Author Topic: Dellorto PHF Carbs - Setup/Synchronisation Procedure  (Read 6125 times)

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Dellorto PHF Carbs - Setup/Synchronisation Procedure
« on: August 18, 2012, 08:52:24 PM »
Our bikes can be made to run extremely well with the stock Dellorto carbs - especially if the carbs are correctly set-up and synchronised.  If they are not adjusted correctly, your bike’s performance won’t be all it should be and the fuel consumption may be quite alarming..!
Dellorto PHF Carburettor – Note the Variations in Some areas…
 
What follows are the steps required to set-up and synchronise the carbs during the  routine service of a V1000 (Vampire models are similarly adjusted, but access is, obviously different), but the same process would be equally effective after a carb rebuild or disassembly and cleaning, etc; or even to set up new carbs.

There is a good exploded diagram of a PHF Carb here:  http://www.thisoldtractor.com/gtbender/mg_images/dellorto_carb_diagram_phf_page_2.jpg

(Way too big to embed into this forum page - sorry).

1.   First step is to check the mechanical parts:  Part of a routine service is to disassemble, clean and lubricate the throttle assembly and throttle cables.  This will require removal of the Right Hand Side (RHS) switchgear from the handlebar.  The throttle tube should be cleaned to remove any traces of grit or debris and lubricated with engine oil, the upper throttle cable should be similarly lubricated and, at the same time, a check should be made to ensure that no strands of the cable inner are broken, and that the cable inner is not kinked or corroded.  Once this is all OK, the throttle tube and RHS switch can be refitted.

2.   The lower throttle cables are more difficult to access:  Lift the seat and turn the fuel taps off.  Undo the two M8 (13 mm head) bolts securing the fuel tank to the frame and lift the rear of the tank.  This will allow access to the fuel lines connected to the taps.  Both must be removed.  Once done, the fuel tank should be removed and placed in a safe, secure place.

3.   Next, the oil-cooler cover and tank skirt panels must be removed:  remove and retain the 4 self-tapping screws that secure the oil-cooler cover to the tank skirts and slide the cover along the choke cable until the cable will pass through the access slot in the cover.  Place the cover in a safe, secure place.  To remove the tank skirts, the tank mount rubbers must be removed and retained.  Then, each skirt panel must be lifted and “rotated” away from the frame tubes until it can be removed from the bike.  Lastly (unless major surgery is planned) the RHS side-cover should be removed and placed in a safe, secure place, to gain access to the rear carb adjustments.

4.   The throttle cable has a 1 to 2 cable joiner, which sits just above the Left Hand Side (LHS) of the oil cooler, just inside the horizontal frame tube.  This unscrews to reveal the inner joining piece and the cables.  This should be removed, cleaned and lubricated as completed for the upper cable..  Once done, the joint should be reassembled and the throttle action checked to ensure that it opens freely and smoothly and that the return action is both rapid and smooth.

Note:   During these checks, and especially for a bike which is new to you, it may pay dividends to ensure that the cables don't bind or have any sharp bends between throttle assembly and carbs.  The damage and inconvenience such binding and/or bends can cause simply isn’t worth not checking…

5.   Next, check the security of the exhausts.  Yes, really… If the downpipes are loose, or the downpipe to silencer joints blowing, then there’s little point in trying to set up the carbs…

6.   Lastly, check the security of the carb/intake manifold securing clamp and that the three Allen bolts securing the intake manifolds to the cylinder heads (via the manifold insulators, which should also be checked for cracks and general poor condition) are tight.

Once you have checked the security of the carbs, insulators and exhausts AND properly maintained the throttle cables, you can turn your attention to the carbs.

7.   How It’s Done:

  • Back out slide screws (Item #47 on diagram) so they are not touching the slides
  • Gently screw-in both carb mixture screws (Item #46 on diagram) until very slight pressure can be felt.  This means that the screw is fully seated.  Now unscrew both screws out 1.5 turns from the seated position.
  • Loosen the carb-top throttle cable adjusters (Item #86 on diagram) such there is at least 1/8” (3 mm) of free play in the lower throttle cables.  If no free-play can be achieved, one solution is to remove the locknut from the carb-top cable adjuster and reinstall the adjuster and cable.

