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MG Midget and Sprite Technical - Weber 45 DCOE - advice please
| I have the chance of a 45DCOE with a long Maniflow Inlet, K&N filter and throttle linkage for the right price :) My question is, should I consider going this route with the engine that I have? My current set up is a 1275 A series re-bored to 1293, a gas-flowed Cooper S head (heavily skimmed), Maniflow LCB and very free-flowing exhaust, Simon BBC electronic distributor. The current Camshaft is standard but I will be fitting a slightly hotter cam over the Winter. My current carb is an HIF44 with K&N and it is reliable and economical. Would I gain much performance from the Weber? Would it make a significant (negative) difference to my fuel economy? Will I need to bash my inner wing about to get it to fit? Glynn (would love to have that Weber noise coming from under my bonnet!) |
| Glynn (1275RWA) Williams |
| My Frog with a 1275 had the same Weber fitted! It looked great, made a great sound..... and was virtually undrivable! Under 3500... nothing (except stutter); over 3500 - went like the proverbial off a shovel. Drank fuel too - the po had to drill a 3mm hole in the top of the fuel cap which was already ventillated) and fit a high output pump to prevent fuel starvation. It needed a rolling road to have any chance of sorting it. Several people (including Alan Anstead whose opinion I value) told me how they had had one and removed it so I followed suit and fitted a single large SU! That's to say I went back to where you are now.Much more driveable. It's gone and best forgotten.  |
| Graeme W |
| A 45 is probably too big for a road engine (as Graeme says, hopeless below 3500). A 40 would be better suited. Malc. |
| M Le Chevalier |
| Ok, that's definitely one vote for the negative then! Thanks Graham for your input. (beautiful engine bay by the way) Glynn |
| Glynn (1275RWA) Williams |
| I've just spent the last few days reading up on how weber carbs work and how to set them up (far too much time on my hands at the mo :-D ). I've concluded it's a bit of a dark art but not impossible with the right equipment! There's no good reason for them to "drink" petrol unless they are set-up very rich or you are using the go fast pedal a lot! Yes, you are likely to get better top end performance especially with your engine (with the mild/wild cam added) but a serious amount of RR time might be needed to get the bottom/mid range running with reasonable smoothness. Adding a AFR meter will help workout what's going on as you drive which in turn helps with the selection of jets etc. The big issue is that no two engines are exactly the same and therefore using a set-up from another will only get you in the ball park. You don't say what the Carbs are coming from in terms of engine spec? I'd say if the price is right, why not. If it doesn't work out for you you can always pass it on to the next man and possibly at a slight profit. Best of.... MGmike |
| M McAndrew |
| Reading this; http://www.s262612653.websitehome.co.uk/DVAndrews/webers.htm would suggest a 45 will be too big. If it's very good value I might be interested for an MGB with a 1950 lump :-D Best of... MGmike |
| M McAndrew |
| A 45 is only an improvement over a hiff 44 with a really hot engine (1380 286cam kind of range) Add to that the fact that most people find a hiff easier to tune. And even when a hiff is tuned badly it will kind of behave where a badly tuned 45 will be a b#tch to drive. So I fitted a 45 (dellorto)! And with work it pulls cleanly from 2000rpm to 6500 (power comes form 3000). Float level can be improved as on after some hard corners it stutters slightly. Fuel economy suffers but that can also be because the sound and acceleration are addictive! This is all tuned without a rolling road just careful reading of "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors" of Des Hamill. With the (now almost finished) next incarnation of my engine it will be extensively rolling roaded. to get the most out of the trick ignition. The point to this story? if you don't need a weber or dellorto roar in your life be happy with the SU easieness |
| Onno K |
| Malcolm, now I've done the research I need a test bed to practice on! Hurry up and get your car finished, bring it down to me and we can have a joint learning experience :-D Best of... MGmike |
| M McAndrew |
| An SU has a great potential for adjustment. My impression of the Weber is that the set up is all about getting the correct tubes and chokes and bits fitted. Probably once set-up it goes on for ever, but then again, we all like something to twiddle with! |
| Graeme W |
