Weber help! 48 IDAs on a 289

[Jeffrotech]

Need some help here... I'll start off by saying that I have rebuilt MANY carbs before (40+ ?), but this is my first time with Webers. I rebuilt a set of Weber 48 IDAs on a SBF because the car was sitting for about 3 years and the gas had turned to gunk and it wouldn't run.

Disassembled all 4 carbs, soaked all the parts in a carb cleaner bucket, repainted the bodies, and reasembled with new gasket/o-ring set. Everything is super clean, and each carb squirts like it should.

Stupidly, I upgraded the distributor w/ an Pertronix ignitor & replaced the plugs. I should have just got her running first, then the upgrades.

Now, she runs REAL hard - smokes the tires at will... but will not idle for crap. I pulled each plug wire at a time (cylinder balance), and only 4 out of 8 made a change. I'm going to try another set of plugs, but don't know if something might be screwed up on the carb side.

Anyone have experience with these???

[6'9"Witha69]

I played with a pair on a 2150 (?) VW. Good grief. IMO anytime you have more than 1 carb you are asking for trouble. I can't tell you how many guys I know HATE adjusting their 6 packs, dual quads, etc.
As for the petronix, are you getting full voltage to the module?
Is it grounded well?
What is the overall charging capacity and output of the electrical system?
Did you also replace the coil to a higher voltage and pulse unit?

It is surprising how picky these ignitions can be without proper voltage.

[b-man]

Have you sychronized the carbs using a Uni-Syn?

If the linkage isn't adjusted so that all 8 barrels are pulling the same vacuum at idle you'll never get it idling right.

I ran a pair of 48IDAs on my daily driver 1835cc VW over 30 years ago, they ran perfectly from idle to redline when the linkage was adjusted correctly. Adjusting the linkage took a little time, but you can't do it without the Uni-Syn. Once the linkage was set once it rarely needed readjusting.

Cheap or poorly-designed linkage is usually the culprit if you find yourself having nightmares keeping multiple carbs adjusted.

With IR (Individual Runner) carburetion like your four 48s on the 289 having perfect linkage adjustment is critical, all 8 barrels must start to open at exactly the same time.

Guys runng 3X2 or 2X4 setups have it much easier. With a 3X2 the center carb is the primary and two outer carbs don't even come into play until you're really into the throttle. No need to syncronize anything, just make sure the 2 outer secondary carbs (no idle circuits) have throttle blades that seal tightly so they don't mess up the idle. I never had to touch my Pontiac Tri-Power setup once during the 5 years and 30K miles I drove with it daily, it's as easy as setting a 2-barrel carb.

Dual-quads are no big deal either, the factory setups used the rear carb as the primary carb with progessive linkage. Setting them up with solid linkage is easy, you can eyeball the opening point on both carbs since they're used on either a dual-plane intake or a single plane dumping into a common plenum, unlike the Webers that are made for IR setups only.

[David Pozzi]

Agree with Bart above.
In addition you have to have a unisyn to syncronise the carbs. Usually you balance front carb with rear carb on each side, then adjust a turnbuckle to balance left bank with right bank.

If you see a difference in vac between each barrel of one carb, it indicates the throttle shaft is bent. They are very soft and bend easily. solution is to twist them back into balance. Insure your linkage pulls from the center, between front and rear carb, - not from the front or rear of the engine. You don't want the rear carb opened by twisting on the front of the front carb, the shafts can't take it. The proper made linkage will have balance screws in-between front and rear carbs, the linkage will pull against the adjuster screw of the other carb, NOT against the tension spring on the other side of the screw. Only use one idle speed screw on one carb, - the carb nearest to where the throttle cable attaches. That way, the linkage is always hanging on the arm that the cable attaches to and does not go out of sync when pulled off idle.

Do not tune idle screws until the intake manifold is HOT. Take the car for a drive of around 10 miles, then set idle screws, turn them all the same amount up or down a little at a time.

Once balanced, then use the idle mixture screws as indicators of mixture requirements. Screws should be 1.5 turns out from closed. If the engine idles better with them farther closed, it indicates the idle jetting is a bit rich. Then turn up idle speed and readjust idle mixture screws for best speed. If the engine runs better with screws farther out than 1.5 turns, then you need a larger idle jet. On your setup, you can do this all the way up to 4500 rpms, until the main circuit starts pulling fuel. Yes, you are on the idle circuit until then!

[Jeffrotech]

I'm a new-comer to this site, and let me say that this forum is probably the BEST one I have seen or participated in! The guys here are nothing but courteous and helpful.

Looks like I'll be buying a Uni-Syn. I was trying to do this without one (dunno why!). Before taking anything apart, I looked at all the linkages, and observed each throttle blade when pulled by the t-cable - all perfect. Once it was all back together, I did the same - and each of the 8 t-blades are in time when pulled by the cable. It's a pretty nice set-up with the linkages being pulled from the center.

I did also attempt to adjust the idle mixture screws by ear, with the motor good and hot - and adjusted each one the exact amount as the rest, starting from fully "in", then backing out 1/4 turn at a time. I really thought I could have gotten very close by this method - well, closed enough so she wouldn't stall when pulled into gear.

So, THANKS again for all the input - and I'll post on here again once she's all set (fingers crossed).

Jeff.

[b-man]

You're probably running 45mm venturies (sometimes called chokes) in those 48s. That's the biggest size offered for the 48IDA.

Hard to believe that four of those carbs flowing over 600 cfm each are just barely big enough for a 289, isn't it? IR manifolding changes all the rules when it comes to carburetor cfm requirements.

When I was into the air-cooled VW scene there was nothing cooler than having a pair of 48s on your engine. When you opened up the decklid guys would freak out. Just one look at those monster carbs intimidated most of them into staying way from picking a street race against you.

I ran 37mm venturies on my street 1835 with home-ported stock 1600 heads, and later went to 42mm venturies for a race-only 1835 with welded and ported big-valve heads. A lot of the fast VW guys are running 58mm versions now.

Back in the mid-'60s the early 289 AC Cobras made the 48IDA carbs available here, so the VW guys jumped on them.

Good luck with the 289.

[Jeffrotech]

Hard to believe that four of those carbs flowing over 600 cfm each are just barely big enough for a 289, isn't it? IR manifolding changes all the rules when it comes to carburetor cfm requirements.

Back in the mid-'60s the early 289 AC Cobras made the 48IDA carbs available here...

Well, the 4 stack set-up is from Inglese... and I'm pretty confident in their size selection and set-up for the 289. It's got great throttle response and it pulls pretty damn hard, so I think they did get it right. Now it's my job to breathe the life back into it.

This one is just like the 289 Cobra - right down to the COBRA finned intake. Should work great once I'm done.

[David Pozzi]

Should be sweet on a 289!
The chokes have the diameter on them in raised letters. Look down the carb throat and you should be able to read the size. I run 45's on a 350, but 37 or 42 chokes are how they came from Weber.
I use the uni-syn with flat base and red plastic "pill" in it. I think Edelbrock has those. There is another one with silver body and rubber seal that sticks inside the carb throat, not sure how good that one is.
David
http://www.jegs.com/p/Edelbrock/Edelbrock-Uni-Syn/743621/10002/-1