tripple weber jet sizes and adjustment

[willybowden]

idle jets are 45 F9, main jets are 125, air correctors are 170. still gotta check the chokes. Air screws were set in a pattern from front to back at 1 1/2 then 2 1/2. Carbs do say weber, bologna, brevedito? made in italy. gonna try posting pic if i can figure it out.

Edited March 30, 2010 by willybowden

[Babalouie]

Yeah i need to find a write up on the basic cettings for Dellorto's, got a new ZX dizzy and new wires so i'm ready to fire them up soon

Chris

There are decades-old charts that Weber and Dell put out that give you the starting point for your jetting, but years ago, a helpful Alfa Romeo enthusiast put it all into a spreadsheet, so all you have to do is plug in your values and it'll recommend settings.

I've attached it, and it's easy to use...just remember that it's set up for 4cyl Alfa Romeo engines and so you have to convert your Zed L28 to a theoretical 4cyl config. So a 2750cc stock L28 would convert into a 1833cc four.

idle jets are 45 F9, main jets are 125, air correctors are 170. still gotta check the chokes. Air screws were set in a pattern from front to back at 1 1/2 then 2 1/2. Carbs do say weber, bologna, brevedito? made in italy. gonna try posting pic if i can figure it out.

Ok, well those jet sizes sound ok for a 30-32mm choke size (which would also work just fine on your stock L28). Open up that attachment (I think you have to save it to desktop before unzipping) and plug in 1833cc and a power peak figure of 5500rpm (probably about right for a stock L28) and tune for Flexibility and you'll find it'll recommend exactly the jetting you got, plus a choke size of 31mm.

Your carbs look like the old ones like mine...there should be a serial number on the top plate somewhere, something along the lines of "40DCOE18K" What's it say? But assuming they are older carbs, it already sounds like your idle screw settings might be too rich. Try setting them at 1 turn from bottom, clean your plugs, and see if it'll fire up clean.

If that works, then to fine-tune the idle screws, here's what you do. With the engine idling and warm, start richening all the screws (turn anticlockwise) 1/4 turn. Give it 5-10secs for the idle to settle, and see if the idle speed goes up and smooths out or not compared to before. If it seems to get a bit rougher, then go back 1/4 turn clockwise back to the original setting of 1 turn. Now try leaning all the screws 1/4 turn (clockwise). Give it 5-10secs and see if the idle gets slightly faster and smoother.

And basically you keep doing that until you find a happy medium. As a guide, Weber says that if your idle jets are correctly sized (and yours are) then the ideal setting will be between three quarters of a turn, to one and a quarter turn from closed. (So straight out, your initial settings of one and a half and two and a half sounds too rich).

Give that a try for starters...if there is nothing else wrong, you should find that tweaking the idle screws 1/4 turn should make a noticeable difference. The idle won't jump 200rpm or anything dramatic like that but it will get noticeably smoother. If 1/4 turn on the screws makes no discernible difference, then that's a sign that there's another problem we got to look at (maybe ignition, etc or maybe another carb setting like idle speed).

If this does the trick, then the next step will be to synchronise all 3 carbs to the same idle speed/throttle position.

jetting.zip

Edited March 31, 2010 by Babalouie

[willybowden]

thanks guys. this has been very helpful. Cant find a good z man is SC anymore. I'm probably the last one left in spartanburg. will report back with findings asap.

[Babalouie]

Well as luck would have it, this weekend I found myself swapping out chokes in a Weber carb So here's what it looks like:

When you get the carb out and onto your bench, you'll see these "inserts" in the throats of the carbs. They're the aux venturis.

The aux venturis just slide in, and have a spring clip that clicks into place, so you just wiggle them out with your fingers. Once out, you can see the choke tube sitting underneath.

The chokes are a similarly loose fit and will just slide out...and here's what they look like. Factory chokes will have the size cast into the front edge, in this case they're 32s. On a 45DCOE there's a bolt underneath that holds in the chokes, but on a 40DCOE it just slides out.

...a better view of the choke and the aux venturi..

What I was doing was installing bigger 36mm chokes for more top end power. The new ones aren't cast, but are machined aluminium and are 36mm (which is the biggest you can fit into a 40DCOE)

As I've said before, the chokes and the jets should be seen as matched, so when the chokes are upsized, the main jets should be too. In this case, we're going from 125 to 140 mains, to stick with the rule of thumb that the jets should be 4 times the choke diameter.

Here I've fitted one of the 36mm chokes on the right. You can see that it's noticeably bigger than the 32mm one on the left.

There's no trick to it, just make sure the chokes are seated all the way home, and when you refit the aux venturi, you should feel it click into position. Just to be sure, have a look from the other end of the carb just to check that the chokes are seated.

