What's the difference in CDI boxes?

[lingeringstin...]

I ordered a bog standard CDI for my Chinese Honda clone engine and then I discovered all manner of "racing" and adjustable CDI boxes offered in various places. Is there really any significant improvement to be had from a "racing" CDI box on one of these engines? I suspect snake oil.

[WD Forte]

Maybe maybe not
Most of those engines have a fixed pulser at a set attitude to TDC
lets say 10-20 degrees.
Its a compromise between retarded enough to start easily , but advanced enough to give it some oomph

IF the CDI box has smart firmware and/or electronics it may be able to trigger a spark a bit
earlier on the rise of the pulse and advance the timing a bit as revs rise. (More powah)
Some may be able to give a bigger better spark.
Without a scope and real world testing we cant know if and how effective they are

Ignitech provided a box used by many CDI engined CX owners which has a good reputation
Mind you the CX uses twin pulsers for each cylinder which helps to time it
and the Ignitech has a serial port and PC software
I've fitted a few and its not snake oil it was a definite improvement over the original 1970s system

The boxes on CMPO and Ebay?
Without the added sensors you'd find on modern engines , I suspect They may just contain a circuit that triggers a spark earlier on the rise of the pulser output waveform.
____________________
bikers smell of wee

[Teflon-Mike]

It' a retard to advance system in the CDi; ie; the static timing is something like 30 Deg Before TDC; the CDi then 'advances' the timing by reducing the lag before triggering the plug.
If you check CMSL part numbers, they seem to use the same CDi on all the benly motors, as well as the small singles..... and I'm pretty sure that they are all the same Pt No as the CB125TDC 'full-power', that has a advance curve that will let them rev-out to 14Krpm!
AFAICT the presumed 'performance' or 'racing' ones flogged on e-bay are for the most part the bog-stock Honda CDi, ad if they have a twiddle-able pot, my best guess is that most likely either adjusts the base timing 'lag' or pulls/pushes the advance lag a little up or down the rev range... after all, unlikely any-one will ever get any of the push rod or OHC engines, and all but the 309 cammed 125 twin to rev anywhere ear as high as that CDi will allow!
Given the spark is coming from a simple mag-winding; the 'performance' CDis cant be giving the spark any extra amps for a beefier spark, all they may do s offer an alternatve advance.. so on a tuned single? If they have a push/pull pot? Yeah.. they 'might' be marginally useful to match curve to tuning, but otherwise? Not going to do much on thier own.
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[lingeringstin...]

So if I was really lucky it might get another whole horsepower or something. I could probably do better by fitting dropped bars and wearing pointy shoes to reduce wind resistance.

[Kickstart]

Hiya

Suspect as standard the ignition is set up for very low octane fuel. Advance the timing a bit and you can probably game a tiny bit of power, at the risk of engine damage if you go too far / forget and put low octane fuel in it afterwards

All the best

Katy
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[lingeringstin...]

I suspect that's probably true. Meddling about with such a small engine to gain only a fraction more out of it would probably do more harm than it's worth. I'd have to increase the horsepower by something like 20% to get much difference out of an engine like this and it probably couldn't handle it even if I could find a way. Best to keep it simple I think.

[1198]

Depending which Chinese Honda clone engine it you may get a 150cc big bore kit off eBay for less than £50. My Huoniao had one, along with a bigger carb, cone air filter and gearing mod's.
Total cost lest than £100.

[kgm]

[pepperami]

[WD Forte]

Kraggem
I'll be as concise as I can so bear with

Years ago when a member of an owners club, CDI stator failure was a common woe
so the club bought an Ignitech to assess it.
I fitted it to another members bike, set up the software etc and off he went

I'd moved on to using the later transistor ignitioned engines from Eurosports by then
but he and others who fitted them gave them very positive reviews in terms of performance and reliabilty
I chatted to guy who's been using one for 7+ years a week or so ago and he said its still working AOK

It's more then the stator though.....

Early CXs sacrificed charge output to fit two CDI source coils to the stator
which gave a 170W output.
TI bikes like mine are charge only and have a 250W stator.
The CDI source coils were often the culprit in stator failure while the charge coils were fine but
it was still an engine out and spendy job.

the CDI boxes were generally good and reliable but nothing lasts forever and after 20+ years or so they could suddenly
fail with no warning.
the electronics inside were easily reworkable but digging them out of the potting compound was a feckin chore.
carrying a spare was advised.

At the back of the CDI engine case are the two advance coils.
these could quietly fail and the engine would still run but lose a bit of power at higher revs
they're NLA and tricky/fiddly little buggers to rewind if anyone wanted to try

Ignitechs only need the two pulsers inside the rear cover to work well and many owners also fitted the
later 250W G8 stator which is cheaper and also widely used on other bikes

Its not hard to convert a CDI lump to a TI one but only if you have the relevant parts to hand
so an Ignitech is often an easier option.

An Ignitech could fail of course but I haven't heard many tales of woe concerning them
I assume they're still in business and have a return policy?
the pulsers have been know to break down and are NLA new, but its rare AFAIK

Before you fitted the rear case I assume you checked the mech seal and cam chain and guides?
In my experience it's better to change the cam chain sooner than later when its trying to chew its way out
or flogged the tensioner to pieces.
____________________
bikers smell of wee