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

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
Adam_Winstone
registered user
Posts: 1769
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP
Contact:

Wed Oct 02, 2019 10:05 pm

I can't comment on the SIP temp range but my experience of EGT use suggests that the temps vary massively from bike to bike so better to figure out what is a safe/normal temp for your engine, then watch for unexpected rises.

Warkton Tornado No.1
registered user
Posts: 87
Joined: Mon Oct 17, 2011 6:16 pm
Main scooter: Lambretta SX200
Contact:

Thu Oct 03, 2019 1:26 am

As this issue has been subject to discussion previously, have a look:

viewtopic.php?f=7&t=32861

There's some advice very relevant, but probably the best is to ask the Manufacturer or Agent.

Hughieboy
registered user
Posts: 60
Joined: Mon May 25, 2015 8:37 am
Main scooter: Lambretta Li S2 GT186
Location: The Shire
Contact:

Thu Oct 03, 2019 7:34 pm

Thank you, I'll see what I can find out/work out.

User avatar
Rich_T
Dealer
Posts: 532
Joined: Fri May 29, 2009 8:07 pm
Main scooter: Li Special
Location: Birmingham
Contact:

Thu Oct 03, 2019 10:32 pm

GT kits will definitely rev a lot higher than 6.5k and they will still rev with a TRS pipe which is fine. My reluctance with IDM variable ignitions is that they have no set trigger point. In engines with reasonably stable RPM's like paragliders it's fine, some use them on GT kits but I've personally had some issues where engines did not perform such as 4 stroking, and limited revs all of which pointed to jetting problems that couldn't be resolved with changing jets. In the end the ignition was changed and the problem immediately disappeared. In the last few years it's been a problem to get a reliable ignition system and GT's are a little more susceptible to ignition faults than other engines because of the proximity of the petals to the boost port. A couple of months ago I built a GT kit with an Indian ignition, I vowed never again! Time is precious and messing around swapping around parts was a total waste of it just like sitting at the side of the road (which will give time to ponder if bagging an ignition system for £100 all in was really worth it). The static Vape ignition from SIP is what I've been fitting or the RS125 conversion, but I appreciate this isn't for everyone. On a previous post I suggest you make a test run with the air filter removed, and to strobe the ignition though the rev range. did you do this?

Hughieboy
registered user
Posts: 60
Joined: Mon May 25, 2015 8:37 am
Main scooter: Lambretta Li S2 GT186
Location: The Shire
Contact:

Sun Oct 06, 2019 9:01 pm

Hi

Thanks for your reply and explanation.

I did try running it with no air filter (I’ve actually replaced it with an MB screw on gauze) and it didn’t really make any difference. Since then I have advanced the timing so that it is at approx 24 degrees btdc at 2000 revs and retards back to approx 16 at full throttle. It’s much better and after a short run it will rev to about 6800 revs, maybe a little more if I hang on to it.

This may be sufficient as I have no real desire to thrash the knackers off it and put undue stress in the engine elsewhere but from what you are saying, which I am starting to understand, I guess the way forward will be to replace the Varitronic with something less variable.

I will have a look at the ignitions you mention.

All the best,

Hugh.

Adam_Winstone
registered user
Posts: 1769
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP
Contact:

Mon Oct 07, 2019 7:39 pm

"24 degrees btdc at 2000 revs and retards back to approx 16 at full throttle", good / normal sort of setting for most road Lambrettas with variable ignitions. Keep an eye (and ear) on it for getting warm at low RPM and reject if you find that you need to. Otherwise, use it evaluate what you've got... most other variables cost more but don't really offer anything more.

Adam

Hughieboy
registered user
Posts: 60
Joined: Mon May 25, 2015 8:37 am
Main scooter: Lambretta Li S2 GT186
Location: The Shire
Contact:

Mon Oct 07, 2019 9:45 pm

Thanks Adam,

I’ve seen a thing that Readspeed do called a Hermes CDI that has four maps on it, designed for Varitronic/Casatronic etc.... one of the maps is static so you can effectively set static timing at 19 degrees or whatever whilst still using the Varitronic flywheel and stator..... I wonder if it’s worth a go and would suit the kit better?

https://www.readspeedscooters.com/produ ... -lamb.html

Hugh.

Adam_Winstone
registered user
Posts: 1769
Joined: Tue Jan 31, 2012 8:54 pm
Main scooter: Lambretta GP
Contact:

Tue Oct 08, 2019 3:49 pm

What is it not doing now that you want it to do?

psychedelicropcircle
registered user
Posts: 792
Joined: Fri Aug 06, 2010 2:03 pm
ebay user ID: 3808_hunter
Main scooter: Series 1 li150 1958
Location: north of hadrians wall
Contact:

Wed Oct 09, 2019 8:15 pm

Running a GT186 on a casatronic 60/110 28mm phbh Mb box pipe. Runs fine & fuel consumption is 12-14 MPL. Will be pulling it apart over the winter if I find anything untoward I’ll report back here,

Hughieboy
registered user
Posts: 60
Joined: Mon May 25, 2015 8:37 am
Main scooter: Lambretta Li S2 GT186
Location: The Shire
Contact:

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....

Post Reply Previous topicNext topic
  • Information
  • Who is online

    Users browsing this forum: No registered users and 3 guests