Topic: Dyna S on a '79 CB750 F.

[thrutheframe]

I bought a '79 CB750 F that was a borderline basket case.  I won't go into the whole saga of troubles the bike had but it was $500.00 and worth not a penny more.  Last week I finally got it started and discovered that cylinders 2/3 had no spark.  Obvious problem with ignition coil 2 or something inline in front of it.  Once I chased it all back to the ignition plate I determined that the Dyna S (installed by Hamfisted PO) was to blame.  I wanted to see if there was a test to determine if the unit was bad.  I called Larry at Dyna and told him my issue and his initial response was "Why do you want run a Dyna S on that bike..."  He proceeded to inform me that the Dyna S does not tolerate oil and is not recommended for the twin cam Hondas. 
  Has anyone else run into this situation?  I don't want to go back stock if I can avoid it.  Any recommendations on an after market ignition for this bike?


Queen City Classics

[BobbyR]

He is full of #$%*. The Dynas made in the recent past are notorious for dropping 2&3. The old Dynas were bulletproof.

I had a problem and did a web search and found they are crapping out all over the place. It can run great until you get it warmed up and then they drop cylinders.

Do Google search on Dyna S problems and you will see what I mean.  I went with PAMCO. 

[thrutheframe]

It could be new, old, I have no idea.  It was on the bike when I got it.  The important thing is I need an ignition that will tolerate oil.


Queen City Classics

[calj737]

The important thing is I need an ignition that will tolerate oil.

I know you are repeating what Larry told you, but I do not unrest and this statement at all. There is no oil involved in the ignition on a SOHC or DOHC that I'm aware. Did you happen to get an explanation to that statement?

[calj737]

I pulled this off another thread attempting to diagnose a problem with their Dyna too:

You can trouble shoot it with a meter or a test lamp Just connect it as you would to manually set the timing,
1; disconnect at the plug that connects to the coil and set the meter to measure between the wire and electrical ground. 

2; Rotate the crank shaft the meter should go from OV to about 11.5 V as the switch opens / closes. if your timing is correct this will be at the F line on the timing mark.

3: check the second switch.

I have an intermittent, heat related, failure that the service department at Dyna has not repaired correctly. They believe no one but themselves can remove and replace the switch modules. 

>>Hope this helps

[thrutheframe]

On a DOHC honda the area behind the points cover, while not under pressure or part of the sump is an oil splash environment.  SOHC it is on the other side and dry.


Queen City Classics

[calj737]

Okay, but a stock set of I points would not tolerate oil being "splashed" onto them any better than an electronic ignition. I remain confused, but admittedly, not at all familiar with your model of bike. The system is certainly listed widely for DOHC 750s from too numerous vendors, so I struggle to understand the limitation

[thrutheframe]

Twin cams are electronic ignition.  I didn't design it I'm just turning the wrenches. and it IS bad, I tested it so I need something I'm cofident with.  I messaged pamco Pete here and he directed me to CB750ignition.com.  I'm waiting for him to reply re: my oil splash concerns.


Queen City Classics

[calj737]

Precisely why I can not understand why Larry would suggest a design incompatibility. Try the test I copied and run a Dyna.

[thrutheframe]

Again already tested it before posting here.  I'm not one to run sonething on a bike that the manufacturer directly says not to.  Sorry that you're not understanding my concerns. I appreciate your input.


Queen City Classics

[calj737]

I re-read your first post earlier before I posted my question. I also searched in this forum about how to diagnose a Dyna S (which was one of your original questions), I also searched the web and found numerous vendors that sell the Dyna S for DOHC 750s. What I don't understand is why Larry told you that the S is not designed to live in the DOHC, since it's sold for it, and the original system is also electronic.

If you have tested your Dyna and believe it to be faulty, then send it to Dynatek for replacement. If you want an electronic ignition for your bike, but don't want to run a Dyna, check Pamco, Boyer or PowerArc for a compatible system. Or, switch from a Dyna S to Dyna 2000/3000 unit.

So what am I missing?

[scottly]

Thru, if I were you I would try to get the stock pick-up plate and advancer parts. The pulses produced by the stock triggers will operate off-the-shelf GM HEI ignition modules.