Hi,
I have built a Lotus 7 type kit car around a 3.5 litre SD1 V8 engine (9.35:1 CR) running standard BAK needles. I think it is running a bit too lean as it is holding back under throttle, is overheating, is pinking and the plugs are too clean. I'm running super unleaded fuel with Castrol valve seat protection additive. My ignition is set to 8 degrees BTDC at 800RPM with vacuum disconnected. The crank damper position has been verified wrt TDC.
The engine is standard except for a pair of ITG foam air filters attached directly to the carbs with stub stack ram pipes inside the filters. I also have SD1 manifolds with custom 2" bore straight-through exhaust silencers each side of the car.
Can anyone suggest a pair of needles to match the above spec as it seems to me that this sort of setup should be quite common.
Many thanks,
Craig.
Which SU Needles?
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Hello Craig,
Do you know at what rpm your distributor is fully advanced? If it comes in too early, this can certainly introduce pinking, especially when working hard.
As for needles, the next one along in terms of richness is BAF. The first two idle mixture points are identical, so you should not need to make any adjustment. After that is BBW, but you may well find that this needle is too rich in the top end, and of course running too rich just loses you power too.
With your current BAK needles, when the engine is idling and you raise each carburettor lift pin, how does the engine react?
What type of oil are you running in the dashpots?
What level have you set the floats too?
These are important points as the cause may well be here, and the BAK needle may well be correct.
Please let me know,
Ron.
Do you know at what rpm your distributor is fully advanced? If it comes in too early, this can certainly introduce pinking, especially when working hard.
As for needles, the next one along in terms of richness is BAF. The first two idle mixture points are identical, so you should not need to make any adjustment. After that is BBW, but you may well find that this needle is too rich in the top end, and of course running too rich just loses you power too.
With your current BAK needles, when the engine is idling and you raise each carburettor lift pin, how does the engine react?
What type of oil are you running in the dashpots?
What level have you set the floats too?
These are important points as the cause may well be here, and the BAK needle may well be correct.
Please let me know,
Ron.
4.6 Rover 3500 P6B
Hi Ron,
Many thanks for your prompt reply - taking your questions in turn:
After I posted this question last night I checked on ebay for SU needles to get an idea of costs and rather impulsively bought a pair of BBW needles. This doesn't mean that I have made up my mind though so please feel free to disagree with this decision. At the worst it will allow me to see what a fairly rich pair of needles will do for my engine and this alone might turn my attention elsewhere if I don't get the response I am hoping for. Given the rather cramped engine bay on my "Seven" I would rather err on the rich side than the lean side to keep the temperature down as much as possible. I should mention that I have fitted a 74 degree C thermostat as I was having trouble with coolant loss at slow speeds due to heat surge. This may have been caused by an air lock which I think I have eradicated now.
One final thing - I checked the compression pressures last night and found a range of pressures from 175lb/sq" to 195lb/sq". This was measured on a hot engine with all plugs removed and the throttle butterflies at idle. I'm not sure if this is within spec but it seems quite high. I wonder if my engine has been fitted with 9.75:1 pistons as I believe it was rebuilt not long before I bought it. Any idea what pressure I should expect from a Rover V8?
Thanks again for your help,
Craig.
Many thanks for your prompt reply - taking your questions in turn:
I don't know for sure but the dizzy is standard 35DE8 as far as I am aware. I also inspected it for damage and cleaned and lubricated it before I fitted the engine to the car. Would it be worth getting a new set of springs for the dizzy? I also checked the vacuum advance and it seems to operate the advance mechanism if I suck hard on the pipe to the carb. It also returns fully to the starting position.RoverP6B wrote:Hello Craig,
Do you know at what rpm your distributor is fully advanced? If it comes in too early, this can certainly introduce pinking, especially when working hard.
