Tuning 3 x 45 DCOE 3 Webers

Thanks James,I will look into all your suggestions, and save some pennies.

Brian

Brian, keep in mind that you'll be able to sell a lot of your old parts to recoup some of the expense. But unfortunately webers are expensive especially when you have three and need six of everything.

Col, I'm happy to help.

James

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,Just ordered the following tubes ,so I will let you know how they go.Venturi Fountain Main Circuit Tubes for Weber DCOE Sidedraft Carburetors

Hi Brian,
Welcome to the team. :-)
To the best of my knowledge you're probably the second person in Australia to have these in your hands. They should arrive in 1-2 weeks.

As a starting point fit your existing main jets and air correctors and test what's happening with those. Now you need to forget about any conventional weber main circuit tuning that you may have read or been told. The main jets only get changed to adjust the high rpm/WOT mixture strength and not the air correctors. The air correctors are to adjust the tip-in mixture strength of the main circuit, this is where you're currently having the hesitation. So by using a bigger air corrector you'll be adding more fuel at this point in time, think about how a suction pot spray gun works whereby as you pull the trigger more air flows through and this additional air draws through more paint, it's the same principle happening with these tubes. A smaller air corrector will obviously have the reverse effect.

The blank tube gets dropped into the bottom of the emulsion tube well and the VF tube then screw in just like a normal emulsion tube except that they must be clocked into the correct position. Screw them in then use a texta to mark the side of the emulsion tube holder that's facing the AV passageway, pull the VF tube out and rotate the VF tube on the holder so that the small slot faces the same direction as your texta mark. Do one tube at a time and if you change the main jets then this procedure will need to be done again.

Feel free to contact me if necessary via a pm.

Enjoy.

James

Hi James,Just ordered the following tubes ,so I will let you know how they go.Venturi Fountain Main Circuit Tubes for Weber DCOE Sidedraft Carburetors

 

You are headed in the right direction, but 40mm chokes on a 186 is far from ideal and you will have tuning woes until you change them. 40mm are ok for a race engine living 4000-7500rpm but in anything less than that, you will lose performance and have fuel pickup issues (which you have identified). I ran 40mm chokes but it was in a race engine running 266@50 duration and 300hp flowing head, that was used on nitrous. The engine could cope with the large chokes on the bottle. 

 

What compression and what cam are you running? Full cam specs would help a lot... also cylinder head flow specs would also help if you have. If you provide these specs we can help you decide on what venturi/choke size your engine will want. 

 

If you tune webers by half you will get half tune. Do it properly and you will be happy, which is why I am suggesting that you amend your chokes now, before you start trying to tune with new emulsion tubes and main jets, only to realise that your 40mm chokes still make the car run like puss (and then you need to do it all again). Your new emulsion tubes will be great (ive read up about them and they sound great- great work JD), but I just think that if it was me, I would drop the choke size now so you are re-jetting once and just get it right once... everything will work better with more suitably sized chokes. 

Edited by LC-GTR-1969, 25 November 2017 - 05:42 AM.

10;1 Comp ratio, XU1 head ported, unable to give you flow data, attached is cam specs

a couple of pic of the head

Thanks Brian... Looks like a nice setup..

 

Thats a fairly mild cam (small hydraulic, 224 degrees at 50') and I would definitely run max 34mm chokes. In fact you could go as low as 32mm chokes with that cam as it will probably make peak out about 5200-5500rpm. Your setup looks pretty much XU1 spec, give or take, which would equate to about 200fwhp in a well sorted setup.

 

Your cam will simply not pull the revs to warrant 40mm chokes. 40mm chokes will not flow enough air to work well until the revs get close to 5000rpm (mine was 4800rpm when I ran 40s), but your cam will be running out of steam by the time the chokes are flowing enough air to work well. You want to select chokes that will work with your cam and heads powerband... which with your cam and head will be about a pretty wide band, like 2500-6000rpm. 

 

If you have short diff gears I would run 34mm chokes- if your running taller/ highway diff gears, you may need to consider smaller again- maybe even 33mm custom bored chokes.

