56 LD Performance Issue

[DeeOrr]

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.

[DeeOrr]

Hello again from DeeOrr – the newest Forum Member (?)

Addendum to my previous – and my very first – post:

I wanted to post pics of my '56 LD-B along with three (3) Wiring Diagrams that I created for LD owners.
Since I was unable to post any images, I chose to delete the following paragraph from my first post:

"Note: If I were to switch to a Varitronic, I would need to understand how to install it first. For one, the existing B&W diagrams being offered for LDs don’t show how the Varitronic color-coded wires connect to my existing color-coded wires. This fact alone confused me. Therefore, in the event that I end up switching, I’ve created my own diagrams - in color - in an effort to give me more confidence. But, I did this without having an actual unit in hand, so the wire colors as indicated – or my diagrams themselves – might not be 100% accurate."

------------------------------------

SHORT STORY LONG: I've created the following three COLOR WIRING DIAGRAMS to share with this Forum, which I will hopefully be able to up-load soon:

Color Diagram #1: LD-B Wiring Diagram as originally found in B&W on page 95 of the "Book Of The Lambretta." by R. H. Warring.

Color Diagram #2: Varitronic Wiring Diagram for LD-Bs showing the original connection from Electronic Ignition to 12v-Battery
where your existing red Magneto wire bypasses your (no longer needed) Rectifier and Fuse.

Color Diagram #3: Varitronic Wiring Diagram for LD-Bs showing an optional connection from Electronic Ignition to 12v-Battery.
This shows you how to bypass your existing red Magneto wire (essentially closing it off) and wire the Electronic Ignition directly to your 12v- battery using a new wire from Ignition to the Varitronic Regulator.

Anyway, as mentioned, I created the Varitronic Diagrams without having an actual unit in-hand, so wish me luck!

DeeOrr

[nickw]

Hi DeeOrr I unfortunately cannot answer your question but welcome to the forum. Not as busy as it was in pre social media days but still a few good peeps with the proper answers to Lambretta queries so hopefully someone will be along to help

[jbcollier]

What colour is the smoke? How does it smell? Acrid? You might have a bad crank seal. The fact it doesn't settle down to an idle means it is getting air from somewhere other than the carb; bad seals, loose head, loose exhaust/intake, etc.

Ignition spark testers flash when the plug fires properly. If the plug doesn't fire, then no flash, even though the points, condenser and coils all did their job. The plug might not fire because of insufficient voltage/too much resistance, or because it is shorted by too much fuel/oil. Spark plug gap is tiny but modern standards.

DO NOT SAND POINTS, EVER. You can clean them with plain, white paper and dress them with a points file. That's it.

Condensors are a common failure, even new out of the box.

Remove the fuel hose to the carb and check for flow and debris.

To your specific problem, it is VERY HARD to diagnose these sorts of issues over the phone. What would be obvious with a quick glance or poke about, takes forever to find using charades. A video showing the problem would be VERY helpful. Just put it on you-tube and post the link here.

All that said, my money is on a gearbox-side, oil seal.

[DeeOrr]

Thanks “jbcollier” for your input!

The issues you mentioned regarding possible leaks never occurred to me. I’ll check to see if I have any leakage in any of those locations, as best I can.

SMOKE
The smoke was blue-ish. And it did smell like gas mixed with oil? Now that I think about it, I’m almost sure it was unburned fuel. Also, my plug was wet upon each inspection. That’s why I soon turned my attention to my magneto – justified or not. Your use of the word “charades” describes my mechanical efforts perfectly!

SPARK TESTS
Oooops. It’s helpful to know that a spark tester’s efficacy also relies on a spark being generated at the plug gap! That explains a lot. And we all know how small that gap is! It doesn’t take much to clog it, good spark or bad spark. I’ll concentrate on actually measuring my magneto’s output. Hopefully it will reach a healthy 6v when I spin the flywheel with my (brand new) drill bit w/socket adaptor.

