I make a new neck for the manifold. I cut a flange to match the carb, then I take square tubeing and weld on the flange, I weld the inside at a taper filling from the throttle bore out, put it on a jig in the lathe and bore it at a taper.
I cut the neck off the manifold and open up the bottom of the manifold. Then weld the new neck on filling the corners so I can cut a large radius. The larger the radius you can cut, the better.
If your rules would allow it, I would make a billet plate with the carb bore and bolt pattern on, machine the other side at a long taper, cut the bottom of the manifold out and weld this on. But of course it's not going to "appear stock"
Or you can simply grind the flange on the carb down, or build up the one on the manifold if they have to match and shoehorn it on. Bore the neck of the manifold and radius the corners. They won't flow near as well as either of the above methods but it may not matter depending on your head flwo and engine requirements. This is much easier than the other methods, and will support most of the small engines just fine.
The manifolds don't move as much air as the head will in stock form, and that TSX 66<67<666 etc carbs without any work will flow more than the manifold will in stock form but it doesn't take a lot of time to radius the corners off on the carb neck and in the runner. Weld up the back side of the corners to cut a larger internal radius. The larger radius you can cut the better. I fill the top corner of the runner where it turns to go into the head also, it's just a dead spot and one can put quite a bit of fill in without hurting anything, depending on the radius cut on the bottom. It's all about being able to get the signal from the cylinder transfered to the carb. Shape is worth more than size, velocity is a good thing.
I've got to make a half dozen flanges and necks here for guys anyday and do a bunch of manifold work. I can send you a few pictures if you're interested. If I get a chance I'll post a pic of mine. 715-790-1869
This post was edited by wi50 at 06:47:11 12/04/12 4 times.
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