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The Magical Mystical Weber DCOE

The
Numbers
Tuning and
Jetting
Do I Run a
Single 45
or Dual 40's?
Tuning and 
Service PDF

(2 meg file size)
Weber
Resources
on the Internet
User Photos
and jettings
  Adjusting
Twin DCOE's
The Fuel
Flow Path
Physical
Dimensions
Excellent Article
by Mickey Luaria

Virtual
Tour

Rasors Fuel
Flow Pathes

The Jetting
Calculator

---------

An email from
a Racer

One end user's                                         
knowledge/experience/comments         

 

     This letter was sent to me after the author stumbled on this site. He offers up the following information based on his own experiences  and years of playing with DCOE's. He makes a good point concerning the idle air bleed screws on the topsides of the throats on the type 152 and type 9 DCOE's. Few books, describe, and even fewer people understand their use.  These are simply 'air bypass' screws that let you 'tweak' the individual cylinders for the proper idle A/F ration through each barrel of a DCOE carb.

 

------------- original email-----------------------

From: <Ingemar.Lampa@tassenet.net>
To: <info @ teglerizer.com>
Subject: Weber info
Date: Tuesday, November 20, 2001 11:21 PM

Hi Paul,

I submitted this on the feedback form on the web, but re-send it using
email, in case it didn't get through. Also, ran it through the spell
checker this time...

Take care,

Ingemar Lampa
*************************************************


Dear Teglerizer,

I have come across your Weber pages as very useful and would like to contribute to this information with my own experiences of 32/36 DGV, 45DCOE152 and 45DCOEE9 on a 1972 MGB.

Background:
In 1997 I moved to Hong Kong and bought a 1972 MGB Roadster, which I started restoring. The car used to be featured on the now defunct MG Car Club HK pages, as the silver roadster. Among the work done over the years, is replacing the original engine with a factory rebuilt unit from Brown & Gammons. Since my information will cover only carb and tuning info, I will skip on the rest of things done, but believe me, it is nice now !

Engine data:
The engine is a 5 bearing 18V which has been factory rebuilt. I have never taken it apart, so I do not have any measures for overbore, etc. but I would imagine it is probably .040" over. The only mods that I have made include installing a B&G 271 "fast road" camshaft (corresponds to Kent Cams 715). This was done when first installing the engine. The standard cam was never used. The head is standard unleaded, no porting or other works. The exhaust system is a large bore Double "S", with stainless header and a single-box at the rear. A Pertronix electronic ignition sits in an Aldon 45D distributor, which has a vacuum advance unit attached.

Before we begin:
As someone who used to race a Honda 750 SOHC Four back in the early 80'ies, I was told by an experienced engine tuner that "The carbs and jettings is the LAST thing you touch. Make sure your plugs are new, timing is correct, valve lash is set, there are no vacuum leaks, fuel pressure and supply is correct and unrestricted, first. Only after this do you start on the carbs." These words can not be emphasized enough, as I have discovered myself over the years. I would want to add that I would also do not only a compression test (max acceptable difference 10-15%) but a leak-down test as well (max acceptable difference 15-20%). Don't bother going further if you have not ticked all of the above.

