1915 40IDF Jetting

[MARKYSTEW]

Hi
Could someone give me a starting point for jet and venturi sizes for:
1915
40 IDF's
engle 120
CB round port heads 40X35
1.25 rockers
55cc cylinder volume
8.5-1 compression
38mm headers
it's a weekend fair weather car (62 beetle) not a race car so am looking for driveability rather than top speed. I live at sea level in the U.K.
Thanks

[yamaducci]

Why not call the store you bought them from?
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[Itisa1835]

Main jet -135-140 Air correction 190-200

[modok]

Could use 30mm or even 32mm venturies

with the 30 vent try 125 main and 200 air

with the 32 vent probably need 135 main and 200-220 air

[MARKYSTEW]

Thanks Modok +Itisa1835
Do I need to change the idle jet(.50), starter jet(80F5), and emulsion tube(F67) or will these work ok?
The carbs are 40 IDF 83 which I believe come from an Alfa or Fiat

[modok]

If you are not planning to use the starter system then it does not matter what size the starter jet is.
I have never encountered an f-67 emulsion tube.

That changes things......... these webers may be very different than what we have in the US, thus what works for US, may not work for you.

These f-67 emulsion tubes may work well,........... but I have no idea what jets or vents they will work with.


If you want to jet it like our "american" webers, then you'll need different tubes, f-11, f-15, or f-9 emulsion tubes, but if the idle circuits of YOUR carbs are different than normal it won't be quite right.

Please check the number of transfer ports(4 or 5) and the idle air bleed size, this will tell us if the idle system is the same, or not

[MARKYSTEW]

Apologies for the slow reply! time difference and shift working patterns tend to interfere with important stuff I thought I would post some pictures so you can see what we're dealing with. they have 5 transfer ports , but am not sure where to measure for idle air bleed size? excuse my ignorance

[modok]

No problem man, I'm impressed with the pictures

I can SEE that yes, in fact these carbs are very different. They have all the same features as my alfa 36 IDFs, and MORE.

I see LARGE idle air bleeds, these are the brass inserts pressed into the top of the main body, about 1 CM away from where the idle jets screw in.
The large idle bleeds and five large transfer ports REQUIRE a large idle jet. I'd start with .60

I also see they have large diameter tops and extended aug.vents (much like the 44idf ) SWEET

SO, yeah, they are quite different than usual, but different in a GOOD WAY

A lot of folks have wished the desirable qualities of dellortos and webers could be combined, to create the web-orto I believe that these hybrid carbs already exist, and YOU have a set!
The odd emulsion tubes may also be part of the improvements, but unfortunately I don't know for sure. If I were you I'd get some normal emulsion tubes(like I listed earlier) to use to get these running and tuned in on your engine, then go back and try these f-67 tubes later on.

[Itisa1835]

Did you buy these from the guy on Samba that had 6 for sell? Mo is right these are for an Italian car, such as a alfa.....

[MARKYSTEW]

I think it may have been a guy on here yes,it was a while ago?he was over here in the UK.

Thanks Modok ,a picture speaks a thousand words as they say!

It's nice to know I have something good how many times do we buy used stuff for our cars only to end up disapointed

I have measured the idle air bleed and it is a 2mm (0.078-0.079") hole

Another oddity with these is the bore size which measures 41.9 mm, meaning they need venturis from 44IDF which with a quick search of carb shops I can find no smaller than 32 mm !

So should I go with 32's or hunt around for some used 30's?

A pic of the pump jet which seems a different style as well?

[modok]

as far as the venturis, EMPI has also used the larger diameter for all their weber copies, so 30mm empi HPMX vents should fit.

The old e-bay guy in italy, Alfa1750, may have some OE vents, or I know he also can bore them out to 30mm, or 31mm or whatever size desired if needed.

Ah yes, those acc squirters are also a little different. I bet they are small 35? I'd drill them to 50

[[email protected]]

I believe the old Italian ones used a 200 Idle Air Bleed, and worked best with 60 idle jets. They setup differently than the later IDFs. The procedure is the same, but you can't follow the normal "rules" when jetting those ones.

Harney has posted this info in the past, I'm just going from memory. Searching his old posts will gleen the info you need. Bruce Tweddle may also know more about these than we do, he's a very sharp guy and been doing this a while.
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[modok]

NEW INFO

I have purchased some of these for myself, idf 40-78/79 from an alfa.
they are identical to the carbs of the OP

UNLIKE the earlier alfa carbs, these come with 3.5mm aux. vents(also much like a dellorto, interestingly)

I do not know the effects of these smaller nozzles, but in general the smaller nozzle is not preferable for using venturies on the large side. I will be replacing them with 4.5 aux. vents that I already have, so I can directly compare them with my spanish 40IDF 70s

[Islandman]

I love em. I've been running these on a 1904 for some time now. Very smooth transitions with a solid idle. I tried F11s with a few different idle/mains. No joy. They appear to run best with the F67s on my setup.

My favorite part are the bleed screws for synchronizing. This lets you use a manometer. Unlike a single snail, you can adjust balance on both sides throughout the RPM range.

Homemade manometer: Baby bottles, brass tubing, vinyl tubing, rubber stoppers, and Auto trans fluid.

[modok]

What size idle jets are you using with those things?

I see the idle air bleed is also a little different VS the 36 IDF, more of a mixing well rather than just T drilled, also has 80 degree throttles instead of 78..........(also like the dellorto)

makes you wonder.......who copied who?

[ridenrace6]

more details and pics of the manometer please

[modok]

That DIY manometer is cool! mine usues mercury, but I bet it works no better than if it used water

[modok]

TEST DRIVE
HOLY CRAP, they run SMOOTH. Smoothest webers I have ever driven, WOT feels even crisper and more even than the spanish webers I had on it yesterday, and I don't even know why that would be. Lean spot after each shift is gone, just like the dells. Idled at 800 rpm bench set and two turns out on the screws, not rich. Idle to 1/4 throttle feels just slightly lean, but there are no hickups or spots in there at all.
And this is without any fine adjustment of any kind, simply WAG jetting and eyeballed sync.


32 vents, 4.5 aux vents, 137 main, f-11 tubes, 215 air, 50 pump jets, about half pump volume .......
and you don't wanna know how big idle jet, I just used the biggest I had, they are huge, I bet it will never clog

THe web-orto is indeed, the cats ass!

[ridenrace6]

it would be nice to try a set of these in a 44 or 48 if they are made but i take it they are only made in the 40?

[Doktor]