Topic: 1975 cb400f what kind of dyna coils do I need?

[adam_chicago]

ok, I have a 1975 cb400f I want to put the electronic ignition into it, and replace the ignition coils, cables and sparks,any advice?

I went to the parts website: www.z1enterprises.com, but they have a couple of them listed under 1975 cb400f 1.5 ohm, 2.2 ohm, 5 ohms , so which ones will be the right ones for my bike? also, there is two different kind of cables 7mm and 8mm ? what kind of spark plugs do I need?

I think dyna electronic ignition  is only one listed below 1975 cb400f, so I hope that will be the right one

I know how to replace the coil, but how hard is replacing the ignition system?


thanks in advance

[Triffecpa]

I use the Dyna S system on my two CB400F race bikes.  Instead of Dyna coils though, I use OEM Honda coils.  I use the early 80's Honda coils (easily found on Ebay for about $20) that have a replacable spark plug wire feature.  Then I buy the $16 Dyna plug wires (7mm) available from Z1 Enterprises.  I'm sure that the Dyna coils work well, but I'm a cheapskate.  However, even though I'm a cheapskate, I like my bikes to run well and I've never had one of the OEM Honda coils fail to date.

Installation of the Dyna S is pretty easy.  You need to hook the wires to the coils and splice into a switched 12v hot lead.  Set the timing and you're done.

Tracy

[tsflstb]

Are any of those 80's Honda coils 5 ohm?  I've thought about getting the CB900 coils but it seems everyone warns against the 3 ohm coils on the 400F for some reason.

[Triffecpa]

I don't know what the ohm rating is on the OEM Honda coils, but they were available on the early 80's bikes that had Honda electronic ignitions.  I have run them on CB400F, and CB750 models with Dyna S ignitions and never had a problem.  Nice fat blue spark and several seasons worth of trouble free use.

TR

[dave400]

Are any of those 80's Honda coils 5 ohm?  I've thought about getting the CB900 coils but it seems everyone warns against the 3 ohm coils on the 400F for some reason.

I have Dyna 3Ω coils on my 400 and never had any problems.

[adam_chicago]

thank you very much for the responses, I called dynatech and they told me that I suppose to use 5 ohms coils for my 1975 cb400f otherwise I will drain the battery out?

somebody said: I use 3 ohms coils, hm... any problems with battery? charging system? do you have electronic ignition installed with them?

[TwoTired]

You can use 3 ohm coils.  But, you better plan on keeping the engine above 3000 RPM 75% of the time.  Otherwise, get 5 ohm coils for a street bike.  Your alternator only puts out 150 Watts at 5000 RPM and about 40-50 Watts at idle.

3 ohm coils will draw 55 watts with point ignition and about 50% more than that with a Dyna-S ignition (if the reports I've seen of it's operation are correct).  5 ohm coils (such as Stock) draw about 33 W. The stock bike normally needs about 100-110 watts without ignition or lighting mods.

Cheers,

[Prospect]

I'm consistently getting a weak spark on most cylinders on the cb400f, to a point that the bike is hard to start and the plugs get fouled. I can't tell if I need to replace the coils or the spark plug wires or   Which is the likely culprit?

[TwoTired]

Carbon is conductive.  Even if you get a spark to jump the gap, some of the power gets siphoned off by the carbon.  Check spark brightness with clean plugs or new ones.

It is unlikely that spark is causing you plugs to foul.  The fact that it left soot on them is evidence that the mixture was ignited, which is the job of the spark.  There was just more fuel in the mix than oxygen to burn the hydrocarbons completely.
Assuming you have done the tune up check list, including the air filter replacement, a rich condition is probably caused by the carbs.

Cleaning or adjustment information about the carbs from you, might help send you in the right direction.

Cheers,

[mr g 400/4]

I have been looking at the dyna s and coils online and they say that you should use the 3 for aftermarket dyna and the 5 for standard. I am looking into this at the moment as i hope to be fitting a 458 kit and hopefully cr26's if i can find a cam to help it all run.

Does anyone know who is the 400f parts specialist in Australia? I am having a few troubles finding things here or on the net. Thanks