Iain T Posted July 12, 2023 Report Share Posted July 12, 2023 (edited) I'm posting so that my pretty extensive needle changes can help someone else. First off I have a modified engine with gas flowed head, valves and inlet manifold and a Phoenix 631 exhaust. The cam has 260 thou lift in and ex with 270 duration. I also have an air fuel ratio meter with the lambda sensor as close as possible to the last exhaust collector. FYI a clean burn is 14.7 on the meter. Suffice it to say the engine breathes better than standard. Carbs are CDS150s with 'half' doughnuts on each inlet for better flow (they put a radius on the carb inlet aperture) and K&N pancakes. Damper oils used are 3 in 1, 20/50, SAE50 and (not tried) yet SAE140. I also have standard blue damper springs (fitted on the car now) and the softer no colour variant (didn't work). Ignition about 12 degrees. Fuel Tesco Momentum 99 octane. Note the more taper on the needle the more fuel can be sucked in. So the standard needles are 6AC and although I can get a decent tickover it goes wildly lean on driving. No amount of tinkering could get enough fuel in for normal driving and acceleration with an acceptable tickover. The 6Js better on normal driving but much too lean on acceleration and higher revs. The 6Ss (are these the standard Mk1 needle?) again too lean on acceleration even with SAE50. The 7Bs are what people say you should have with pancakes etc. Well I tried these for a few hundred miles and they over fuelled on normal driving 12-13 on the afr and under fuelled on higher revs. No amount of tweaking could get an acceptable reading and the plugs were black indicating too rich. Now to the 5th set of needles the 6As. Instantly better on normal driving with a reading of high 13 to high 14. Tickover hovering around 14. On WOT down to 12 or just below. No pinking under low rev load. On slight acceleration the afr goes up to 15-16 with 20/50 engine oil in the damper. I'll try SAE 50 and SAE 140 (sounds high but in non EP form the next viscosity up from SAE50) to see if I can get the low/slight acceleration number down but I feel pretty happy with the 6A needles. I'll report back after I've changed the oils. It is impossible to get a carburettor to perform perfectly under all conditions hence fuel injection and it's important to get the car setup as you drive it ie a race car will be setup to fuel high revs and be lumpy on tick over. As to oils 3 in 1 was too thin and allowed the air piston to rise too quickly and lean out the mixture. 20/50 oil is ok. SAE50 could be going in the right direction and SAE 140 a thick long shot. Keep twiddling! Iain Edited July 12, 2023 by Iain T added chart Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 12, 2023 Report Share Posted July 12, 2023 good to see the twiddling is getting you some good results youk now there are heavier damper weights around that richen mid range ( the thicker ring that holds the diaphragm) may help in minor twiddles Pete Link to comment Share on other sites More sharing options...
Iain T Posted July 12, 2023 Author Report Share Posted July 12, 2023 (edited) 42 minutes ago, Pete Lewis said: youk now there are heavier damper weights around that richen mid range ( the thicker ring that holds the diaphragm) may help in minor twiddles I don't think damper weight may help as it will lower the air piston on normal driving? I'm looking to restrict damper rise on slight acceleration to high revs. But I might be wrong! You've introduced another variable..... There is a red damper spring but it's about 290gms vs the blue which I think is 120gms so a big difference. Anyone tried them in a CDS? As with all constant velocity carbs it's an unknown where the needle is so a near impossible balance between air velocity vs available fuel from raising the needle. Lower velocity and bigger needle gap vs higher air velocity and smaller gap. For me the biggest leaps in auto development are fuel injection and climate control! Iain How much heavier are the clamp rings? Edited July 12, 2023 by Iain T Link to comment Share on other sites More sharing options...
Steve P Posted July 12, 2023 Report Share Posted July 12, 2023 55 minutes ago, Iain T said: It is impossible to get a carburettor to perform perfectly under all conditions hence fuel injection and it's important to get the car setup as you drive it ie a race car will be setup to fuel high revs and be lumpy on tick over. Can`t agree with that,my tuned 2.5 Vitesse putting out 172BHP on 2 x HS6 carbs setup on a rolling road runs great through the range, even on tick over with a TR5 Cam and 10:1CR. Standard dizzy at present but soon to be a 123 Tune. Steve Link to comment Share on other sites More sharing options...
Iain T Posted July 12, 2023 Author Report Share Posted July 12, 2023 2 minutes ago, Steve P said: Can`t agree with that,my tuned 2.5 Vitesse putting out 172BHP on 2 x HS6 carbs setup on a rolling road runs great through the range, even on tick over with a TR5 Cam and 10:1CR. Hi Steve, do you have an onboard afr meter? To be honest without that showing instantly what the mixture is doing I would be very happy with the 6As. The car pulls and revs very well. The answer is turn the afr off! Iain Link to comment Share on other sites More sharing options...
Steve P Posted July 12, 2023 Report Share Posted July 12, 2023 I don`t, I have enough worry checking the oil pressure gauge. Its got Bosch 3 prong plugs so If they look ok and It`s running well I leave it alone. Pretty good on economy If you don`t have a lead right boot. S Link to comment Share on other sites More sharing options...
