28/36 Weber Jetting

[Evan G]

gday fellas,

 

just bought this 28/36 weber carby from ebay for a measly $180 with a air cleaner and recently rebuilt :D. it was off a fiat 1600, so I'm guessing its still jetted for one?

 

primary says 195

secondary says 150

 

now the FAQ says for a 32/36 i should use

 

•130 mains

•170 air jets

•50 idle

 

its going a 4k thats been rebuilt. 60 thou pistons. torquey cam. ported head. balanced. (std exhaust)

 

i don't no much about webers so mains/ air jets/ idle I'm clueless. could anyone else shed some light on what jets they used/would use?

 

also Ive attached some photos of ports that I'm not sure what they do. i know theres a fuel return next to the fuel in. that i have to T before the fuel pump

 

thanks for your help

Edited January 8, 2011 by Evan G

[doecke55]

Hey mate, i recently put a 32 32 on my std 4k, i suggest getting a 2 inch system on it asap after you put your carb on, i got a custom job done for like 600 extractors and a high flow muffler (for the back pressure), with your carb i suggest slap her on and see how it runs, tune accordingly. Google stuff about tuning carbs there are some useful articles you can find, idle jets run up to about 2000- 2500 then the mains kick in and up around i think 5000t to 6000 the air correctors kick in. blowing shit out the exhaust, spluttery and when throttle is applied sluggish rev gain then its too rich. revvy but running hot, and sometimes a higher idle too lean, that is most dangerous can shag your engine quick smart, better to run slightly rich for safety sake. for working out what jets are what google for a blown image of your carbie with labels and you should be able to work out idle, mains and air correctors from that. it can take a while to tune but once you know its on its obvious how a little tuning can change an engines characteristics. primary i'm running 55 idle, 135 main and 165 air, secondary is quite similar, you will also need to play with your mixture screw.

hope this helps

Edited December 16, 2010 by doecke55

[KE20rollabus]

every engine is different, put it on a dyno with a wideband and do it propperly.

[Felix]

Hey Evan, got your PM. I'd look at what model weber it is, find the baseline jetting and start from there.

[Evan G]

on the base of the carby it says "28/36 DHSA2 1L"

[Evan G]

can anyone shed some light on the vacuum ports and where they go (pic 3)?

[altezzaclub]

Just idly reading google...

 

http://www.mirafiori.com/~corey/How-To/Carb.htm

 

Fiat 124 Spyder.. but don't use his link to the jetting page, it has a Google malware alert come up on my computer.

 

Vacuum-Operated Carburetors: The DHSA and ADHA

 

The DHSA and DHSA2

 

The DHSA was installed on the original 124's up to 1971. Difficult to find parts for and generally notorious for secondary vacuum leaks, the DHSA is not a popular upgrade nor is it recommended as a candidate for a rebuild.

 

The DHSA2 and later models were used from 1971 through 1973 and offered larger primary and secondary barrels. Difficult to find parts for and often hard to rebuild correctly, unless absolute originality is required, this carb should be removed and replaced with a later, mechanically-operated model.

 

Pros:

 

o Maintains originality.

 

Cons:

 

o Hard to find parts for, hard to rebuild, difficult to diagnose.

o Most examples of DHSA carbs have passed 30 years of hard, every day use.

 

Another page had this for the 124-

 

Carburetor: Vertical dual barrel downdraft Weber 28/36 DHSA2 with a vacuum operated secondary throttle. Cold starting provided by strangler valve choke.

 

Carburetor Data:

Primary Barrel mm Secondary Barrel mm

 

Main Venturi diameter 23 28

Main jet diameter 1.25 1.55

Idling speed jet diameter 0.50 0.70

Accelerator pump jet diameter

0.50 (single pump)

Main air jet diameter 1.95 1.50

Idle air jet diameter 1.60 0.70

Full power device:

air jet diameter 1.90 1.55

fuel jet diameter 1.10 1.10

mixture jet diameter 1.20 1.80

 

and this might teach you a lot about DD Webers- Also has the engine sizes of the 124s for different eyars.

 

http://files.meetup.com/533614/Artigue_FIAT_124_MM.pdf

Edited December 18, 2010 by altezzaclub

[Evan G]

interesting info there, thanks mr altezza

 

someone has to be running a 28/36 weber that can share some info

 

does anyone know if the 32/36 weber use the same vacuum ports? i got no clue what they hook up too

 

edit - that last link really helped me understand how they work! thanks champ

Edited December 18, 2010 by Evan G

[altezzaclub]

Always happy to be of service.... :wink:

 

Anyway, you could always block all the ports and get it running, then open each one at a time and see what vacuum it pulls and when. Straight manifold vac will be strong at idle and die as you open the throttle, and the ported vacuum will be about zero vac at idle but suck as you open the throttle before dying off.

