243 replies to this topic

[Brian Pascoe]

Here is some data I recorded.

1000 = 12.5 AFR

1500 = 11.5

1800 = 14.9

2000 = 16.6 to 17.7

2100 = 16.3

2500 = 13.8

2600 = 14.4

2800 = 17.5

3000 = 17.1

3400 = 19.0

3500 = 13.8

3800 = 13.6

4000 = 12.5

5000 = 11.0

It seems that I have two flat spots,one around 2000rpm and the other 2800 rpm to 3400 rpm.

Edited by Brian Pascoe, 17 December 2017 - 08:02 AM.

[jd lj]

Having an overly rich pump circuit can actually temporarily wet foul your spark plugs and cause a hesitation. When this is the case your AFR gauge can be deceiving because it only measures burnt fuel in the exhaust gases and not liquid or unburned fuel and therefore may indicate a lean mixture when in fact its excessively rich.

Another time that a similar situation can arise is if the weather is very humid. High humidity will lower the oxygen content of a set volume of air because the higher percentage of water particles displaces the oxygen particles and makes your mixture richer. Last summer after several days of rain the humidity here was so high that the mixture on my car got rich enough at certain times to produce a very minor hesitation that actually read lean on my AFR meter, I believe that this was caused by the lower O2 content of the air at the time as I hadn't changed anything that day and next time I drove it everything was back to normal with the only change being the humidity level.

[jd lj]

Brian I'll get back to your AFR figures later, but for now I'll ramble on about the pump circuit some more.

Having checked your pump rods and springs it seems that your pump rods are a medium length stroke and I wouldn't worry about playing with anything different at this stage.

Your springs however are rather heavy duty and not what I'd select myself. I've tried those in the past and found that they made the accelerator pedal heavy and actually held the throttles open to a degree causing the idle rpm's to rise, they would have required a heavier return spring set up on my linkages to compensate for this. They'll provide a shorter pump shot under more pressure at a higher volume per second.

I find that even a medium tension pump rod spring can be a tad heavy and lose a bit of control of the throttles when coming off idle which gives me a bit of leaning out at that point that I don't have when using lighter springs. This could be tweaked by making linkage / pedal modifications to gain more leverage. Once off idle both the medium and light springs perform well for me. It's worth noting that different pump rods will apply different amounts of tension to the same springs by having varying differences between the two halves of the pump rods.

A light pump rod spring will give you a longer duration of the pump shot but under less pressure which will mean that the shot won't travel as far. If you had a low air speed at the time of the pump shot then a heavier spring may help get the pump shot further towards the head where the air speed should increase and help carry the shot along.

[jd lj]

There's quite a few different length pump rods available. A rod with a shorter stroke means that the piston on the end of the pump rods is positioned closer to the bottom of the pump rod well and therefore that well has a smaller volume of fuel available for the shot. This will reduce the duration of the pump shot. The spill jets/ pump jet discharge valve will also vary the duration of the shot by allowing a portion of the fuel from the pump jet well to be bleed back into the float bowl. The size of the pump jets themselves will also control the duration of the shot by controlling the volume per second of the shot, as does the pump rod springs. As you can see the function of each component is all very intertwined.

During light accelerations the total stroke of the pump rods may not be used up and on a longer rod if there's enough stroke left another shot of fuel may be available. This means that a rod with a longer stroke is capable of another shot at higher rpm's than a short rod which will have no more contribution at a smaller throttle opening.

Slow revving engines may require a longer duration of the pump shot than fast revving engines because the pump shot only needs to contribute fuel to the mixture until the rpm's are high enough for the main circuit to tip in. So if your main circuit isn't tipping in early enough a longer duration would help to get you through but the real solution would be to fix the main circuit tip in timing. The above situation is in relation to going WOT at low rpm's. In this situation the idle circuit plays very little of a role because when suddenly going WOT from low rpm's such as idle the vacuum level acting on the idle circuit drops so quickly that very little to no fuel would be drawn through the progression holes, this is why the pump jets are required.

