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Author Topic: 1.23 2 bbl. carb-Watch this guy pull a rabbit outta that hat!  (Read 1319 times)

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Offline amc49

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You will love this one, an experiment that once again looks like will work solid as rock. Gotta go to hardware store tomorrow to cobble up screws to both block off vacuum ports and mount a choke plate to replace the bulky one used on a Motorcraft 2100. AMC 1.08 venturi one.

Carb lying around, I'll never use it again so I got really stupid. Wondering if I could bore it somehow to make it more useable on a 2.3. Was looking at 1.21. Here's the stupid part, I have no mill but can I carefully index the casting upside down on a $100 drill press I have to use a cheap Home Depot wood/metal holesaw to cut the bore bigger?

I bought a 1 3/16" Milwaukee cutter from Home Depot, already had a 1 1/8". Idea to hog out most of the meat then finer cut later to maybe stay reasonably true at final cut. Telling myself 'you are going to ruin this carburetor forever' of course.

I made sure top flat with cover off was dead flat with a fine file, made up a plate to go over bottom of carb for a c-clamp to put most force on plate so carb bottom not warped; it's gotta be at least a certain amount of tight there. The plate made same time as one I made for testing Focus stat housings for leak, so make it same part and two birds killed there. Set up and carefully piloted the holesaw several times over and over in the bottom angular change in carb bore, it is perfect to center off of too. Once satisfied (yeah, that I'm about to destroy this part) I used lots of lube from like 30% used motor oil with the rest old phase separated gasoline to cut, every thing has a use around my place. I found out real quick so much cutting going on there you have to act like egg under the hand pulling carriage down. The cutter cuts so much it chatters very easily. When done with that, tear it all down and go to the bigger 1 3/16" cutter and carefully set up again, this time you can tell the lesser cut, it's smoother. Then go to other bore and the same.

I am not going to disiilusion you, I didn't myself, the finished part at this point showed signs of cutter wandering sideways wildly from flex, the probable chattering I heard. In short, junk. I threw carb in a corner and went to other things, my mood being well you knew what was going to happen there.

Maybe 2 weeks later I'm farting around and thinking of it and why not? I chucked carb into vise and dug out a hone used for honing master cylinders. I ended up having to mount a rubber freeze plug (the expandable one) in bottom of bore to keep hone from snapping into the lower portion of carb, it could tear up the bore right at throttle plate and not wise. It also allowed me a setpoint to gently bump hone against in one direction, which if you've ever honed you know helps out the quality of the job, you need a stop to help you control really short stroking. I began to hone on one bore with the drive as straight as I could get it, the plug allowed me to flood the hole with honing lube as well. I had to stop and rebuild the hone once when stones began to fall off, they were loaded pretty good (why do they glue them with SILICONE??!! which simply allows the stones to slowly unhook in solvent). Yeah, I cursed people again.

End result? I did one and it seemed to clean up REALLY well and even certainly much more than I would have thought with that wildly moving cut. SURPRISE the second hole does the same and I'm kinda like wow........... . I then matched the two bores at top and bottom and to each other within like .0015" bore tolerance. The bores are absolute located within like.005" on the pre-existing machine work and angles top and bottom, or well within passing coreshift numbers. Measured when done I now have a 1.23 carb, had to go a bit over to recover some gouging there. But carb when held up bores look centered and actually better than the original casting which had slight coreshift from bottom angles to the top. It looks perfect as well when booster assembly is in place, the boosters are centered close enough I cannot tell any difference at all by eye. Wow again. The machined surface looks finely honed like an expensive $500 race two barrel would, I have no idea of the flow recovery angles coming off tail of venturi of a true 1.23 (356 cfm) carb, but I cannot see why this one won't work like gangbusters.

There are enough caveats in this I would say most will probably bobble up the carb attempting it. I am not saying I'm any better than the rest of you, luck fits in there somewhere. But I've done one off stuff like this before on a whim. Knowing when to stop is much of it.

FYI, any of you that have worked on inline 4 bikes, I have hand cut the 4 bore holes in a crankcase top to fit super big liners when I was stupid enough to not send case off at the same time the cylinders were pressed out and bigger ones installed. You generally do all that at once on a boring bar while tooling is setup. What an idiot.

I did the work with a dremel LOL, and when done the work ended up with bores I made being from .005"-008" clearance all the way around on all 4 holes. Incredible, I surprised myself on that one as well. I won't say that one was the easiest $250 I ever made, but I still made it. You'd laugh if you heard how I controlled all the grinding to not go too far. The method worked great though.

If you have the will and can think there is no stopping you.