Iain T Posted July 12, 2023 Author Report Share Posted July 12, 2023 I bet if you had an afr you may see the variations on different driving conditions/load and weather. I use the Bosch multi prong plugs, brilliant kit. I'm being nitpicky with the mixture control but as you say looking at the plugs there's nuffin' wrong! Iain Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 12, 2023 Report Share Posted July 12, 2023 42 minutes ago, Iain T said: How much heavier are the clamp rings? at a guess about double the thickness 1600 and 13/60 used them without springs i added /tried a spring to my 1600 and loverly black smoke all the time Ha " Pete Link to comment Share on other sites More sharing options...
Iain T Posted July 12, 2023 Author Report Share Posted July 12, 2023 (edited) 43 minutes ago, Pete Lewis said: i added /tried a spring to my 1600 and loverly black smoke all the time Ha " Like Bonds DB5! Edited July 12, 2023 by Iain T Link to comment Share on other sites More sharing options...
Puglet1 Posted July 12, 2023 Report Share Posted July 12, 2023 Ian T. Thank you for taking the time to share your results with us. I find it very interesting. Do you have any idea what BHP you are developing? Pete. Link to comment Share on other sites More sharing options...
Iain T Posted July 12, 2023 Author Report Share Posted July 12, 2023 1 hour ago, Puglet1 said: Do you have any idea what BHP you are develo Before I had the carbs and dizzy rebuilt and sorted out the air leaks it was 112bhp. I think that was with 6J needles. Now with 6A needles and above sorted it's much more powerful and responsive, almost a different engine. I'm not putting it on a rolling road again but would be very surprised if its not north of 125bhp and more like 130 with much better torque. Iain Link to comment Share on other sites More sharing options...
Puglet1 Posted July 12, 2023 Report Share Posted July 12, 2023 4 hours ago, Iain T said: Before I had the carbs and dizzy rebuilt and sorted out the air leaks it was 112bhp. I think that was with 6J needles. Now with 6A needles and above sorted it's much more powerful and responsive, almost a different engine. I'm not putting it on a rolling road again but would be very surprised if its not north of 125bhp and more like 130 with much better torque. Iain That sounds good! Link to comment Share on other sites More sharing options...
Iain T Posted July 17, 2023 Author Report Share Posted July 17, 2023 (edited) Tried sae140 (non EP) in the dash pots. Definitely harder to raise the air piston than 20/50. On a short run, bloomin traffic jam, it did seem to stop the lean out under medium acceleration. I need a longer high speed run to fully evaluatethroughtge whole rev range but providing it doesn't get too rich and bog down its looking better. I might splash out for 2 red heavy springs to see how they perform. Its now a mission! Iain Edited July 18, 2023 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 20, 2023 Author Report Share Posted July 20, 2023 (edited) New toys arrived today, red heavy springs which are longer and much stronger than standard blue springs. Before I fitted I did a cruise and fast road trial with 6A's and EP140. Cruising fine afr high 13 low 14 and on light acceleration just below 13. However is did feel as though it was marginally bogging down and did go up to 15-16 at high revs. So fitted the much stronger red springs and changed the damper oil to 20/50 as I thought EP140 would be a step too far and result in a black smoke cloud! I had to lean off the carbs around 1/2 turn which told me the springs were having an effect and holding the air piston down. On a run it was much better at high revs, in the 14s. However at light cruise 40-50mph in 5th gear (the same ratio as 4th+od) the mixture was in the high 12s so too rich. Plenty of torque in both trials and tick over around 14. So thinking of the next step(s) I'm wondering if a spring rate between blue and red could be the answer? However such spring doesn't exist so I'll have to modify two. Another trial is a light damper oil but that mainly effects acceleration which is fine. I want to hold down the air piston more at high revs for fuelling but not too much that it is too rich at cruise revs (2000-2500). If all else fails I'm pretty happy with the blue spring/EP140 combination with a bit more fine tuning. But....due to the oil being gloopy and the spring low in pressure it does take a while for the tick over to settle down! I do hope this helps someone as the men in white coats are hovering.... Iain Edited July 20, 2023 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 21, 2023 Author Report Share Posted July 21, 2023 (edited) Spoken to Burlen and the only three air piston springs available for CD150's are:- B18276 rated 56g at 2.09" (53mm) B18275 rated 280g at 53mm B18274 rated 99g at 53mm I have the set so decision time as I reckon I need at least 200g with 20/50 damper oil. I don't think I can make the heavy 280g work and as they are much, around 30+mm, longer than the medium 99g I'll cut off 15mm to reduce the compression force at 53mm. I'll make a simple test rig and measure both before I cut! Iain Edited July 21, 2023 by Iain T Link to comment Share on other sites More sharing options...
johny Posted July 21, 2023 Report Share Posted July 21, 2023 Dont know if this helps but I believe thin oils viscosity varies less with temperature (I know its gets complicated with multigrades). This comes from motorcycle forks where to achieve the same damping youre better off having small orifices and thin oil than larger ones with a thicker oil.... Link to comment Share on other sites More sharing options...
