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lambretta advance and retard
Posted: Thu Jun 24, 2010 10:49 am
by cezeta
on my varitronic, when i strobe it the tippex mark sits steady at 21 degrees then as the revs increase the tippex mark fizzles out then returns clear again at high revs.
camlam say this is normal, is it happening on everyone else's varitronics or augusto ect
i would have thought that was showing the spark breaking down as it fizzled and disappeared, any other timing ive done has seen the tippex mark move smoothly and constantly from advance to retard.
anyone able to give me a lesson in whats going on?
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 11:30 am
by J1MS
Not too sure what's going on, but if you use the un-used spark at BDC (This is 180 degrees out from the correct ignition spark) you should be able to see the spark at bdc relative to the flywheel without it vanishing and returning, possibly to do with resistance being lower at bdc than Tdc.
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 11:35 am
by firekdp
The only reason I could see for that is, if the spark isn't steady between low and high revs the image you see wll be fainter. So the timing must be constantly moving around between those points for you not to get a clear image. Although I don't know whether that is normal for a varitronic.
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 12:51 pm
by paul213
can your strobe cope with the number of sparks per min , remember although your engine is only firing at tdc there is a spark at bdc
4000 rpm equals 8000 flashes per min , more than some cheap strobes can keep up with , also tried to time my varitronic with a snapon strobe that was even worse flashing all over the place
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 12:59 pm
by cezeta
yes its the varitronic strobe from cam lam.
are there any better methods of seeing whats going on?
also whats going on at 180 degrees? exhaust open? transfers pumping? so is the charge to the exhaust being wasted and a lean mix being pushed back into the barrel?
i need a plastic working model to see whats going on
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 1:09 pm
by cezeta
the second picture shows roughly the second firing point. so is the mixture being burned early and what is the expansion then forcing back into the barrel? burned gases?
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 1:28 pm
by wack 63
I had the same when I fitted mine 2-3 years ago.Marks were all over the place I even JPEG ed a video to Tino.I must say that it has been a faultless(so far!) system just the lights are crap at low speeds.I found on two engines, cast and TS1, that I had to down jet on the idle and alter needle as they ran far too rich and I wondered if the twin spark had anything to do with it. I timed them both at 25 deg @2000 rpm.
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 1:37 pm
by cezeta
More importantly, we moved over to a non wasted-spark ignition setup, using a custom-designed, fully-programmable twin CDI ignition unit by Ignitech with programmable parameters for ignition timing; power-valve control; electronic power-jet control and throttle position system (TPS.) This is a twin ignition coil system that does away with the dreaded 'wasted spark' system, enabling each cylinder’s firing event to be timed independently of the other; freeing-up ignition timing options beyond the stock Yamaha 180 degree timing layout; making possible 90 degree crank firing layouts.
so why is it the dreaded wasted spark?
im not dis'ing the varitronic just trying to understand it
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 3:45 pm
by cezeta
Re: lambretta advance and retard
Posted: Thu Jun 24, 2010 5:10 pm
by J1MS
Maybe Tino designed the Variatronic with the twin Targa in mind