Author Topic: 750 F2 Coils  (Read 128 times)

Offline born to be mild

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750 F2 Coils
« on: May 22, 2020, 10:17:50 AM »
Does anyone know if coils specified for CDI units can be used on existing points ? I appear to have one of each type on my '77 F2 , looking at the previous owners invoices he has fitted a CDI type coil and now some years later the other [ original ? ] coil has failed , the bike wont tick over when hot and i cant get continuity through the plug leads. The reason why I want to fit the cdi type coils is that it has 100mm hole centres, the 90mm version wouldn't fit my bike. The SKU number of the newer ,working coil is 713712 looking at the paperwork. I understand that it's worked thus far but I wondered if adding another 'incorrect ' coil would cause problems.

Online AshimotoK0

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Re: 750 F2 Coils
« Reply #1 on: May 22, 2020, 11:00:22 AM »
Measure the primary resistance if you can get access to a multimeter. If they are any less than 4 Ohms you are asking for trouble IMHO
as you will be passing more current than the ignition primary circuit is designed for ....... plus a CDi specific coil will not be designed for continuous high current duty (e.g the situation when the ignition is on, the points are in their closed position and the engine is not running).  It is designed for short bursts of high current discharge from a high voltage capacitor.
« Last Edit: May 22, 2020, 11:03:40 AM by AshimotoK0 »
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Offline K2-K6

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Re: 750 F2 Coils
« Reply #2 on: May 22, 2020, 12:55:31 PM »
Wondering if you'd spot the post Ash.

I was looking at it too and found that the coil mentioned is rated at 12volt 5ohm for primary circuit,   matches original for that.

 But it's rated at 18ohm for secondary resistance.  How would that be measured?  Is it from tip of one HT  lead to other? And does it match original spec.

Looks like 713712 part is original to 1980s superdream,  also Honda CM 250 . Is that the Trigger special  ;D

Offline born to be mild

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Re: 750 F2 Coils
« Reply #3 on: May 22, 2020, 05:19:39 PM »
Ok Gents, thanks, I think I know where I'm going now;

Coil for 1&4 reads     Primary 4.8 ohm
                               Secondary Nil [ I've taken plug caps off to double check that they weren't the problem ]

Coil for 2&3 [ CDI type replacement coil ] reads    Primary 2.5 ohm [ which looking at the responses is at least 1.5 ohms too low]
                                                                         Secondary 27.9K ohms .

So it looks as though the coil for 1&4 has given its all after maybe a mere 43 years [ its a TEC one so I'm assuming it's original] and coil 2&3 has been replaced at some point with the wrong [CDI type] of unit and also needs replacing because it's only reading 2.5 ohms. The 102mm versus 90mm debate is now thankfully a moot point as I've discovered that the mounting bracket is moveable at the rear so I could go for either mounting option.

Thank you both for your advice, much appreciated. Ash, I found your download for coil repair too which if I was keeping the bike I'd definately have a go at on the non cdi type but as I'm selling the bike  at some point this year I think I'd best buy new.
                       

Offline Bryanj

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Re: 750 F2 Coils
« Reply #4 on: May 22, 2020, 06:10:34 PM »
Got a set of old goldwing coils here, in theory if you fit a balast resistor,or fix the one with them, they should work.
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Offline born to be mild

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Re: 750 F2 Coils
« Reply #5 on: May 22, 2020, 09:22:53 PM »
That's really generous of you Bryan and thanks very much, unfortunately I ordered a pair online just after leaving my last posting here and just before you posted. Sods law at work again ! it was a kind offer though, thank you. I'm sure some other needy soul lacking sparks will benefit instead at some point.

 

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