243 replies to this topic

[Brian Pascoe]

James,

Here is some data from my idle jet change for you to chew on.

The 55F8 with the 3 mm counterbore and the repositioned F8 read in 2/3/4th gear cruising at idle 9AFR but in neutral 12.5AFR. But it was 13/14 AFR under slight  acceleration.

The 50F9 with the 3 mm counterbore and the repositioned F9 read in 2/3/4th gear cruising at idle 12AFR and also in neutral. But went 16/18 AFR under slight acceleration.

What would you try next.

Brian

[jd lj]

I wouldn't do any more tuning until you remove the balance tubes.

I need to know what the rpm's are at each point instead of stating it as light acceleration or cruise.

James D

[Brian Pascoe]

Ok, I will do as you say.

Brian

[natcamp10]

Talking about drilling new progression holes, the link I posted above has a special jig for doing just that.

If anyone is using 45dcoe152's but not 152g's and has a hesitation when coming off idle then they may need to drill another progression hole closer to the manifold. But this isn't a job for someone with their makita drill as much more precision is required. An alternative is to get throttle plates with a different angle to put the top edge of the throttle plates in the correct position in relation to the progression holes at idle. This model of dcoe has the progression holes further upstream (closer to the ram tubes) than others and may in some cases cause an off idle stumble. However if you have a strong manifold vacuum level then this model of dcoe can be suitable without any modifications. If you are experiencing this problem it may be possible to reduce it by increasing the idle mixture strength and upping the idle rpm's.

Brian this is unrelated to your problem but I just figured I'd add this information to the thread.




James

Hi James and brain..
brain sorry to thread steal again but we are doing same thing here . The only difference is I’m running 45 dcoe 152”s
James do you have a the part number for the modified throttle plates handy by any chance , I seem to have this stumble issue just off idle
My vacum is 22hg in the manifold , I don’t run any balance tubes between the manifold
I’m running this as follows in my carbs
F2 emulsion tubes
36mm chokes
150 mains
190 air correctors
55f8 idle jets
I did play with the carbs yesterday and richened up the idle mixture which helped but it’s a fine balance between getting rid of the stumble just off idle and creating possible a over fueling problem hitting the tipping point ( it would tend to splutter and carry on if I open the idle mixture screws up to far when about to hit the secondaries but run good just offi idle ), I did as mentioned this arvo and ran the car without the emulsion tubes and checked the float levels which was interesting cause I checked a few times and my float level is 28mm on all carbs which is wrong due a post at the start of the thread saying it should be 25mm .. so In saying this I’m going to raise the level but I suspect it’s going to cause another problem due to the f2 emulsion tubes .. Im going to order the 06 tubes from frank this week but before I do I want to do some loggin first ..i got the lm-2 meter today as well so I will weld in the sensor bung and try and get some data , I brought the full kit but for some reason I didn’t get the software CD
I do have spare 210 air correctors and spare 50f8 idle jets, I’m also chasing a spare body for one of my carbs if anyone out there has one
One other thing I noticed playing around is the more I open the idle jets up I can get rid of the pinging when i trump it but again when I go to far it’s doesnt like it , I’m supecting I’m lean on my low speed circuit
Cheers fellas
Nathan 👍

[EunUCh]

36 mm chokes are far to large for triples fitted to a 9 port , the reason is that when you crunch the numbers of the combined csa of the chokes compared

to the csa of the valve throat they sort of are just no where near what the point of most restriction is in the intake tract, which is the valve throat.

 

36mm chokes have a csa of about 1.5 sq inch and there are two of them per carb  giving 3 sq inch total feeding 1 valve and one cylinder at a time.

Suppose we have a valve throat of 1.5 inch diameter , this gives a csa of the valve throat of around 1.7 sq inch , this causes problems for starting the main

circuit due to lack of signal at the choke , (the carb chokes have almost double the csa of the valve throat).....usually causes a leaning out when the main circuit starts which can obviously be over come by playing with tubes/jets , 28mm chokes give a combined csa of around 1.9 sq inch, obviously depending on how well

the engine breathes and what rpm it goes to etc. will have a say in choke size , the weber tuning manual is pretty close to the mark on choke selection for rpm and capacity .....but we must remember that those numbers are for an isolated runner not a siamese port as is the case with the 9 port , point being , I think

we need to select the choke size based on an isolated runner but then work out the csa of that selection and work to get as close to that as possible keeping

in mind that on the 9 port we are feeding one valve with two chokes which will mean going smaller.

