Will this panel filter work?

[jonw]

I don't like running open mouthed carbs, although I'm not totally averse to the idea.

I rode to Davos with this same engine (in a different Lambretta, mind) with an MB panel filter. Despite the GT being a reed valve, every day mid afternoon, I'd have to stop and clean the filter as it was clogged up and really strangling the engine.

When I came back, I ditched the panel filter and replaced it with a Breathe Sweet. However, it was a Series 2 and I could do that. With a PHBH 30 and the GT manifold I have, the Breathe Sweet won't fit inside my Series 3 panels.

Anyway, that's the history of why I have arrived at this:

I have an S3 150 Special with GT186, 30PHBH and Breathesweet and have no issues of compressing the elbow against the panel but I am using the left hand 30mm manifold from Rich T.

[Storkfoot]

Good call. The left handed one didn't exist for the larger carbs when I got this GT

If the filter is problematic, I may buy the left manifold. Thanks for pointing that out.

[coaster]

Have you tried it with GP bellow rather than the Breath Sweet elbow? The airflow won't be as good but then as you said earlier, it's all about compromise.

[jonw]

Good call. The left handed one didn't exist for the larger carbs when I got this GT

If the filter is problematic, I may buy the left manifold. Thanks for pointing that out.

I couldn't avoid the elbow touching the panel badly with the short righthand manifold, I tried very short manifold rubbers but to no avail which is why I bought the lefthand manifold.

[Storkfoot]

Have you tried it with GP bellow rather than the Breath Sweet elbow? The airflow won't be as good but then as you said earlier, it's all about compromise.

This is such a lively fun engine, I'd be reluctant to do anything to suffocate it, Col.

Still waiting for DVLA to do their stuff so I can road test it.

[Storkfoot]

Finally, I have it road legal and have just done a quick road test, about 10 miles. It does suffocate it a bit in comparison with the breathe sweet filter. It's especially noticeable whilst accelerating, not so much when it is near WOT.

[Storkfoot]

Well, having put the scoot through it's paces with this filter, open and with the old MB filter that I stopped using on my old Series 2, I'm currently back with this:



It is an easier fit on a Series 3 as the panel supports it against the carb. However, the white stuff at the bottom (baking powder) was my not so scientific way of seeing how much of the filter was being pressed against the panel. As you can see, not a lot, so it is effectively running open. That said, it's stopping some of the stone chippings that may be heading the way of the bellmouth.

So why has he ditched the Hi Flow filter, I hear you say? I think this would work okay if it wasn't pressed and condensed so much against the panel. The more I ran it with this on, I realised it was just too restrictive. I put some holes in it but it didn't noticeably improve things.

For the time being then, I'm going to leave the MB filter on. I need to do some choke tests near wide open throttle just in case it is now too lean although gut feel tells me it isn't.

In the long run though, I'm going to get the manifold to fit the other way and try and get the Breathe Sweet to work again. From memory, I think it ran better with the Breathe sweet (when it had room on a Series 2) than it does open mouthed on this scoot, but quite close to the panel.

[Adam_Winstone]

I'm not really surprised that you've come back to the idea that the Breathe Sweet are less restrictive as this is exactly what I've found when trying different filter setups, with many of the concertina paper type and Ram Air filters being too restrictive, especially the smaller ones. Indeed, some of the small Ram Air type that some dealers sell would restrict air-flow on a 125 Special! The larger Ram Air that I tried gave sufficient flow not to restrict an iron 175 but anything bigger was strangled by it. However, the Breathe Sweet has been suitable for use on all of the top ends that I've tried it on.

Sure, I get it that you need a certain amount of restriction in order to provide worthwhile filtration, however, you have to balance this against the area for air transfer and the volume of clean air available to the carb and the space for a big enough filter is limited on a Lambretta.

Adam

[Storkfoot]

Hmmh, you have me thinking, Adam. I could try my Breathe Sweet on my TS1 which currently has a RamAir through the panel

That said, I think I really need to just get out riding rather than tinkering

[Warkton Tornado No.1]

I'm not really surprised that you've come back to the idea that the Breathe Sweet are less restrictive as this is exactly what I've found when trying different filter setups, with many of the concertina paper type and Ram Air filters being too restrictive, especially the smaller ones. Indeed, some of the small Ram Air type that some dealers sell would restrict air-flow on a 125 Special! The larger Ram Air that I tried gave sufficient flow not to restrict an iron 175 but anything bigger was strangled by it. However, the Breathe Sweet has been suitable for use on all of the top ends that I've tried it on.

Sure, I get it that you need a certain amount of restriction in order to provide worthwhile filtration, however, you have to balance this against the area for air transfer and the volume of clean air available to the carb and the space for a big enough filter is limited on a Lambretta.

Adam

Well said Adam, but that’s not a derisory comment against the principle of panel filters or those that want to try them, although they may be unfortunate guinea pigs.

Don’t get me wrong as I’d love the things to work, but suspect the principle may be flawed.

It is not my intention to take this thread ‘off track’ & I confess to having no experience of the Breathe Sweet filter, but I have been trying to configure a useable 90° elbow type filter myself.

What amazes me is that some Forum users have had success using the generic Lambretta type convoluted elbows on tuned engines! If I mount one on my own Rapido (which only has a 30 mm Dell’Orto) it kills the engine even without a filter!

That leads me to believe that the actual area immediately upstream of the carb needs to not only be as unrestrictive as possible, but also act as a kind of plenum chamber with quite a large volume, as well as providing any twist & turns of changes in direction to be as gentle as can be.

I hope to be proved wrong, but I just can’t see that being achieved with the panel filters that have come to market, especially when the proximity of the panel to the carburettor is so tight.

[Storkfoot]

....... I think I really need to just get out riding rather than tinkering

Well, that was the plan, however, when I sat down and thought about it, £30 for a new manifold and some gaskets and a couple of hours work, isn't too much tinkering.

As you can see below, now that I have a GT manifold on the left side, my old Breathe Sweet bellows fit without even touching the inside of the panels and this is on a PHBH, a wide carb.




The proof, of course, is out on the road. I'm glad to say that reuniting the Breathe Sweet filter has brought my lively GT186 engine back to life

So, what have I learnt from this? It's reinforced what I already knew that carburettors on two strokes need to aspirate properly and sticking a bellmouth an inch from a panel isn't going to help that. Even more so, when you wrap a compressed filter around it Also, the Breathe Sweet appears to me to be a decent bit of kit.

[Adam_Winstone]

^... yep, they really are very good at allowing a motor to breath correctly, yet still filters out most of the crap that would quickly wear out an engine.

[Leotech]

I've used this in the past where space is at an optimum. It's sump guard foam for off road bikes. It's open cell so breathable.

If you soak it in specific air filter oil (messy) or light fork oil (less messy but less good) it takes quite a lot of dust out of the air before it passes into the motor.

It's very cheap, come in big pieces and squashes nicely between the panel and carb mouth.

[Paul_from_Thornbury]

Been through various iterations of filters and paper filter bell mouths with little success.

I also tried a breathe sweet which was compressed against panel no matter which way I pointed it.

The solution, not cheap, which I installed when rebuilding my RT195 kit with the new Meteor piston is the new MB flanged manifold (about £75). Doing all the measurements before comparing other manifolds on the market, this pulls the bell mouth of the carb a good 15-20 mm away from the inside of the panel.

Also, the rubber carb mounts used with this appear to be a lot more durable than carb rubbers which you change at least once a year at £15 a pop.

Installed with my breathe sweet now and comfortably sits away from the panel.