Weber 32/36 DGV:
This carb was first installed when the engine was brand new. The carb was bought as a kit from Northwest Import Parts and came with a Pierce manifold and linkage. Due to the fact that cars here in HK are British spec (RHD) and that the kit came from the US, I had to modify the linkage and cable setup in order to install the carb correctly - which means Float Bowl in Front! This is very important and sometimes not highlighted enough in docs. Initially I had set it up in the most practical way, bowl at the back. the car would stumble, sputter and I had virtually no power going uphill (there's a lot of those here) at all. Reading up on the web, I came across some obscure article regarding BMW 2002 DGV, where this point was made. Turned the carb around and a whole new engine emerged!
The initial jetting was PM 135, PA 175, SM "97", SA 170. The car would run fine, but a bit lean on the primary barrel, but sputter and die when secondary barrel was opened (+2/3 accel travel). Upon inspection, I noticed that the SM jet was stamped "97". Odd. Even worse, it was not drilled! Actually, it seemed to be a plug with the year of manufacture, instead of a jet. I installed a 145 main and the car would now run on WOT. Also, float-level was completely off the chart, so this was reset to specs. Lesson learned: Please check all jets and levels on factory kits before installing.
The engine seemed to run a bit lean, which I didn't regard as a problem, since the weather was cool and I was running in the engine. My thinking was that I wasn't pulling full power often anyway and that running rich during break-in could wash away lubrication in the cylinder bores. Also, ignition timing had to be advanced to 23 degrees at 800rpm, in order not to get a stumble on take off. Documents and messages on the web confirmed this "problem". As soon as the break-in period was over, tuning began. I went up to PM 150, PA 165, SM 155, SA 160. Ignition still at 23. The engine was still running lean (hot). The problem was further compounded by the arrival of HK tropical summer. The car was not useable in traffic in town. It would overheat, even thou an electric fan w. override switch had been installed, thermostat replaced with a racing style sleeve, new radiator fitted, etc. Next, I replaced the OEM style radiator with a large capacity aluminium racing style rad from Griffin. Slightly better, but still no avail. Was considering stamping in louvers in the new bonnet, but refrained. Also, the progressive nature of the 32/36 did not please me. Noting-nothing-nothing-Boom! Not user friendly in traffic. "Progressive" was a buzz-term some 20 years ago, with carbs, suspension and worst of all, brakes, being set up like this. Decision: Change from the progressive DGV, to a linear 45DCOE.

45DCOE Type 152 (Spain):
This kit was imported from New Zealand as a complete setup. Manifold is a Cannon long-runner copy, smooth finish and large bore. there was no provision for booster or vac advance. A tap for the former was installed, while vac "advance" was simply disconnected. Since the VA actually retards the ignition at cruising, I gathered I could do without by fiddling with mechanical timing. The original long air-horns were fitted with "sock-type" ITG air-filters.

The initial jetting of the carb was as follows: Mains 145, Air corrector jets 155, Idle jets 55F8, Acc Pump jets 45, Aux Vent 4.5, Emulsion Tubes F16 with 36mm chokes. The Type 152 are the new style DCOE which are made in Span. The differ from the old E9, 18 etc. in design, whilst they incorporate an Air By-pass screw (P/N 26 in drawings), nitrogen filled plastic floats and different layout of progression holes. Tinkers beware! Most manuals and docs refer to the old style DCOE. There is for instance no data on the settings of screw 26 that I have come across. A very experienced racing buddy from Macau told me to just close them off, for instance. Whilst this is OK for racing applications (more below), streetability suffers.
I retarded the timing to standard +2 degrees (12), did the required general tune-up according to my biker buddy and set off tuning.

First, the idle screw had to be turned out 3.5 turns, to get steady idle. Odd. All books state that if one is out more than 2.5 turns, one is lean. Idle jets were changed to 60F8, 55F9, 60F9 and even 60F6, in this order. Screw still required 3 turns for idle to be comfortable. Seems that docs DO NOT CATER for Type 152, with its screw 26 bypass. Subsequently, this was closed off (as per my Macau buddy) and I found that the best idle and low speed cruising was obtained using 55F9 jets. You can tell you are going rich on the jets when the engine becomes erratic and hesitates or surges just as you open the butterfly from the closed position, when cruising at low speeds in 2nd or 3rd gear. A chase-car would perhaps also notice puffs of black smoke. the problem is compounded as engine temperature increases, as another indication. However, there was another problem: coasting downhill with closed throttle would give pops and cracks from the exhaust. The exhaust system was checked for leaks (most likely source) but it was still popping like mad. Docs state: Other sources can indicate lean mixture or not enough ignition advance. Checking, double checking and adjusting mixture and ignition (until pinging) did not solve the problem. Alas, on to screw 26. I figured, they must be there for a reason. Slowly opening them half a turn at the time ALMOST solved the problem at 2.5 turns out. The pops were fewer and farther in between, but seemed louder when they did appear. I figured I would have to live with this.