We’re now at the point where the bike needs fuel.  It’s possible to refit the standard fuel tank and work on the carbs, but I prefer to use an “auxiliary tank”.  This is a small tank, holding about 0.6 gallons, removed from some decrepit moped or other, way back when… It has two outlets, so can feed both carbs simultaneously (the moped used a remote fuel tap, hence the two outlets… I connect this to the carbs, secure it to the bike (folded old towel and two bungees) and then add the fuel.  The tank even has a gauge, so I know when I need to top it up… MUCH better than working in the shadow of the Hesketh tank…  A similar auxiliary tank will rush you a tenner at your local breakers…

Note:   If the carbs have been re-built, the accelerator pumps will be empty and will need to be primed.  It’s a good idea to check that the pumps are working, even if the carbs haven’t been stripped:  When the throttle is pulled wide open fuel should squirts out of the pump jet on each carb.  If it doesn’t then you need to prime the carbs:  Seal the non-return valve on top of the accelerator pump housing and twist the throttle open until fuel squirts.  Do both carbs. If you have trouble, remove the non return valve and put 6 to 10 drops of fuel in the hole and reinstall.  Try to prime the pump again..  If it still doesn’t work, you may have a split pump diaphragm…
  • Remove and retain the carb-synch blanking screws and fibre washers from the sides of the inlet manifolds and connect a pair of vacuum gauge take-off tubes (M5 thread).  These should be connected to a pair of vacuum gauges or mercury columns
  • Start the bike and allow it to warm up (not too hot though, these adjustments can be tricky…!)
  • Adjust the carb slide screws to obtain an even idle tick over with even vacuum readings, don't worry about the rpm at this point, just work to attain the same vacuum readings for each cylinder.
  • Twist and hold the throttle so engine speed rises to between 2,000 – 2,500 rpm and hold her steady (a helpful friend here makes it easy).
  • Adjust for even vacuum at this rpm by turning the cable adjusters on top of carb(s) in or out – You should start the adjustment by backing out the adjuster on whichever carb needs the vacuum increasing for the two readings to be even.  If you’re confused as to which one to start with, try pulling the lower cables to see which one makes the readings more even.  That’s the one you should start with…
  • Release the throttle and check the tick over vacuum readings again. Re-adjust the slide screws as necessary (screw in to increase vacuum and vice-versa). Adjust for correct  tick over rpm now, using the slide screws only.
  • Adjust the carb-top cable adjusters such that each has just a small amount of free-play, check the 2,500 rpm vacuum readings again and re-adjust at the cable adjusters as required to balance the vacuum readings—this is a VERY important step. You MUST have a bit of free play in the cables!
  • Now we need to adjust the idle mixture screws  (Item #46 on diagram) for the best idle speed/mixture (screwing the adjuster in makes the mixture leaner by reducing the quantity of fuel that can pass). 

Note:   Listen for changes in the sound of the exhaust note, and use your fingers over the end of the silencers to feel for a stronger exhaust pulse, whilst turning the mixture screw on that cylinder's carb.  If you’re right-handed, start on the rear cyl as you can twiddle with your right hand and feel with your left (Ooh-Er!)  It pays dividends to work back and forth between the two carbs (sometimes several times) making little adjustments, always listening for the highest  tick over and feeling for a stronger exhaust pulse. A dull “woolly” exhaust note indicates that there’s room for improvement.  Keep adjusting until you hear a crisper note and feel a stronger exhaust pulse..

You may need to perform this process regularly (cables stretch) if you are to ensure that your bike is running as well as it can all the way through the rev range.  A well sorted pair of carbs really delivers, particularly with better fuel consumption, and that’s REALLY important nowadays..!!

Hope that helps...

Jeff
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Re: Dellorto PHF Carbs - Setup/Synchronisation Procedure
« Reply #2 on: May 01, 2018, 10:50:26 PM »
Thanks REMF;

I'm updating the site presently and will incorporate the change.

The feedback is appreciated.

HOCAdmin
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Re: Dellorto PHF Carbs - Setup/Synchronisation Procedure
« Reply #3 on: May 25, 2018, 10:12:29 AM »
I am stripping and refurbing my carbs, and came across this thread.
The link http://www.thisoldtractor.com/gtbender/mg_images/dellorto_carb_diagram_phf_page_2.jpg no longer works.
This one does
http://www.dellortoshop.com/drawings/dellorto_phf_carburetor_exploded_view_drawing.jpg
as does this one
http://www.thisoldtractor.com/dellorto_parts_diagram_for__phf_carburetors.html

The required diagrams have been added to our own Spares and Technical page and can now be seen as 'thumbnails' here:

Click on the thumbnail image to see the picture in full size.

If anything else is required, don't hesitate to contact me and I'll see what I can do.

Regards

HOCAdmin
A man with a plan... occasionally...