ok, so the weber is on, Ive played around with the idle mix screws, gone from 1/2 turn right through to 2 1/2 turns and the best spot is about 1 1/2 turns.. but... it still back fires through the carby at about 2000 revs under load. Ive asked around town and no-one down here "knows" webers that well.
According to my description it appears that it is running lean and it may help to go back to my original chokes that are bigger than the ones that are now in it.
My question:
Is changing the chokes (venturi) a matter of removing the air cleaner and then a screw or two to remove and replace the venturi? Is there anything special to adjust or watch out for?
I have the original venturi. I think I have 34-36 in it now, the old ones were 38-40mm, not perfectly sure of the sizes but thats close enough. I have no idea what jets are in it, but they as far as I know havent changed. Its only the venturi that got changed when it was rebuilt, and it previously ran beautifully on the original venturi.


Thanks if you can help

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com

If you have the cash, get it to a dyno, and quick smart!
Ensure its a place that knows webers/minis at least.
They DO charge a lot, but get things spot on.
They will do timing - bad timing does bad things
A lean tune is also very harsh on the engine.
Larger chokes will slow the air speed and therefore richen the mixture slightly.
On a 1275 - 40mm chokes are HUGE.

Jill
first we better find out exactly which bits you are wanting to change because chokes and venturi are totally different part of the carb, the chokes are the nearest part of the throat closest to the engine and the venturi actually sit above them at the backside at the back of the carb. Now fitting bigger chokes will actually allow the carb to flow more air and the result is you will have to increase the size of the jets, both mains and idles but not so much the idles, the symptons you have are the type you get when you have the wrong emulsion tubes or pump jets or pump stroke, At what revs is the car backfiring through the carb on trailing throttle, if its below 2000 revs its the idle jets if above its the mains and if it hesitates at about 2000 when you put your foot down its the emulsions. Remember that chokes control the amount of air the carb can pass and only really effect the top end of the rev range and power, to big can effect the lower response but give great top end HP, to small in chokes can improve lower response but restrict top end , 36 mm chokes are about right for a mini, even 34 mm are fine may cost 1 or 2 HP at top end, maybe if you can find a Fiat or Alfa mechanic they might be able to help you, ask whoever rebuilt the carb for you what the settings were befor and what they changed, if it was running alright before they rebuilt it they should put it back to what it was assuming it is the same engine

Jon

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Roundies and Clubbies(except vans) are both ugly that is why I have Midas and a van
1293 Mini Midas Bronze,1275 Clubman van

sounds like you are talking about the "Chokes",,,they have the size maked on them & are simply a rolled shaped tube sort of looking thing with a big hole thru the guts

& yeah, take the screws out from under the throats & they`ll pop right outa there,

the "Venturies" will be numbered as 3.5 or 5 or something like that & have the main fuel feed & a smaller venturie looking thing braced through the middle of them. (you should have 3.5s in there)

If you`ve gone to smaller chokes then it will make it run richer,,, air """speed""" is increased across the main fuel feed & therfore basically sucks harder on it taking more fuel with it

if you go to larger chokes , then it will run leaner as air """speed""" is reduced across the main fuel feed hole & therfore sucks less upon it taking less fuel out of it

it`s that simple really

Sounds like you simply need to sort maybe a fuel blockage (crap in your carb---- not sure how often you have to do that tho Joke )

or maybe have the jets looked at

I`m a firm believer that if you changed to smaller chokes & it is coughing back thru the carb ,,,,,then maybe it`s too Fat & is drowning the plugs

but then , like i said above, you may just have some sh!t in the fuel passage

i really can`t say much about """YOUR""" carb, as it`s not in front of me,,,, but, surely you can find someone down your way to have a gork for you, it`s not rocket science, it`s just sucking fuel.air mix out of a hole

Buy a wever book too,,,(if you`re gonna stay with webers)
there`s a good one called

"How to build & power tune WEBER & DELLORTO"

speedpro series, Des Hammill,,,Veloce publishing

OR,,,

"WEBER CARBURETORS" ,,,,By Pat Braden ,,,HP Books,,,Berkley publishing group

otherwise, send your whole car up here to me, i`ll fix it & send it back, would hardly cost $2000 & it`s be sweet (another joke)

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

Thanks guys, yeah Id take it to someone tomorrow if we had someone down here that knows Minis/webers and has a dyno, but no such luck. I'm now quite worried that I'll damage the engine if I drive it to Perth, so I might not make it to the BMC day, sorry peeps. If I do come up Id put the SU back on, bring the weber with me and stay in Perth till I can get it looked at/tuned.
I have found someone that knows Minis and webers down here but I cant get a booking till mid Nov

Jon, thanks for that, I think its the venturis that got changed (to a smaller than I had before size) I still have the old venturi. They are aluminium (I think), cylinder shaped, about 36-40mm in diameter and about the same in length (from memory). 2 of them.

I have to get it tuned, simple, thanks guys, will let you know how it goes.

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com

I'll second Matt's endorsement of that Des Hamill Weber & Dellorto book.

Also see his book "How to Power Tune the BMC/BL/Rover 1275 A series engine", the settings in it are pretty spot on for a Mini.

Both books are about $39.95 ea, at www.pitstop.net.au in Perth.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

ok the bits that have been replaced are stamped with a 40, so must be the chokes.. and thats prolly why its running richer than before (coz I have smaller ones in now). Its running reasonable now (after changing the timing), so will be ok till I can get it tuned.

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com

Al Munday (Mini Central) was able to fit me in on Monday morning after the BMC day Sunday. He replaced the main jets (were 180s) went down to 175s I think, but will try 160/165's when I/he can get hold of some, we took the idle jets down a size too I think they were 60's we went to a size smaller but will try 45F9's when I/he can get hold of them too. Put a new set of plugs in it too, that helped
Its running MUCH better from mid to high range, still farts about through idle and low range, but will spend more time playing with jet combinations and try and get it to a dyno for tuning when I have some jets to play with. I have David Vizards book, least Ive got some idea what he's talking about now

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com

Sorry guys but "Chokes" and "Venturi" are exactly the same whereas above them are the Auxilary Venturis - so Jill knows exactly what she's talking about here and she's totaly right with her terminology, no need to confuse her.

too late

but thanks Mike

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com

Mike

chokes are never called venturi in webers or delllortoes, Yes the top bit is the Auxillary venturi and as both I and the Miniman have said it sounds like Jill has changed chokes as the number they have mentioned relates to throat size

Jill I am glad you have it some what sorted

Jon

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Roundies and Clubbies(except vans) are both ugly that is why I have Midas and a van
1293 Mini Midas Bronze,1275 Clubman van

k, obviously different parts of the country call different bits different names. I remember as the guy (then Automotive Tuning Centre, Perth) who handed me my old "venturis" and said Ive replaced your Venturis and Ive gone a bit smaller... they are the aluminium collars. The ones he took out were stamped 40. HE referred to them as venturis, but IT DOESNT MATTER guys, yeah Im a little confused, but also Im learning about jets and webers. its all good and thanks for your patience

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78 van 1300 cam extractors weber, 12" Superlights Metros Konis HiLos MP3 Amp Sub Alpine speakers and lots of fur
www.crazybitchracing.com