Weber DCOE Progression Holes.

S

Sunroof

Well-known member
VIP Paid Subscriber
1000+ Posts
Fellow Frogger
Joined
May 31, 2005
Messages
3,426
Location
Boonah Qld
I have tried a lot of things to get my Weber DCOE's tuned right. They are on an R17 TS. The problem is surging between 2000 rpm and 3000 rpm, and poor idle. I have read many pages of stuff on the Web and my thought is that the carbs I have, have only have two progression holes. There are a number of people I know who have given up and fitted a down draft Weber saying it is too hard on these motors. I have heard that people have got carbs with two holes working and yes so can I if I make the idle jets and idle screw rich and probably if I try and drop the rpm when the mains come in with an appropriate emulsion tube, air corrector etc. But this is at the expense of top end performance, a big cloud of black smoke on acceleration, and higher than normal fuel consumption.

I need to point out for those that are not aware, the idle jet also supplies the progression holes. They provide the fuel until the mains come in normally from 2,800 rpm to about 3,200 rpm. 3200 rpm is 100 kph so there is a lot of driving done on just progression holes. Just to complicate matters the accelerator pump allows fuel to flow not only during hard acceleration but during normal running. There is a document on Renault engines with these carbs that translates to "if progression isn't right then poor idle and progression will result".

Now 1600 cc Alpine 110, 310, and presumably R12 G have 3 progression holes except for very early carbs. The general consensus is don't try and drill additional holes unless you are a professional. It is essential that any additional hole is the correct size and in the correct location. But Alfa's have the same problem and drilling an additional hole solves it for them. Ford Zetec have 4 holes but run smoother with 5.

So does any one have the correct carbs and can they tell me the size and location of the progression holes or am I talking crap.

The correct carbs are No. 29 and 30, or 36 and 37, or 38 and 39,or 62 and 63. Note they are not pairs as one carb has and air corrector screw for one cylinder to get it to balance. Apparently a problem, as I was told by a mechanic from the R16 rally team that different emulsion tubes were used in the rear cylinder to get it balanced. Incidentally they seemed to be reasonably smooth when I had them on my R12G replica using the same jets, emulsion tubes etc.
 
Are all the linkages unworn, as well as opening the butterflys in a synchronised manner? Also are the carbies in decent condition such as butterfly spindles, bearings, etc
 
Hi Sunroof

What are the specs of your carbys? 40 or 45 and also what jets are you running?

I did have DCOE40's on my R12 (engine removed from car with carbys because of ring problems) and I got the car to run OK, I also had my carbys setup on a dyno.

Also is your timing correct? (this was adjusted when I had the carbys setup)

The carbys I used were bought off Ebay and I think they were off an Alfa or a Fiat. Here are the jet sizes that I used

TIPO 40DCOE 32
Air corrector 200
Main jet 130
Emulsion tube F9
Idle jet 50 F8
Pump Jet 35
Venturi 32
Aux Venturi 4.5
Starter Air Jet 65 F5
Pump spill 60
Needle valve 175
 
COL said:
Also found this: Weber DCOE45 152 45DCOE progression circuit modification - Alfa Romeo Bulletin Board & Forums
Click to expand...

Col that is one of the most precise 'How to fix this..' I've ever read in regard to DCOE's. Then again fuel pressure is quite low with carbies and Alfa's aren't know for reliable electrics...QED leaking EFI and non-Marconi (last good Italian electrician!) wiring and everything turns Orange and Hot. :2cents: :cheers: Brendan. p.s Does Iain Stewart still run his carbie business in Brisbane? Font of knowledge. Murray Coote, Ohlins distributor, maybe of help to get in contact. Murray is based in Brisbane and a Peugeot tragic in the best sense.
 
Last edited:
Can you post up exactly what you have that is where to start
Some carbs are better than others some don't work at all
Webers were set up and drilled for a particular application and sometimes that is all they will do
some are excellent and very adaptable
40 dcoe 2 are excellent 22 and 32 are good
new 40 dcoe 151 are basically old 2's with air bypass
new 45 dcoe 152 are murder to set up on anything hence the 4 and 5 hole versions which are better
Its not how many holes but where they are new 45's are too far back so the fuel runs out before the 1st hole is uncovered
I ended up redrilling my new 45's 15 years ago but it is not for the untutored
Tell us what you've got and we can go from there
cheers
 
Hi Sunroof could the problem be that the electric fuel pump is putting out too much pressure. I know that the TS head will not accept a mechanical pump. but maybe a pressure regulator may help. we had the same problem with our R12 & found that when we put a mechanical pump back in all was well. just a thought David
 
