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 Post subject: Dellorto PHF 36 float height for F1B
PostPosted: Mon Oct 17, 2011 12:19 pm 
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Joined: Mon Oct 10, 2011 2:31 pm
Posts: 45
Location: Los Gatos, CA
Ciao Ducatisti,

I've recently taken possession of an F1B that belonged to a dear friend who passed away a couple months ago. It joins a 66 MachOne replica, a 91 851, and a 95 916 in my Ducati stable. The F1 is in pretty good condition, with 44K km on it, and a Verlicchi 2-1 exhaust. The machine was in storage for several years as my friend's health deteriorated and so I'm going through the usual items that need attending (battery, stale fuel, shagged tires, etc). I have removed both carbs to clean them as the bike is exhibiting a massive flat spot/lack of power in the mid-range, a symptom which goes away once the throttle is opened <75%. After disassembling the first carb to clean it, I noticed that the floats are not set to the same height, which I am sure is not correct. I don't have a workshop manual (yet) for the bike and am curious if anyone knows what the proper float height should be for this carburetor.

Grazie mille,
-tj in los gatos

_________________
2012 KTM 450 XC-W
2008 848
1995 916
1992 900SS
1991 851
1987 F1
1966 Mach 1 Replica
1963 Lambretta Li150 Special
1957 Alfa Romeo 1900C SS
1966 Alfa Romeo Giulia Sprint Veloce


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 Post subject: Re: Dellorto PHF 36 float height for F1B
PostPosted: Tue Oct 18, 2011 10:59 am 
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Joined: Mon Oct 10, 2011 2:31 pm
Posts: 45
Location: Los Gatos, CA
As a follow up to this initial inquiry I'd like to share what I've learned in the hours since I originally submitted it. I found a copy of the F1 factory workshop manual on the Bevelheads site, but the information there was confusing, and seemingly incorrect. "Check with a gauge that the distance between the float base and the flange on the carburetor body is 4mm". This is technically impossible as the float itself is about 20mm in diameter, and even if it were to be forced all the way up in to the top of the float chamber there would not be enough room for it to expose only 4mm to allow for this sort of measurement. Pressing on, I found a datasheet on Dellorto's own website specific to the PHF36, which cites 18.5mm as the distance between the bottom of the carb flange and the bottom of the float chamber. A repost of the diagram and settings can be found on the Ducatimeccanica site here http://www.ducatimeccanica.com/float_levels.html. What's confusing in this diagram is the 18.5 + 17.5 specification. I've never seen something like this. Often times you'll see "18.5 +- 1" or something to that effect (as in the range of acceptable values for piston ring end gap tolerances, but this is a new one on me. Does anyone have an explanation?

In the end I used 18.5mm specification. I had to fiddle with the float levels and stops quite a bit to achieve this specification, and while something didn't quite right with this adjustment (there's much less range of motion for floats, but maybe that's the way it's supposed to be) I set them up accordingly, checked to see that the needle valve is open with the float at its lowest level, and reassembled the carbs.

I have not yet had a chance to test ride it, to see if it fixed the huge flat spot above 4K RPM but I will do so this afternoon and report back.

-tj in los gatos

_________________
2012 KTM 450 XC-W
2008 848
1995 916
1992 900SS
1991 851
1987 F1
1966 Mach 1 Replica
1963 Lambretta Li150 Special
1957 Alfa Romeo 1900C SS
1966 Alfa Romeo Giulia Sprint Veloce


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 Post subject: Re: Dellorto PHF 36 float height for F1B
PostPosted: Sat Oct 22, 2011 10:40 pm 
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Joined: Mon Jan 17, 2011 3:32 am
Posts: 7
Images: 7
Location: Sydney, Oz
Gday TJ,

The Dellorto manual for PHF36's shows 17.5mm to 18.5mm. Don't let the way it's expressed concern you.. it just means 18mm +/- 0.5mm.

Setting them is easiest (for me anyway) by attaching a fuel line and holding the carb in it's running position. Set your vernier to 18mm and manipulate the float up and down till you find the exact spot fuel stops flowing. It should be at the 18mm (+/- 0.5mm) mark. The manual shows the 'flat surface' method but that isn't the way I was shown, so it isn't the way I do it.

Float movement (up and down) should be the same for both carbs, if it isn't you have a problem somewhere. Check that both 'float balls' on the float mechanism are at the same level.

Carbs that have sat for long periods (especially, it seems, with what you unlucky yanks get given as fuel) full of fuel can clog up or 'varnish'. Could be the cause of your problem(s).

I'd also be checking everything is in a 'standard' state. Including jet sizes and needle positions.

HTH.

Ciao,

Garry.

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*If you enjoyed this thread - Dry Clutch Gearbox Mainshafts may be donated to.....*


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