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SU observations from a noob

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jvandyke

jvandyke

Luke Skywalker
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I've been playing with my HS2s (car as a Weber on it now).
During the winter I went through them, had both pistons moving well, jets centered, decently matched, one would sometimes stick when I pushed the piston all the way up. Took it apart to play. I put fluid in the dashpots for the first time, ATF as I read that was good to use.
I was very surprised how much resistance there was when replacing the damper rod/cap into the dashpot.
I was more surprised when I then lifted the piston with my finger, wow that's a lot of resistance. Pistons both fall back to the bottom but a lot slower. If I raise the piston all the way; now the OTHER piston doesn't want to fall back down. If I take out the damper rod it drops like a stone.
Is this normal? Does the piston not ever get all the way up under normal operation and therefore I don't need to worry about that "bench test"?
And: I put a tiny tool mark on a needle trying to extract it, is that wrecked now?

I need new springs, one hook broke off of one, other looks near to the same fate. Anyone have some spares?
 
I don't think they would ever go all the way up. But they do need to move freely. And yes there should be resistance. The more resistance, the more fuel the engine vacuum will pull through the jet. And even with dashpot oil, they should still "clunk" when let them go.
 
I would think that the engine vacuum would also cause them to get pulled down faster. When the butterflies close there is low pressure inside the carb, but normal pressure in the bell so it is forced down faster than with just the spring.
 
Look up university motors (John Twist) on Youtube. He has some really good videos out there on SU carbs and the pistons.
 
I watched John's videos several times. His piston test is with empty dashpots, mine fell with a solid clunk until I filled them, now they drift down slowly (maybe 2 seconds)but do still bottom out. All seems well except the tendancy to stick when all the way up. I didn't consider vacuum pulling them down as well as lifting them up though. Okay. The gross jets seem okay, float level looks good, 12 flats for starters...I feel like I'm almost ready to try them.
I have two sets of air cleaner cans, the originals have a fitting for vacuum line from rocker cover, the ones I got (better shape) don't. I plan on using the one with the fitting to see if I'm getting enough vacuum to keep the engine from leaking, if so, I'll add a fitting to the good set, if not, I might tap the intake somewhere for that line. I think I'm almost set besides springs, maybe John at University has some....they are close to me, although I heard a rumor that they might have to close shop. Better hurry.
 
get new dampner springs from Joe Curto, if you sure you have no stick with the piston and ID of the dashpot. Also make sure the vent hole in the dampner cap is not clogged.
 
Maybe overfilled dampers? Although it just gets pushed out if there's too much right? I emptied and refilled to about 1/2" below the top of the piston's "chimney" I took them apart to do this more precisely. They are both happy now...No sticky and they both fall at the same rate. Got to get some springs.

Now, float level. The stuff I read shows 1/8" like this
floatlevel.jpg

the inset in red is the way mine look, grose jets (which seem to work, I'll try them but will keep on eye on them).
BTW I have the Weber running really really well at the moment.
 
j, bend at the red spot. The idea is to ~just~ contact the needle at the 1/8" setting. Not to have the arm pushing the ball into the needle... you may want to hold it so the float hangs vertically when measuring instead of allowing the weight of the float to rest on the needle.
 
I just calculated MPG with the Weber, was low 30s last year, now it's 22, yikes! And that's after a full tune up and running really well (I thought). That stinks, no? Okay, SUs on the way.
 
You sure it isn't that your boot has got a bit heavier? :jester:
 
There is no doubt I'm giving it a work out but almost 10mpg, hmmmm.
 
The Weber has what's lovingly referred to as an "Accelerator Pump". Push the pedal and "extra" gas is squirted down th' rabbit hole. :smirk:

SU's have no such animal. Fiddlin' th' pedal with the engine not spinning does NOTHING but flap the throttle linkage about. No gas goes down the throats.
 
Another stupid question....where does the vacuum advance line hook up? I'm thinking of tapping one of the bosses on the intake balance tube as a source for vacuum for whatever...valve cover or vac adv.
 
So it seems SUs have ported vacuum for the distributor, small port. Weber is normal manifold I assume, where it comes off the bottom of the carb. So, unless the distributor has been modified to handle more vacuum, it has been advancing sooner/longer with the Weber? Good time to get a timing light with vacuum advance I think.
 
You need vacuum for your distributor, unless it's the early 23D4 with no vacuum advance. I doin't like to use vacumm for evacuating the crankcase pressures, the factory did it that way later on, but only because they were made to.
 
So I don't need to overly concern myself about the SU's ported vacuum vs. the Weber's normal manifold vacuum? My 1098 valve cover vents to the air cleaner (normally) now (with the Weber) it's going straight to the intake (air cleaner wasn't pulling enough). Without this it's the Valdez.
 
Bolted on the HS2s. Fired right up and ran really well, cold, no adjustments at all yet but good feeling to have the original 46 year old car, with it's original 46 year old engine now powered by it's original 46 year old carbs. I think I saw her smile. I blipped the throttle a couple times just to see the pistons rise and fall. Too cool.
Interestingly it sounds much much better. I always had a funny rattling sound that I chose to ignore as I was worried it was deep in the bowels of the motor. That noise is gone. Not that that means much but I'm pretty encouraged so far.
Let the tuning begin!
BTW I love the cable operated starter, can simply reach over and pull the cable to engage the starter which allows me to use one hand to hold the choke/throttle where I want it while cranking.
 
These little cars are not without their charm. Great to hear you didn't have any trauma with the changeout. You're better off with the SUs fer sure.

Enjoy!!
 
It's a long way from running down the road nice but so far so good. I have to figure out the choke cable (mixture adjustment cable sounds better) attachment method yet too.
 
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