[jd lj]

Here's a bit of a summary of the role of each pump circuit component. The pump circuit is rather complicated as you'll see because each component varies the shot in multiple ways.

Pump jet - Volume per second and duration.

Spill jet /pump jet discharge valve -Total volume and duration.

Pump rod -Total volume, duration, pressure and rpm's that more pump shot is available.

Pump rod springs -Pressure of the shot and therefore distance that the shot travels, volume per second and duration.

So if you know how long your engine takes to go from idle until the main circuit tips in when the appropriate mixture is supplied then you can tailor the duration of the shot to last for this amount of time. The first step would be to select the right pump jets to give you the most appropriate volume per second when using a spring that gives you good delivery of the shot and pedal and linkage control. Next adjust the spill jets to achieve the suitable duration. If you have an AFR meter with recording capabilities you should be able to see when the main circuit begins especially if you know the rpm's that this happens and under WOT conditions see how long it takes to reach those rpm's and adjust the duration to suit.

Brian, for your situation I'd suggest you leave the pump rods alone for now and fit 40-45 pump jets and a lighter spring and test both the blank and size 50 spill jets. If the 50 spill jets work just as well as the blank ones they'll be more fuel efficient.

Also try main jets a size or two leaner.

I should have the enhanced VF tubes to test in the next week or so and then we'll look into your lean spikes further.

James

[Brian Pascoe]

Hi Fellas,Please disregard the above data as I had a loose VF tube in no 6 throat.Getting some more data together now.

Edited by Brian Pascoe, 17 December 2017 - 01:25 PM.

[Brian Pascoe]

NEW DATA

1000 = 14.6 AFR

1100 = 14.4

1500 = 11.9

1600 = 12.6

1800 = 15.9 TO 17.9

2000 = 15.8 TO 17.1

2200 = 10.9

2500 = 16.1

2900 = 19.0

3000 = 13.8

3500 = 15.0

3900 = 15.6

4000 = 14.7

4500 = 11.5

Edited by Brian Pascoe, 17 December 2017 - 02:01 PM.

[LC-GTR-1969]

I may be barking up the wrong tree here, but the erratic data you are seeing reminds me of when I had a vacuum leak.

 

Intake pulses would change and I would have somewhat erratic AFR across a wide rpm spread- it was a very slight leak between the intake and the head. This caused lean spikes that I figured correlated with intake pulses. I could not identify the vacuum leaks through typical means (ie carby cleaner or aerostart around mating surfaces) but it was easy to see when using a colortune. I installed my colortune and sprayed aerostart around whilst watching the colortune. When it took in the extra fuel you could see the rich flame. Revs were not effected at 850rpm. For some reason revs were stable. Nonetheless I had a leak. 

 

This very well may not be happening with your setup, but in all honesty if It were my car and I had your data in front of me, I would run a few further checks for air leaks just to be certain that I did not have any issues confounding my tuning. 

 

Furthermore, a spark issue, such as a dodgy lead will give what appears to be a lean spike.. Unused Oxygen with unburnt fuel reads as lean- hence a spark related quirk or issue can present as lean spikes when in fact fuel has not been burnt, as JD mentioned. I have had a single dodgy lead that caused me grief like this before. Worth a quick look anyway. 

[jd lj]

Brian,
I'm just checking, but are all your AFR figures whilst the engine is under a steady load. If you were free revving the engine in the driveway to get these figures they would be different to real world driving, as would if you were off the throttles at the time.

Reading your AFR gauge fitted to the lower dash panel can be difficult at WOT and high rpm's and if you look as soon as you back off from the throttle it'll be irrelevant too.

James

[Brian Pascoe]

Yes James,all the figures were recorded on the road through all the gears.I done this several times and took an average of a minimum of 3 readings.

[LC-GTR-1969]

How did you record the data? I find a go pro or a video camera (mobile phone etc) setup to see the wide band can help.. I've done this myself when my LM-2 wasn't recording (its fixed now). I used a strap to setup a go pro pointing at the LM2. It shook a little but was good enough to capture the readings. You can hear the engine and knowing my shift points etc it wasn't hard to establish the pattern. A sucksion cup style mobile phone carrier (normally used on the windscreen) but mounted on the rear screen with the camera pointed towards your wideband could work as well. 