 

Everything will be better, and the new E-Tubes will also help smooth everything out. You wont regret it.

 

Do you have access to a lathe?

Edited by LC-GTR-1969, 25 November 2017 - 06:07 AM.

yes I have my own mill & lathe,

yes I have my own mill & lathe,

 

Ok, so I think 34mm chokes are probably about right, but seeing as though you have a lathe, you could buy 32mm chokes, try them and if you think the top end hp is weak, you could bore them to 33mm- you just need to ensure you dont bore straight, give it some slight taper as per the original chokes. Worst case scenario is you end up with 34mm but at least you dont need to buy multiple sets (as you can just step bore them as required). 

 

Its a bit of friggin around though. If you are short on time, the 34mm chokes will work well in your setup iMHO. I guess it depends on how much you want to tinker with these things. 

 

EDIT- Just buy and run 34s- they should be fine and save some stuffing around, and as pointed out by JD- 4.5 auxiliary venturis should be about right.

Edited by LC-GTR-1969, 25 November 2017 - 06:27 AM.

As stated above if anyone decides to bore out there chokes to a larger size then they shouldn't be bored straight through. If you hold unmolested choke onto the back of a AV you'll see that the narrowest point in the choke lines up with the rear of the central booster of the AV, this is to take advantage of the venturi effect. However I have been told that if you are using these special venturis fountain tubes (VF tubes) as Brian has ordered then boring straight through isn't a problem, as their manufacturer says "the force is strong with these tubes" (there's got to be a star wars reference in that).

Don't forget that while you're have your AV's out preferably a set of replacement 4.5's to spend a few hours on them and clean them up of all the molding ridges etc, you won't regret it.

And definitely fit the smaller chokes sooner rather than later.

James

Hi James,While I have been waiting for the tubes from Keith,I installed a vacuum gauge and the reading is 10 to 12 inches of mercury at 1,000 rpm when warm.What is your feedback on such a reading. I also read the conversations on side draught central as Keith seems to know his stuff also .

Hi James,While I have been waiting for the tubes from Keith,I installed a vacuum gauge and the reading is 10 to 12 inches of mercury at 1,000 rpm when warm.What is your feedback on such a reading. I also read the conversations on side draught central as Keith seems to know his stuff also .

 

It means your brakes will work... 

 

Vacuum at idle is relative to engine configuration and has little to do with carbs. The important thing to do is that the carbs are drawing equal vacuum each- but the actual number doesnt mean anything as far as the carb is concerned. If they are drawing the same vacuum it means they are pulling the same air (which is what you want).

 

10-12hg is typical for a cammed engine with some but not a lot of overlap. A stock motor (with stuff all overlap) will pull higher HG. A high overlap cam will reduce manifold vacuum- ie my race cam pulls stuff all but its the cam and compression that dictates the vacuum.

 

Just make sure the carbs are all even to within .5. Also, you should check them at a high idle, like 3000rpm to ensure that they are also high speed synced.

 

EDIT- Just to clarify, are you talking about taking a reading from the manifold using a vacuum guage, or are you measuring vacuum at the carb throat using a sycnromoter? Both measure vacuum but the readings mean different things. If your using a typical vacuum gauge, there are things to look for like inconsistant vacuum, spike or drops in vacuum etc etc... Did you check it to help determine a possible air leak? The reason I ask was when I saw your OP it occurred to me that the lean spike could possibly be a slight manifold vacuum leak. 

Edited by LC-GTR-1969, 30 November 2017 - 05:12 PM.

I took the vacuum from the brake booster hose, no spike or jumps, no vacuum leaks at all 10/12 hg Also took a reading from carby throat which is 5 kg/h @ 1,000 rpm.VR's arrived today, looks like a fun weekend

I took the vacuum from the brake booster hose, no spike or jumps, no vacuum leaks at all 10/12 hg Also took a reading from carby throat which is 5 kg/h @ 1,000 rpm.VR's arrived today, looks like a fun weekend

 

All sounds normal. Just make sure that each throat is even. 

