Italian 44IDF´s bypassing too much air at idle

[Alstrup]

Hello
I have got a car in the shop for tune up and a couple of repairs.
Now, one of the reasons I got it was that he could not back it down enough to get a decent idle, like 900 rpm or so, unless the timing also was backed down to like 5 degrees AFTER TDC.
I took the carbs off and had a thorough look at them, thinking that something prohibited the butterflys to close. But no. They close as good as can get. I couldnt really find anything wrong with them, so I installed them again, only to experience the same behaviure.
Bypass valves are 100% closed, so that´s not it. It seems that the carburettors are dragging air from somewhere else (!)

Has somebody experienced that issue before ? Cure ?

Thanks
Torben

[FreeBug]

What size is the engine?

I am also looking at a similar, but probably different case, here what I found is even though both throttle plates looked like they closed ok, the shaft was warped enough to cause the first progression hole to be ever-so-slightly solicited.

I could never get fron-to-back snail readings even, was even beyond the range of the bypass's flow ability to correct.

orders a new shaft and waiting to see...

What are you seeing on the snail? Doei it still have the choke slider-valve thingys?

[MURZI]

Make sure the carbs are not units designed for "single" use....like with holes in throttle plate.

I would also check for vacuum leaks.... Early HPMx's had a bad rep for leaking at the throttle shaft.
_________________
62 vert
2276
Tim’s welded heads
45 Dells
A1 sidewinder
Fk44 cam

[modok]

I have a set from an alfa, the throttles had too much end-play, and wore the sides of the throttle plates.
Looked ok at first, but with flashlight on other side I can see gaps all the say around throttle plate!

[Alstrup]

2165
Butterflys close, and no slack.

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You are making an incorrect assumption that just because the bypass screws are closed, that they are sealing and no air is passing through them. Just sayin'.

Use a snail gauge and figure out which bbl is the one with the problem. It may be more than one FWIW.

Intake leak will also do it.
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[mark tucker]

my gess would be intake or shaft leak or the bypass screws are sorta afu....or possiably a set of ported heads that went a bit too far. any vacume ports or hoses any where?

[Alstrup]

The snail gauge show the same within 0,5.
The bypass srews or seats my be the problem. I replaced the carbs with a Spanish set I had on the shelf this afternoon, because I had dyno time and needed to finish the car for delivery. I will take a very thorough look at them when time permits.
I´ll post the dyno sheet later. It came out quite nice for what it is.

But thanks for chiming in.
T

[[email protected]]

some IDF throttle shafts also leak at the center locations, where it's bushed (no bearings).
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It's just advice, do whatever you want with it!

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[käfertom]

[drumbum68]

Sometimes people strip 'em down for a soak, but don' remove shafts or bearings, bye-bye grease. Older webers used shielded bearings (leak like a sieve w/no grease) instead of sealed like dell'orto.