r75/7 Dyna III question

[Rohls]

Hi All,

So I am trying to get a new-to-me R75/7 up and running. Valves set, fresh gas, rebuilt carbs, spark to both cylinders and still the left cylinder is not firing properly.

I suspect the new-to-me Dyna III ignition.

I have it set according to the included procedure, though may have messed it up. Please help.

The bike will start but only runs off the right cylinder, and will die if any throttle is applied. Only runs on full choke. I know this is not deal, so I am not running it like that.

What baffles me is that I have confirmed there is spark on both plugs and the above items, though the cylinder is always cold (ie not firing) after every time I try to get her running...weird.

The inclosed directions mention that the left cylinder not firing may be due to a faulty left sensor...is this possible if the Dyna III is brand new? ever heard of this happening out of the box?

Any advice?

Thanks,

nick

[Garnet]

If you have stock coils they are wired in series. Both fire at the same time. If only one cylinder fires it is not the fault of the Dyna, it is further up the line.

Swap the plug wires from one side to the other to see if the fault follows. Then swap the plugs. Just because you can see a spark does not mean that it is strong enough to fire a compressed cylinder.

Also remember, most ignition problems are carb related and most carb problems are ignition related.

[Rohls]

Thanks. I checked compression and they are both 130 psi +. Both cylinders have a fat white spark. I will try swapping the plug wires. One of them is brand new (I just bought it) and the other pretty old. Maybe that will be the problem.

This may sound silly, but to verify, I wouldn't see a spark on a cylinder with a 'bad sensor' in the Dyna, right?

Thanks again,

[Deleted User 72]

Thanks. I checked compression and they are both 130 psi +. Both cylinders have a fat white spark. I will try swapping the plug wires. One of them is brand new (I just bought it) and the other pretty old. Maybe that will be the problem.

This may sound silly, but to verify, I wouldn't see a spark on a cylinder with a 'bad sensor' in the Dyna, right?

Thanks again,

Not familiar with the Dyna system, but I think both plugs should still spark every revolution. Only the cylinder with an explosive mixture will fire that revolution.

[Kurt in S.A.]

Correct, the system is still a wasted spark system. The thing that it adds is the ability to individually adjust the primary firing point for each cylinder independent of the other. In the stock system, the firing point is fixed for left and right as the cam rotates with the advance unit. If there are variations in the mechanical makeup of the system, or a bent camshaft tip, etc., one cylinder will fire slightly off of the proper point. This is where the double image can be seen in the timing window. But with the independent adjustment, the firing can be such that the S-marks will be right on top of each other, showing only one image.

Kurt in S.A.

[Garnet]

I too am not an expert on the Dyna, but there may be a chance that if one of the pick up coils is bad it will only create a spark once every cam rotation which is once every two crank rotaions, meaning it will only run on one cylinder.

How many wires come off the pick up? If there are only two, that means the p/u coils are wired is series and the above statement is false. If there are three or four wires from the pick up to the balck box the p/u coils are wired parallel and the first statment MAY be true.

[Garnet]

Before getting too deep, check some other obvoius things. Float level in the non-firing carb? Is the plug wet on the non-firing cylinder? Is the choke working correctly on that cylinder?

Back to ignition. Are the plugs new? There are faulty ones out of the box sometimes. Check the connections on the Dyna. Are all the wires pluged into their correct mate? Clean and test all the connectors. The current strength between the pick-up and black box is very low and a poor connection will cause no end of grief. That is the single most common fault with ALL aftermarket electronic ignitions. BAD CONNECTIONS.

[Rohls]

Thanks guys.

Yup, the carb was rebuilt a hot minute ago; currently it has a wet spark plug when I crank it a few times. The carb float is good; new float needle, and it shuts/opens properly. The choke seems to opens/close properly...I'll have to double check to be positive.

The sensor has two wires coming out I believe; one black and one red.

I've tried a couple plugs right out of the box and otherwise....

Hmmm....lemme swap the right/left plug wires and see what happens....the right one is brand new, and was replaced b/c of a poor resistance reading...though the resistance of the left wire is within spec, maybe something funny is going on...

thanks again.

[Rohls]

So the latest is the 'spark plug wire' swap didn't do anything. Still the left cylinder doesn't ignite properly. The bike will start and run poorly on the right cylinder. The left will fire intermittently, but that's it...

Maybe something in the carb is losing vacuum? How could I check something like this?

Confused in CA,

Nick

[Garnet]

Did you unplug the plug wires from the coils and swap them or did you just change the plug ends? In other words did you try the right coil on the left cylinder?