Author Topic: What function does the CDI perform?  (Read 178 times)

Bob the B

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What function does the CDI perform?
« on: June 08, 2018, 03:09:01 PM »
I'm slowly working through a poor running problem on my 2MA. The bike starts easily and revs freely to 10,000 revs in the garage but on the road it won't rev above about 7,000.

I'm pretty confident the carburation is OK and the power valves opens at about 7,000 revs.

I've checked through the electrics according to the workshop manual and all the resistance checks are in tolerance (except the pick up coil which measures 244 ohms compared with the manual spec of 94 - 140 ohms. But I've raised this issue before and I think later 2MA's have a higher resistance which isn't reflected in the manual. Others on this forum have confirmed their's also measure around ohms)

I intend to put the bike on a dyno but want to get more miles on the engine following a rebore and new crankshaft seals.

In the meantime I'm a bit lost for where to look next. I was wondering if the CDI might be the problem but realise I'm not quite sure what it does! My guess is that it provides a signal to the YPVS unit to command the power valve and advances the spark. if so are these separate functions? could the powervalve be activated but not the spark advance? Are there any checks on the CDI that can be done? Help!

Cheers Bob

teezer250

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Re: What function does the CDI perform?
« Reply #1 on: June 08, 2018, 03:57:26 PM »
I can't see it being the cdi if it revs to 10,000 in the garage.
It could be the ignition coil breaking down under load and when hot.
Testing in the garage is not really putting the coil under load and is not getting hot as it would on the road.
If it is the ignition coil,buy a genuine yamaha new one,not a cheap chinese copy as they are known to go faulty.