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I have an original paint Li150 S3. It has been bored out to 175 and has a SH/20 carb and clubman. It was on original points but the lights were as you imagine and it would never start from hot. I fitted an electronic kit during lockdown and all seemed ok at first. Ignition timing is a black art to me so I took it to a friend who has a lot off experience not only in Lambretta’s but historic racing engines in general. He knows what he’s doing is my point. Now, I fitted the stator very roughly so the bolts where in the middle of each slot. It ran ok, so I took it round to his. He got a strobe gun out and worked out the timing was 18 degrees which he was happy with. Great. However on its first run over 10 miles it was running very very weak off throttle. Gasping for fuel coming up to junctions after sitting at 50 odd for 15/20 minutes. I couldn’t really understand why the mixture would change, it was before the electronic. So I went up from a 45 pilot to a 50 and up from 106 to 108 on the main jet. Then it was four stroking all over the place but still gasping off throttle. Anyway, I noticed the air scoop was standard Li150 and had a tiny air inlet so I opened that up and removed the air filter and went down to a 48 pilot. That cleared up the four stroking but I checked the plug the other day after doing about 5 miles through mostly 30 mph zones and it’s whiter than a Morris Dancer. It’s also ruining incredibly hot. So, my question, finally, is the ignition timing out? Is that causing the apparent weakness?
I originally thought perhaps with a stronger spark it was burning more or all of the fuel in the chamber and that had caused weakness but I think that may be a bollocks theory.
Thanks in advance,
Steve

I think i'm only confirming what you think ……… the only thing that has changed is the stator/timing. I'd definitely check the timing.

Yes, thanks. Does 18 degrees seem like a safe timing these days? Assuming it is correct.

16/17 is the new "safe" but I wouldn't be too concerned at 18 with your set-up

Great, thanks Mick

You need to be certain that the TDC mark on the mag flange is actually the true TDC. A lot of bitza built engines have very inaccurate TDC marks. Assumption can be the mother of all screwups here.
Follow the advise in Sticky's manual on how to do this and confirm that the existing mark is "true". If it is, then use a degree wheel to measure what the stock stamped BTDC timing mark is.
If it proves not true, then restamp it, and again, using a degree wheel (or a Buzzwangle, if you wanna go posh ) re-stamp at 10, 15, 20 and 25 degrees BTDC on the mag-flange lip and time up the engine from there.
Ideally, this should be done after the mag-flange has been purposely centered on the engine casing first, as described in Sticky's 3rd edition book.

Quick postscript, the timing was indeed around 5 degrees out! Now at a healthy 17 degrees and running great. Trust your instincts! Thanks again,
Steve

Just completed the rebuild of a friends blown engine. TDC mark was 4 degrees out.
Tip:- The cutting disc on the Dremmel makes neat new timing marks.

Fast n Furious wrote:Just completed the rebuild of a friends blown engine. TDC mark was 4 degrees out.
Tip:- The cutting disc on the Dremmel makes neat new timing marks.

Agreed