 

I know the sensors can be a handy tuning tool , ears are another one , if an engine with webers does not sneeze through the carbs on warm up when started

from cold with no cold start (choke) , the low speed circuit is too rich., usually only lasts a minute or 2 on light throttle just to keep the revs up.

 

 

 

 

 

[jd lj]

Nathan,
Feel free to jump onto the thread, it's there for anyone with dcoe's.

Your problem with the spluttering I suspect will be due to your high level of manifold vacuum. I had a friend who's car had 22-23hg of manifold vacuum and was spluttering from about 2000 - 3000 rpm's even though the fuel mixture was perfect. When I had a look at the trace of this rpm's range on the lm-2's software the mixture was fluctuating very rapidly and the trace line showed this however this was happening to fast for the lm-2's display to actually show it. To eliminate this you'll also want a set of Keith's "auxiliary air leaks" (available from the "Webstore" via my previous links).

I don't know if different angle throttle plates are commercially available, you may have to find someone who can custom make them for you. Otherwise it's probably easier to also buy Keith's jig for drilling the additional progression hole so that it's directly above the top edge of the throttle plates at idle. I hope that you don't mind me spending your money for you here.

Most manifolds have the carbs parallel to the engine but the front of the engine is angled upwards so this means that the fuel level in the rear emulsion tube well of each carb will be different to the front e tube well. Set the rear e tube well level to 25mm and the front wells will just have to be a mm or so lower. There's not much that can easily be done to overcome this. Your f2's will be better with this fuel level than a lower one but they still won't work as they should.

James D

[jd lj]

If you were to set the fuel level of the front e tube wells to 25mm there's a possibility that the rear wells may have fuel dribbling over into the auxiliary venturis passageways even before the main circuit begins and especially with the movement of a cammed up engine at idle.

For f2 emulsion tubes to work as I've described at the start of this thread the fuel level would have to be set to I think 21mm, but the bottom edge of the auxiliary venturis passageways are 23mm down so as you can see it's simply not possible to set the fuel level that high because the fuel will start flowing down the auxiliary venturis passageways from 23mm.

For the O6 tubes the air correctors that you will require will be most likely around 160 - 170, there's a very successful formula for working out this size with the O6 tubes that doesn't follow the traditional air corrector selection technique.

The chart in the weber factory tuning manual that refers to choke selection of independent runner (one choke per cylinder) states it as being for "sports engines" but referring to them as "race engines" would have been more appropriate.

James D

[jd lj]

https://www.webstore..._id,other_items

Here's the link to where to purchase the components I've mentioned above.

[jd lj]

Nathan,
Are you looking for a Italian or Spanish 45dcoe152?

[natcamp10]

Nathan,
Are you looking for a Italian or Spanish 45dcoe152?

Hey James
I’m looking for a Italian model

[jd lj]

Nathan,
Since your in the planning stages of building a new engine it may be worthwhile to talk to your cam supplier about selecting a cam that will give you a lower manifold vacuum level than you currently have. This way you shouldn't have to worry about the surging problem that you currently have. If you had a manifold vacuum level in the high teens that would be preferable.

An alternative to having to drill new progression holes above your throttle plates at idle would be to use a different model of dcoe such as 9's (note there are several different types of the 9's and you'll need a matched set), 13's or rt charger dcoe's 53-56 or 152g's these have more favourable progression hole patterns. The 152g's are the same as the 152's but with an additional progression further downstream (closer to the throttle plates at idle).

[Brian Pascoe]

James.I removed the balance tubes from in between the Manifolds and tested the vacuum. It hovers around 12 HG.Also I had to lean the idle mixture to 12.5 AFR as it was reading high 10's AFR before I removed them, whether that tells us anything or not.I went to do some road testing ,but the diff just started to make a horrible noise, so it looks like a rebuild.So I will be off the road for a while, but will still monitor this thread.

