Calling DCOE Owners -Looking for any progression hole pictures!

Hi all,

I'm trying to get hold of a photo of the progression drillings on a 152-G to compare to the three holes in my own and attempt to unravel the fact that it is impossible to properly tune the operation below 2500 rpm, but haven't had any luck. Do any of you lovely people who have these carbs feel like taking a picture and posting it?

Much appreciated!

 

I've got a few sets of twin 40s kicking around, mostly from old Alfas. I'll have a look.

Are you using 40s or 45s incidentally, and what's the spec of the engine?

 

Cheers Mike, the full spec is on post 4 on this thread.

I'll take a picture of mine later and post it up for comparison.

 

Have you had a wideband AFR gauge on it?


From Jon Olds' thread on the setup of his similar but different engine.

Strikes me that you're running bigger main jets than Jon, although his engine is a higher spec in terms of head and cams.

 

Sadly no wideband as yet, got my eye on the SLC PP2 here.

I bought a 4-2-1 with a lambda plug in it a while ago and I'm trying to get hold of a compatible system to go with it before I can think about getting the AFR. I'm very much looking forward to getting some actual measurements as I suspect there is quite a bit of refinement to be done!

Back to the progression drillings, I took some photos earlier:
These carbs were originally fitted to a Sunbeam Alpine

TIPO 34


TIPO 35


I suspect that the first drilling on the 35 is smaller than on the 34, which would explain the off-beat running at small throttle openings and low RPM. I've ordered a set of hole gauges to quantify the difference and I'll set about enlarging the smaller hole to create a matched pair after that.

It also looks a little like one throttle butterfly sits different to the other, although the carbs have been very carefully balanced with a synchrometer, not really sure what's going on there.

I'd be very interested to see anyone elses prog drillings as a point of reference, obviously I'm pretty keen not to mess the carbs up!

 

Just changed the thread title as it would be great to see the differences between the different carbs progression drillings as I think this is one of the key features that make any particular DCOE unique, and get peoples opinions on how well suited they are to the engines they're fitted to.

I've heard that the 152G is ideal for the VW 16v so that one is of special interest to me but I'd love to see the others as well.

 

I brought a pair of DCOEs home from the Alfa stash tonight. They're a 44 and 45, which are 3 hole items similar to yours. Originally fitted to a 1600 Alfa twin cam lump. I'll have another dig and see what other sets are there. I know that one of the cars is on Solexes, so they're no good, and one of them is on Dellortos. I've got another set of Webers sat there from my mate's 1600 giulia super, so they should be the same as the ones I took home tonight.

Where are you based? I have a hand held AFR meter which would give you an idea of how rich it's running at different points in the range, and under different throttle openings, as long as it's legal and driveable.

Did you have to use the air bleed screws to get the carbs to balance, or did they balance without having different bleed settings?

 

First off, I don't have pics, but I have to agree that the 4 hole progression 152g's worl exceptionally well at low revs. Both my 2.1's have had them and they work well.
The original John Jones 2.1 I bought was using a pair of 48 dellorto's, that worked well at WOT but lacked control and finesse one light throttle.
You need to get the drilling pretty spot on too, that is if the other holes are in the right place first.

 

I have 40's on a kr, as mentioned, 45's on an abf, and 48's on a shelf. Can take pics and email them to someone, if this would help. Someone pm me an email, Ta

 

It may well be that progression drillings are part of your problem, and I'll supply the ones I can find.

However, if you don't know what your AFR readings are doing at part throttle (and I expect that the rolling road setup would have mostly been at WOT) then I think maybe there's a step you should take first - to try and optimise the part throttle jetting without modifying progression holes, particularly because it's a step that's tricky to undo.

 

luminition AFR004: I swear by them

 

I'm based in Coventry, the car is legal and driveable. I'd certainly be interested in quantifying the AFR.

Unfortunately I don't have air bleed screws on these, I have played extensively with the idle fuel screws and got it as good as it will go in terms of smooth running.


Hotgolf: that's the symptoms mine has, goes great at wide throttle openings and at higher rpm

Jon: PM sent

Mike: I have tried about five different sets of idle jets and I can get it to run smoother with richer ones but judging by the fuel consumption I am richening the whole idle circuit to compensate for a small flat spot, can't be sure without AFR data though.

I'll check the drillings when the hole gauges arrive, I'm sure it can't be good if the drillings really are asymmetric, and I will definitely try to modify them (carefully) to match.

Thanks for the input guys!

 

I've been having a look for other carbs and here are a few, clearly there can be some serious variations between them:

152 (normal 3 hole type) Interesting how far they all sit toward the front of the carb
#

151 - 3 hole. This comes from a thread where someone else is having flat spot problems


Not sure what this one is


DHLA 40, not sure what kind of variants these come in, or what this one is


A different DHLA 40


DHLA 40-E 5 hole

 

Just reading and re-reading pages 41 and 42 of the excellent weber book regarding idle jets and progression . the bible for info IMHO. (Webcon sell it : 01932788805)No ISBN

 

What's your base ignition advance set at?

 

Good question, I set it to the Haynes (I thibk) spec, 19deg BTDC with some specific conditions (vacuum hose disconnected and at a certain rpm)

The big problem with the ignition system is that the vacuum signal to the ECU comes from a single tapping on runner #1, which of course pulses like crazy. Previously, the car was put into storage (nearly three years ago), I attempted to fix this by restricting the vacuum hose and running it through an inline fuel filter to act as a damper. I suspect that it works ok-ish at smoothing the pulse but its still an awful bodge and definitely takes too long to respond to changes, and I suspect does not allow the full vacuum to build at no load. I ordered all the bits on Monday to drill and tap into all four runners and do it properly. I also got a 0 to -1bar vacuum gauge (the cheap kind with no glycerine so it will flutter like crazy if the vacuum isn't constant) that I'm going to connect to the feed to the ECU before and after this mod in order to quantify how bad it is at the moment and make sure that the new system works as planned.

 

Duplicate post

 

My KR (I think: its too cold and dark outside to look..) has all four runners T ed before going to the ECU. The guys that built it may have had experience in that direction, it was an ex tuner car.
A restriction in the line will damp instabilities, well it 'snubs' gauges anyway

 

I thought a KR (and I haven't set one up for a while) was 6* BTDC at idle, probably with the ISV pipe blocked off, but I don't really remember.

What's this vac pipe you speak of? A KR dizzy doesn't have vacuum advance, so I think when you say Vac Line you mean the one to the ECU? Are you running a KR dizzy and ECU or some other combination?

 

You're probably right Mike, I think I had to set it at x000 rpm rather than idle, sounds like this is worth checking though.

As for the vac pipe yes this is the one to the ECU, I am running a KR dizzy and ECU, the engine note changes when this is disconnected or when I suck on the end

Jon, all the best installs for this setup I have seen are using all four runners and if the map in the KR ECU is similar to other maps I've seen then there is a retarded section at idle to stabilise the engine, I'm not convinced my bodge is allowing the full vacuum to reach the ECU at idle. The gauge turned up yesterday so I'll try to get out there tonight and see what the vacuum quantity is at idle, and how quickly it responds to changes in throttle position.