Making the Weber DFAV 32/36 carburettor work

Discussion in 'How To' started by mikedjames, Dec 18, 2012.

  1. Just recently the choke linkage wire fell out. It is held in with little "fins" which are squeezed out of the wire. One of these wore out and it just fell off.

    So I took the chance to bodge it while the replacement £10 part comes from www.dellorto.co.uk.

    And then I hit a problem that may be familiar.. I reassembled the carb after stripping it down and put the EMPI branded choke capsule in with the mark lining up with the mark on the casting.
    After that the engine would not start or would only just run with the throttle hard on the floor.
    What was going on with the carb was that the choke flaps were not opening so the engine was starved of air and would not pick up.
    Adjusting the choke capsule turning it about 30 degrees anticlockwise so the choke flaps are closed but drop down with light pressure and it started perfectly..
    And once I tweaked the fast idle screw to make allowance for the bodged linkage wire it idles sensibly not at 3000rpm
     
  2. And further to the choke link wire I realised that it was actually holding the throttle open slightly sometimes. By adjusting the cold idle screw and bending the linkage wire I got it so the wire is rattling around when the choke is fully off.
    And the cold idle is still ok. The hot idle is properly under the control of the screw on the throttle arm not down to a wobbly bit of wire that would sometimes jam and hold the throttle open a bit more.

    I had idle between 800 and 1500 rpm which changed with a tap on the pedal.

    Basically the expensive bit of wire is a bit short.
     
  3. Hi I have followed you set up with interest, I recently built a trike with a standard 1300cc twin port and after feeling there was not enough power I set about building another engine, I built a as41 case 1641cc twin port with a scat c25 cam, using a new vac distributer and fitted a powerspark ignition, set timing to 30 degs at 3000+ rpm and checked with the vac hose reconnected at nearly 40, the carb is an empi set up with an facet electronic fuel pump, and jet sizes to you last set up.
    It starts fine and pulls like a train as still running in run up to 75 mph no problem, it ticks over fine but the only problem is when using the throttle lightly is stutters slightly give it a hand full (twist grip throttle) it pulls fine, after a run I filled up and I am getting about 28 to the gallon, as the engine has only done 200 miles since full rebuild I have not thrashed it but I am sure it will reach 80mph no problem.
     

    Attached Files:

    vanorak likes this.
  4. when you give it a handfull, you're also squirting neat fuel in via the accelerator pump jet, hence the rapid pick up.....the light load stutter could well be to do with a lack of advance at low rpm....the vac signal from the prog. may not exactly suit the characteristics of the advance curve 'built in' to the dizzy....try bumping up the timing by a degree or two, and see if it picks up any better....provided you're not pinking, at high load (hills etc.) it won't kill it


    sounds like it's good fun though:D
     
  5. yep good idea, I was wondering if it was because I did not have a fuel regulator in line, but then again it ticks over at a constant 800rpm and does not miss a beat, only in slow moving traffic as I open the throttle does it stutter
     
  6. quite a few problems with webers using stock fuel pumps have been down to over fuelling....if it seems fine now, it probably is, but if it starts running like a crock, it's worth checking the fuel pressure, befor anything else...Gunsons do a 'low guage' for a few quid, that you can stick in the end of the fuel line, or (better still) inline off a Tee piece, to see what you're running at
     
  7. will try that,set everything else up apart from checking fuel pressure as it stated the pump was 4 psi rated
     
  8. definitely worth a check...i had a 'universal low pressure pump' from a reputable source that was rated at 2.5 to 4 PSI....checked it and it was around 7PSI at 3000 RPM....not ideal by any means...I trust the guage, but it could be out.....reset the pressure (via a decent regulator) and never had an issue since....


    lots of anecdotal evidence on here from folks who run stock pumps without issue, and those with fancy dan pumps and regs that play up....if it ain't broke.....
     
  9. fuel pressure checker on order
     
  10. I have just made a new throttle linkage component - the old one with a ball bearing race in it bent and showed a crack across a narrow part.

    [​IMG]
     
    Last edited: Feb 5, 2017
    tommygoldy likes this.
  11. I recently cleaned the jets and readjusted the idle mixture.
    And currently the jetting I am running with is
    Primary : Idle 45 main 130 air 170 with standard emulsion tube as provided
    Secondary : Idle 80 main 132 air 180, standard emulsion tube.
    Idle 850rpm @ 14.7 AFR.
     
  12. Having just fitted my engine and started to assemble the accelerator linkage I have discovered that I too have the problem where the cable is at the wrong angle for the progressive carb, limiting the opening of the throttle at the high end, hopefully with the diagrams you have done above I can make some sort of mechanism like yours to solve the issue before then letting an expert fine tune my carb.
     
    mikedjames likes this.
  13. 2021 update. Still using the progressive.
    Replaced the fuel pump with an SSP rebuildable from Heritage. 3psi pressure.
    Changed the secondary main jet to 125 to lean it up slightly.
    Adjusted the slack out of the linkage. Back to 70 mph.
     

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