I'm struggling to replace my OK running 009 distributor with an SVDA. Got it installed and tooka drive but was getting alot of popping on deceleration so I started fumbling with the mixture screws and now everything has gone off of the rails.
So I've put my old 009 back in, have it timed, but can get it to idle at all now.
So I'm starting all over.
I think most of my problem is that I have been turning the "mystery screw", in addition to the mixture screw, below thinking it was the idle, but now im thinking probably not.

Can you guys post up what screw this is and confirm that the screw slightly off the to the right is idle speed? What screw I have been turning?

Bonus for screw 1 and 2

THanks

Click to view attachment

Screw the idle mixture screw all the way in, then back out all four the same 1.5 turns to start with

The idle air bypass screws should also be the same on all four

http://www.redlineweber.com/html/Tech/idf_...nt_controls.htm

Does the svda have vacuum advance?
If no, shoot for total of 27-28 degrees at 2500-3000 rpms

It will be what it is at idle.
Same for the 009

So screws 1 and 2 are air bypass it seems. Is my idle speed screw label correct?
Know what the "Mystery screw" is?

I believe the "mystery screw" is an idle jet. It should be fully seated and there is no adjusting that. 1 and 3 are the by pass screws

yes the idle speed is labeled correctly

Looks to me like your mystery screw is actually your idle jet. Needs to be screwed in all the way but not over tightened. If you need to change idle jet size, then you unscrew it and pull it out, and it should have a rubber o-ring on it. It’s not an adjustment type of screw. Edit: Oops…Zambezi beat me to it.

Mystery screw == idle jet
Tighten it, leave it

Idle mixture, closest to the middle
Should have a spring on the shaft
Turn in all the way, turn out 1.5 turns to start

Open the link attached
Look at the picture

Use this process, in the doc

Open the link attached
Look at the picture

Use this process, in the doc

Lean Best Idle” Procedures

After confirming the linkage allows the throttle lever to seat against the Idle Speed Screw. Back off the Idle Speed Screw, then turn the screw in until it contacts the throttle lever and turn it in ½ turn. Turn in the Mixture Screw in until it “LIGHTLY” seats, then back it out 1 full turn. Loosen the 8mm wrench size nuts on the “air bleed” screws, turn in the air screws until it seats then tighten the nut.

a. Start the engine, it will run slow and like a tractor. As long as it will stay running, the idle speed is not important at this point.

b. First, turn in the mixture screw until the engine runs worse, then back out the screw ¼ turn at a time. The engine should start to smooth out. Continue to back the screw out ¼ turn at a time until the screw does nothing or runs worse. Then turn it back in to the point where it ran best. You want to tune the engine by sound. Adjust each mixture screw to the best, fastest and smoothest running point. Do this procedure with each mixture screw.

c. Now you may adjust the Idle Speed Screw. It should be sensitive and only require ¼ turn in or out to achieve the idle speed you like.

d. These carbs are commonly used in pairs, this makes the synchronization important, be sure to bring the high flowing carb down to the low flow carb. Then bring them both up to “proper” Idle speed. The Idle Speed Screws are not opened more than ½ turn in.

e. After synchronizing multiple carbs, reconfirm steps b. c. & d.

Thanks everyone, that helps. I found the "Lean Best Idle Procedure" above when googling and followed it, but fouled things up turning the wrong screws.
I'll hit it again in the morning and post back. It will come together. Once thats sorted, I'm going to toss the 009 and go from there.

Great idea.
Changing too many things at once makes troubleshooting very hard.

Be patient. Every adj requires a bit of time to settle in/take effect.

Wait...there's an easy way...?

take your time and research, research and do it again. Carbs are very simple contraptions, but need to be dialed in a certain way. There is tons of information available including at least several books on the Weber carbs. In my experience a lower fuel pressure is better than a higher pressure.

I’m only guessing
But the popping you experienced prior to touching the carbs could have been from timing. And may not have been from carbs

Set them to baseline
It will take a couple of hours the very first time
You’ll learn a lot and it will help down the road

Some progress here. Its now running again and idling somewhat smoothly. Timing seems to be ok at at 28 degrees at 3200 RPM. I put the snail in both carbs with the linkage disconnected and they are matching now as well.
The only issue is when revving the engine, the #2 stack pops pretty bad and I can see a spark down in it when looking over it. Thinking this is too lean from what I have read, i backed the mixture screw out to make it more rich and it doesnt help, still pops. Too much makes the engine bog.
Both mixture screws for #1 and #2 are almost all the way in. I tried backing both out and various intervals and it just runs worse at idle.

Any ideas here?

Intake valve leaking?

Popping can also be caused by clogged or dirty jets. Have you recently cleaned your idle jets or taken out the main jet stack, disassembled , and cleaned it? If not, it might be worth a try…..maybe just do #2 to start with to see if it makes a difference.

Maybe my linkage is off at the higher throttle position. GOing to recheck that.

