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914World.com _ 914World Garage _ OMG! Carb manifolds are crap...
Posted by: McMark Feb 24 2010, 06:33 PM
No real surprise here. The manifolds for carbs are pretty crappy. I just spent WAY TOO LONG truing up a set with sandpaper on glass. I snapped a couple of pics to show just how not flat these things are. I would expect a huge vacuum leak if I had left these guys alone.
The area in the circle shows what hasn't been touched yet by the sandpaper. This is after a LOT of sanding. And it took a LOT more to get it completely out. This is a cheap, and relatively quick project that any carb owner can do with the engine in the car. All you need is a piece of thick glass, which most any house glass shop should be able to cut for you and round the edges, for cheap. Some sandpaper and tape and a sure, steady hand. Hold the manifolds flat against the glass and use long, even, slow strokes. You can also use a sharpie to check your work as you get closer to finishing. Draw on the surface, take a couple strokes, then see how much sharpie has been removed.
Attached image(s)
Posted by: Gint Feb 24 2010, 06:36 PM
BTDT Most of those cheap manifold bases for Weber carbs are crap out of the box.
Posted by: hwgunner Feb 24 2010, 06:38 PM
That sucks. I will have to pay attention to mine when i put them on.
Posted by: McMark Feb 24 2010, 06:40 PM
Best I can guess, is that the surfaces are machined at the factory while the metal is still REALLY hot and distorts when it cools.
Posted by: kg6dxn Feb 24 2010, 06:42 PM
Just TIG weld them to the head. They will seal great! 
Posted by: URY914 Feb 24 2010, 08:22 PM
I fitted a steel spacer to pull the base down to the head so it will seal. Have a look...
Posted by: Ferg Feb 24 2010, 08:34 PM
I fitted a steel spacer to pull the base down to the head so it will seal. Have a look...
That spacer looks heavy
Posted by: SirAndy Feb 24 2010, 08:34 PM
Another reason to use the thick FI spacers with the carb manifolds ...
Andy
Posted by: McMark Feb 24 2010, 08:39 PM
Just cause they're thick doesn't mean they seal better. Most of the thickness of the thick FI seal is plastic that doesn't really deform, so essentially it's just like a paper gasket. But the FI gaskets do keep heat out of the carbs, and I use them on carb installs. I only mean to point out that you can't expect the FI seal to solve this particular problem, cause it won't.
Posted by: shaggy Feb 24 2010, 09:19 PM
you could have someone build tig on them then have them milled. kinda a lot of work for 914 carb manifolds though...
-jim
Posted by: URY914 Feb 24 2010, 09:46 PM
Yes, the hard thick FI spacers are not meant as a seal. If you want a real seal you'll need to machine a grove and O-ring them.
Posted by: Eric_Shea Feb 24 2010, 10:14 PM
1350 lbs. 4 oz. Bummer... 
Posted by: URY914 Feb 24 2010, 10:18 PM
1350 lbs. 4 oz. Bummer...
Nope. It did it on my street car not the race car,
Posted by: burton73 Feb 24 2010, 10:19 PM
No real surprise here. The manifolds for carbs are pretty crappy. I just spent WAY TOO LONG truing up a set with sandpaper on glass. I snapped a couple of pics to show just how not flat these things are. I would expect a huge vacuum leak if I had left these guys alone.
The area in the circle shows what hasn't been touched yet by the sandpaper. This is after a LOT of sanding. And it took a LOT more to get it completely out. This is a cheap, and relatively quick project that any carb owner can do with the engine in the car. All you need is a piece of thick glass, which most any house glass shop should be able to cut for you and round the edges, for cheap. Some sandpaper and tape and a sure, steady hand. Hold the manifolds flat against the glass and use long, even, slow strokes. You can also use a sharpie to check your work as you get closer to finishing. Draw on the surface, take a couple strokes, then see how much sharpie has been removed.
Silicone Carbide I take it but what grit?
Bob
Posted by: Eric_Shea Feb 24 2010, 10:20 PM
Posted by: Mark Henry Feb 24 2010, 10:39 PM
If you think it's bad on that end don't look at the other end and the nice smooth transition from the carb bores
Posted by: yeahmag Feb 24 2010, 11:35 PM
I'm still a fan of nice, thick, fiber style carb gaskets...
Posted by: lotus_65 Feb 25 2010, 04:02 AM
good even contact should aid in heat sinking too...
another thing i see with my manifolds is the mold edges in the bore. should i ream/clearance them smooth?
Posted by: Vacca Rabite Feb 25 2010, 07:54 AM
I had to glass sand mine too. A lot. In order to get them to true up.
I thought that was all just part of the game? One look at the ones that I had, and there was no way they were sealing as is, w/o some sort of filling sealer, unless I smoothed them.
I used 320 grit sticky backed sand paper over window pane glass. Worked like a charm.
Zach
Posted by: vsg914 Feb 25 2010, 08:11 AM
Looks like someone been beating on your framing square. I've got two of those!!!!!!!
Posted by: '73-914kid Feb 25 2010, 08:18 AM
Huh, my CB Performance manfiolds were actually pretty nice. I had to do almost no final filing to get them perfectly flat...
I'm surprise that the factory will let those go out that uneven.
Posted by: ME733 Feb 25 2010, 09:00 AM
......AND some people wonder why It,s expensive to build a quality engine.The problem you have pointed out applies to the carburator top side also...THEN you should go in and port out/detail up the casting flash and extranious undulations cast into the manafold ports. THEN....CC all the port runners and get them equal.....M.M.
Posted by: SirAndy Feb 25 2010, 11:49 AM
I'm surprise that the factory will let those go out that uneven.
What factory? They're all aftermarket. Who knows who actually makes them ...
Thick FI spacers, a little bit of "magick goo" on both sides and voila, no leaks! Has worked for me in the past ...
Andy
Posted by: xperu Feb 25 2010, 12:32 PM
I'm surprise that the factory will let those go out that uneven.
What factory? They're all aftermarket. Who knows who actually makes them ...
Thick FI spacers, a little bit of "magick goo" on both sides and voila, no leaks! Has worked for me in the past ...
AndyI was told that they are made in China and Italy and to stay away from the Chinese; you can tell by the SR#, is this true?
Posted by: McMark Feb 25 2010, 01:06 PM
There's no numbers on these. They can all be fixed with a little work, so it's not really a reason to 'stay away'. You really should check any manifolds before installing them, regardless of the source.
Posted by: Jake Raby Feb 25 2010, 01:51 PM
Our common practice is to deck these on the belt sander before even thinking about installing them.
And then after the engine runs they generally need to be decked again after they stress relieve.
Posted by: McMark Feb 25 2010, 02:45 PM
Yup, after the first, I switched to the belt sander to take off the majority, then finished on glass.
Posted by: Dave_Darling Feb 25 2010, 02:56 PM
Talk about overkill. A flat surface and a paper gasket will seal more than well enough; there is no need for all the extra work for an O-ring IMHO.
--DD
Posted by: URY914 Feb 25 2010, 04:04 PM
Talk about overkill. A flat surface and a paper gasket will seal more than well enough; there is no need for all the extra work for an O-ring IMHO.
--DD
I should have changed my type to green. I wasn't really being serious about the O-rings....
Posted by: McMark Feb 25 2010, 04:14 PM
Boost.... 
Posted by: McMark Feb 25 2010, 04:14 PM
Boost....
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