Any real benefit to a downdraught inlet manifold?

[storkfoot]

Recently rebuilt SR193. Changed carb from a PWK28 to a TM24 and have used a stepped rubber to fit on the old manifold.

However, whilst I haven't got the panels back from the painter yet, I'm pretty certain (pillock that i am ) that I've put the hole in the panel for the filter, in the wrong place. I say this as I measured the panel up on my other lammy which, yes you guessed it, has a Mugello downdraught manifold on and which pushes the filter up higher.

Anyway, thinking over resolving this by getting another Mugello downdraught inlet manifold. This got me thinking as to whether there was any meaningful performance benefit from these manifolds?

One other question, anyone know of a smaller downdraught manifold that would fit a TM24, PHBL 25 etc rather than the larger Mugello one? Just trying to avoid using the stepped rubber as it doesn't seem the best quality.

[CPH Lambretta]

I think MB do a good one.

[storkfoot]

Only one I can see on their site is:
http://lambrettaspares.com/spareparts/1 ... 0051k.html

but it's the wrong angle by the look of it, unfortunately. Cheers anyway

[Honeymonster]

Beedspeed do one for their TM 24 kit which is more downdraft, might be worth a call for the manifold alone?

[storkfoot]

Cheers, pal. I see what you mean, the pic of the TM shows it fitted on a downdraught, but they don't stock one according to their website

[J1MS]

Anyway, thinking over resolving this by getting another Mugello downdraught inlet manifold. This got me thinking as to whether there was any meaningful performance benefit from these manifold

As I see it the Lambretta Inlet design (Side draft) is deficient in the fact it enters from the side and because of the Lambretta's frame design, the inlet has a 90 degree bend in the manifold ... This slows the air speed of the incoming charge... The new down draft manifold reduces the angle that the incoming charge has to navigate to less of a degree so the same charge can travel faster... But still side draft... but now on a 30 degree down draft...

[storkfoot]

Out of interest, what do 2 stroke bikes have? Acknowledging that 2 stroke bikes were, in general, built to go fast, whereas scooters were not

[J1MS]

Out of interest, what do 2 stroke bikes have? Acknowledging that 2 stroke bikes were, in general, built to go fast, whereas scooters were not

Most Two stroke parallel twins have Two carbs with direct inlet trackts rear facing... some are on a downdraft with the carb itself being set at 30 degrees to the float bowl... Then there are V twins some having one forward facing carb and one rearwards...most are on a mild downdraft... but not all... More modern two strokes have well worked out inlet tracts and air box or/and filters which meter fuel/air much better than a Lambrettas sidedraft system...

[storkfoot]

Ta for the replies, lads. I'll get the panels back next week and then I'll have my suspicions confirmed as to whether I need a downdraught

[storkfoot]

Well the good news was that despite me putting the hole in the panel in the wrong place , it was still OK with the non-downdraught manifold.

However, as I mentioned in the first post, there is a problem looming with the Beedspeed stepped rubber. Whilst the TM24 is hardly a heavy carb, the rubber is already sagging in the middle of the rubber, and trying to detach itself from the manifold.

As Beedspeed were the only people I could find who did a stepped rubber to use a 24mm carb on a 28/30mm inlet manifold, and as it's clearly not up to the job, I think I'll have to try the MB Dell'orto 25 inlet manifold and one of their new rubbers.

Thanks again for all the replies