hey lads, im pretty limited with my knowlege on webbers. Im after the help of someone experienced to help me make my decision on which webbers i shall set out after, if any at all.

I'm going to run an a15 with a ported gx head and high compression. extractors lightened fly wheel etc. otherwise ill just use a polished standard a15 carby.

Will I achieve much more power? It will be for circle track racing so i want the power, straight to the point. As i said my knowledge is limited so any help would be apreciated. Also if anyone has some they want to sell or knows of any for sale, greatly apreciated once again, Cheers!

hey mate,

I would reccomend 45dcoe9s if car will be doing track duties occassionally.atleast thats what my reading around has led me to believe.
il be running 45dcoe9s once i build my a12.Problem is getting a matching pair made from italy. ive heard alot of negative feedback about the new ones from spain.but always do your research.

the 'old school' ones pop up once in a while in yahoo japan and you could use vendors like importmoster or jesse streeter to purchase from japan.In good condition,expect to pay alot.

other forum members with first hand experience should be able to assist you further with detailed info.

cheers

thank you for your advise. its for a race car, no road use what so ever. once again, thanks.

if only for race,then the 45dcoes9 will suit it very well.any bigger i.e ida 48s arent too ideal for capacity of 1.6liters and under.
also if you can,make sure you get a matching pair otherwise it greatly hinders tuning.
some race cars are using 40dcoes so hoping the more informed members and esp the ones already racing with webers can give us a better insight

40's will be fine. the biggest chokes you would ever use would be 36mm, even then, that's at the sacrifice of bottom end response.

I dont understand when it comes to fuel why most people over size their carbs. A car basically can only burn so much fuel. Yes the more you push in the more you get, there has to be a limit, but over fueling seems to be the go now a days. I use to know quite a few blokes in the 1600 scene and they'd be running 1800's and 2L's with 45's 48's 50's and one bloke 55's. Back then I ran an 1800cc bored out to 1910cc and from memory they were 42" jetted down to 38's. And mine was an animal compared to theirs. I cant see a A15/14/12 running anything bigger than 36's on a serious engine. But I see blokes who's street/race cars running 42's 45's . Has technology gotten so good that they need that much feeding ?? Wouldnt they just flood and splutter down low ?? Can someone explain it to me......

.

I have 42's on my coupe (lightened flywheel, GX head, double valve springs, balanced, extractors, electronic ignition)

they seem ok but I really need to get them tuned properley - The car is just getting back on the road after 15 years in various sheds

I am also interrested in the right chokes etc to use

Refer to this tech wiki section to begin:
http://datsun1200.com/modules/mediawi ... tle=Weber_DCOE_carburetor
It would also be helpful if you pruchased on of these manuals to gain a better understanding of the carburettor itself. :
http://ecx.images-amazon.com/images/I ... dZpoQEL._SL500_SS500_.jpg

I run a single dcoe sideraft 45 choked right down on my mild a12. It goes a treat!

Whether it's 40 or 45s (you can run _appropriate_ sized venturis in either to get the result you want) I definitely second the dcoe9 advice. I'm mostly familiar with the 45s (and using them on other cars) but basically these are the (relatively) earlier more racing oriented pieces. There are more recently manufactured ones including (iirc) 13s and 152s (or similar numbers to that) but aside from being more recent manufacture, they have differences in the idle and off idle (not sure what weber refers to these circuits as, they might use 'transition' circuit, I don't know). circuits and they tend NOT to be as tuneable with regard to optimal throttle response and part throttle smoothness. They might work well on streeters and (potentially, though I haven't seen this fully explored up close so I can't give any concrete feedback) - but for racing the dcoe 9 is the pick of the litter. If you notice webers coming up for sale here, it's actually one of the main questions potential buyers ask. There is probably a few hundred dollars in resale price between them.

THere's also some others - that have slightly different lettering to dcoe. I can't think of the letters off the top of my head, maybe dcom, but there's a couple of people selling them from time to time on ebay and their write up claims that they are just a 'modern dcoe' . This is not in fact the case, there are differences, irc the accelerator pump is a diaphragm not a plunger (and in this case is a little trickier to tune, though on other carbs the diaphragm type is usually better) and I'd put them in the same category as the later made 152s in terms of desirability.

Make no mistake, if there was nothing else available, I'd go the other dcoe variations for sure. But the dcoe 9s aren't that scarce, you _will_ be able to get them if you keep a close eye on ebay, and the various datsun (and other car) for sale forums.

A quick note on venturi sizing (and tuning in general) although maximum power is important, the car will actually be faster (and considerably so) if it has more 'average' power over a wide enough rpm range (basically whatever rpm range it has to operate in during the race). About the only exceptions are tractor pulling, land speed runs - both of which require peak power and (relatively speaking) a concentration of it up high in the rpm range (whatever rpm the engine can safely spin of course). To a lesser extent (provided it runs a really loose convertor or particularly close ratio gears and low diff gears) it is the case in drag racing.

Point being, there probably is a choke size (what weber venturi sleeves are called) that will make perhaps 2-3% more peak power, but the size just one step lower than that, although down on peak power, will likely have as much as 5-10% more power at all rpms lower than that peak hp rpm point. And such a combination will absolutely slaughter the opposition if the opposition ran the larger choke size.

So basically bigger isn't better. That said, there is such a thing as too small a venturi. It's about the 'right' size not the biggest possible.

you could actually go even further with this. twin webers (or any one carb throat per intake port setup) will not actually make the best peak power (no matter what choke sizes you run). Technically a large single carb, and large plenum will make more power. In the case of the a-series, no such manifold exists, but if it did, and was well designed and fine tnued, it would make more power. this is the case with other engines too. However webers (or individual throttle bodies) are used on practically any racing engine where they are legal to fit. Because they produce a wider powerband, and more average power (with that small peak hp drop).

The next big thing is throttle response - and properly setup webers are sensational on that front too :) Apart from accelerator pump circuit tuning and idle off idle/transition circuits (all of which improve throttle response) well apart from that, optimally sized chokes again come to the party - avoiding going 'too big' there means they develop signal strength more effectively, so they get the main fuel circuits flowing in a more responsive manner than chokes that generate weaker signals. So it's just one more benefit of not going too big on the choke sizing.