LCGB Forums

Ideally I would have liked to have run my 25mm carb through the airbox, but the MB manifold comes off the barrel at something like 45 degrees. I'm sure there must be a reason for doing this, but it doesn't make things any easier. I don't really want to have to use a remote filter if I can help it. So, what can be done short of buying a new manifold to put the carb in a better position?

I ran my 25mm PHBL thru a drilled air box using a mb manifold, the connection hose did sit at a bit of an angle but worked .

There are very good reasons to filter the air to a carburettor, though I admit I am a 'convert' principally because of the mess created otherwise.

IMO some makes of carburettor are much more filter friendly than others. In my experience, the most common PH range of carburettors have a tendency to flood on a filtered, hot Lambretta engine, yet, with adequate, well designed air boxes, work well as OEM equipment on, say, a Honda Foxeye.

I am not clever enough to know why some carburettors struggle to breath when others function well. Even the old VHB converted to two stroke with later PH parts will gasp for air if just a 40 + mm elbow is fitted with not even a filter, so I'm not just being prejudiced against the PH range, though it is a fact that I consider their slide design wrong for a two stroke.

If you can overcome any tendency to bog or flood, no matter what the choice of carburettor is, there is money to be saved by persevering. Less fuel gets wasted to atmosphere & less fuel should get used. Allied to the fact that the engine should last longer through lack of wear cannot be underestimated, ultimately improving reliability.

Yes, something odd there. I've run mb 25mm manifolds with phbl no problem through the air box.

Do you have a reed manifold?

No, just a standard 200 MB inlet manifold to suit the stud spacing on a RT195 kit. Strangely enough a mate is working on a scooter with the exact same set up and the manifold is just the same on that. Maybe it's to allow room for the bellows under the panel, I don't know?

Sounds like you have a down draft manifold. I believe that conventional wisdom on these is that they permit the air and petrol mix to enter the cylinder at a better angle and improve performance.

They will tilt the carburettor on its back slightly but that should not adversely effect the running of the carburettor.

I have used them before but never through an airbox.

Get in touch with mb,tell them what you've got and what you want to do.Im sure they will have seen it before and they will have an answer.

Storkfoot wrote:Sounds like you have a down draft manifold. I believe that conventional wisdom on these is that they permit the air and petrol mix to enter the cylinder at a better angle and improve performance.

They will tilt the carburettor on its back slightly but that should not adversely effect the running of the carburettor.

I have used them before but never through an airbox.

Ah, is that what they call it. It is tilted back slightly. I've no doubt it will run just fine. But I won't be running it through an airbox either by the look of it. I've decided to bite the bullet and try a remote filter instead. I didn't like the idea of it initially, as it's not something I've tried before. But, it ought to be fun.

I have used plenty of remote filters over the years. For ones on an elbow under the panels, Breath Sweet ones would be my recommendation. The do allow the carburettor to breath easily in my experience.

As it happens, I was rooting through a box today and found the one I have ready to go on a Mikuni TM24 on a 175cc. I got this from Camlam. I was hoping that the elbow would be smooth like the bigger Breath Sweet ones and not ribbed. I have since seen that bgm do another elbow that seems wider than this.

It could be this one, which is the one I've ordered. From Germany! No way of knowing when I might get as yet.

https://www.scooter-center.com/en/air-h ... M2570D50KT

I'll probably be picking your brains on remote filters, when I do eventually get it.

That is the one I was thinking of. Hopefully, it works well.