Cheers Brian

[jd lj]

Brian,
Did your idle mixture change due to removing the balance tubes or was it idling that rich prior to removing them?

James D

[EunUCh]

Not sure on set of afr numbers to go on , their is a lot to read in this thread , but I think their was a point where things were quite good down low until the "idle"

jets got bored out and things got a bit rich in that area but still had problems higher up.

 

Not sure how many turns the idle mixture screws are supposed to be out on a set up like this because there are two idle ports feeding one cylinder but usually

the idle is not too bad to get pretty right.

The idle circuit also gets used while transfer starts as well then drops off as main starts.

Here is what I would do , go back to the smaller idle jets and tidy up that area to get it not too bad, going on the #s it looks like it is leaning out as the main circuit is starting to pull over as the transfer is dropping off (from around 1800 rpm) . The reason i think this is quite simple , take the e tube and turn it upside down , yes upside down with the main jet pointing up.

On the f2 from memory there is a ring of holes around the barrel area of the tube and some more further down looking at the tube with the main jet up.

That lower set of holes is the low end of the fuel curve and that is where it seems to be leaning out from post 82  , solder the lower holes only and see if that richens up that area , it may not be a lot but it might be enough to see which direction to go.The tube will now look close to an f16.

Just had the opposite fault with f16 tubes going too rich in the very same rev range so had to drill holes........some people don't like drilling holes but Dave Vizard would probably know a little more about these things than me  so i took his humble advise and it does work.

[jd lj]

Now that Brian has removed the balance tubes from his manifold he now needs to drop back down to the idle jets with the 0.5mm fuel inlet as opposed to the existing 0.55mm fuel inlet and this will hopefully resolve the richness that developed at idle. By removing the balance tubes the manifold vacuum won't be dampened so much and I suspect that this is why the mixture richened up after doing so. So now that this is resolved the off idle leanness that he was having should be taken care of. Altering the emulsion tubes will have no benefit on the off idle leanness, this is caused by the low manifold vacuum. Increasing the internal diameter of the idle jets makes them work better on engines with a low manifold vacuum level.

F2 and F16 tubes are both flawed when being used in a dcoe because the ring of bubbling holes are situated high and dry above the fuel level and therefore cannot perform the function that they are intended for. The two sets of holes higher up the emulsion tubes on the F2's will also delay the main circuit tip-in so plugging them as described above would be beneficial, but this doesn't change the fact that the bubbling holes are still too high above the fuel level. The holes can be plugged temporarily for testing with tooth picks and also using high strength loctite and then heating it until it hardens. One of these holes must be kept open to act as an anti siphoning hole. To make F2's almost work correctly they need 2mm cut off the bottom of them and this will put the ring of bubbling holes on the fuel level when it's set at 25mm down from the top of the emulsion tube /idle jet tower, ideally these holes need to be 2mm below the fuel as they are on Keith's O6 tubes.

F16 tubes have a larger outside diameter than the F2's and this extra surface area increases the impedance on the fuel having to travel past it and therefore delays the tip in further.

Earlier on in this thread I've gone into much deeper detail on the working or lack of of std emulsion tubes but if necessary I can go deeper and elaborate further if there's any unanswered questions.

Brian is no longer using the horrible F2 tubes so the modifications mentioned are not relevant to his current set up.

Over 10,000 hours over many years have been spent reverse engineering dcoe's by Keith and he's developed a series of components to resolve their problems.

James D

[natcamp10]

Ok guys I have just purchased the o6 tubes from Kieth .
Found a good blue motor crank so the bottom end for the new donk is starting but this won’t go in until early next year I would say ,
Also I’ve done some data logging and I have a leaning out problem on my current motor between 1700rpm and 2200 rpm , it hits 16/17 to 1 , all this time before findthis thread I thought it was running rich
Nath

[jd lj]

Hi Nathan,
Can you post your current jetting specifications and measure your manifold vacuum level. You'll need a one way check valve fitted in the hose to get a steady reading when doing this. You can measure this vacuum level from the brake vacuum port on the manifold.

