Technical 123 ignition
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Technical 123 ignition
There's been a fair amount of discussion of it on the forum, have a search, it makes for interesting reading and it seems some still prefer the old points and condenser, others love the 123, while others think the cheaper Acuspark system is the good middle option.
I took the middle option and regretted it. Wasted time & money hunting for a fault that I didn't suspect originated in a brand new Acuspark.
If you must go electronic, it's better to fork out for quality that's an actual upgrade.
Sachse is another option, much used in classic bikes, I haven't seen it dicussed here but they do one for the 500.
https://www.elektronik-sachse.de/sh...dg-3-10-for-fiat-500-marelli-distributer.html
If you must go electronic, it's better to fork out for quality that's an actual upgrade.
Sachse is another option, much used in classic bikes, I haven't seen it dicussed here but they do one for the 500.
https://www.elektronik-sachse.de/sh...dg-3-10-for-fiat-500-marelli-distributer.html
Well, after ensuring that the engine is at top dead center and the rotor is pointing to the spot on the distributor that would fire piston #1 , you’re supposed to rotate the distributor body clockwise until the green LED comes on, then keep going until it just goes out. Then rotate back counter clockwise until it just comes back on. That should be static timing of 10 degrees before top dead center. On mine, I checked that with a strobe but it looked to be off a bit - too advanced- so I had to rotate the distributor a few more degrees counter clockwise to get the timing marks close to 10 degrees BTDC at idle. When I revved it over 3000 rpm, it looked like it advanced to the specified 28 degrees BTDC, which is what the 123 unit is programmed to do. My only problem now (besides being unable to get the starter cable to stop breaking its clip) is setting idle speed and mixture. Seems like it wants to idle closer to 1000 rpms than the 700 or so that I thought was correct. Also my mixture screw seems ineffective to change how it runs! Good luck with yours. All of this is not too hard, just fiddly.
You need to get the idle speed really low...almost stalling, before adjustment of the mixture will make an obvious difference to the tickover. Then too far in and it probably will stall, too far out and it will falter; adjust it halfway between the extremes and it will be about right. Then adjust the idle screw if needed. It's not essential to have a really slow idle speed...I go for steadiness and smoothness.
Also if the mixture screw makes no difference at low idle speed there May be an air leak where the carbie bolts on
nathanrobo
Member
Could also be that the carb slow jet is the wrong size. This is a critical point as if the engine runs too 'clean' the engine will run too hot (big issue for a 500 engine)
the hobbler
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I realise that, as my 652cc engine is very well tuned, it will need slightly different jets in the carb (32/28 FZD)---I have had to go UP from a '38' slow running/idle jet to a '40'--definitely smoother. I also found that I had to go DOWN with the accelerator-pump jet from a '50' to a '45'. The reason for this change was that when the engine was cold the engine 'blipped' smoothly on a double-de-clutch down-shift, but as the engine warmed up, the down-shift 'blip' often became 'fluffy'---the squirt of fuel from the pump was making the mixture too rich. As John (a very fine precision engineer) with the lovely 'Italian colour' engine has found out, as he has a '595' engine, he can run 1 jet leaner. Nathan is correct---these engines tend to run hot, so you do not want to run them too 'clean' (lean)
nathanrobo
Member
I've two tuned engines that built earlier in the year (balanced crank, warm cam, ported and gas flow drilled head, 123 ignition - SS exhaust), both have 28IMB carbs which will need jetting.
My question is... Is there any way to set the carbs up properly, other than on the dyno? My understanding is that when the engine is under load it will behave differently and therefore a few runs on the rolling road will allow the correct selection of jets. Is there a different way?
the hobbler
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There are 2 ways to get the jetting correct on a non-standard engine---you either bugger about for ages, hoping to hit the correct specification, or you spend an hour of so on a dyno and get it right. The 28IMB is a bit small for a tuned 650cc engine, but suitably re-jetted will cope with a tuned 500, and possibly 595. If you are going to try and set it up yourself, go up 1 jet at a time and one jet size at a time---don't forget to log what jets you started with and what you have changed EVERY time you change a jet. Depending on the state of tune, you might find that 2 up on the main jet and 1 up on the low speed/idle jet will suffice. Having said that, if it was me, I would use the dyno. If the 2 engines are too the same spec, you will probably only have to put one engine on the dyno. I don't know if they are still available, but at one time you could buy 29LMB carbs (Proietti, in London used to sell them)
nathanrobo
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One of the engine's is a 595cc and that will be the first one I commission - So I think you've confirmed what I was thinking, which was RGS Motorsport (dyno).
The other is a 650 - I the 29LMB sounds interesting.
