idle mixture screws

markQLD

markQLD

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QLD Australia
to suit Dellorto PHF 32  ??

most (99%) of the mixture screws, i've unscrewed, have had the short tip (~2.4 mm)
but once in a while, i've unscrewed mixture screws with a long tip (~5.0 mm)

Dello-mixture-03.jpg

so, i just 'assume' the long tips are incorrect and have been swapped by a dpo.

but, when and for what are the long tips required?

  curious Mark  ???
 
Hi Mark,

I've come across those long-tipped screws as well, a right bugger to find if only one is fitted in a set of 3 carbs... afaIk, all Laverdas used the shorter type, there is only one screw part # for the different carbs.

Don't know where they are normally used, suspecting Moto Guzzi.

piet
 
thanks Piet.
i'll keep replacing them. i always like to have a few spares, but when desperate, i have been guilty of getting the file out.

but really ??
sfcpiet said:
Don't know where they are normally used, suspecting Moto Guzzi. 
Click to expand...
i am farken speechless !!  :-X    :D
  Mark
 
& i should add, that if they are for another engine, i hope they're not also PHF carbs?
that would mean two types of PHF carb body.  surely not.

maybe the long tips are for PHM carbs ??  just guessing ay.  :-\  :-\  :-\

come on all you Guzzi blokes?  i know you're out there. 

 
Is the total length from end to end the same or do the longer tips protrude further?
If you trim the long tips are the 2 types the same overall length then?
 
Different overall lengths Grant.

They seem to work well enough if all mixture screws are of the same type, but throw in one rogue screw and you've got a fucked up afternoon, chasing ghosts!

Because you generally adjust all screws equally, you end up with different openings that will muck up idle completely... don't ask why I know that. ::)  As the screw seals at the base of the taper, it can be seen that the longer type goes in the threaded bore further, but you really don't expect something as stupid simple as that.

piet
 
sfcpiet said:
They seem to work well enough if all mixture screws are of the same type, .........
Click to expand...
yea but, i seem to recall, from a few years back, that to get the mixture correct with the long tips, they were unscrewed so far, there was bugga all spring pressure holding them in, and they looked to be close to falling out.
  hence i got the file out.  it worked ok.

<edit>  & i nicked this pic from a Dellorto page.
Dello-mixture-04.jpg

i read the two on the right are adjusting the air flow, before it gets to mix with fuel.  not for PHF carbs.
 
There was a long discussion on the Old Oz Guzzi Form when Pete Roper was there re these Smogged Dels on Guzzis,they have a shroud like brass bit where the needle passes through above the main jet and in the throat of the carb and the jetting was a lot different to non smog type Dels.Blokes were converting the jetting to non smogged setting with really poor running.
 
According to Bevel Heaven and as far as I understand it there are two part numbers for the PHF mixture screws 53022.78 which measure 33mm which inc a tip of 2.5mm  and 53023.78 which measures 35.5 with a 5mm tip.
The 53022.78 is for the earlier PHF with the smaller float bowl retainers ( 14 and 17 mm )  whilst the 53023.78 is for the later PHF which use the 21mm float bowl retrainers, which may be due to emission strategy as these later carbs were in more emission influenced times. ( Maybe influenced also at the time which export market they were bound for )
Guess the main thing is that they should be the same across the set of carbs or as Piet states would do your head in trying to understand why one carb is different to the others. Plus if you are getting optically challenged as a number of us are in our later years not so easy to pick the difference always.

 

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  • PHF Needles and differences.jpg
    PHF Needles and differences.jpg
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One that was designed to run in an atmosphere that contained little breathable air. eg LA in the 70s or Beijing today.
 
thanks Brett & George.  it looks like the Ducati blokes have been wondering, as well.  i.e. PHF C ??
http://forum.bevelheaven.com/viewtopic.php?f=26&t=4684&p=19886&hilit=mixture+screw#p19886

also snapped a similar pic this morning, while over at the Redax shed.  yes, while working on someone else's farken Laverda.  ::)
IMG_1416c2r.jpg


and a while ago, when working on a very late series 2 180?, i've seen that 'tiny little jet' that the BevelHeaven blokes refer to.
IMG_2279c2.jpg

i'm guessing it is an extra emulsfier tube (?) that has been fitted above the pilot jet.  those tubes were a nightmare to unscrew without destroying the brass slots.
reckon next time, i'd be tempted to leave the fuckkers in there!  8)
 
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