With the O6 tubes don't follow the std procedure normally used in selecting the air correctorsfor dcoe's, there's a formula for this that I'll elaborate on later. I've requested that Keith make the bubbling holes on your O6 tubes slightly bigger to suit the Holden 6 better.

James D

[natcamp10]

Hi James
I’m running as follows
150 mains
190 air correctors
55f8 idle jets
Float level set to 25mm on the back section of each carbies float chamber as per pre posts on this thread
Vacum is hi atm 21 hg and I know I need to bring this down , i do have a different cam I was thinking about putting purely for learning purposes
Also 36mm chokes
Do you have spare body / butterfly assembly 45mm 152 Italian Webber that you might want to sell ?
Cheers
Nath

[LC-GTR-1969]

What cam are you running now?

[jd lj]

Nathan,
I'll see if I can track down a 45dcoe152 for you, give me a few weeks and one will show up soon enough that model is quite common.

I just went back a few weeks through this thread and realised that I'd already requested for you to list your jetting specifications and manifold vacuum sorry to get you to do that again. However how the pump circuit, what's your specs on that? I assume that you have the std short pump rods and light pump rod springs as originally fitted to 45dcoe152's, but check these and the pump jets and discharge valves (the valves are in the bottom of the float bowls).

When you are experiencing this leaning out as mentioned above is that whilst at a steady cruise or with acceleration?

If the surging you have is as I expect then from everything I tried on my friends car with the same problem and high manifold vacuum such as yours then jetting changes alone won't cure it. You need to bleed off some of the manifold vacuum within the progression circuit with Keith's Auxiliary Air Leaks (available through the Webstore linked previously),as you gradually open these up you'll need to increase the size of the fuel aperture on the idle jets to compensate for the extra air that will be entering the circuit. On my friends car his idle jets ended up being customised with a 0.6mm air bleed and a 0.95mm fuel inlet. This sounds excessive but keep in mind that once the manifold vacuum level is reduced the vacuum acting upon the idle jets is reduced so therefore so is the rate that fuel is drawn through it.

I suspect that as it is you may need a richer idle jet which you could work towards that but keep in mind that if you're going to reduce the surging then you'll need to increase the idle jets further once you use the auxiliary air leaks. For this reason just use a set of jet drills to modify the idle jets and save yourself some money.

[jd lj]

Nathan,
If you do order a set of Keith's Auxiliary Air Leaks you'll need the ones with a M9 thread. The newer model dcoe's such as 45dcoe152 and 152g have progression hole covers with a M9 thread.

Older model dcoe's like 45dcoe9's and 13's have a M8 thread on the progression hole covers.

James D

[jd lj]

After more recent testing I'm happy to confirm that on my car there are no negative effects by removing the softmounts and using the bakerlite dcoe spacers that I made. For a long time I've thought that the softmount requirements with dcoe's was a load of BS.

Just to prove it I'd like to get a spare lid and cut a large section out of the top but retain the float and needle and seat and then watch / video what's happening in the float bowl as the rpm's rise. However I don't have a spare lid to sacrifice.

James D

[natcamp10]

What cam are you running now?

Hi lc
I’m not sure atm as I didn’t build this motor, I’m actually pulling it out in a few weeks and having a look in it so will post , it’s got a really nice head on it tho with really good port work but it’s not very lumpy like I want it lol
Thinking of purting a spare cam I i got cm2050
Which is a high stage 2 hydraulic cam which should drop my vacum

[natcamp10]

Hey jd
Just saving a few pennies for the air bleeds
The hesitation is more under sudden acceleration between the above .
I will check the pump springs when I get home but sure they will be standard
Changing the idle jets before did help with so I will get the get drills and open them up as per pre posts in this thread .. 3mm I think what’s was discused
I will post more soon as I got go right now

[jd lj]

Hi Nathan,
On your engine drilling out the internal bore of the idle jets won't be suitable. Doing so is only for engines with a low manifold vacuum level. For your vacuum level this mod isn't necessary.

Due to your lean spike being at sudden acceleration I think that you'll need to work on your pump circuit, you may need to use the medium pump rod springs instead of the std light ones.

I expect that you're new emulsion tubes will also help this somewhat.

James D