McBob's new Mac big gun Twin 101B's

[mcbob]

A couple more questions regarding the Ryobi ignition (what is the part #?) ... I am still a neophyte at building motors so hopefully someone else will chime in where my understanding of the ignition system falls short. Just to be clear, you are using the Ryobi coil as a direct replacement for the Mc coil. Are you still using the factory points and condenser? I think I misinterpreted that you had found a replacement for points and condensers

Dan

I took the punt and tried the ryobi unit and for my application it works no more points or condenser only fresh air under the flywheel.

A while back there was a discussion on the ATOM modules and the use of the Yamaha module in lieu of points and condensers. I think Steve O made the point that it wouldn't work because the timing of the spark at higher RPM. There are a couple of replacements out there for the lower-revving motors, but nothing for the higher revving Macs. With the saw motors it seems like you are idling or a full throttle, what happens in the low-mid rpm ranges? What about changing the timing for alcohol? Would you use a stepped key in conjunction with a 5 deg flywheel or ????

Well whether it would work effectively in a Kart i'm not 100 percent certain as i don't have a test rig or for that matter a Kart but hey you could test one using a not so important engine and let us know what it's like in a Kart engine.

I'll get a few pic's and post them here today as i don't have a part number

Have a good fall season and happy cutting.

Dan[/quote]

[Rob Voska]

I don't know about the timing but I have plugged in a Yamaha module into a Mac coil and I got a good blue spark.

[allan savins]

Hi,
You will find the ignition advances up until about 2000rpm and then steadily reduces as the rpm increases. I forget how many degrees the ignition retards per 1000rpm...
Allan

[Rob Voska]

How many deg & what if the coil location was changed?

[mcbob]

Here's a few pic's of the Ryobi unit now the whipper snipper/ brushcutter comes in either curved shaft or straight shaft so have a look around the local rubbish tip or scrap metal dealer as thats were i get mine and so far i haen't had a crook one and in my case there free.





This is what they look like they must have made millions of them

[Dan Flanders]

Hey Bob-
Thanks a bunch for the pics. I did some digging around last night, but quality information about the CDI module's is pretty sparse to say the least. That said, I did come up with one decent reference from Walbro, which actually maps out the timing based on RPM. Take a look and see what you think.

Does anyone out there have a reference for what the timing should be at various RPM's for the MC91 and 101's? That would be a good starting point to see whether the modules will work or not.

Dan