Button it all back together and you're good to go

Edited April 3, 2010 by Babalouie

[willybowden]

well I finally got around to setting the screws at a little less than 1 turn. Car wouldnt hardly run. put them at a little less that 1 1/2 and seemed much better, BUT, the car still sounds like its missing on 1 cylinder. Pulled each wire and put a plug in it in a dark garage, and each one lit up nicely. Its acting like it still has a fouled plug. I pulled them and cleaned them with a wire brush, again. I do have an electronic distributor on it, just two wires going to the coil. Very frustrating!!! If I could ever get this thing to run right I'd be amazed. Should I run a compression check to make sure somethings not stuck? Any advice is greatly appreciated.

ps just figured out a couple of things. In my haste, must've crossed #3 and #6 plug wires. I know, pretty stupid. Anyway, believe the new plugs could be gas fouled already. Secondly, upon removing the top of carb #1, the paper gasket is deteriorated badly. Soooo, I suppose I'm gonna replace all the paper gaskets, then try a new set of plugs and try this all over again. Fun fun fun. thanks for putting up with me fellas. pss Where should I get the gaskets?

Edited April 5, 2010 by willybowden
more info

[Babalouie]

If the motor hasn't been run for a few years, it could be a heaps of things at play here. Checked the ignition timing yet?

As for gaskets, I found that the Weber UK distributor is pretty sharp on pricing, (especially now that the pound is in the toilet). I'm not sure if these are cheaper than USA prices tho: http://stores.shop.ebay.com.au/FAST-ROAD-CARS-LIMITED_Weber-Service-Kits-Gaskets_W0QQ_fsubZ3QQ_sidZ21855701QQ_trksidZp4634Q2ec0Q2em322

My mnemonic for remembering the plug wire order is "too young....too old...just right": 15 - 36 - 24

[willybowden]

Now I'm not to sure about the wires being crossed. Ive found 3 different books saying 3 different things!!! Gotta take a break before I lose it. Arent all the in line 6's wiring the same. Got a 79 sitting here, and I swear its different!!! HELP!!!

[Babalouie]

Well you got nothing to lose by trying 15-36-24 as a firing order (with #1 being the closest to the radiator)

Hang in there, you'll get it working soon I'm sure! Here's some motivation (my car and it's got the same carbs as you got):

Edited April 6, 2010 by Babalouie

[70 Cam Guy]

It is probably worth your time to verify your fuel pressure as well. Some fresh gas probably won't hurt.

I got my car running after sitting for years. There were some major cob webs but with patience and some stubbornness I've got it pretty well sorted. I don't have Weber's yet but I have driven cars with Weber's that run like mad. They are a fantastic carburetor when you get them tuned.

[willybowden]

thanks guys. love the video. wires were correct to start with, couldnt be that simple. I'm using an aftermarket electric fuel pump, Holley I belive, mounted in the engine bay. Tried a generic fuel pressure regulator once, but made no difference. Figured if it was pushing past the floats I'd see raw fuel dumping out. Cant remember which distributor i'm using, but i have 2 wires off the top of the module going to each side of the coil. also looks like there is a place on the side of the module for a clip of some kind. filled her up with high test before starting this venture. Running NGK BPR6ES plugs now gapped at 42 instead of 38, just to try something different. Car hadnt been cranked in maybe 6 months or so. Any other ideas? Thanks fellas.

[Babalouie]

So it's starting and running, but the current status is that it's a bit rough and maybe missing on 1 pot? Does it idle by itself, or does it need revving to stay alive?

Pull all the plugs and compare colour, just to eliminate any issues that might be only affecting one cylinder. Check if they are all the same colour, or if one is blacker, or if one carb's plugs are blacker. That'll narrow it down a bit more, if it's say a problem from just one carb, then we can take off the top plate and start looking checking float levels.

Pull all the main jets out again, and this time pull the jet off the end of the emulsion tube and look to see if there's garbage blocking some of them. Ditto the idle jets. If they're second hand carbs and an unknown quantity, you never know, it might be as simple as garbage stuck inside the carbs.

Distributor sounds like the usual E12-80 electronic upgrade from the 280ZX too.

[ChrisZ]

Clip of some kind ? sure sounds like a ZX dizzy, try to look at the mudule, do it say E12-80 or E12-90 ?

Back to the start.

Is your valves correctly adjusted.

Check that you have your timing right.

What coil are you running and are your BR by passed.

Re gap your plugs, to big a gap and weak spark is bad.

When you tried thar regulator, what preassure did you set it to.

If all above is okay, it's time to do what Babalouie say, start with the float level, dunno about weber but in Del's the fuel should be 27 millimeter below the top of the bowl.

Chris