 

Check the leading throat of each carb and adjust to the lowest vacuum. If idle is too low- slowly raise them and check each leading throat as you go until you reach your desired rpm for idle. 

 

I usually then check the back throat of each carb to see that they arent out. If they are out, you can use your air bleeds (if you have some, some models do not) to equalise the air drawn between the two throats on the same carb.

 

Then get someone to hold at 3000rpm and re-check. If your linkage geometry is off you may find at 3000rpm you are pulling a fair bit more on one carb. If this is the case you will need to inspect as to what could be causing opening rates to differ between the three carbs.

Brian your 45dcoe13's don't have the air bypass screws mentioned above but I'm sure that you probably already know that.

LC-GTR-1969 I don't mean to undermine the information that you have given above but the amount of manifold vacuum has recently been found to have an impact on the idle circuit of dcoe's.

Instead of getting someone to hold the throttles at 3000rpm's whilst you check the sync it is far better to advance the rpm's via mechanical means, such as a wedge to hold the pedal off its stop or something similar. The reason being is that someone just holding the throttles open is more likely to unknowingly fluctuate the revs slightly without even realising and this will throw your readings out.

The reason that I asked you to measure your manifold vacuum level at the start of this thread is because it's recently been discovered by Keith on Sidedraft Central that engines with a lower manifold vacuum level respond better to a different type of idle jets as opposed to engines with a vacuum level of around 20Hg or so or over. Engines with a high manifold vacuum may benefit from a set of Keith's hypojets which by opening more air bleed holes in the jet allows it to increase the richness of the upper range of the idle circuit by operating as a venturi vacuum pump (in much the same way as the "VF" tubes do).

On engines with a lower manifold vacuum Keith has found that idle jets with an internal bore diameter of 3mm drilled all the way to the bottom (but obviously not through the bottom) provide a better mixing area and pumping action than std weber idle jets. Standard weber idle jets of different sizes do feature various diameter internal bore sizes along with different air bleed hole sizes and quantities.

Brian, since you have access to a lathe you could make this modification to a set of idle jets yourself and see how they perform, you'll probably have to play around with the air bleed hole sizes too.

Have you obtained some smaller chokes to fit? Doing so will be very beneficial. Changing the choke size doesn't normally require a change to the idle circuit itself.

For anyone who is new to Sidedraft Central the following terms will be useful to understand, they are just abbreviations.
Wet jet = main jet, it's submerged in fuel and wet
Dry jet = air corrector, obviously it's not submerged, it's dry.
Tip-in = the moment that the main circuit begins.

Some of the information can be rather technical to a newcomer but don't be afraid to ask.

James D

LC-GTR-1969 I don't mean to undermine the information that you have given above but the amount of manifold vacuum has recently been found to have an impact on the idle circuit of dcoe's.

The reason that I asked you to measure your manifold vacuum level at the start of this thread is because it's recently been discovered by Keith on Sidedraft Central that engines with a lower manifold vacuum level respond better to a different type of idle jets as opposed to engines with a vacuum level of around 20Hg or so or over. Engines with a high manifold vacuum may benefit from a set of Keith's hypojets which by opening more air bleed holes in the jet allows it to increase the richness of the upper range of the idle circuit by operating as a venturi vacuum pump (in much the same way as the "VF" tubes do).

 

 

No problem at all James... its all interesting reading from this Keith fello...

 

From Brian's post about manifold vacuum my interpretation was he was checking the mechanical condition of the engine through checking the manifold vacuum- something which I have done many times in the past to help diagnose mechanical faults in the engine (leaks, valve issues and weak spark etc). I was not aware you had specifically asked him to undertake a manifold vacuum check to see if he needed any of these emerging technology/ more modern idle jets. 

 

What I meant by 'manifold vacuum at idle has to do with engine configuration not the carbs' simply meant that by doing a manifold vacuum check, it was not going to give him much information about the condition of the carbs (it will give you a little info but not much). The carbs however, will obviously respond differently to varying manifold vacuum and it makes sense that a low manifold vacuum would warrant a more efficient idle jet to help ensure sound fuel delivery. This is why engines with higher compression will tend to give a better signal to the carb at part throttle and in transitions. 