| I fitted a DCOE45 to our 1380 for a while, and had the opportunity for a back-to-back rolling road session, where the '45 produced an additional 4 bhp over the HIF6, BUT its road manners were atrocious! It has 38mm chokes, so maybe a bit too much? Nothing below 3,000 rpm at all, but after that went very well, and sounded superb. Some more work, Piper 270 instead of the Kent 276 and replaced the MG Metro air cleaner box (with K&N filter element) with a K&N large round filter + stub stack saw the HIF produce 6 bhp more than the Weber, but no comparison this time, so maybe the Weber would have produced more again? The RR man reckoned that the Metro air cleaner 'box' although cleaned up, was most of the restriction and thought that unless I went to at least a 286, I would not see much benefit from the Weber. It's about time for another RR session, so maybe should do a comparison this time? |
| Richard Wale |
| Yeah, interesting article that Mike. I have done similar to you and read everything the internet has to offer on Webers. I have guessed some settings and the car runs but it needs tuning in properly (I think it is running pretty rich). Malc. |
| M Le Chevalier |
| Malc, Out of interest, do you have a note of the carb set-up eg choke size, idle, main jets, air control and emulsion tube fitted? Is it rich at idle or flat out (not that you should be able to get it flat out on the road yet!). Best of... MGmike |
| M McAndrew |
| Yup, I will start a new thread. Jamie was asking about settings too (dunno where he has disappeared to over this last week...) Malc. |
| M Le Chevalier |
| Well, so far, based on your replies, REALLY not too keen to go for the Weber! Anyone got a positive story to tell? (By now, I thought we might have had a "there's books with this sort of stuff in"...) Glynn |
| Glynn (1275RWA) Williams |
| Glyn, Graeme's appears to have the short swan-neck manifold, which won't help low rev performance. With a long manifold its manners are a lot better but you will probably need to cut a bit of the inner wing away if using a decent-sized K&N filter case. I would expect fuel consumption to increase an appreciable amount. I wouldn't fit it until you change the cam, then be prepared to spend a half-day at a r/road. |
| David Smith |
| David I would not call Graeme“s manifold a swan-neck by a long shot! It seems to be at least 3inch long with a nice flow to the curve. The swan-neck I have around (got it once in a job lot) is 40mm deep and is almost right angled to make it clear the exhaust. But the basic principle of the longer manifolds is indeed preferable. Though if you have a shorter manifold you can compensate to a degree with longer ram-pipes. If there is not enough space for a K&N type filter use a foam filter or filter socks. The argument for a 45 is to drive a car with a well tuned one. The accelerator pump is a genius device and the sound is eppic |
| Onno K |
| Glynn, If you insist ;-D http://www.amazon.co.uk/Weber-Carburettors-Tuning-Tips-Techniques/dp/1855207591/ref=pd_bxgy_b_img_y There's lots of books.... And online references similar to the one I posted earlier. Best of... MGmike |
| M McAndrew |
| THis was the manifold. Not sure whether that is regarded as long or short, but it did allow fitting without taking an angle grinder to the bodywork. Exciting over 3500 though! Nightmare in traffic. Accelleration from low speed was interesting. You needed to match the throttle position with the rate of speed build up. Over do-it and it just died.  |
| Graeme W |
| Engine: overbored 1275 (nearer 1300 now). Big valve unleaded head, 45 DCOE, high lift cam and roller rockers, tubular manifold, free flow exhaust. Matched electronic ignition. Alloy rocker cover. Last time on the rolling road it put out ~98bhp. Thermostatic oil cooler, alloy radiator and silicon hoses. Breathers to catch tank. AFFF plumbed in extinguisher. Uprated alternator. Runs perfectly with none of this useless below 3500 - its all in the correct jetting that can really only be done on the rolling road. Luv David |
| d brenchley |
| A mate had a similar experience to David fitting a 45DCOE to his 1275, or a bit bigger, with ported head, tubular manifold and slightly better cam, quite drivable at the bottom end and better top end. He didn't have it rolling roaded but fitted it as it came with the suggested set-up. All down to getting a suitable main venturi size and jetting. My main experience is with 40DHLA courtesy of rusty Alfa Romeos. First fitted one to a 1098 with a 270 cam and found that more drivable at lower revs, it pulled better under load, than the twin SUs it replaced, better top end also. That was later fitted to a 1215 (Imp pistoned 1098), then on a 1420 with a plenum and that required reducing the main venturis to get it to pull low down but once done and jetted was very drivable. |
