Hi, This is my first attempt at setting the timing on a CDI ignition. I have taken my dial indicator and marked TDC and .043 BTDC on the case. When I hit it with the timing light, I am firing right between the two marks. Am I correct to say I should be firing dead on the BTDC mark? It is not running yet, fresh rebuild, just cranking the kick start by hand. Thanks,
Ralph
Thunderdog CDI timing
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Ralph Hecht
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- Joined: Mon Nov 25, 2013 2:01 pm
Re: Thunderdog CDI timing
Hi again, I am guessing BTDC fire is correct, I am concerned about what RPM is needed to set it. Paul's specs say," .043 static (see page 13) " but I do not have page 13. Any help would be greatly appreciated.
Ralph
Or, if the information is in a Resonator somewhere
Ralph
Or, if the information is in a Resonator somewhere
Re: Thunderdog CDI timing
Hi Ralph,
I don't pretend to have the right answer but I will throw something out there to help get a response. The .043 static setting will establish the trigger point and is the farthest that the CDI box can advance the timing. The CDI box will establish the timing curve by retarding the timing at low RPM's and perhaps retarding the timing again at high RPM's but can never advance the timing to a point before it receives the trigger signal from the ignition. It would be reasonable to assume that the firing point could be retarded by the CDI box at cranking RPM's by hand and that might explain why your timing light is showing a firing point between the two marks. Now the experts can explain to us what is really happening and why I should keep my mouth shut.
I don't pretend to have the right answer but I will throw something out there to help get a response. The .043 static setting will establish the trigger point and is the farthest that the CDI box can advance the timing. The CDI box will establish the timing curve by retarding the timing at low RPM's and perhaps retarding the timing again at high RPM's but can never advance the timing to a point before it receives the trigger signal from the ignition. It would be reasonable to assume that the firing point could be retarded by the CDI box at cranking RPM's by hand and that might explain why your timing light is showing a firing point between the two marks. Now the experts can explain to us what is really happening and why I should keep my mouth shut.
Ivan AKA "Pop"
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Ralph Hecht
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- Joined: Mon Nov 25, 2013 2:01 pm
Re: Thunderdog CDI timing
Think I got it. If you look on the case, I have marked .043 BTDC (top mark) and TDC ( bottom mark). The flywheel mark is positioned where it is firing as slow as I can turn it with hand or screw gun. Of course the faster I crank it with the screw gun, the further the mark travels to the BTDC mark. I just don't know how to get it right.
Ralph
Re: Thunderdog CDI timing
Ralph,
Your experience would seem to bear out my theory that as RPM's rise the firing point will approach your static setting. I would expect that at some (unknown to me) specific RPM the firing point would coincide with the .043 BTDC timing mark. I know there are folks on this list that have way more knowledge of this than I, since I basically make all this up in my own mind. Everything I say is speculative. I think my ancestors used to think the earth was flat and it made a lot of sense to them too.
Your experience would seem to bear out my theory that as RPM's rise the firing point will approach your static setting. I would expect that at some (unknown to me) specific RPM the firing point would coincide with the .043 BTDC timing mark. I know there are folks on this list that have way more knowledge of this than I, since I basically make all this up in my own mind. Everything I say is speculative. I think my ancestors used to think the earth was flat and it made a lot of sense to them too.
Ivan AKA "Pop"
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Bullfrog
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- Location: Oregon, 12 miles from the center of the Hodaka Universe(Athena)
Re: Thunderdog CDI timing
Ralph:
You may (or may not) have the information from the Owner's Manual (see scan below). The information calls out the firing point in degrees at two RPM situations. Unfortunately, it does not provide the initial static set point in degrees for comparison.
This information reveals that the CDI system provides for 2 degrees of "advance" of the firing point as RPM increases from 2,000 to 6,000RPM.
I'm sorry but I don't have enough information on the 250 components (missing the precise center-to-center length of the connecting rod) to use a spreadsheet to calculate degrees of rotation for the Before Top Dead Center positions which are important in this discussion.
Finally, the firing points you report from the use of your timing light are "safe" in that they are not more advanced than the mark on the case - so the timing is NOT dangerously advanced.
Ed
You may (or may not) have the information from the Owner's Manual (see scan below). The information calls out the firing point in degrees at two RPM situations. Unfortunately, it does not provide the initial static set point in degrees for comparison.
This information reveals that the CDI system provides for 2 degrees of "advance" of the firing point as RPM increases from 2,000 to 6,000RPM.
I'm sorry but I don't have enough information on the 250 components (missing the precise center-to-center length of the connecting rod) to use a spreadsheet to calculate degrees of rotation for the Before Top Dead Center positions which are important in this discussion.
Finally, the firing points you report from the use of your timing light are "safe" in that they are not more advanced than the mark on the case - so the timing is NOT dangerously advanced.
Ed
Last edited by Bullfrog on Thu Mar 24, 2016 5:35 pm, edited 1 time in total.
Keep the rubber side down!
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Ralph Hecht
- Posts: 10
- Joined: Mon Nov 25, 2013 2:01 pm
Re: Thunderdog CDI timing
Thanks Ed. I do not have a owners manual so your explanation and scan puts it all together for me. Ivan, thanks and my ancestors were brave sailing men who didn't even whimper as they sailed over the edge.
Since I am in a safe range, once I get it running I will give it a check!
Since I am in a safe range, once I get it running I will give it a check!
Re: Thunderdog CDI timing
THanks Ed for posting that picture from the owners manual , you beat me to it
Rich
Rich
Re: Thunderdog CDI timing
That T dog is looking nice
Rich
Rich
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Bullfrog
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- Joined: Mon Jul 22, 2013 4:05 pm
- Location: Oregon, 12 miles from the center of the Hodaka Universe(Athena)
Re: Thunderdog CDI timing
Oooopsie. I have edited my previous message - the scanned page was from the 250SL Owner's Manual - so I replaced it with a scan of the page from the 250ED Owner's Manual. While the ignition timing information is exactly the same, the spark plug info is different - be sure to use the proper plug in your machine.
Actually, there is a bit of additional information in the ED manual. Timing advances 2 degrees when the lights are on (surely the same thing applies to the 250SL), so you have a 2 degree ignition timing "map" change available at the flip of a switch!
Sorry for the error.
Ed
Actually, there is a bit of additional information in the ED manual. Timing advances 2 degrees when the lights are on (surely the same thing applies to the 250SL), so you have a 2 degree ignition timing "map" change available at the flip of a switch!
Sorry for the error.
Ed
Keep the rubber side down!
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