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75' with 123 recently installed and running rough


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So... This is my first experience with installing a distributor or timing at all. I just installed a 123+ bluetooth dizzy and a new Bosch red coil per Blunttech's recommendation. I installed the dizzy per the instructions with the engine at TDC. After the green light came on, I tightened it down and checked a known point on the curve with the timing light. I saw the ball mark not the TDC mark with the light when I checked it at 2,000 rpm. 

 

So it seemed to work great at first, then I changed the curve and tried hooking up the vacuum line from the carb, then changed it to the nipple on the manifold. It ran like shit with the vacuum line hooked up so I put it back to no vacuum. I have this curve loaded right now and it runs ok but seems to stumble at idle and you can hear its a little rough when revved up. It is also idling higher than with the stock dizzy. I have a 32/36 with stock everything else. 

 

Does this idle sound like a timing issue? 

Thanks:)

Tiicurve.jpeg

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Ok, few things to cover here:

1.) Use a timing light to confirm that the numbers you program in the 123 are what you ACTUALLY see happening at the crank. I.E. 12 degrees at idle is really 12 degrees BTDC at idle.

2.) I don't like how your curve goes to zero ~500 RPM.  Keep the idle advance (e.g. 12 deg) flat from idle down. I.E. make points 1 and 2 also 12 degrees.

3.) MAP curve looks weird with that asymptotic jump at 30kpa.  Also I expect you idle somewhere around 45ish kpa, so your running rough is likely because you're running 12+10 = 22deg of advance at idle, which is too much. You CAN have 10 deg at low MAP like that, but if you do you'll need to take some of the base advance out of the RPM curve to compensate.  Total advance at idle for the M10 likes to be in the 12-16ish range.

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The Manifold Pressure Advance curve is configured for a the carburetor port vacuum connection, not the manifold.  Ported connection pressure is near atmospheric (100kPa) at closed throttle and begins to decrease as the throttle blade lifts over the port in the throat for low load operation.  At some throttle opening the pressure at the port increases again to near atmospheric at high loads (no vacuum advance).

Connect the tube to the ported nipple on the carb.  Hacking up the curve will get you more confused than now.

The units being used are confusing for the old timers that can only think in inHg gauge,  instead of absolute pressure.:lol:

 

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2 hours ago, AustrianVespaGuy said:

Ok, few things to cover here:

1.) Use a timing light to confirm that the numbers you program in the 123 are what you ACTUALLY see happening at the crank. I.E. 12 degrees at idle is really 12 degrees BTDC at idle.

2.) I don't like how your curve goes to zero ~500 RPM.  Keep the idle advance (e.g. 12 deg) flat from idle down. I.E. make points 1 and 2 also 12 degrees.

3.) MAP curve looks weird with that asymptotic jump at 30kpa.  Also I expect you idle somewhere around 45ish kpa, so your running rough is likely because you're running 12+10 = 22deg of advance at idle, which is too much. You CAN have 10 deg at low MAP like that, but if you do you'll need to take some of the base advance out of the RPM curve to compensate.  Total advance at idle for the M10 likes to be in the 12-16ish range.

Thank you for your response, I'm not clear about the yellow text above. You mention how 12 deg is 12 deg BTDC at idle... When I stabbed the dizzy I did it with the crank at the CP mark not the Z ball mark and the rotor pointing at the #1 spot. I also just used a curve that I found on the forum. I have no reasoning for any of the points other than they sounded like they worked for others so I copied them hoping to just get to a good smooth (correct) place. Im in no place to start tuning curves since I really don't understand what I'm doing and I would hate to hurt my engine. 

 

Is the 12+10 deg because the Z ball is set at 10 deg? does this mean the entire curve needs 10 deg subtracted from it? Or is there just a nice factory curve that will give me nice power and longevity that can be loaded into it?

 

Thanks so much, 

Stephen 

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Jimk, 

Thank you as well! I did play around with both carb port and the manifold port. I found it to run crappy on both (slow turnover when cranking and then rough idle and rough as revved up) Like AustrianVespaGuy was saying about too much advance at idle, should I find a curve that is less advance? 

