Trying to get an understanding on ignition systems for GT186...

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Adam_Winstone
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Wed Oct 09, 2019 11:46 pm

"I was hoping to get it to pull right through the rev range.", does it not do this now with your 24-16 range? It should do. If not, I'd start to question whether this is an ignition issue.

I'd not get too worried about the specific '19 dbtdc' suggestion as all/any recommendation is only ever a starting point... and you should find that the variable ignition advance actually betters a static 19 when wanting it to 'pull right through the rev range' as that is one of the biggest reasons to fit variable ignition. Indeed, I only fit variable when another factor (e.g. porting or pipe) is making it peaky. If all else is set correctly then your configuration should already pull through from tickover to top end revs.

I fear that you might be chasing your tail with ignition options, whilst the ignition is no longer the issue. Having myself spent endless sums buying ignition components that collect dust on my shelf, I'd consider taking your bike to Readspeed to have it dyno'ed, especially as the components that you're considering are from there. However, first thing I'd do is let Jerome dyno it as it is, giving you feedback and ideas. I've never had Jerome try to push unnecessary parts on me whilst on the dyno, indeed, he has been quite up-front about me not needing some of the components that I was quite prepared to buy! I have bought a number of variable ignitions that have a range far beyond what benefits my motors and I've often found that the variable ignitions with a fixed profile are best as they limit your ability to forever search for an 'improved' setting.

It would be a shame to chase your tail over a flat spot somewhere up the range, only to keep buying and testing components / adjustments for no gain. This is one of the reasons why I keep asking, what it isn't currently doing, what your concerns are and what do you want it to do? Your bike should be 'pulling right through the range' with what you already have.

If any of Jerome's products may offer benefit then the best way to determine what that is would be to get the bike up to him for a dyno session , during which he could actually try components and show you what does or does not work. Jerome doesn't mess about... he determines what your existing setup is like, where the problems are, then rectifies them. If it is an ignition issue, the dyno will show it. Likewise, a jetting issue, a fueling issue, a heat range issue (something as basic as plug grade or compression effect on combustion), and/or other factors will show themselves.

Good luck, whichever course you choose... but your current components list should allow your bike to pull beautifully through the range, if adjusted correctly and working in harmony.

Adam

Warkton Tornado No.1
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Thu Oct 10, 2019 11:31 am

Adam is quite correct, IMHO!

I think that you are tying yourself up in knots about the ignition.

'Programmed' ignitions are nothing new in two stroke engine optimisation, but that doesn't mean that they are essential @ this level. If I were you, I would seek advice as previously suggested & contact the manufacturer or CamLam. Did you read that Post that was mentioned previously here? It's all very well seeking opinion, & the fact that the manufacturer of the cylinder kit has responded, is good to see. However, the 'issue' here is the ignition.

My own opinion is that if the ignition is set @ a recommended DBTDC with figures stated by the manufacturer or agent, then you will have taken the best advice possible.

If that would still cause you to worry, then 'go back' to a fixed ignition. If you do that, you'll no doubt worry about what DBTDC to use. :D I think a variable ignition is very good for a performance engine & have used them for decades on track machines. That said, it was proven to me that they are not essential as the last time I went to Cadwell Park, only a few years ago, despite the results & hype that was made public, the fastest scooter on track was Ralpth Saxelby's with Ryan piloting it. He came from behind due to his oversight in not turning the fuel on! Despite the 'Red Mist' factor, it goes to show that the engine works really well, despite the technology being decades old. Given an extra lap to the race, he would have blitzed the Italians on those engines that are now available for sale for significantly more than the value of the scooter they are fitted to!

(For the record, the other significant thing about the race set up was that we removed the anti-dive from the front end, so that goes to show it is not all that some would have you believe.......)

Hughieboy
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Thu Oct 10, 2019 12:18 pm

Thank you both for your in depth explanations, I really appreciate you taking the time. Due to a bit of impatience on my part (coupled with an irrational habit of buying stuff for my scooter!) I called Readspeed before these replies. I spoke to someone there (not Jerome) who thought it would be the right thing to fit.... however, I really do need to get it dyno’d by an expert so I know exactly where I am.

I will fit the part now I have it, if nothing else it gives me a spare CDI and I’ll see what it does. However, I will get it booked in for a dyno session, preferably with Jerome as soon as time permits.

I’ll report back on the results once it’s fitted.