The main jetting was changed from the standard setting until I felt I had good power across the revs until I ended up with the following settings for my configuration: Mains 165, Air 210. All other jets and settings remained standard. A few points noted during this process:
First, economy seemed to improve when GOING UP in jet size. This is probably due to not having to open the butterfly as much as with leaner jets, for the desired power to be applied. Second, Any change in Main jet size, roughly corresponds to 3 steps in Air size. In essence, if you notice a difference whilst changing main size one step, you will probably have to change the Air size three steps for any change to be noticed. usually, what you want to have is steady idle (mixture screws and idle jets) smooth progression (idle jets, by-pass screw and progression holes) good pull through midrange (main jets) and free revving up and beyond the redline (mains and air corrector jets). On the B series engine with its rather archaic (and by modern standards inefficient) Westlake combustion chambers, the ideal mixture curve would thus become lean-rich-lean (15:1, 12.5:1 and 14.1:1) over the revs. Once you have gotten the idle and progression right, the mains and airs are quite straightforward. Just use your senses and listen to the engine sound. When you go rich on the mains the engine sound will become more deep-tone, sound somewhat "rough and laboured" and you will spend more time pulling through midrange. Back off two steps and try again. As far as the airs are concerned, you stay with a given size main that gives you good power midrange, then go up 3 steps at a time, until the engine starts to sputter at WOT and high revs, refusing to pull further. Then you go down until the sputtering is no longer there. Done. The trouble with this is that unless you do this on a dyno, you would have to find a stretch of road where you can go WOT on 3rd or 4th for quite some time. Public roads are NOT recommended for this. I did not mention that I also own and race a 1966 MGB Roadster with a Peter Burgess engine...The race track is the ONLY place you can find the PRECISE air jet size, outside a dyno bench, but you can get pretty close whilst still keeping your driving license, although you might have to pay a few speeding tickets along the way. Happened to me and should be budgeted for in the conversion cost... The same also goes for those who want to fiddle with emulsion tubes. As a reference, my racing engine uses a DCOE Type 152 with the following settings: Mains 175, Air 205, Pump 60, Emul F16, Idle 55F9, Choke 36mm, screw 26 closed. Since less time (I hope!) is used in low revs, the idle circuitry and screw 26 have less importance on the track. For information, I can mention that when I bought the race car, it had 155 mains and 210 airs. It was popping like mad from 6200 revs and up with poor power deliver. Rejetting did away with sputtering and gave far more power This together with Hoosier R3S03 tyres and more track-time made me cut my lap times with 16 seconds on Johor Bahru circuit in Malaysia and granted me first-in-class and 3rd overall, in the Classic Car Club of Hong Kong 2001 racing series. I also competed in the-class-above, B-class, at the Merdeka Classic Support Race 2001 at the Sepang F1 circuit, where I pinched 2nd in class, after a VTEC Honda-powered Mini (Yes ! they do weird conversions here. You should see that thing go).

Back to DCOE settings. After a while, the coasting-popping became too much for my ears and I decided to do something about it. I spied an old style DCOE Type E9 on an A series manifold in one of my parts bins. The carb looked somewhat sad on the outside, but the inside was not bad at all. A quick disassembly, lots of carb-cleaner, cotton-swabs and a careful grind of the outside with a soft rotating brass brush (never use steel brushes on aluminium !) and the assembly looked if not exactly new, then "fair vintage style". Good enough for me. The Type 152 was replaced with the E9 and off we were again to challenge CO levels, power curves, air/fuel ratios and the Hong Kong Police, alas.

DCOE Type E9 tuning:
The carb was configured as follows, when out of the bin: Mains 195, Air 165, Acc Pump 40, Idle 60F6, Emulsion F9, Aux Vent 4.5, Chokes 40mm. This leads me to believe that the carb had never been run on an A series engine. Checking manuals I suspect this setup to come from an Alpha Romeo or possibly from a racing Austin Healy big six, Aston Martin or other large displacement or high rev application. Attempting to change the chokes I noticed that one of them was oxidised fast to the housing. It was also damaged to previous attempts to loosen it, so the theory of an ancient race application seems most compelling, doesn't it Watson ? Logical deduction if summed up suggests that it once belonged to an owner with a large, high revving engine who also like to fiddle with things, but was not very handy. This profile of a person actually corresponds to a former CCCHK racing member - no one named! Anyway, I digress.