| David Billington |
| We have also had no problem getting a 45 DCOE to behave at lower revs. It's all in the jetting. Too often people tune for peak torque and poer, and leave it rubbish at the bottom end because that's what they were expecting rather than finishing the job properly. |
| Paul Walbran |
| I keep having the 'do I or don't I' conversation in my head regarding fitting a Weber. Most people use them as a matter of course on competition cars (class allowing). I quite often get asked why I have an SU on mine, usually accompanied by a puzzled, are you mad/stupid look on their face! All I can say is that it pulls like a train, revs as high as you like, is nice and civilised on the road, starts easily, still does 35mpg and only cost £25!! But I still want to try a Weber!  |
| john payne |
| John, The 6 40 DHLA I have cost me on average £7.50, 4 from breakers, I think those days are long gone though. The first one I bought for £5 from a guy that removed the pair from his Alfa Romeo when he scrapped it, he then fitted one to his Harley Davidson bike but the performance increase scared him so he put the original carb back on. He later sold me the other of the pair. They basically have cost me jets and the odd main venturi and service kit but like DCOE they are a high quality carb and the main bits don't wear much. I've made 3 manifolds myself out of steel, one of which seems to have made its way to the states judging from a posting about it some years back on the BBS. The standard jetting for the 2l AR twin cam seemed to suit the 1098 engine reasonably well but I'm sure could have been improved with RR set-up but seemed to work well enough at the time to not require that expense. |
| David Billington |
| Definitely starting to feel more and more tempted now! Worst comes to worst, I'll take it back off and go back to my HIF44 I guess... Still interested to hear if anyone else has an opinion though? Cheers to everyone that has made an input to my decision making thus far :) Glynn |
| Glynn (1275RWA) Williams |
| One of the interesting things about keeping these cars going and asking on BBS is that there is very rarely a simple answer to anything. It comes down to opinions and experience and very rarely is there a majority with the same idea. Look at the current thread on rear hub nuts as an example... or the sucking oil into the inlet manifold! If you feel so inclined, give the Weber a try. If it works, 50% here will say "we told you so" and if it doesn't..... the other 50% will say the same thing. You will be happy I guess having the opportunity to give it a go and polarise your thoughts for when in 12 months time someone asks the same question again. |
| Graeme W |
| If you are looking for a good book on Webers I would recommend Weber Carburetors by Pat Braden published by HP Books. It's the best book I have read on the subject and covers all Webers not just the DCOEs. Trev |
| Trevor Mason |
| How about motorbike carbs...? i'll get my coat...  |
| Andy Phillips (frankenfrog) |
| Andy, it's been done - Amal,mikuni etc but I still prefer a dcoe, which reminds me must get the frog one out of the garage and clean it up. 😀and if you want to go really ot try minnow fish carbs... |
| d brenchley |
| Basically the engine will try and suck in as much air/fuel mix as it requires. No more, no less. Sticking a bigger carb than standard on a standard engine will thus do no good whatsoever. The engine must be modified to suit if it is to do any good. My take - pretty standard engine - standard carbs; modded head, better maniflow, mild cam, etc - HIF 44; race engine, yes 45 DCOE or similar, but we are talking big money spent on the engine beforehand. |
| Mark O |
| Glynn, If you do feel tempted, then to achieve good manners and economy on the road the key is to get the right progression jets. Start with a set of jettings which are from a car in simlilar tune to yours. Set the idle screws to a nominal 2.5 turns from closed, then step-by-step change the progression jets until you get the best light/part- throttle performance between 1000-2000 RPM on road test. In my experience better transition results are achieved from road tests than rolling roads. On the other hand full power set-up is definitely best done on the rolling road, but useful information can be read from the spark plugs if the engine is cut under full throttle and the plugs are known to be of the right heat range. (If the plugs aren't scorching or fouling at present they are probably right.) From your desription of the engine tune I would go for 34mm venturis, but 36mm could be worth a try afterwards. You don't mention compression ratio other than the head has been skimmed heavily. The effective compression ratio (combination of actual CR and inlet valve closing point) is the major factor affecting heat range in these engines. I found one of our 1275cc engines needed N6Y/BP8ES on 9.7:1 and a mild-ish fast road cam, anything hotter running than that would cause a misfire towards the end of a very long hill thanks to the electrodes heating up too much. |
