r75/7 Dyna III question

[MikeL]

I just had a similar problem (opposite cylinder) with my Dyna III on my R75/6. Take a close look at the 3 small wires coming off your Sensors, particularly the left sensor. In my case, one wire got pinched by the front cover and ended up shorting out. It was giving me intermittent spark in one cylinder... good luck.

[Garnet]

I just had a similar problem (opposite cylinder) with my Dyna III on my R75/6. Take a close look at the 3 small wires coming off your Sensors, particularly the left sensor. In my case, one wire got pinched by the front cover and ended up shorting out. It was giving me intermittent spark in one cylinder... good luck.

That tells me that the pick up coils are wired individually, and a bad p/u coil or in Mike's case a bad connection will cause it to spark once every two revs of the crank. It will ony run on one cylinder even though both plugs are sparking.

[Rohls]

I swapped the spark plug wires; pulled them from the coil and tried it. No change unfortunately.

The mechanical advance; does it have to be 'disabled' for the Dyna to function? The instructions are vague and mention bending the little metal strap down, but don't mention how far. Are the cams suppose to 'open' when increasing revs? Is there a good link someone could point me to?

Thanks,

Nick

[Garnet]

The Dyna is only an electronic switch. It requiers the stock mechanical advance to function, IE the wights should expand as the revs increase.

From what MikeL said above it apears that you may have to do some testing of the Dyna pick-up. If yours has 3 wires as his does it means that the Dyna "reads" the signals from the individual pick-up coils sepeartly.

Look closley at the pick-up and see if you can follow where the wires attatch to the coils. You may have to remove the p/u. One wire will attatch to both coils, this is called the common, and the other two wires will go to one each of the coils. Put one lead of your multimeter on the "common" lead and attatch the other lead of the multimeter to one of the other wires. Set the MM to the OHM scale and see if you get a reading. You are mesuring the resistance of the p/u coils. They should be very close to the same. If one has a reading and the other is 0 then you have a broken wire somwhere between your meter and the p/u coil, or a defective p/u. If you get a reading from both p/u coils but they are vastly different you may have a bad pick-up.

Remeber to check the connectors to make sure a wire hasn't been pulled out when plugging in and out. Look for damadge to the wires where they pass through the pionts case as it is easy to pinch them there.

[Rohls]

Thanks. I'll test the pick ups on the Dyna per your instructions.

Why in the instructions does it say to 'slightly bend the tabs' on the advance...? Are there any images that show the proper way to do this?

I think the pick up has two wires (red and white) coming from it. Maybe the ground wire too...
I'll check the wires and get back to ya.

Thanks again,

Nick

[Kurt in S.A.]

Nick -

I installed my Dyna III and didn't do squat to the advance unit. Leave it alone...don't know what this "bending" is all about. As mentioned, the Dyna is nothing more than a switch just like the original points were. It's advantage is that you can adjust the switching for left and right cylinder firing on the compression stroke to optimize the spark timing for smoother running.

Kurt in S.A.

[Motorhead]

Its just easy to look the Dyna spec's on line even wireing instructions

there are 2 long wires that do go back to the coil area 1 for power the other replaces the wire to the points

piggy back to the power on the left of coil and replace the wire from the BMW with the Dyna

mine seemed to be color coded to BMw meaing green power, Brown to point connection

[Rohls]

Nick -

I installed my Dyna III and didn't do squat to the advance unit. Leave it alone...don't know what this "bending" is all about. As mentioned, the Dyna is nothing more than a switch just like the original points were. It's advantage is that you can adjust the switching for left and right cylinder firing on the compression stroke to optimize the spark timing for smoother running.

Kurt in S.A.

Thanks Kurt, but unfortunately I have already bent these two straps (grr...) per the instructions from the Dyna site..It didn't make a lot of sense to me at the time, but I fear bending them back might screw things up more.

I still have to recheck the wire connections (though I have a feeling they will be fine), and test per the mentioned method.

This seems crazy b/c I have spark at both plugs when I take them out and crank it over...compression fine and both getting fuel.


Would I be right in tearing the left carb apart and seeing if something is crappy there? I have gone through it before. Is this vacuum problem? What about that rubber boot connecting the carb to cylinder? It doesn't seem cracked....

Thanks,

Nick

[Rohls]

I just had a similar problem (opposite cylinder) with my Dyna III on my R75/6. Take a close look at the 3 small wires coming off your Sensors, particularly the left sensor. In my case, one wire got pinched by the front cover and ended up shorting out. It was giving me intermittent spark in one cylinder... good luck.

That tells me that the pick up coils are wired individually, and a bad p/u coil or in Mike's case a bad connection will cause it to spark once every two revs of the crank. It will ony run on one cylinder even though both plugs are sparking.

'It will ony run on one cylinder even though both plugs are sparking.'

Could you expand on this please ?

[Garnet]

I just had a similar problem (opposite cylinder) with my Dyna III on my R75/6. Take a close look at the 3 small wires coming off your Sensors, particularly the left sensor. In my case, one wire got pinched by the front cover and ended up shorting out. It was giving me intermittent spark in one cylinder... good luck.

That tells me that the pick up coils are wired individually, and a bad p/u coil or in Mike's case a bad connection will cause it to spark once every two revs of the crank. It will ony run on one cylinder even though both plugs are sparking.

'It will only run on one cylinder even though both plugs are sparking.'

Could you expand on this please ?

Each coil of the pick up sends a signal to the black box every time a magnet on the rotor passes it. That signal makes both coils spark at the same time. One spark happens on a compressed the other is wasted. This happens twice per cam rev and which is once per crank rev, meaning, there is one pair of sparks per crank rev.

If one p/u coil does not send it's signal to the black box then there is only one pair of sparks per cam rev or one pair of sparks for every two crank revs. Both spark plugs still spark but only one of them is hitting a compressed cylinder.

I must point out that I have VERY limited knowledge of the Dyna as I have not owned one for over 30 years. I am basing my statements on basic theory. Hopefully someone with more knowledge will step in.