The E9 was installed jetted as follows: Mains 165, Air 210, Idle 55F8, Pump 45, Emulsion F16, Chokes 36mm (removed by soaking the housing alternatively with Carb-cleaner and WD40 and leaving overnight, then tapping GENTLY with a plastic hammer. The 40mm choke could not be saved, but the housing was squeaking clean, just needed a final removal of aluminium oxide using a tooth-brush style brass-brush). You just HAVE to love DCOEs for their flexibility!

Setting idle mixture, I was now able to follow the books! Best idle was obtained at 1.5 turns with the 55F8 jets. However, slow speed and progression transition tests gave some hesitation. Up in jet size, all the way to 60F9, when surging started to appear, then back to a 55F9, which gave perfect results. General notes: The change in jet size MUST be accompanied by re-adjustment of idle mixture screws. For the 60F9 0.5 turns was enough and 1.0 turns for the 55F9 gives best idle. Changing the jet size seems much more subtle with immediately noticeable results on the E9. This must be attributed to the additional parameters that screw 26 introduces on the 152. On the E9, you just change jets and adjust mixture. On the 152 you would have to accompany every jet change by mixture AND screw 26 adjustment. This is why my Macau buddy told me that he had scrapped a set of 152s on one of his race cars, because he could never get them right - and he has 25 years plus DCOE experience!

With the 55F9 jets and idle mixture 1.0 turns out progression is smooth, yet powerful and without stumbling or hesitation. Best of all: There is NO POPPING AT ALL ANYMORE!!! Magic!

Idle is nice and even, with minimal engine rocking motion. When using the 152 the engine would rock and shake quite violently under 1000rpm. All gone now.

The rest of the jet settings were basically transferred over form the existing 152 setting, with good results. But, but...Once a fiddler, always a fiddler, so I tried various other combinations, like Mains 150, Air 200, Emulsion F9, Pump 40 etc., but always came back to the settings that worked with the 152: Mains 165, Air 210, Emulsion F16, Pump 45. As you "grow closer" with your particular engine and car, you CAN start doing advanced fiddling, such as Emulsion tubes. However, in my experience, be methodical - only change one parameter at a time. Check/adjust all other settings back to your baseline of tune, i.e. valve lash, ignition timing, etc. Because of the subtle nature of the advanced tuning, you MUST make sure you maintain a correct baseline. I repeat: Only ONE parameter at a time! Oterwise, using a dyno is your
only choice.

I did pick up yet a few speeding tickets in the process. HK Police (a.k.a. HK BPFMCB, don't ask me what it means - that could be considered slander!) know the silver roadster pretty well by now and waive either furiously or with a broad smile, depending on a combination of jetting factors, such as speed, amount of black smoke, engine sound, etc. Go figure..

Conclusions:

Weber carb tuning is simple if you do it step-by-step in a methodical manner. However, it is not for the "weekend mechanic" unfortunately. Better leave it to the pros or a dyno shop, in that case. Be prepared to spend LOTS of time (and sometimes money) before you get it 100% right.

The Type 152 is definitely more difficult to tune for road use. It does seem, however, to give a bit better fuel-economy over the old E9, maybe due to "magical screw 26", or just to the fact that manufacturing processes have certainly changed over the past 25 years to computer controlled and designed approaches. I could do with a bit better economy on the E9 in its current setup, but guess what: When you hit that pedal and take off like a rocket, you don't want to give up one ounce of power! Besides, the HK Government needs any cash-contribution they can get in these hard economic times...

The E9 (or Type 18, or any other old style DCOE) is personally recommended for the everyday-street-Johnny-Rocket-Tuner. The 152 is fine for racing applications. In fact, since I have in this process "liberated" a second 152, my plan is to build a third race engine with a cross-flow aluminium head, special long-duration, high-lift cam, etc., for class B racing at Sepang next year. However, you CAN get the 152 pretty right, it will just take longer to tune. I must admit, I cut the process short and gave up at 90% of the race. A DNF, I guess...But I had the luck and luxury of having an E9 handy. They are getting rare and the information within this article will probably hike the prices even more!