The carbs are 45mm Type 13. I have checked the barrels with a torch to ensure each butterfly seats properly. The shafts are not bent and the butterfly's aline correctly. I have a pressure regulator controlling the pressure from memory at 2.5 lb per sq in. The floats are currently set at 5.5 mm but I have tried as far out as 8mm. All linkages and shafts have no wear. Currently I have

45DCOE 13
Air corrector 200
Main jet 130
Emulsion tube F11
Idle jet 50 F8
Pump Jet 35
Venturi 34
Aux Venturi 4.5
Starter Air Jet 65 F5
Pump spill 60
Needle valve 175

But I have tried a number of combinations 40f9, 45f9, 50f8 and 55f9 idle jets. 125 and 130 mains. 180, 200 air bleed. f9 and f11 emulsion tubes. Once on mains it always runs ok. Runs best on 55f9 idle jets with rich settings on the idle screw. But clouds of black smoke until on mains.

index_001.jpg
 
Forgot to mention I have 4 carbs the same, and tried them all. I have tried 3 different distributors. One set up especially for the car to Alan Moores specs. One from a 16 TS with the vacuum plate fixed. One off my R15. They make little difference. I have tried a range of timing positions some more successful than others. Currently runs fine with a standard R15TS set up although it has a lumpy idle. The cam was reground but was supposed to be standard R17G/TS, whether it is is another possibility. With the two side draft on it easily runs up to 7000 rpm. With the down draft not so keen.
 
Just looked at my Dyno report and it mentions replacing two missing washers under front jets. This was causing fuel to leak past causing problems at idle and when running on the progression circuit. May pay to check that all washers and seals are in place.

When I got my Webers all I did was get them out the box and bolted them on the car without checking anything.
 
Interesting !!

Hi:):)
Nothing to add here. Just to say there is always something new to learn and AF is the place to find it :approve::approve:

As dauphproto said the carbs are drilled to suit a particular application. I recall getting them in the old days in cardboard boxes with a Ferrari or Maserati part number and model application printed on the box. You had to change all the chokes jets etc etc to make them run, as some people found out if they fitted them as supplied. :joker::joker: Never heard of redrilling the progression holes then. Interesting discussion for sure.
:cheers: Jaahn
 
No luck Col, all washers in place.

Jaahn.

Apparently

Lamborgini350GT, Maserati 3500, Aston Martin DB4 and 5, Lotus Elan, Fiat 2300S, Alfa Giulietta SV and GT, BMW 1800TI/SA, Renault 12 G, Alpine 110 1600, Alpine 310 1600. All used the same carby numbers so one would assume that they were all with 3 progression holes.
It seems they were designed for high revving engines where the power was developed at higher than was normal rpm.
 
You're 13's should work fine and the basic set up is close
First up you need to check over the installation if the motor is surging it would suggest it is getting supplied with more fuel and air than the thrttle position would suggest which may be an air leak someplace. are you using O rings and holders or bonded (misab) type I prefer the latter as they are less fussy. I have never got on well with the older types and thackery washers

The progression hole problem usually gives very weak spots where the motor almost stops requiring big idle jets but never any black smoke
If you could try a set of F16 emulsion tubes (borrow) it would be worth a try as its also possible that it is drawing off the mains early as from memory the 11 is a richer tube than the 16 (they are listed in no particular order)
Timing. Lock the baseplate as the vacuum system will not work anymore, as the motor is not very hot it will stilll want 35-36 degrees max advance at 4000-5000rpm Idle setting will be where it is when you have set the max value probably around 6-10 degrees depending on the advance curve of the dizzy
Sorry there is no definative answer here as final set up is down to the man turning the idle and balance screws and I would be lying if I said I could do it well.Lucky for me my mate is one of the best set up men I've seen he can always get a significant improvement on my set ups do you have anyone locally who can help??
cheers
 
If it is a matter of checking for balance of carbs, or bent or damaged butterflies or shaft - you may find this interesting.
You can get motorcycle vacuum gauges with the right attachments to connect to webers, then adjust each individual carb until you get them matched as close as possible in vacuum. Inability to do so could help identify which carb(s) is at fault and perhaps even help with why.

All the reading and troubleshooting I have done suggests poor linkages and carby balance is more often the cause of issues than jetting/setup.
 

Attachments

  • weberbalance.jpg
    weberbalance.jpg
    95.1 KB · Views: 3,916
in the early 1970 with my 17 we had a lot of problems with what we thought was carby problems after a fair bit of trouble shooting (money) we found out that the cam was the problem. it had been reground which was the causing the problem. In my 17ts I have a the same problem but it is caused by the fuel injection between 2800 rpm & 3000 rpm.
 