 

For a baseline, seeing as though you already have them, it might be worth putting your F2 tubes back in and re-testing and re-posting the data- that way you can build more data to help with your diagnostics. I am not suggesting that the F2s are better in any way, just that a one step swap to different tubes might help with diagnostics. When testing, my procedure is to change ONE thing at a time and record data- then analyse and write down observations... If the pattern is the same with the F2s- ie lean spikes every 900-1000rpm to me it would point quite strongly to secondary mechanical issues (such as spark or vacuum issues). The lean spike at 3900rpm is quite strange and not something I would have expected with these new tubes (hence my thought to isolate the tubes as being a contributor by re-installing your F2s for diagnostics purposes). With your 155 mains and 34mm chokes this really is not expected (at 3900rpm). Your MJ should be well and truly flowing based on my experience with F2s. 

 

Are you running points or electronic ignition? What plug gap?

 

There is also the possibility that your wideband has a delay in display- they all have a delay to an extent but it usually moves quick enough to give you a pretty clear baseline to work with. 

 

How does the car feel with the 34mm chokes compared to the 40mm chokes? Probably not a great comparison as you are comparing a poor tune to a poor tune, but I imagine your throttle response is now much better below 4500rpm.

 

Kind regards

[Brian Pascoe]

I've been filming with a sony vid .Also my dizzi has been modded, remapped to 14 initial to 32 deg full advance @ 3000 rpm with an electronic accu spark conversion, plug gap 1 mm. Car seems to pull a lot better with the smaller chokes but still not perfect

[jd lj]

I've been filming with a sony vid .Also my dizzi has been modded, remapped to 14 initial to 32 deg full advance @ 3000 rpm with an electronic accu spark conversion, plug gap 1 mm. Car seems to pull a lot better with the smaller chokes but still not perfect

I'm glad to hear that you're feeling some improvements so far even though we're not finished.

James

[Brian Pascoe]

Hi Fellas, Hope you have a nice xmas and will talk to you after its all over.

Regards Brian

[LC-GTR-1969]

Good luck with it all Brian. You will get there mate. They just take a little persistance at times. Just remember to take notes and be methodical. Oonly make one change at a time and re- test, record data and so forth. 

 

Have a great break!

[Brian Pascoe]

Hi fellas, Back on board again. Will be doing some more testing shortly and will post some data to chew on 

[jd lj]

Hi Brian,
When I tested the std VF tubes I was still getting a hesitation with those that I had eliminated with other tubes from Keith, so don't get to worried if your std VF tubes don't resolve your problem. I'm currently testing the enhanced VF tubes with far superior results for my application.

What's your current plan for the testing that you are about to do? Have you fitted smaller pump jets yet?

James

[jd lj]

I did some more testing of the enhanced VF tubes this morning with size 220 air correctors which was an increase from my previous 205 air correctors. These tubes are performing very well and I couldn't induce a hesitation even when I tried, which is a promising sign. When I tested the std VF tubes I had some hesitation that my previous O6 tubes didn't. The enhanced VF tubes appear to be providing a better mixture at a low power hwy cruise speed than the O6 tubes did. If my memory is correct I'm currently using 130 main jets and 34mm chokes. I've also recently tested an enhanced version of the O6 tubes which also gave excellent results. I haven't used std weber (f2) emulsion tubes for a few years now and it looks like I never will again as what I have been using and testing is so superior.

I'm also currently using a set of Keith's W55 idle jets which are proving to be the best idle jets I've used. They are providing a very stable mixture across the rev range of the progression circuit. Prior to this I had been using a set of Keith's hypojets which were also very good, but these W55's are proving to be more suitable for my engine which has an idling manifold vacuum of approximately 13Hg. The hypojets are more suitable for engines with a high manifold vacuum level.
Both the hypojets and W55 idle jets have a split collar which can be rotated to open or close more air bleed holes making the idle jets adjustable themselves.