Iain T Posted July 21, 2023 Author Report Share Posted July 21, 2023 (edited) Cut around 20mm off the heavy springs, no going back now! On the left is a standard medium spring, middle is uncut heavy and right cut heavy. The cut heavy measures about 250g at 53mm. All fitted and tweaked so both carbs have identical settings. I think I'll have to wait until Saturday for a run as Friday afternoons are a nightmare on the roads. Johny the problem with thin oil is leaning out on light acceleration. I've used 20/50 as a damper but have single grade sae50 and 140 and an atf. Iain Edited July 21, 2023 by Iain T Link to comment Share on other sites More sharing options...
Ian Foster Posted July 21, 2023 Report Share Posted July 21, 2023 Iain The photo shows the shorter spring has a tighter pitch. Is that relevant? Ian Link to comment Share on other sites More sharing options...
Iain T Posted July 21, 2023 Author Report Share Posted July 21, 2023 (edited) 38 minutes ago, Ian Foster said: The photo shows the shorter spring has a tighter pitch Yes but it's a thinner gauge wire hence much easier to compress. The big issue with springs is making sure the fully compressed length is less than the length you want to compress. It's the same with valve springs with crazy cam lift. Iain Edited July 21, 2023 by Iain T Link to comment Share on other sites More sharing options...
Ian Foster Posted July 21, 2023 Report Share Posted July 21, 2023 Tricky thing springs! Ian Link to comment Share on other sites More sharing options...
Iain T Posted July 22, 2023 Author Report Share Posted July 22, 2023 (edited) 13 hours ago, Ian Foster said: Tricky thing springs! Said Florence.... Trial run last evening, not good. Still too rich on cruise revs, in the mid/high 12s. I'll take a bit more off the length of both heavy springs and see if that helps. Sticking with 20/50 oil as afr readings at medium and wot are fine. NOTE the perfect mixture burn stoichiometric value of petrol is 14.7 but due to the ethanol content for E5 it's about 14.4 and E10 14.1. I only use E5. On driving my car and from other reports our older engines run better at high 13s to 14. Iain Edited July 22, 2023 by Iain T Link to comment Share on other sites More sharing options...
Iain T Posted July 22, 2023 Author Report Share Posted July 22, 2023 Cut another 15mm off the heavy springs. On measuring they are both 200ish grammes at 53mm and the same length. I also measured the standard medium 99g springs which are actually about 150g! Hissin down and the forecast says I'll have to wait until Wednesday until it stops. The suspense! Well I did bomb up and down the 7 storey car park and it seemed smoother but that's not a real test! Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 23, 2023 Author Report Share Posted July 23, 2023 Not raining so out for a run and it's looking good! Tick over bumping around 14, at 40-50mph, 2000 to 2500 revs, afr meter reads high 13s and 65-70mph low 14s. At wot mid 12s. I will try and see what difference sae50 single grade makes to light/mid acceleration but I'm happy (for now) with my twiddling. So to recap I cut down the heavy springs to give 200g at 53mm compression and used 20/50 as a damper oil and have 6A needles. It may be stretching the standard 99g (actually measuring 150g) to 200g would have the same effect but it all depends on the initial spring compression force at tick over and mid range. Iain Link to comment Share on other sites More sharing options...
Iain T Posted July 24, 2023 Author Report Share Posted July 24, 2023 Update, I measured both modified heavy and standard blue springs at my lab aka kitchen worktop. The modified spring measured 200/210g at 53mm and the standard was in fact the correct rate of 100g not 150g as I reported earlier. I don't think I could stretch a standard to 200g as that would result in the effective diameter being reduced which may then bind on the cap spigot. Iain Link to comment Share on other sites More sharing options...
Iain T Posted September 27, 2023 Author Report Share Posted September 27, 2023 (edited) Latest update. A few weeks ago visited the Shuttleworth Collection on a Herts area meeting. Had a great time thanks to all. Had the 6A needles in and apparent early on it was getting too lean at 60-70mph. Just shows you need a god run (135 miles) with varied speeds to really test a new setting. I did richen up slightly before the run back but then tick over was too rich. After a brief spell with 6S needles went back to 7B's. I don't think I had tried the 7B needle with my hybrid damper spring so was interested to see if they worked. They do! Now done three long runs each 120+ miles plus a few small outings and it's, I'm reluctant to say this, seemingly very good. The afr at around 60-70 in the mid 13s as is tick over. At 30-50mph cruising in high gear the reading is 12.5ish but I think that's due to a lot of accelerator feathering in normal traffic which initially sends the mixture to rich before going lean on complete accelerator off. WOT is 12 or just under with no hesitation and bags of torque. The jet adjustment between vroom and lackluster is very small only 2-3mm of turn. Bit surprised at that and glad I invested in the Innovate afr! As to fuel consumption on mixed but mainly 60-70mph trips it's working out to be 28-30mpg. I think given how lively the engine is now I'm happy with that and reluctant to twiddle any more! It's the damper spring rate that for me was the key factor as none of the needles worked with standard springs. In my engine anything over 14 on the afr meter reduces the torque exponentially and is very noticeable. Iain Edited September 27, 2023 by Iain T Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now