POINTS
I did clean the smooth surfaces with plain paper too, and the contacts are definitely good to go. I also checked the gap again, and again, and again. Hmmm.

FUEL
To direct my mind away from the fuel quality, I will install a small in-line fuel filter next week. My tank “appears to be clean” (famous last words) but I did find some very tiny particles of “something” in the carb screen on the first cleaning. Very fine particles: just small enough to clog the idling jet if by chance some of the particles had escaped! And…I just finished cleaning the carb a third time. Hello to charades, again.

If I can’t resolve my issues with the help being provided, then I will have to keep my day job, which I have to do anyway, seeing as how I now own a vintage Lambretta!

Thanks. I’ll post my progress as soon as I can find some.

DeeOrr
(Daily Driver: 2022 Sei Giorni)

[DeeOrr]

UPDATE - ‘56 LD-B 150 Running Issue

As suggested by jbcollier, I finally made a YouTube video (link below) that better defines my problem.

SOME RECENT CHANGES: A new intake manifold gasket, plus an in-line fuel filter were installed. I also re-attached the muffler using a thin glaze of High-Temp Gasket Material on the washer and threads.

FYI: Here are two more tests conducted BEFORE making my video:

1) SPARK PLUG OUT-OF-ENGINE TEST
This time I removed the spark plug and connected it to my in-line spark tester. I then spun the flywheel with a corded drill. (It’s a small drill with a top speed of only 2,000 RPMs.) But I could clearly observe a strong spark in the test-light as well as on the spark plug. In addition, the spark was visible and constant even at lower drill RPMs.

2) MULTIMETER TEST
I attached my multimeter to the magneto wire that feeds the HT coil. I spun the flywheel again with my drill. Although my magneto, HT coil, and spark plug seem to be working fine, I could only achieve 4 (+ -) volts when spinning the flywheel as fast as possible. (My flywheel was re-magnetized recently, so I think it should be OK too.)

QUESTION: How many RPMs does it actually take to generate 6 volts from a 6-volt magneto?

As you can see in my video, there are two scenarios being “suggested” by the occasional misfiring of the engine at low RPMs.

A) THE CARB IS FLOODING THE ENGINE – but only during brief “slightly above idle” RPMs, which then causes the spark plug to momentarily start misfiring.

B) THE SPARK PLUG STARTS MISFIRING – but only during brief “slightly above idle” RPMs, which then causes the engine to perform like it’s momentarily being flooded.

Carb adjustments: As you see in the video, I played around with the IDLE SPEED Screw and the IDLE MIXTURE Screw (positioned 1-1/2 turns out to begin) in attempts to settle it down. It idled best when the IDLE MIXTURE Screw was positioned at only 1/2 turn out! (My current Idle/Pilot Jet is 40. Too large?)

Additional suggestions will be greatly appreciated. By the way, if a faulty engine seal ends up being part of my problem, does this particular seal have a product number? I can’t seem to locate a potentially critical seal on any of the LD Engine Diagrams.

Thank you!
DeeOrr
PS: I desperately want my LD to be my new Daily Driver!

https://youtu.be/yy48TDnpjJg

If the above link does not work, simply search for "1956 Lambretta LD150 Mk2 Running Issue" and you can find my video that way.

[gerryjunior]

Remember an ld has a built in advance retard system on the flywheel, small springs and weights, make sure it’s working,

[DeeOrr]

Hi gerryjunior,

Thank you for reading my posts!

I have inspected the small weight/lever (?) on the inside of my magneto and it appears to be original and intact.
It hinges fine, and the spring returns the lever to its original "retracted" position without any hesitation.
Also, the cam lobe responds to the outward movement of the arm as designed.

CARBURETOR
In the meantime, I did order a smaller-sized IDLING JET for experimental purposes.
The jet that I have in my MA-19-B4 carb right now is a number 40; and according to some info I encountered
on the web, the jet needs to be smaller if I'm having to position my Idle Mixture Screw at only 1/2 turns out!