 

Taz will know!

[Evan G]

ill go down and see my carby expert, he'll know where everything goes and what jets i should use.

 

i could tune it myself if my dam A/F gauge worked!. i think it has something to do with no setting the 1V base voltage for the gauge? ive lost my instruction. do you still have them mraltezza?

[altezzaclub]

I do- I thought it needs a 0.5volt calibration to set the 14.7 mark, and I've wondered a bit how to find a half volt source. I meant to ask my old boss what resistors I should put on a 1.5V battery to give a reliable 0.5V but haven't got around to it.

 

I'm getting finickity about the equality of the two carbs and making my own needles now, and I'm nervous about the accuracy of the figures it shows. Maybe I'm chasing phantoms because the 14.7 is atually 14.0 or 15.0.... anyway, I won't be touching it for a while as the daughter took it out last night and at 2am when she was driving various girls home someone threw up "out the window" at 100kph... as well as anyone drunk enough to spew can find a window... so this morning I found her sprinkling perfume inside the car. I didn't go near eough to check out the smell!

 

I can scan whatever bits of it Evan, if you have an idea of what you need.

[Evan G]

I do- I thought it needs a 0.5volt calibration to set the 14.7 mark, and I've wondered a bit how to find a half volt source. I meant to ask my old boss what resistors I should put on a 1.5V battery to give a reliable 0.5V but haven't got around to it.

 

I'm getting finickity about the equality of the two carbs and making my own needles now, and I'm nervous about the accuracy of the figures it shows. Maybe I'm chasing phantoms because the 14.7 is atually 14.0 or 15.0.... anyway, I won't be touching it for a while as the daughter took it out last night and at 2am when she was driving various girls home someone threw up "out the window" at 100kph... as well as anyone drunk enough to spew can find a window... so this morning I found her sprinkling perfume inside the car. I didn't go near eough to check out the smell!

 

I can scan whatever bits of it Evan, if you have an idea of what you need.

 

i had another member come over and we started talking about it and he said he used a 1V for calibration. i didnt calibrate anything hence not working correctly

 

could you pretty please with sugar on top scan the part where it tells you how to cali it?

 

thanks mate

[altezzaclub]

Yeah, it looks like you set the 0.00 mark using VR3 with 5V, then you need a 1V to set the span control VR2 to the top level 10.0, so the unit reads the full range of the EGO sensor's output, zero to 1.0V. It displays that as 11.8 to 20.6 to one, both of which I've seen on mine. They talk about motors cruising at constant throttle on 19:1 leaness, but I only see that on idle or over-run, and that is with the SUs set to a very lean idle.

 

I was looking for a 0.5V source to see if 14.7 was the reading for half a volt, on the assumption that 14.7 would be the mid-point of the curve, but on reflection that might not be a good assumption to make. Mine was setup before I got it, and I've never fiddled with it.

 

It would be good if you can get yours up and running correctly, the SUs are so variable it drives ne mad. Once its warmned up the readings show every gearchange as a quick drop down into lean, any over-run on a slight downhill or slowing down for an intersection dive down to 17 or 18, with a slightly jerky over-run feeling, and any squeeze of the throttle to go up a slight hill (Orange has NO flat land I've found!) goes into rich figures. Give it a quick boot and it just shows "R".

 

Its never still, although having the headlights on tends to stabilise it. I don't know if that's from a slight voltage drop in the "12V" supply or the effect of the alty loading up the motor. Overall its very hard to keep it between 14.0 and 15.0, but I've got no comparisons to know if that is normal... The SUs vary by the needle shape, the oil in the dashpot piston, the spring strength above the floating piston, and overall on the air flow the motor draws. You might find the Weber is far more constant with a fixed jet, either too rich or too lean right through.

FMD1.pdf

FMD2.pdf

FMD3.pdf

FMD4.pdf

[Evan G]

you legend! ill grab my gauge from work and potentiometer tomorrow and report back my findings

 

thanks a million!

[Evan G]

orite little update.

 

went down to my carby guy and he told me to slap it on first. O2 gauge was forked so i bought a autometer one for $130! .so today i slapped it on and allll good.

 

a couple of hick ups

 

- idle wont go down from 1500rpm, no vacuum leaks, idle screws out. nothing

 

mixtures

 

- when i take off from a standing start. it runs stoich in the prim.

 

- once moving at 60kph touch the gas on the pri and it goes real lean and stays at the same rpm till the sec kick in, then its rich till redline. come to think about it once moving. feathering the gas on the prim reads lean

 

bigger jets for the prims? and slightly smaller jets in the sec to get it stoich