Final note on air-filters, air-horns, installation, manifolds, linkage,
etc:

Air Filters:
Sock type=they suck. Because you place an individual sock over an individual air-horn, you alter the balance of the setup and will never get jetting spot-on. This becomes a serious problem when raining or wet (often does in HK during summer). I do NOT recommend any sock-type filters.

K&N Pancake filters:
Work great on 32/36, because there are now air-horns! Also, due to the downdraft design and clearance, this is the only filter available for the 32/26. However, when used on a DCOE, the front-plate will seriously restrict the flow. Also, you will be forced to use short air-horns, to fit them inside the filter assembly. This, combined with short intake manifolds, as required for clearance on a rubber-bumper MGB, and you have lost a huge amount of low-end torque. I don't like the K&N.

Piper Cross "bomb-style":
This is the best filter you can have! Accommodates full-length air-horns, is yet compact in design and good for 50.000k plus operation. Give it a wash and go for another 50k, like other "eternal" brands. Warmly recommended.

Air-horns:
Full-length standard air-horns=great torque, plus, they look good ! Hey, that last point IS important, you just doled out $$$ for a setup. Better look nice too. Don't believe me ? Why do people send in pictures of their setups to this site then ?

Short-length standard horns=great for racing. Gives you those extra few revs on the straight-line. You do loose a bit of low end torque, but if that is your concern on the racetrack, then you might as well pick up stamp-collecting, embroidery, or something equally exciting...

Full-radius horns=even better. Computerised design gives 5% performance increase across the revs. Downside is they are not standard, but if you are looking in to changing horns, go for these from the start. Buyers note: Some carb vendors strip off fuel-banjos, air-horns, etc., and sell these bits as "standard options". Tell them they are stealing crooks and that when the carb leaves the factory, those bits are attached to the main body! Some people do anything for a buck...

Installation:
Please, please install the carb correctly. Float bowl in front for the 32/36. Soft rubber mounts and O-rings for the DCOE. DO NOT over tighten the DCOE mounts. Just enough to stop any vacuum leaks. Good testing procedure (credits my Macau buddy): Initially tighten up mounting studs only until they grip. Start up engine (don't worry about mixture setting etc. at this time), let it warm up completely. Adjust idle to around 1000 revs. Grab the barb by both air-horns and move it side-to-side, up-and-down slowly. Be firm, but not violent. If engine speed changes, or if it stumbles, you got a leak. Tighten up nuts some more, repeat, until nothing changes when you "shake" the carb. Stop there.

Manifolds:
They come in various lengths and qualities. TWM=only provide short
length (rubber bumper style) models now. OK for racing, but you must use
long horns in this case.
Pierce=Good quality. Nice length. Inexpensive.
Cannon=Best quality. Nice length. A bit more expensive.
No-name copies=Look out for casting errors, provisions for booster vacuum hook-ups, etc. Can, or can not be a cost-effective alternative. All depends.

Linkage:
Be prepared to pay a bit more for the linkage. The only model I personally recommend is the racing-style dual-cable and spring setup. This linkage installs under three of the top screws of the float bowl. If you don't use a quality model linkage, you can not expect to get a precise tune out of your setup. Also, check the Yearbook of Racing and look at the number of DNF due to accelerator cable snaps or carb linkage failure and you will get my point. Silly to have to end a weekend you just spent $1000 for, just because a failing $10 cable. In the street, it could mean getting you home, versus spending a few hundred for the towing vehicle. Bad economy, in my mind.

Well, folks, that is all I have to contribute with right now. Hope someone out there benefits from all this mumbo-jumbo.

I will keep you updated on my future setups, like the X-flow dual DCOE B series engine, the V8 MGB GT Sebring replica I am building - it will have a 3.9 Rover V8 with either 4 x DCOE on a cross-ram manifold, or 4 x 45 IDA (hopefully 48 IDA, if I can find them). Target HP 280, with target weight under 2000lbs.

Take Care & Safety Fast !
Ingemar Lampa
Hong Kong

------ end of original email-----------

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