"Normal" Spitback?

[vegansydney]

Believe you me, if there were a suitable elbow/bellows 'off the shelf' for even a moderately sized carburettor.... such as 30 mm, I would have bought one.

Are the BGM 'Armadillo' air hoses not 'off the shelf'? I've been running one on a Mikuni flat slide with a wide neck airbox for close to 2 years on scooter that is ridden multiple times a week. I've been impressed enough to use another on my current build. They come in 4 sizes and fit a range of flat slide, D slides and round slides such as PWK, Polini, Mikuni and Dellorto -- including the SH2/22. Something for everyone.

[Warkton Tornado No.1]

It would be wonderfully convenient if the OEM bellows could cope with larger carburettors, let alone more efficient carburettors requiring a greater volume of air.

Truth is, no such luck! The 26 mm carburettor you have needs 40% more air even if it is only of the same efficiency as an SH22. If the bellows depicted are for the smaller size SH's then that makes the scenario even worse!

Believe you me, if there were a suitable elbow/bellows 'off the shelf' for even a moderately sized carburettor (coming from somebody that has run 39 mm venturis......) such as 30 mm, I would have bought one.

That is the only reason I have been compelled to resort to making my own which, in turn, has gained me some knowledge about filter manufacture & the inadequacy of certain carburettors leading to hot start problems when filtered.

What size is the spigot on your carburettor? That is, the part to which any bellows or elbow can be affixed? What distance is between it & the side panel? Is it difficult to get the carburettor closer to the engine, as is the ideal for two strokes? Do you have any objections to the inlet manifold being downdraught? It may be that I can suggest an available elbow that can be utilised.

I am aware of the belief that a modified OEM air filter box can be made to function, but I have my doubts that even they can function when a certain size of Venturi is reached. That size will be something less than 30 mm so it would be useful (& brave!) if the sellers of such devices put their b@lls on the line & guaranteed a definitive size.

Thanks for your help! Tbe spigot on the carb is 44 mm. Need to check gap to side panel tomorrow. Sorry don't really understand how I would move the carb inwards or what a downdraft setup would look like ?

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I checked and there seems to be space between carb and side panel. 4 to 5 cm I think.

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In general, the majority of larger carburettors have been persuaded to fit in the UK by using the CDC type downdraft manifold as originally manufactured for the VHB Dell'Ortos.

There must be many thousands of them that have been turned back to make them shorter, modified to fit A/V rubber connections etc.

In addition they offer the downdraft mentioned which IMO gives a more natural flow into the Lambretta piston port inlet.

However, I am aware of the trend to maintain the generic positioning of the OEM carburettor, presumably to be better able to utilise the standard air box positioning.

Believe you me, if there were a suitable elbow/bellows 'off the shelf' for even a moderately sized carburettor.... such as 30 mm, I would have bought one.

Are the BGM 'Armadillo' air hoses not 'off the shelf'? I've been running one on a Mikuni flat slide with a wide neck airbox for close to 2 years on scooter that is ridden multiple times a week. I've been impressed enough to use another on my current build. They come in 4 sizes and fit a range of flat slide, D slides and round slides such as PWK, Polini, Mikuni and Dellorto -- including the SH2/22. Something for everyone.

Taken literally my comments, you are correct. It is good that such a product exists & functions well on @ least some Lambrettas that have been modified.

It would be interesting to see how the Armadillo would cope with a larger capacity engine. I concluded that for the current set-up on my SX, the minimum CSA would equate to about 50 mm diameter. Obviously anything larger would be a bonus.

What I do remain doubtful about is the ability of the modified air box & frame hole to not stifle a large capacity, optimised engine on full chat.

In certain motorsports the air boxes are very cleverly designed so that they are not any form of major restriction. They offer volume in abundance, might be pressurised but also serve as a plenum.

Immediately upstream of the carburettor doesn't need to be incredibly smooth or flowing, but it does need to have significant size.

That's why I have adapted the silicone bends that are unequal. They increase in their CSA as they go upstream of the carburettor. Further upstream, there can be large diameter flexible pipe & filtration.

[tippo88]

I haven't changed anything on my carb, still waiting for an armadillo I ordered to arrive and try. However I've taken the side panels off to get some touch up painting done and with the panels off its much harder to start. Could it really be that removing the side panel makes enough difference to air flow to an open carb to affect starting?

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[Warkton Tornado No.1]

With the close proximity of the panel to the carburettor inlet, then there will be a tendency to run rich.

With the panel off, there will be a tendency to lean off.

IMHO the shorter the inlet manifold, the better. All the better if downdraught the consequences of both being more plenum/bellows/filter friendly....

