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SP2 timing and idle problems

Discussion in 'Loop & Tonti' started by vitjakes, Aug 7, 2020.

  1. vitjakes

    vitjakes Just got it firing!

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    Good day, fellow riders,

    I have just recently become a Moto Guzzi owner as I got myself a well-used '84 SP2 with 162 000 km on it. Despite the milage, it looks nice and original, doesn't sound terrible and it's got 150 psi of compression on both cylinders and it even seems to charge, albeit only at 13 V (checked the AC feeds, all off them put out 40 V, had a spare regulator, tried it, no change, but I'll cross that bridge when I get there.).

    To begin with, the bike came equipped with some kind of a home-made Volkswagen pointless ignition unit from a MK2 Golf. It seemed to work fine, but I got the original points plate with it so I retrofitted them to know what I'm dealing with. But prior to this swap, I carefully set the valve clearances to spec and then went through the lean-burn PHF36 BS carbs (probably from a LM3), which were absolutely flawless, including all o-rings. The only thing I noticed that was off was the float height, which I carefully adjusted to 18 mm with the carb resting on the intake as per the DellOrto manual.

    I then tried and started the bike just about fine, bled the accelerator pumps, it rides and reacts to throttle promptly, basically no issues there. So then I thought I'd try and balance the idle and slides by ear and sight. I set the mixture screw to highest idle on both cylinders and started fidling with the throttle screw. All went well until I got to a point where I just can't get the idle any lower than 1200 RPM. When I twist the screw further out, the idle seems to pick up as it probably starts sucking air through the screw as there is not enough spring pressure to keep the o-ring sealing. If I physically reach inside the carburettors, I can feel a palpable wiggle of the slide as it's pretty worn out. Could this be the reason I can't get the iconic low idle? I'm doing all of this at operating temperature without the airbox fitted.

    And now to the points. I tried my best to find the static timing and full advance marks on my flywheel. While turning the fllywheel anticlockwise and waiting for the marks for the right cylinder, at first I can see an unmarked line, followed by another one and then two lines with the letter "D" under them. If I understand the manual correctly, the first line is the full advance, the second one is for static timing and the "D" is TDC right cylinder. The trouble, however, comes with the left cylinder, where I can only see one line, followed by S. How the hell am I supposed to time it with a strobe? If anyone could chime in with a tip, I'd be incredibly grateful.
     
  2. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    As viewed form the front, you should be rotating clockwise to check the timing marks. With the slides that worn, you may be getting some air leak. If the idle mix screws are set too rich, you may have this issue also. The exposed screw is the slide stop for idle speed. Idle should be around 1100 RPM so the 1200 isn't bad. BTW, the gauges on this bike lie, so you may have the correct idle speed and not know it. Idle speed too low isn't good for the engine as oil pressure drops. Looks closer on the "S" side. The lines may be weak but they are there. I use a white marking pen to highlight the lines.
     
  3. Moto-Uno

    Moto-Uno Cruisin' Guzzisti

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    I believe the flywheel ring gear has teeth that are 3.75 degrees between them . Go to top dead center (on compression)
    for your left cylinder , then go back 8 (or 9) teeth and mark with a bright white paint , that should be your visible left hand
    cylinder full advance mark . Definitely agree with above concerning lying tach readings at low engine speeds . Also, you may
    find that the idle screw adjustment that gives you the highest idle speed may be a bit lean , I've found that the idle was somewhat
    better with a small turning out of the mixture screw (enriching). Costs nothing and only takes a moment . Peter
     
  4. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    Peter, agree with the idle mix screw. Once I get a good idle, I turn that screw in. When the engine begins to stumble, I back it off half a turn. That technique has served me well for years. I've found that when that setting results in 2 and a half turns from fully in, you have the correct size pilot jet.
     
  5. vitjakes

    vitjakes Just got it firing!

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    Thank you, everyone. It took me a while to find out that static timing is actually just 2° BTDC, which is practically right next to TDC. At first I thought it was a double line indicating TDC, but in fact it's TDC and static mark right next to each other. The tooth-rule works great, both of my full advanced marks were exactly 9 teeth BTDC and the lines were there, nice and visible. In the end I timed the bike statically after I ground off a good amount of the points plate to actually get there on the left cylinder.

    I then started the bike, set the mixture screws for highest idle and gave it another half turn out, which brought the idle down a bit. After that, fully warmed up, I synced the bike by ear and she now idles beautifully.
     
  6. Moto-Uno

    Moto-Uno Cruisin' Guzzisti

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    ^ Yahoo , great to hear success stories :) . Peter
     

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