James

[Brian Pascoe]

Hi James,I have been reading your posts on side draught central and it sounds like you are getting to the bottom of it all .Keep me posted on your progress.I have'nt had a chance to do any work on mine as yet.No I have'nt put smaller pump jets in yet, they are .45 at the moment.The jetting at the moment with the VF tubes are as follows. 190 air, 155 mains, 34 chokes,4.5 aux,50F8 idle.What are your cam specs.

Brian

Edited by Brian Pascoe, 26 January 2018 - 07:19 AM.

[jd lj]

Hi Brian,
Keith is planning on making a set of enhanced VF tubes for you when he gets a chance. I'm sure that these will help sort out your problems when used with a suitable jetting combination. Keep in mind that your 45dcoe13's will have a slightly shorter dynamic range of the progression circuit than my 45dcoe9's due to mine having an additional progression hole. This also means that I require a richer idle jet than you because that additional progression hole also acts as an air bleed and allows more air into the progression circuit.

My current jetting specifications are as follows :
45dcoe9's
34mm chokes
4.5 AV’s
Enhanced VF tubes
130 main jets
250 air correctors
W55 idle jets with 3 holes open.
Idle mixture screws are set at 3 full turns open from lightly seated, giving idle AFR of approximately 12.8-13.2.
40 pump jets
40 pump discharge valves
Light pump rod springs
Med - long pump rods, part number 10410.004.
(these pump rods aren't readily available, but don't get too caught up on those as others will also work well, these are just what my carbs had).

I'll go through my notes sometime and list other jetting combinations that I've had work well for my application, I'll include some with std weber jets too for a reference for other members in the future. It's worth noting however that this would just be a starting reference only and each engine will have its specific needs due to different cams, head mods, manifolds, carb models, compression ratios and usage etc.

James

[Brian Pascoe]

Hi James, I believe you could be looking for some drills. There are number and letter drills on the market. There is a company called BLACKWOODS which sell engineering supplies that you could try as I am a retired Fitter and Turner and  have purchased stuff from them before and they are very helpful.

[jd lj]

Thanks, I hadn't considered Blackwoods, they're just around the corner from work so I'll look into that.

James D

[Brian Pascoe]

Hi James. I did did shorten the F2 tubes before I changed to 34mm chokes and 4.5 au. Now I have the VR tubes in and 50F9 idle jets. It has improved it out of sight, but when cruising in any gear it is showing me 9.9afr,but when I slowly depress the accelerator it goes to 15 to16 afr then seems to flatten out to around 12 to 13. Do you want me to order the EVR’s tubes from Keith or will you discuss it with him.Also do you recommend the advanced idle jet as I only have 2 progression holes.

Brian 

[jd lj]

Hi Brian,

From my recent experience with my W55 idle jets that I got from Keith I'd highly recommend them to anyone who has a low manifold vacuum level such as mine which is 13Hg. These are by far the best idle jets I've used for my application. This doesn't guarantee that they'll suit everyone as each case will have its own requirements.

When you say that your cruise AFR is in the 9's at what rpm's is this?

I assume that you're going to require the enhanced VF tubes like I did. Judging by some recent posts on Sidedraft Central I get the impression that perhaps Keith is refining these further as these are all so new that more testing is still underway by both Keith Franck and myself. From my side they are working very well, I'm planning on testing these further to find the point of diminishing improvements as I like to know what the limits are instead of just settling on something. I very much doubt that I'd use std emulsion tubes again and I'm giving my f2's and others to a friend as I have no use for them.

I suggest that you update your thread on Sidedraft Central to let Keith know where you're at on your tuning journey. As I said previously he's expecting to make a set for you. If you can achieve results like I have then you'll be over the moon.

[Brian Pascoe]

Hi James,I am going to talk to Keith shortly and see if I can purchase a set of EVF and some idle jets.Do you recommend the W55 's for my engine.When I purchase the above, I will have the STD VF tubes available if anyone needs them or would Heith accept them back in exchange for the EVF.I haven't been for a cruise yet as it is to wet.

Brian 

Edited by Brian Pascoe, 03 February 2018 - 09:32 AM.