[tippo88]

Latest update. The Armadillo elbow arrived. After fitting ( open no filter) she started first kick, took on a roughly 7 mile run, went fine maybe a little bit boggy. No petrol on the floorboards so I thought all was sorted.
Next day started first kick, rode for about 5 mins and stopped. Wouldn't start, would start with full throttle and chug at very low revs but couldn't rev at all. Pushed her home.
Next morning started first kick took on a 10 mins loop, stopped and same thing, wouldn't start. Pulled the plug and a bit of carbon as per photo which easy wiped off with finger.
Today took the Armadillo off. Started first kick, same 10 min loop. Stopped. Started again first kick.
So seems like even the Armadillo is restricting air flow enough to affect performance.
Am wondering now whether to try and retune the carb to work with the Armadillo or just leave it alone and live with the spitback.

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[Warkton Tornado No.1]

I am disappointed for you, but hope the new air hose will eventually contribute to reliability.

I must confess my aversion to round slide carburettors on two strokes, but plenty of you seem to like them, despite the fact that OEM Innocenti Dell.Ortos were not round slide after the 1950's

Do you have access to other carburettors, perhaps two stroke specific?

I think your carburettor, like a Dell'Orto PH type, is prone to flood with an air hose connected.....

[tippo88]

Thanks! What carb would you recommend? It's currently running an Indian SR 185 kit but if I am to invest in a new carb I would like to take into account that I might change to a different cylinder kit at some point in the future, probably something with a reed valve

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[Warkton Tornado No.1]

To clarify my opinions & experience, I have continuously owned Lambrettas since 1973, the majority which have been tuned. My history includes a fair amount of racing.

I mention the above as it has not been practicable to run to a dyno operator. Also, like many of my contemporaries, we learnt 'work-arounds' as in the case of the Dell"Orto VHB which only nowadays seems to have other slides than the 50 they all came equipped with!

Nowadays, I know how to fit a two-stroke atomiser to a VHB. Also, I know how to convert slides to 40 or 45.

I only say the above because it truly makes for a cracking, responsive carburettor (with it's flat guillotine type slide) & would have been a far better evolution than the PH range. Opinionated Me?

Anyway, even better than either of the above are the current two stroke specific Dell'Orto range VHBC''s etc. Sorry folks, but I don't think you'll find PH's being used on the track Lambrettas....

However, a PWK carburettor made under license from the originators Keihin is my current best choice for the road tunes.

The KOSO's, OKO's, STAGE6 etc are all good but should be checked over like ANY carburettor. Blue-printed if necessary. Information is available on t'internet.....

They work well with filters & have anti-flood. Easy & incredibly cheap to set up.

They work well, fuss-free across quite a range of capacities/states of tune. For example, a 30 mm venturi might be considered oversize for a 185 by other readers, but it would work well.

Conversely, a smaller Venturi would also work well & be just as happy on a 240 plus.

For your current engine, I'd look @ what best fits the spigot & orifice sizes of what you have then make a decision based on that.

Good Luck!

[ktmh5]

Latest update. The Armadillo elbow arrived. After fitting ( open no filter) she started first kick, took on a roughly 7 mile run, went fine maybe a little bit boggy. No petrol on the floorboards so I thought all was sorted.
Next day started first kick, rode for about 5 mins and stopped. Wouldn't start, would start with full throttle and chug at very low revs but couldn't rev at all. Pushed her home.
Next morning started first kick took on a 10 mins loop, stopped and same thing, wouldn't start. Pulled the plug and a bit of carbon as per photo which easy wiped off with finger.
Today took the Armadillo off. Started first kick, same 10 min loop. Stopped. Started again first kick.
So seems like even the Armadillo is restricting air flow enough to affect performance.
Am wondering now whether to try and retune the carb to work with the Armadillo or just leave it alone and live with the spitback.

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I cured this problem by using a Chiselspeed panel filter.

[tippo88]

Latest update. The Armadillo elbow arrived. After fitting ( open no filter) she started first kick, took on a roughly 7 mile run, went fine maybe a little bit boggy. No petrol on the floorboards so I thought all was sorted.
Next day started first kick, rode for about 5 mins and stopped. Wouldn't start, would start with full throttle and chug at very low revs but couldn't rev at all. Pushed her home.
Next morning started first kick took on a 10 mins loop, stopped and same thing, wouldn't start. Pulled the plug and a bit of carbon as per photo which easy wiped off with finger.
Today took the Armadillo off. Started first kick, same 10 min loop. Stopped. Started again first kick.
So seems like even the Armadillo is restricting air flow enough to affect performance.
Am wondering now whether to try and retune the carb to work with the Armadillo or just leave it alone and live with the spitback.

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I cured this problem by using a Chiselspeed panel filter.

Thanks might give that a try.

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