Anyway, my mission continues. I really do want to get my LD running "good enough" to take me to work every day,
weather permitting, of course.

Updates forthcoming...

DeeOrr

[jbcollier]

The video shows an LD that is running pretty good actually. Can you drive it? Does it pull well?

[DeeOrr]

Hello jbcollier and all,

IN APPRECIATION
Thanks for the compliment “jbcollier”. The series of “Booms” as heard on my video are gone. It finally runs fairly well, and yes, it pulls in all gears. Well, first gear is extremely low, but once in second and then third, it finally pulls as expected for a 150cc! And she revs just fine in all gears. No more “Booms”.

The following is a detailed update.

As you can see on a previous post, forum member “gerryjunior” made a point of highlighting the importance of my flywheel’s FLYWEIGHT lever in relation to performance.

That one comment (and other suggestions by this forum) finally got me thinking all over again!

The initial inspection of my flywheel had me convinced that the small lever inside – the flyweight as I call it – rotated just fine. But on re-inspection, I did experience a very slight “resistance” when the lever was initially pushed toward rotation. And after I overcame that slight resistance with a tiny push, my flyweight rotated just fine. This initial resistance was so slight that I had completely ignored it. I believed that this minor resistance – evident even after cleaning my flyweight and surrounding components – was normal? Duuuhhhh…

SECOND MAGNETO INSPECTION
After my initial posts, I purchased a complete (obviously used) magneto off eBay for its internal parts: Coils, points, backing plate, etc. Out of curiosity (thanks to this forum) I inspected the eBay-purchased flywheel’s flyweight action too. I immediately noticed something different.

Unlike my original, the eBay-purchased flyweight never demonstrated any resistance at all when I began to rotate it from its resting position. So I removed the eBay magneto’s points cam, and its associated flyweight, and installed them in my LD. This gave me a much smoother operating flyweight – one that demonstrated no hesitation at all when touched and rotated against its spring as it rotated the points cam. Very interesting.

NOW THE GOOD NEWS
Those previous misfires – the series of “Booms” as demonstrated in my video – are gone for real! But my IDLE MIXTURE SCREW still wants to be turned completely in to achieve an idle. I’ve even tried different IDLE/PILOT jet sizes too, from as high as 42 down to 35. The smaller jets made the idle even worse at “any adjustment” of the idle mixture screw! Weird and confusing.

The final jetting combination that allows me to finally drive my LD around town: Starter-55, Atomizer-255, Main 75, Idle/Pilot 40. And the Idle Mixture screw still has to be turned all the way in! Oh well. I’ll take it! It idles fine, and runs like a bat out of, well, you get the picture.

Thanks to all. Second video forthcoming, hopefully.
DeeOrr

[gerryjunior]

Glad you got it sorted, the advance /retard system was great for its time, but their bound to give trouble at this age , same with carbs , their just worn out after so many years, would you consider fitting a modern carb , it will make life much easier, scooter surgery sell modern carbs to fit,

[rlpembridge]

Hello DeeOrr,

I experienced idling issues with my 1957 Ldb MkIII 150 for a considerable time, with the same original carburetor that you have. I, too, went through the process of cleaning, re-jetting, replacing gaskets, etc. on the basis that there was probably an air-leak. There was but I didn't discover it until after I had replaced the carb. with a new model.
The source of the leak was the mounting sleeve of the carb. body, where it fits over the inlet manifold.
There are four splits/slots in the carb. manifold that are compressed by the clamp ring. Over the course of (many) years, the act of the clamp ring repeatedly compressing the manifold sleeve (when mounting and dismounting the carb.), had distorted the shape.
Upon inspecting the open end of the inlet manifold (with the carb. dismounted and cold), I saw that the four splits/slots were variously too-wide apart and too-closely compressed. Evidently, the clamp ring was therefore no longer evenly closing the splits/slots and was leaving a gap which allowed additional air to be sucked into the engine, together with the already atomised fuel-air mixture.
I'm happy using the new carb. now and will get around to attempting to re-set the shape of the original carb. manifold sleeve at some future time.