 

In saying that, whilst these modifications may help with the overall refinement of the carbs and therefore improve the drivability, I firmly believe that the main source of the issue Brian originally posted about is predominantly from the overly large chokes to suit the engine configuration (poor airspeed) combined with incorrect mains and air correctors. 

 

Although, as I have always said, tune webers by half and you'll get half tune, so if you can improve the whole system and refine the fuel delivery, go for it! James is onto some great info and it all sounds very interesting and exciting- He should get you were you need to be but it can take patience tuning webers (the payoff is worth it though). 

 

Simple caveat though- give your engine what it wants, not what a tuning manual or another engine wanted (ie like a weber specs guide etc) and not the jetting from someone else's car... it will get you started but your specific combination will want its own configuration to find its sweet spot. There are common tricks  and common / typical configurations though as JD has pointed out- and these will have common truths...

 

1) Ensure your engine and carbs are mechanically sound.

2) If above is fine, read your wideband and analyse based on that. 

3) Ideally, take it to the drag strip and verify tune through mph trap speed, or dyno it. 

 

So many times what I thought was a good tune (ie 12.7:1 AFR etc) and felt great, was not actually perfect for peak hp- my setup wanted richer than I would have thought to give max mph (11.9-12:1 AFR at wide open 6500rpm). Give the engine what it wants. If anything is out of the typical range, do some tests for a sanity check.

 

Have you tested any of these modified jets James? Id be curious to hear more about them...

Edited by LC-GTR-1969, 01 December 2017 - 08:04 PM.

I've got to agree once again that the overly large chokes are going to severely hinder your progress, that would be a problem on a street driven 202 let alone a 186.

Over two years ago I made the switch to using f2 emulsion tubes that I had 2mm machined off the bottom of to reduce my tip-in hesitation this worked well but did give a slightly rich low power cruise (approximately 3000rpm).

For about the last 15 months I've been using Keith's hypojets (special idle jets) these have a split collar that can be rotated to open or close varying amounts of air bleed holes which is such a great addition as opposed to changing jets, they also have other features built into them.

A bit over 12 months ago I switched to a set of Keith's O6 emulsion tubes and with these combined with the hypojets my engine really responded well and runs super smoothly. I could happily leave it as is and be very happy with the state of tune, but I've got an interest in how all this works and what can be achieved so I kind of enjoy fiddling with the carbs. My friends wonder why I want to change things when it runs as well as it does. I have all my settings noted down and can very quickly switch back if any changes prove not to be beneficial.

I haven't tested any idle jets to suit the low manifold vacuum yet as this is only a very recent discovery and I need to check my manifold vacuum level first to see if I would benefit from them. I've ordered a one way check valve and vacuum gauge but I'm just waiting for the check valve to arrive which is literally on a slow boat from China. The check valve is required to hold a steady reading on the vacuum gauge.
James

Hi Fella's, Received the VF tubes and installed them.In ran worst then ever. Couldn't do AFR as the sensor malfunctioned, I think due to cold start, moisture in exhaust on start up.Have you guys had this problem ?

Ive never run VF tubes so cannot really chime in here- JD will have the info you need regarding these tubes- but I imagine that you will need a number of jet changes with the different etubes, so I would not give up on them.

 

The wideband malfunctioning is however something that I have experienced... for some reason mine also gives an error reading from time to time. In honesty, I usually just switch off the ignition and back on again and its sweet. Never really thought why it might be behaving that way though as its only an occational glitch and I rarely drive the car anyway.

Brian,
Have you fitted smaller chokes and AV's yet?
What main jets and air correctors are you currently using? Try increasing the air correctors as with the VF tubes doing so increases how much fuel is getting drawn through.

Don't despair, your in capable hands. If you give Keith the appropriate information he'll guide you through the tuning process.

James

not yet still saving for those. MAINS = 155 air correctors = 210

the above are what I tried in the VF tubes

What collections of weber parts do you have?

 

Main jets/ air correctors?

 

Do you have a soldering iron?

 

Do you have jet drill bits?