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SU jet centering

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Nelson

Nelson

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I am having a bear of a time getting my jets centered. With the locking nut very loose I can get the piston to fall freely and land with a soft thud. As I slowly tighten the nut I keep dropping the piston after every very slight tightening and I get the thud until the nut begins to get tight at which time the piston no longer falls freely. If I use the lifting pin the piston lifts but will not fall without a slight push. The carbs are on the car and I would prefer to do the adjusting there but if all else fails I guess I'll have take them off and try it that way. I have watched John Swift's video and the adjustment looks so easy when he does it. Is there a trick to getting them locked in the proper position???
 
Without the "anvil" centering tool, patience is the only thing.
 
Could you clue me in on what the anvil tool is? I have a lathe and wonder if I could make one.
 
Absolutely!

Imagine a teeny-tiny hockey puck with two short pins in the center. One pin is the shank diameter of the needle shoulder (that is inserted into the piston), the other is the diameter of the jet orifice (less a thou or two for fit). replace the needle in the piston with the anvil, jet all the way at the top of the tube, make sure the anvil is in the jet orifice and tighten the locking nut.

The ones I have are aluminum, but about anything will work. Good luck and report back! :savewave:
 
Doc - you wouldn't have a pic of this beast would you? Where did you get it? I bought a jet centering tool..(looks like a punch) it doesn't seem to fit HS2's
Thnks
 
Hmmm, take tops of of carbs the part we shine with the piston in it.

Leave piston in the seat, Kind of wiggle is about as you tighten the seat.

Good job, all done. seat centered. replace top with piston in it. test.
 
I tried that but when I replaced the domes and tightened the screws the piston hung up. I'm going to make my own version of the Moss tool. It will fit snugly through the dome and then I'll have it centered with the dome in place. It is a good use for my lathe.
 
I think what happens is that, after being tightened a few times, the parts take a set. Then, you can get everything centered perfectly when the jet is loose, but when you tighten it, bumps fall into grooves and everything shifts. To get around this, loosen the jet assembly, move things around, and then slowly--really slowly--tighten it as you lift the piston and drop it. If the needle starts to bind, loosen the nut and move things around again. Eventually, with a little luck, you'll get things so you can tighten it without the jet moving. It's a real pain, but it can be done.

If you want to try the anvil, at least one is included in the set of SU tuning tools that comes in a blue wallet--I don't know who makes them. You can see one here. There might be a couple of different sizes, though, so you might have to get a specific one.
 
Rotate the jet inside the nut, most times centering the jet by just loosening the nut lets it go right back in the same spot time after time.
Turn it by hand 90* or so and try it again.
Patience for sure but then again, I have a jet centering tool :wink:
But I used to do it the hard way.
 
Rotating sounds like a good idea. Tomorrow I'll machine my own tool and give the rotation a try along with the tool.
 
The tool comes with the SU carb tool, really the only reason to buy one fo these and it does not come separately, I got my toll kit form Gordon at the B Hive. It just as Doc stated, so if you have a lathe, then sure you could make yourself one. There are also two different styles of jet bearings, the ealrier one leave a fairly good gap arounf the jet bearing bore hole in the carb body, the later one fit the bore fairly snugly. The earlier ones can be a bear to center, what happen over time the flat area that snugs up against the carb body can get a burr on or be slightly salnted over time, Joe Curto recommended fix for this is the face that area on a lathe so it is flat and tru again, I've done that and it work, but what I do mostly since tons of scrap SU padrt lying around is get a later jet bearing and stick that in there.

Here's another thing I do, mechanics are always trying to fiquire out ways to save time, do the job just as good, and beat the clock as well, so when I rebuilding a set of carb, I leave the jet bearing and retianing nut in place when I clean and media clean a set of carb bodies, then I have a small flex hone the proper size to hine the ID of the jet bearing, it's a huge time saver when rebuilding SU carbs.
 
Again, I am impressed Hap. Would not have thought of that. Think my rear carb needs that trick.
 
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