back. only the real anal guys (myself included) invest in the instrumentation. so we can see what the effects are from the changes we make.

What would you think would need be changed to get a lean burn on a D-jetted car? howmuch more advance might be needed, and how can the advance be backed down for acceleration? That is the biggest question I have on this issue.

I have run Zeniths that gave fantastic mpg on a 356, yet still allowed spirited driving. i wonder how they would have read on a Air Fuel meter?

So, it is really the combination of the special dizzy and the idf carbs. thanks for clearing this up for me.
My 914 (just got back from driving it ) is still d-jet and I've never been much of a carb guy. However, I must say that this set up sounds interesting allowing both economy and power.
Maybe I'll look into it for a future mod. Can more HP be gained by this over d-jet? Is a special cam needed; Raby's 9550?

One other thing that can be added to the tunning tool box is an automatically adjustable fuel regulator. Upon senseing the manifold vacuum change when the accelerator is floored from a lean cruise, the fuel pressure can be bumped up, maybe from the leaner end of 27 psi to the richer end 34 psi or what ever. Some Vanagons have a regulator like this, maybe can be adjusted to needs, some other cars should have simular regulators, so there should be plenty of choices.

so we got these things we can tweek on an engine, hopefully finding a nice combo of good mpg, good sporty performance, and cool running.........

spark timing, Use an electronic adjustable unit, knob or switch(es) on dash for adjust lean or sporty performance.

mixture via MPS, Use two differently adjusted MPS one for lean cruise, one for power, switch on dash.


mixture via fuel pressure, Use automatic regulator to boost pressure when power required.



for carbs you need carbs that allow a cruise in idle circuit,
and ...

Adjustable or adjusted dizzie for spark timing to allow the greater advance need for lean cruise.

Call Elgins Cams, or check website. They know the cam stuff and have a huge selection of type IV grinds, they are real helpful on the phone and can suggest a grind (or custom grind) for your needs, they have been around for near half a century I think. Their prices actually are better than Raby. I have several Elgin cams in my cars and am very pleased.

http://elgincams.com/

By the way, cabinetmaker, not ape has the last locked post of record.

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Chris explained a different way of setting up carbs properly while driving.
I hope he takes the time to explain it, cause it made some sense.

rich

No different, I got the procedure from mrbubblehead.

The following chart shows CHT, EGT etc...and relation to stoic 14.7Click to view attachment