 

Also, with this being the 123 dizzy, is there any way the dizzy is not timed correctly if I clamped it down when the green light came on? I was worried about twisting it once the light was on in fear of adding or subtracting advance degrees to the whole curve. 

Thanks:)

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1 hour ago, sczapiga said:

...is there any way the dizzy is not timed correctly...?

 

Do you have a timing light?

 

One way to see if you have the distributor clocked correctly is to use the Z-ball, which is at 25 degrees BTDC

 

For example, if you make the 2000 rpm advance point = 25 degrees of advance and then shine a timing light down the hole in the bell housing, you should see the Z-Ball lined up with the driver's side edge of the oval hole at 2000 rpm.  

 

Are you sure you have the #1 plug wire where it belongs on the cap, followed by #3,4,2 clockwise?


Tom

 

Edited by '76mintgrün'02
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1 hour ago, '76mintgrün'02 said:

One way to see if you have the distributor clocked correctly is to use the Z-ball, which is at 25 degrees BTDC

 

For example, if you make the 2000 rpm advance point = 25 degrees of advance and then shine a timing light down the hole in the bell housing, you should see the Z-Ball lined up with the driver's side edge of the oval hole at 2000 rpm.  

Yes, I have a timing light. If I understand correctly, if the z ball is at 25 (before top dead center) and I set the dizzy to be 25 deg advanced at 2000, the two should cancel each other out and the z ball should show up at 2000 because the ignition is at zero degrees correct?  
 

thank you very much, I think this is starting to make sense:)

 

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The timing light is at zero degrees, if you have a basic timing light.  It flashes when the spark happens.

 

(If you have a variable advance timing light, you can dial advance into the light).

 

If you follow the "2000 rpm advance set to 25 degrees on your curve" scenario, then seeing the BB in the window (with your basic light) at 2000 rpm will confirm that you have the distributor body clocked correctly.  To be exact, the BB should line up with the driver's side of the oval hole.

 

They are not cancelling each other out, really.  The advance is 25 degrees at the BB, not zero; but I think you're getting the idea.

 

If you had a variable timing light, you could set it to any amount of advance on your curve and check to see that the OT line on the flywheel shows up at the rpm your curve prescribes for that advance.  The BB is a useful mark for a basic light.


Tom

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Ok cool, I have an advance light. So when I run it I just find a easy spot on the curve that’s easy to hold a consistent rpm, set the advance, then I’m looking for the ot line, NOT the z ball. Right? 
Thanks 🙏🏼 

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13 hours ago, sczapiga said:

So when I run it I just find a easy spot on the curve that’s easy to hold a consistent rpm, set the advance

Tip:  You can save a lot of fiddling to hold the rpm constant if the two rpm points on the curve are programned to the same advance.  Try 1000 to 2000 rpm at the same advance 15 degrees.  Then set the timing light to 15 degrees setback.  While using the light, the rpm can float anywhere between 1000 to 2000 rpm and the mark wont jump around.

 

After synchronizing the distr to the engine, reintall the advance curve you want.

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52 minutes ago, jimk said:

  While using the light, the rpm can float anywhere between 1000 to 2000 rpm and the mark wont jump around.

Brilliant 👏🏻 So simple but I wouldn’t have thought of that. Makes perfect sense. 
 

Thank you and everyone that has chimed in, I truly appreciate it and this 2002 community is one of the best parts of owning one:) 

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On 7/31/2021 at 10:15 AM, jimk said:

Tip:  You can save a lot of fiddling to hold the rpm constant if the two rpm points on the curve are programned to the same advance.  Try 1000 to 2000 rpm at the same advance 15 degrees.  Then set the timing light to 15 degrees setback.  While using the light, the rpm can float anywhere between 1000 to 2000 rpm and the mark wont jump around.

 

After synchronizing the distr to the engine, reintall the advance curve you want.

^ This, and this is effectively what I meant by making sure you programmed timing matches your actual timing, because you need to make sure of that first, and then move on to tuning your curves.  Great that you have a dial-back timing light, as that makes things much easier!

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