Thanks James,I will look into all your suggestions, and save some pennies.
Brian
Posted 21 November 2017 - 01:13 PM
Thanks James,I will look into all your suggestions, and save some pennies.
Brian
Posted 21 November 2017 - 02:45 PM
Posted 21 November 2017 - 06:07 PM
Posted 23 November 2017 - 12:08 PM
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
Posted 24 November 2017 - 04:30 AM
Posted 24 November 2017 - 06:09 PM
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.
Posted 25 November 2017 - 05:47 AM
10;1 Comp ratio, XU1 head ported, unable to give you flow data, attached is cam specs
Posted 25 November 2017 - 05:56 AM
a couple of pic of the head
Posted 25 November 2017 - 05:57 AM
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.
Posted 25 November 2017 - 06:19 AM
yes I have my own mill & lathe,
Posted 25 November 2017 - 06:25 AM
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.
Posted 25 November 2017 - 06:50 AM
Posted 30 November 2017 - 01:09 PM
Posted 30 November 2017 - 05:02 PM
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.
Posted 30 November 2017 - 05:54 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
Posted 01 December 2017 - 12:39 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
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.
Posted 01 December 2017 - 05:09 PM
Posted 01 December 2017 - 07:25 PM
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.
Posted 01 December 2017 - 08:29 PM
Posted 02 December 2017 - 07:45 AM
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 ?
Posted 02 December 2017 - 09:05 AM
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.
Posted 02 December 2017 - 09:43 AM
Posted 02 December 2017 - 01:31 PM
Posted 02 December 2017 - 01:34 PM
the above are what I tried in the VF tubes
Posted 02 December 2017 - 04:45 PM
What collections of weber parts do you have?
Main jets/ air correctors?
Do you have a soldering iron?
Do you have jet drill bits?
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