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Burnside
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Thu Oct 10, 2019 1:24 pm

Hughieboy wrote:
Wed Oct 09, 2019 8:56 pm
Adam_Winstone wrote:
Tue Oct 08, 2019 3:49 pm
What is it not doing now that you want it to do?
I was hoping to get it to pull right through the rev range. Unless I’m mistaken, the preferred timing set up is a static 19 degrees btdc to prevent it hitting its ceiling and sort of ‘four stroking’ at high revs. So by using the Hermes CDI it can be set at static timing (or there are two variable settings) that can be used without the need to set the timing high in the first place. I’m guessing that to get 19 degrees at above 5000 revs, say, I would need to be setting the initial timing at about 27 degrees btdc which seems very high. With the Hermes I could set it at 19 static, or switch it to 5 or 7 degrees advanced before 5000 rpm or 2 degrees below (17 static) if needed for any reason.

It seems like a good compromise to retain the Varitronic system but hopefully make it more suitable for the kit.

Or at least that’s how I read it....
Static timing for the GT kits is 17 degrees BTDC

Hughieboy
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Thu Oct 10, 2019 7:29 pm

Burnside wrote:
Thu Oct 10, 2019 1:24 pm
Hughieboy wrote:
Wed Oct 09, 2019 8:56 pm
Adam_Winstone wrote:
Tue Oct 08, 2019 3:49 pm
What is it not doing now that you want it to do?
I was hoping to get it to pull right through the rev range. Unless I’m mistaken, the preferred timing set up is a static 19 degrees btdc to prevent it hitting its ceiling and sort of ‘four stroking’ at high revs. So by using the Hermes CDI it can be set at static timing (or there are two variable settings) that can be used without the need to set the timing high in the first place. I’m guessing that to get 19 degrees at above 5000 revs, say, I would need to be setting the initial timing at about 27 degrees btdc which seems very high. With the Hermes I could set it at 19 static, or switch it to 5 or 7 degrees advanced before 5000 rpm or 2 degrees below (17 static) if needed for any reason.

It seems like a good compromise to retain the Varitronic system but hopefully make it more suitable for the kit.

Or at least that’s how I read it....
Static timing for the GT kits is 17 degrees BTDC
Is it?

I got this from the Lambretta-images GT set up page...

"All ignition systems must be reliable and timed accurately to 19 degrees BTDC (2mm BTDC with 58mm stroke and 107mm rod), electronic ignition is preferable. Barrel studs & threads must be in good condition. Gear selectors, clutch and chain must also be in good condition. Series 1 & 2 cranks with plain bush small-end bearings must not be used..."

Is there something else I should be looking at?

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Rich_T
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Thu Oct 10, 2019 8:27 pm

Static timing for GT kits is 17-19 degrees depending on pipe or box exhaust. I would strongly suggest you borrow a proven static electronic kit and see if that cures the issue immediately, I'd be surprised if it didn't

Hughieboy
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Thu Oct 10, 2019 9:11 pm

Thanks for the info... although borrowing/fitting another ignition system to try out might be easier said than done, I wouldn’t know who to ask. I’ve fitted the Hermes CDI and a quick fire up and strobe has shown the timing to be static now, however I haven’t had chance to set the timing and try it out. Hopefully I’ll get time tomorrow...

Hughieboy
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Sat Oct 12, 2019 3:59 pm

So.... just to report back on what’s happened.
I’ve been out on a test ride today and all seems well. I’ve set the timing at 17btdc bang on which was easier running static timing. It seems to rev up to around 6900-7000 now, maybe that should be higher but I’m not going to touch it now until I get chance to put it on a dyno as recommended.
Has it made a huge difference performance wise? Well, I don’t know if I’ve ‘cured’ anything specifically but the flattening off of power doesn’t seem so abrupt or apparent now and it feels more comfortable knowing the timing is not going to be overly advanced, that’s probably just my inexperience and over worrying.

But for now, I’m happier! Thanks for your input fellas :)

Adam_Winstone
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Sat Oct 12, 2019 5:15 pm

^... glad to hear that you're liking the change and that performance is more in keeping with what you were initially looking for at the start of this thread :)

Hughieboy
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Sun Oct 13, 2019 2:01 pm

Adam_Winstone wrote:
Sat Oct 12, 2019 5:15 pm
^... glad to hear that you're liking the change and that performance is more in keeping with what you were initially looking for at the start of this thread :)
Thanks Adam.... :)

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