| Paul Walbran |
| One thing not mentioned here is just how quick and easy it is to change jets on a Weber which is one reason they have always been favoured by racers as it is so quick and easy to alter just one part of the range. The down side is that it can be expensive if you don't have a range of jets to hand because things like emulsion tubes and main venturi soon add up. The other thing is most people buy one for performance but they can just as easily be tuned for economy if that's what you want. Trev |
| Trevor Mason |
| Spot on Graeme. There's fact, and there's opinion. And on here at least, ne'er the twain shall meet. lol. So the best advice is, ask the question, filter the answers, and prove it to your own satisfaction. |
| Lawrence Slater |
| Mark, That isn't true as the maker will often not tune the engine for maximum power but drivability so the carbs fitted won't be sized for peak power, it also helps keep the stresses on the engine down as it's less likely to be used at the higher revs. I don't know what benefit a larger carb would have for a standard A series but the standard FIAT twin with downdraught Weber would go from about 120bhp in 2l form to about 140bhp or more with suitable sidedraughts and no other change. |
| David Billington |
| Glyn A Weber will outperform an SU every day of the week Choke size selection is the important bit to make it work. Chokes down to 28mm are available for 45s but I doubt you will need to go that small , probably 30 or 32 for what you have at the moment We run a 45dcoe on a 1000cc Morris Minor racer with 32mm chokes and it is fantastic -smooth as everywhere A mate had one on his 1400cc mini with 38mm chokes and that car absolutely flew As you say if you don't like it , it is a very saleable item to sell on willy |
| William Revit |
| David Not sure if you are saying the same thing in a different way. I agree that the A series in standard form is not tuned for max power, and as such has the appropriate carbs fitted to deliver the necessary fuel mix required given its state of tune. Your Fiat on the other hand may well be engineered - in standard form - to accept more mix, usually by having an oversized head, and thus adding more mix via larger carbs would be beneficial, but "the engine" I was referring to was an A series. |
| Mark O |
| Don't buy a Weber, buy Reece Fish. No tubes or jets to change. Only need adjustments on a rolling road to get the best power out of it. Hasn't anyone consulted Vizard yet? |
| Lawrence Slater |
Vizard says. For a 45 DCOE |
| Lawrence Slater |
And Vizard says. |
| Lawrence Slater |
| I ran a 45 dcoe, 1293cc longman incline valve head (that dates me!) extractor exhaust and 731 cam,11:1 CR,. It was fine after a good RR set up with smooth progressive acceleration. Even used it for auto testing as well as sprints. I would agree with Graeme go and try it! |
| Bob Beaumont |
| Glynn Good on Lawrence for digging out Vizard's power curves with typical engine specs. 1 3/4 inch SU seems to be pretty good, and you have one of those already working well. Guess if you were really go for a reasonably modified engine, including offset bore 1380cc then you may want a 40 or 45 Weber or Dellorto, but for less modified 1275 (such as a 1293) you may be happy with twin SUs or a single 1 3/4. Eurocarb in Reading were a good source of Dellorto bits, as well as Weber Concessionaires - I think the former does both now. I know the feeling of 'I have one of them in the garage, so why not' - a 40 Dellorto that would be good on a modified 1275 that will one day be built... Correct or good quality manifold for your carb? If not, try Maniflow. Also, have you got a decent exhaust system (e.g. RC40) and suitable extractor manifold on the car? See: http://www.magicmidget.co.uk/ and http://www.maniflow.co.uk/?view=category&category=139 http://www.dellorto.co.uk/ Cheers Mike |
| M Wood |
| Also see: http://www.sprinzelsebringsprite.co.uk/page7.htm And http://www.sprinzelsebringsprite.co.uk/page6.htm http://www.petermayengineering.co.uk/catalogue6.htm#catalogue6 |
| M Wood |
| Thanks Mike for your input. To be honest, I'm still undecided and I've got until this Saturday to make my mind up! Decisions, decisions...... |
| Glynn (1275RWA) Williams |
| do it- be a happy man |
| William Revit |
This thread was discussed between 02/11/2014 and 13/11/2014
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