On another matter you describe, I also suffered poor generation of electrical power for lighting. The original magneto unit (mine is Marelli; is yours same or Filso?), generates a maximum of 28 Watts of power and at low / idling rpm, this is reduced such that the lights were more of a barely visible, pulsing glimmer. Since 6V 25/25W bulbs are the only avialable option now (the machine was designed for 24/24W bulbs), slightly more power is required to achieve optimal illumination. The consequent low-wattage pulsing of power at idle causes bulbs to fail and this became a particular issue with the 3W festoon bulbs in the tail lamp (in an act of purest optimism I fitted an additional festoon as a stop-lamp).
I had the flywheel re-magnetised by Patch at Scooter Surgery in London but this did not resolve the problem and when I recently learned that the Ducati Stratos kit (converts from 4-pole 6V to 6-pole 12V power + electronic ignition), was available for the D / LD series, I jumped at it.
I am presently fitting the kit to my Ld and will re-post with results once completed.

In one of the previous post replies to you, JBC also suggested an oil leak into the crank case and asked about the colour of the exhaust smoke from your machine. This is worthy of serious consideration as the crankcase / gearbox oilseal assembly can fail. Last time I stripped my engine down I not only replaced the oilseal and the O-ring which fits over the shoulder at the gearbox side of the assembly (between oilseal plate and bearing), but I also tapped out the three fixing bolt holes (oilseal plate into engine casing), and re-fitted the assembly using slightly longer bolts, with a drop of thread-lock on each.

Best regards,
Richard

[DeeOrr]

Hi Richard,

CARB NOTES
I have a spare MA-19-B4 (in fairly pristine/cleaned condition) that I purchased on eBay, which had given me similar issues with its IDLE/MIX Screw when I test-installed it a while back. After reading your post, I just checked its 4 manifold-side slots. There are two larger slots and two smaller ones. The largest slots are approx. .75mm wide, and a credit card barely slides into those two. The other two are probably around .70mm wide or so, and a credit card has to be forced into the slots. Not too bad. Next month or so, I'll pull my original MA-19-B4 Carb and check its carb slots. Also, I'm going to re-test both carbs in the scoot - perhaps next month - with smaller (matching) Idle Jets again. Note to self: I may be the actual cause of some of my issues!

MAGNETO
I'm running the Marelli version of components too. My hope is to keep this baby bone stock, but if I have sparking issues while driving it to work, I may start switching out components. Hope I don't have to.

LIGHTING
I'll keep an eye on my bulbs too - front and back. FYI: I installed the aftermarket tail light that holds two Festoon bulbs, so I have two bulbs to worry about now. Although, my brake light works off my 6v battery, which means that one of the bulbs should perform with some consistency. The other (tail light bulb) will be monitored more closely. Also, to babysit my new 6v battery, I've installed a cut-off switch under the passenger saddle. Those LD-B specific batteries are not so easy to come by.

SMOKE
The good news is that once my engine warms up, the smoke is almost non existing. Or put it this way, I can't see any smoke when I arrive back home after a short test drive. My spark plug looks good too. It's dark chocolate with no oily mess. I do notice a small amount of oily "spooge" residue on my center stand; but it's not enough to worry about now. It's just something that I need to keep an eye on when I start putting on more mileage. Short test rides don't reveal the complete story.

I'm just glad to get it running good enough to ride. I'll worry about the fine tuning later on when I have more time. On this upcoming Easter Saturday (3-30-24) my LD-B 150 will be on display at a local car show - our yearly show entitled "Wheels Across The Pond", making reference to British and European Vehicles only - including motorcycles, etc. As long as my LD makes it to the show (only a few miles away from home) I'll be a HAPPY MAN!

Dee Orr