Bell mouths

It's doable, but unless you got an engine that can turn lots of rpm and makinng triple the stock power or more, these things are really of no use... A good tapered inlet would do some good on a stronger engine that's making close to 10hp for an extra 1/4hp at best so the results one would feel on the street would be none to very neglidgeable, now if you're on a track with an accurate timer, you may see some shorter lap times...

tuning the carb is the important thing. if you can find one straight forward carb mod that makes the needle work better we all would be greatfull.

Yup... and all those engines turn some serious RPM to make their power so there's a lot of air velocity going into these carbs and the right bellmouth will make a small difference at power... Have you ever heard of that saying "every little bit counts"? This holds ture here... on the street you would barely notice the difference on a CG engine at 7 or 8 thousand rpm, but the same engine at 12000 rpm it may make a noticeable diference.
We used to do a mod on the CAG carbs which was far from a real bellmouth, but more of just tapering the opening and it was enough to gain a mph or 2 on top, but again, this engine spins at 13000 rpm and uses a 13mm carb.

I'm not saying it doesn't work, but just saying don't expect a big gain if you try it, it Will give some gain on top but even on a 40mph bike you might get it up to 40.5mph with this added into the mix. Anything that directs or smoothes out the airflow into an engine will give it some type of benefit and what you would most likely feel on the street would be to use a small carb like the NT,RT, or NT Speed, then add a 10" or longer tapered tube directly to the carb inlet, the taper would need to be somewhere close to 1.5 degrees so it can accelerate and cram in the air really well, but it also needs to be long enough to be effective at midrange, but unrestrictive enough to be invisible to the engine at higher rpm's since it will eventually reach a point where it can't cram in anymore and it becomes more of a hinderance at high rpm... but the same thing set up for high rpm would be really short like an inch or less with a similar taper angle and the inlet rolled so it can grab more air than just what's directly in front of it.
I'm not shutting down the idea completely because if you can find the right length and taper angle as well as rolling the inlet lip for a smoother inlet flow you could actually get a gain you would feel, the thing is most people at home don't have the tooling to do a nice even taper down a tube that's about a foot long and around 14mm inner dimeter.

Snorks I did this for cosmetic appeal only. Seen it before on other 2 strokes. Don't know if any perf gain perceptible no science. Good strong GT 5 tho. All stock except for the plumbing fixture on the carb.
http://motorbicycling.com/album.php?albumid=655&pictureid=7682

Remember the mechanical fuel injectors made by Enderle? The one with the calliope looking bell mouthed tubes sticking up?

They used tubes specifically tuned for the desired RPM range which gives a ram air effect somewhat like a tuned pipe. The length makes ALL the difference and even then, it only comes into play at high air velocity. This different tube lengths are for a broader RPM range
Mostly appearance on a typical chinadoll.

Yup... Love the old Enderle systems and you can buy the velocity stacks in a number of sizes depending on where you wanted the engine to make the best power, Those shorter ones shown in the pic are set up for good high rpm performance and then the longer ones help out on the bottom end, or more like around the midrange which is why they are unequal lengths, I've seen these set up like this with 4 shorter ones and 4 longer ones to broaden the power curve on certain engines and I've seen them all equal length like on the old Hilborn systems where all 8 of them are the same length or also unequal depending on application, it's just easier to run all 8 long tubes on the Hilborn systems since the runners all point straight up, but on the Enderle setup it's near impossible to run all 8 long velocity stacks because they will hit in the middle cylinders, I have seen one before where the stacks were trimmed and welded together in the middle tho.

This is actually a stainless steel cup I bought with hopes of turning it into a velocity stack for these carbs. Never got around to putting it together, but I can't see why it wouldn't help at least a tiny bit, plus it'd look cool.

Even if it makes no difference AT ALL, it's worth doing. Simply screams custom.

maniac57 said:

Even if it makes no difference AT ALL, it's worth doing. Simply screams custom.

Click to expand...

I agree... even if it does nothing and as long as it cant hinder performance I'd say go for it... it'll look cool... and maybe with a little ebay or amazon searching ya might find some stainless shot glasses that all one would need to do is cut out the bottom and find a way to attach...

Here's a little food for thought... you can do this with a wood lathe and make the mandrel out of hardwood, then ya just need to make up a similar roller jig to mount to the lathe which could be made from wood or metal... this is the same method they use for making brass instruments, cymbals, and all kinds of stuff and all you need is a wood lathe or a metal lathe and a few leverage tools, I've seen the forming tools made from wood, aluminum, or steel with a roller on the endnlike this guy's using...
https://m.youtube.com/?#/watch?v=bXu_16eZKnw

Yep it'll look good even if there isnt a performamce gain....

As we say out here in the sticks... " go fur it "