MY NEW LAMBRETTA --- ‘56 LD-B 150 Mk2
OVERVIEW
My LD-B will dependably start on the second or third kick (+ –) with choke. It then seems to idle OK with the choke off. I can see it firing steadily at idle using my spark-test light, and I can slowly start revving the engine too. But the engine now suddenly starts misfiring while I’m carefully increasing the revs ever so slightly, and even when I let off the gas in an attempt to stop the misfiring. Check this out…
FLASHBACK
Before my first (and only) road test, the engine seemed to rev up just fine. I could rev it quickly in fact. And I did this several times. There was no hesitation at all. It sounded great. And the engine would promptly return to a nice idle speed as expected too. The timing felt right on, so I headed down our street. The good news? I was able to reach second gear with no problem. The engine performed as I hoped it would. The bad news? It soon began acting up. Misfiring quickly became normal, so driving it farther down the street became impossible.
BACK HOME
The engine currently fluctuates from making some “Putt, Putt, Putt, Putt, Putt” kinds of sounds at idle – and even a little above idle with a tiny bit more throttle. But then, with slightly more revving, it will suddenly transition into sounds that are more like “BOOM” – – “BOOM” – – “BOOM” – – “BOOM” – – “BOOM”, which prompts me to immediately take my hand off the throttle.
Please note the time lapses implied by the dashes between each intermittent, spark-induced BOOM.
PHASE ONE – THE CARB
I thought my carb might be the cause of my problem, even though I can clearly witness the steady firing at idle – and the dramatic misfiring above idle – with my test-light. And it could still have something to do with the carb. I’m just not sure. My Dellorto MA-19-B4 was taken apart and cleaned anyway. Twice, in fact. All orifices and jets are clean and clear. And yes, I almost overlooked the tiny “idling/pilot jet” hidden from view. (Jets: 55 starter / 72 main / 255 needle.) Also, I’m using fresh gas, pre-mixed with 3% Motul 710.
My current assumption: Even if an engine were being flooding, the spark being generated by the HT coil would remain consistent and predictably visible while employing an in-line spark tester. Correct?
PHASE TWO – THE SPARK
All changed-out parts that I tried are brand new. At each step, there was no difference in the engine’s behavior. And there was plenty of smoke being generated during the intermittent “BOOMS” even as I let off the throttle. It reached a point when I could not increase the RPMs hardly at all without causing it to intermittently start coughing and misfiring. Also, after the series of BOOMS, it takes forever to return to idle (4 + – seconds actually, which seemed like a long time to me).
I also adjusted the stator plate (with no benefit) in small clockwise increments from its original maximum counter-clockwise position. My magneto’s “advance arm” and its spring, etc. are intact and the arm does pivot as designed.
Other things I tried, one-at-a-time, with no benefit:
1. Changed out the plug wire and cap.
2. Changed out the spark plug – NGK B8HS gapped at .020”.
3. Removed and inspected the two stator coils and their windings, wires and connections.
4. Fine-sanded and then cleaned the like-new contact surfaces of the points.
5. Checked the points gap (.018”) and the opening time relating to advance and TDC marks.
6. Changed out the condenser. I even tried a second brand new condenser.
7. Changed out the HT coil.
8. Installed a single wire from my magneto’s “ignition socket” directly to the HT Coil to eliminate some unexpected switch interference. The interior of my switch looks clean and unmolested. Whenever I connected and then switched my lights on during the tests, my headlight and taillight would flicker in perfect sync with the dramatic misfiring.
PHASE THREE – THE FLYWHEEL
I also had my flywheel re-magnetized by Casa Lambretta North America. They utilized the same vintage equipment originally designed for Lambrettas. Unfortunately, this didn’t improve the performance either.
BOTTOM LINE:
If the OEM ignition-related parts were available, I would love to maintain a points-style ignition for the sake of model preservation. But for now, a Varitronic is starting to look good. Before I spend more money that my wife doesn’t have, I could use some advice.
If at all possible, please let me know how – or even if – I can solve my problem without going the electronic route? Thanks!
DeeOrr
New Lambretta enthusiast!
PS: I was unable to upload relevant photos...yet. Stay tuned.