Easy. Warmed up. Raise the idle a bit with one, 1, idle speed adjustment screw. 1.2k or so. The other one should now be off the stop. Dr’s side is easier. The linkage is now in a natural state and not artificially balanced by the ISASs. Measure the flow on the front 2 Venturi then all 4. How much do the number values vary?

The mystery nut on the rod below the Weber plate (center line of the carb)? Pump jet (operates a diaphragm) adj nut.

A bit of a long shot suggestion. If you have screwed the air by pass screws all the way in, as suggested earlier in this thread, you probably need to use your air flow meter (snail) and fine tune your idle adjustments with the help of balancing the air flow with the help of these bypass adjustment screws.

I tend to agree,there are other factors to consider,as this is a carb tune you need to take into account your electrical ignition system and valve settings ? have they been checked and up to scratch ? otherwise you will be chasing your tail,start from the start before attempting carb setup .
Once you are happy and all the above is ok by all means pull the idle jets and clean ,check the result and see, you could also have a vacuum leak on that side of the motor if the other side is responding to the mixture screw adjustment ?,check the bolts anyway.
Something more to go on with and good luck,cheers.

What size "idle Jet" do you have? pull the mystery screw and check...and make sure your engine is at full operating temp before making any adjustment.

I'm sure the jet sizes are all good because the car has been running perfectly for years with this setup. I'm going to hit again tonight. Almost there just need to get the acceleration smoothed out.

I would start by pulling the jets and cleaning them.
Remove, blast with air, install.

Set crossbar linkage to only rest on one side at idle, screw the other one out.

Problem solved. Embarrassed to say that the plug wires into the distributor cap were in the wrong firing order. I dont know how/why I did that or how the car was even running to this point.
Just nee dial in the timing and I think she'll be OK for now.

She's idling good and I can take it around the block, but still have 1-2 pops on deceleration, but the occasional pop out of one the carbs. ??
I put the snail vacuum reader on all four stacks and noticed that 1,3,4 all read "6", but cylinder 2 reads "5". If I increase the idle speed on that side, it will bring up 1 with it, and be more out of sync...
What could cause this on to be lower than the one on the same side? A misadjusted valve? (Thats where I'm going to check next. )
Clogged jet?

First off….firing order is key….we would all raise a beer to you for that.

Second, get used to removing and cleaning jets on carbs.
It’s once or twice per year, and more frequently if racing

While using the Snail air flow meter, open the #2 air by-pass valve to bring the reading up tot 6.

On the 13th @914toy asked if you seated all of the air bypass screws. Did you do that?
If you did then use the adjust the air bypass on your low throat to match its twin.

When I ran center pull linkage, I synced with the linkage disconnected. You can make them work, but it is a PITA. It would take me hours. Invest in a CSP linkage and save yourself some frustration.

The saga continues. I bypass screws were all the way seated on 1 and 2. I loosened #2 to try to bring it up to sync with the stack on the same side, #1. I didnt help and the carb started whistleing, so I put it back all the way in. Changeing #1 had no effect either.
Its strange because it idles really well, takes off fine, but decelerating downhill and it pops and backfires.
Timing is on, valves were checked this morning. I cleaned idle get #2 as well. GOing to clean all of them next. Not sure where to go from here.
Its never backfired or popped up until I messed it up initially, so I know it can run right.

Do the air bypass screws work as expected on the other carb?

At this point I would swap the carbs from side to side to see if the problem moves with the carb or stays with the cylinder.

It's possible that you have an intake air leak and could explain no adjustability with air bypass.

^agree with this statement. If air bypass does nothing there is something wrong.


My carbs backfire on decel. Never bothered me. They were syncd, dead accurate. Linkage was sync link so I knew that was in sync too.

There is no load on decel. No need to worry if backfire occurs.

Back fire on decel can also be an exhaust gasket leaking

Did you have the exhaust off when this started
Usually a decel pop would be the gasket at the HE/to head

If those adjuster screws with the lock nut won’t bring a cylinder up…. I assume the whistle sound was the screw backed out to far

What if you brought the 3 other cylinders down to match the snail reading of 5. ?

Have you ever removed the large main jets and f-tubes to clean them during this saga?

Update. All appears well now. I revisited the air bypass screw without much luck. Then removed and cleaned main and idle jets. Took it around the block and was still backfiring and popping out of the passenger carb. Riched the mixture on that side and all was well after that. So not sure what the issue was but no more backfiring or popping as of last drive. Thanks everyone. Carburetors are no longer a mystery, just frustrating.

Loosening, opening, the ABPS LOWERS the flow that Venturi sees. The ABPS are lower on the carb than the Venturis. Fully, turning in, closing the offending screw increases the flow the Venturi ‘sees’. Don’t go all Hercules closing the screws. Gently seated. Close every one of them and re-meassure. Bring the highest ones down to match the lowest. Hense ‘BY PASS’ing the Venturi. Linkage disconnected.