Hey sunroof, I'm just looking at your combination of carb bits and you have a mixed bag really, your main venturi is a bit on the large side and the emulsion tube is a bit on the small side. An F15 or F16 may work better along with a 180 air corrector and try going down on your main venturi to a 31 or a 32.
The problem that you seem have is that the air is stalling as it is drawing through at lower revs and you are relying on the butterfly to speed the air up which is past the entry point for the main jet so you get poor fuel atomisation and fuel drop out, hence why all the black smoke until you are at higher revs. The emulsion tube needs to control the flow of fuel to the main jet along with the air corrector to control air bleed.
There is a common misconception that big chokes must be best as people wrongly assume more air in means more power. if you come down on the choke size it speeds the airflow up, increases low to mid range torque and also feels faster as the throttle response is better, lets face it, its good to have lots of power but why only at 7000 rpm if it splutters all the way there. Its better to sacrifice a few horses at the top end and a little lower red line for a more drivable car with mid range punch.
The cylinder capacity is a fixed thing on your engine along with cam duration, (unless you start re boring and changing cams before anyone says), so therefore with a 400cc piston and bore you can only draw in under normal atmospheric pressure 400cc. (again before anyone says it is possible with a highley tuned efficient engine and fancy inlet tract tuning to draw in more than the given volume of a cylinder but that is a whole different game, i'm talking theoretical here) In reality due to restrictions on manifolds etc you may only draw in 320cc. If you reduce the size of the inlet tube to draw into then in order to draw in the same volume it has to speed up through the venturi so with a small opening the pump has to suck harder to get the same volume therefore speeding up the flow and drawing the fuel through quicker. This is why you get a flatter torque curve, also the exhaust pipe size needs to be closely matched to the inlet size so if you have too large an exhaust pipe the same applies that the exhaust gasses stall and don't assist with self scavenging of the cylinders and also helping to draw in the inlet mixture for the next power cycle. This applies more to long duration cams than standard ones but it can help somewhat on standard engines.
I used to build engines for rally and fast road and I always used to use a cam that was a bit wilder than you would expect to work with any given state of tune and fit slightly smaller valves and also choke the carbs down to suit and it would give a really drivable engine which would pull from 1500 all the way to 7000 (even 8000 with a wild 1404 mini I used to have) so what i'm saying is not all theory from books.
 
Hi Sunroof

I have a Alpine A 310/4 1600 VE which runs the same spec engine as the 125 HP 12 G motor
it is running 45 DCOE WEBERS on the standard factory settings and it runs very well.
The model numbers of the carbies used are 38/39 62/63 68/69.
They all used the same jets etc , except for the 38/39 which used a 50 f 10 idle jet ,the other models used 55 f 8 idle jet.


DCOE 45

Air corrector 220
Main jet 135
Emulsion tube f 9
Idle jet 50 f 8
Pump jet 35
Venturi 34
Starter jet 85 f 5
Pump spill 60
Needle valve 1.5 mm
Float height 5 mm to 11.5 mm



The above sizes come out of a photo copied Alpine work shop manual.
I remember when i had them reconditioned the man in the carby shop said that they were different inside to normal webers, how they differ i don't know.

I hope this sheds some light on the problem.

Cheers 27 of 85.
 
Thanks guys for the interest and the input.

The barrel and venturi are the factory sizes for these engines. I know Autokar they are not the same as generally recommended by Weber but they are Renault factory recommendations that work as 27 of 87 has just said.
I have the jets sizes etc for all the variations for A110 and A310 as well as the R12 G. According to my book 27 of 87 you are correct for the A310. What I need is to know what progression holes your carby has. If I fit the correct jets for an R12G etc and the progression holes are different the problem will not be solved. Can 27 of 85 and Col take the progression hole plug off one carb and check the number of holes if more than two and I believe there will be, draw a diagram of the hole lay out or take a photo, with if possible the sizes. Usually the main hole (the one nearest the engine) is 1 mm and the others possibly .8mm or .75 mm. I have fitted almost identical jetting etc including the emulsion tube to what is recommended for the R12G. The exhaust is standard and Dave the cam is supposed to be standard but may be it is not. This could be the problem.


Thanks guys it is really the size, location, and number of progression holes that I need. If you only have two progression holes then I'll look at playing with jets etc. If more than two holes then I'll be very tempted to drill some in my carbys. If it doesn't work I can fill it up again with Devcon.
 
You must log in or register to reply here.
Top