Weber 28/36 Setup

Hi all, I have a Weber 28/36 for my car, along with manifold and K&N filter. Has anyone successfully used one of these on a 1275?

Looking at Vizards book, he chokes the carb down to 24-26 Primary and 25-27 Secondary, depending on engine spec. My carb currently has 26/27 choke tubes from the original Ford application in. I've tried to get some smaller chokes, but either no where has them or they are expensive as they are old stock.

What I need to know is, would 26 Pri and 27 Sec Chokes be ok for my engine? If so, what jetting would I need?

Unless anyone has some old choke tubes they want to sell me??

Engine Spec:

1330 Mspd engine
Phase 2 Mspd cam
Lightened flywheel
Standard 12G940 head (soon to be MG Metro (35.7mm inlets)
Megajolt

eurocarb are very helpful

another 28/36 owner hurray!

first of all go to http://www.southerncarbs.co.uk/ and give them a ring thats where I bought my chokes, and jets from and the guys there I found were very helpful.

I can only tell you what i know from running a 28/36 on my 998cc and that is that is was waaaay better than a single 1.5" SU and Twin HS2 (obviously my personal opinion but after tying all of them that is my conclusion). Felt more responsive, good economy, lovely sound when you have opened up both chokes.

with a 12g295 head, forged rockers, cooper freeflow RC40 puting out 61bhp and 61 lb/ft it was using

Primary Choke - 23mm
Primary Main - 125
idle - 45
air corrector - 185 (if not it was 180 or 190)

Secondary Choke - 24mm
Secondary Main - 130
idle - 45
air corrector - 185 (if not it was 180 or 190)

Pump jet 70
Emulsion tube F30
bleedback valve cannot remeber i don't think i changed it.

Best thing is to use the vizard chart to get an idea for bhp/secondary choke size and then either go 1mm or 2mm smaller for the primary. Southern carbs did a bit of a deal where I bought about 6 main jets for the price of 4 as when you go for an RR no one will have the parts so take a few sizes bigger and smaller with you. 70 is the biggest pump jet you can get so use it. Idles jets are not so crucial so i would have though 50 or 55 should be fine. Emulstion tubes are always as F30 as vizards sais. And as with the main jets get a few different air correctors, but on the whole Vizards guide of engine types to what jet you need is pretty accurate so use that as a starting figure and work either side.

A little thing to watch out for unless you have already fitted the manifold and carb is to make sure it does not foul on the exhaust manifold! i had this problem with my manifold which sits the carb 90 degrees to the line on the pistons. and depending on what air filter you use that it fits under the bonnet with a 45mm K&N it just fits under, though i had to counter sink the bolt/nuts for the filter so they did not protrude above the filter.

I hope this helps!

Edited by cap'n crunch, 02 November 2010 - 07:28 PM.

If you really MUST continue with this hopeless carb - get the largest chokes in that you can find!

If you really MUST continue with this hopeless carb - get the largest chokes in that you can find!

Roy, you keep saying this, but have you actually ever tried this carb?

If you have, what was the engine spec you fitted it to, and what were the choke sizes/jets you ran with? You sure it wasn't your setup that left you unimpressed? Or have you never actually tried this carb, and you are going on something that a friend of a friend's Mom's baby sitter's boyfriend once told you?

Show us proof and I might believe you! What were the difference in power figures between the 28/36 and the HIF44?

Also.... why get the biggest chokes possible? Vizard suggests 26/27 for a 1275 with semi-race cam and head, and as small as small as 24/26 for a standard 1275.... is there something you know that Vizard didn't?


DILLIGAF, don't suppose you remember what jets/chokes you ran on the MG Metro do you?

i never got on with a webber progressive when i switched to twin deli's my engine made much much more power

i never got on with a webber progressive when i switched to twin deli's my engine made much much more power

I'm not looking for all out power though. I'm looking for good economy and less flat spots than a HIF.... oh and not to mention a carb that doesn't keep changing the mixture depending how warm it is under the engine bay!!

the piston quarter of a inch down the bores

Hmm... sounds like my engine (not going to mention the name as I will be threatened with court action... but if you're observant I've already said above who's engine/cam it is). My piston's sit 60 thou down the bores - which is far from ideal. Would never buy an engine from the builders I bought this one from again!

Cheers for any info you can give re: chokes/jets - will all give me a rough idea what to go with!

Edited by ian2000t, 03 November 2010 - 11:07 PM.

Not really to be honest mate -I wouldn't have thought Vizard would use them on a 1275 race engine if they weren't up to it! And most of them come off 1500GT Ford's, so would imagine they are at least good to 90bhp!

It's more other people telling me they don't think it will make power... however this is normally keyboard-warriors that haven't actually tried the carb! I'm not after pure power anyway - if I was I'd have a 286/296 cam and a DCOE 45! I'm after an economic more tractable/torquey engine that still has a good kick when you floor it!

They are correct it won't make more power, you can only gain power by changing carb if the original carb was not sufficient to meet the engine demands. Like using a single HS2 on a 1380 then changing to a HIF44.

When changing from Twin HS2 to a weber 28/36 according to the RR result I lost 1bhp but gained 1lb/ft. But that is purely because there will be discrepency as no readout from a RR is 100% accurate there will be a margin of error. As long as you use suitable choke sizes a weber 28/36 will always meet an engines maximum output. After a 100-110bhp maybe it will start to fade but i don't think you will be pushing that somehow.

Oh and as briefly mentioned on another forum cross sectional area of the choke means nothing. It is all about Air flow capacity. A quick check in the yellow bilbe shows...

HIF44 will flow 240cfm with a cross sectional area is 1520sq/mm
Weber 28/36 using 26mm/27mm chokes flow 225cfm cross sectional area 1102sq/mm

418sq/mm less but only 15cfm difference...

If you maxed out the choke sizes in a 28/36 (and I am not sure what the biggest chokes you can fit are) it would not suprise if the sq/mm was still less than that of a HIf44. And produced an equal or marginally more flow.

Edited by cap'n crunch, 08 November 2010 - 06:45 PM.

I haven't said it will make MORE power.... as long as it makes the SAME power that is fine by me if the engine drives better. I.e. better economy, light throttle torque and response. My dig was at people telling me it will make considerably LESS power - this can't be the case as it can produce 100+bhp - which is much higher than my engine will put out!!

As I said above, one main reason is I'm fed up with flat spots with the SU, and also I'm fed up with the variable jet holder depending on the engine bay temps!! One minute it idles great and feels really responsive, the next it feels flat and struggles to idle.

Probably a bit late with this reply. I ran a 28/36DCD on a 997 balanced cooper engine with 544 cam. It was brilliant. Normal driving on first choke but foot down and second choke was like a turbo boost. Changed from twin 1.5 SUs. They were more torquey but the weber one on acceleration and reliability, never needed attention. It didn't ice up like the SUs either.

Never got round to trying this unfortunately. Mini is off the road now, but I've changed the build completely now. In source of more torque to drive a taller FD, I'm now going down the turbo route - GT1752.

 

Can't find anything about running the Weber with a turbo, so will likely be the Turbo HIF I'll be using. BUT, if I have to use the SU I am definitely getting rid of that stupid bi-metallic jet holder POS!

You can turbo a 28/36. Dont know of it fits behind the bonnet without mods though.