This is the technique I have used to set the idle mixture and I can get it to the point where it raises RPM very slightly and then falls back to normal or slightly below normal RPM. It seems to be quite sensitive and 1/4 turn either way can make the engine reduce or increase RPM more substantially when lifting the pin. Actually I don't use the lifting pin I just use a long screwdriver down the carb throat as I can see more accurately how much I am lifting the dashpot that way. I stay well clear of the needle when lifting to avoid disrupting the airflow over the jet.As for needles, the next one along in terms of richness is BAF. The first two idle mixture points are identical, so you should not need to make any adjustment. After that is BBW, but you may well find that this needle is too rich in the top end, and of course running too rich just loses you power too.
With your current BAK needles, when the engine is idling and you raise each carburettor lift pin, how does the engine react?
Just using the same engine oil I use in the engine. It was bought at Halfords as mineral oil designed for older engines and I think it was either 20w/50 or 15w/40. The dashpots are topped up correctly.
What type of oil are you running in the dashpots?
The floats were set to whatever was specified in the Rover SD1 workshop manual I had to hand at the time. I can't honestly remember off the top of my head but I definitely set them both up when I cleaned out the carbs.
What level have you set the floats too?
Yes I know there can be 101 reasons for just about any form of poor running but I am pretty sure that my induction system and exhaust system will be more efficient than a standard SD1 so I expect to need some degree of richening of the fuel mixture. My very clean white spark plugs would tend to support this conclusion, especially since I am only running the car for short journeys where I would expect the plugs to be a little bit sooty if anything.
These are important points as the cause may well be here, and the BAK needle may well be correct.
Please let me know,
Ron.
After I posted this question last night I checked on ebay for SU needles to get an idea of costs and rather impulsively bought a pair of BBW needles. This doesn't mean that I have made up my mind though so please feel free to disagree with this decision. At the worst it will allow me to see what a fairly rich pair of needles will do for my engine and this alone might turn my attention elsewhere if I don't get the response I am hoping for. Given the rather cramped engine bay on my "Seven" I would rather err on the rich side than the lean side to keep the temperature down as much as possible. I should mention that I have fitted a 74 degree C thermostat as I was having trouble with coolant loss at slow speeds due to heat surge. This may have been caused by an air lock which I think I have eradicated now.
One final thing - I checked the compression pressures last night and found a range of pressures from 175lb/sq" to 195lb/sq". This was measured on a hot engine with all plugs removed and the throttle butterflies at idle. I'm not sure if this is within spec but it seems quite high. I wonder if my engine has been fitted with 9.75:1 pistons as I believe it was rebuilt not long before I bought it. Any idea what pressure I should expect from a Rover V8?
Thanks again for your help,
Craig.
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CastleMGBV8
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Craig,
Slightly off topic but you say you are using valve seat protection additive, if the engine is an SD1 it already has hardened seats and ordinary unleaded should be fine.
Whats your engine number in case its a P5/6
Long time since I used SU's but I thought you need to use a light oil like 3 in 1 but I could be wrong.
Kevin.
Slightly off topic but you say you are using valve seat protection additive, if the engine is an SD1 it already has hardened seats and ordinary unleaded should be fine.
Whats your engine number in case its a P5/6
Long time since I used SU's but I thought you need to use a light oil like 3 in 1 but I could be wrong.
Kevin.
Hi
Dashpot oil viscosity (along with how worn the dash pot is) controls your acceleration enrichment, new SU's with the mixture on the rich side, 3in1, older SU's (say 40 to 60k) and set up to get through an MOT you need 15/40 or 20/50, best to try different oils once the mixture is set up for steady state (or just try different ones and see what suites you driving the best).
Mike
Dashpot oil viscosity (along with how worn the dash pot is) controls your acceleration enrichment, new SU's with the mixture on the rich side, 3in1, older SU's (say 40 to 60k) and set up to get through an MOT you need 15/40 or 20/50, best to try different oils once the mixture is set up for steady state (or just try different ones and see what suites you driving the best).
Mike
poppet valves rule!
Kevin, you are quite correct I don't need to use additive but I had some handy and thought it can't do any harm. I probably wontbuy any more once it's finished. My engine is a 10A SD1 engine from October 1976.
As for dashpot oil Mike, I will do some experimentation once I get my steady state mixture sorted but if it is running lean with 20w50 then anything thinner is only going to make it worse if I understand correctly.
Thanks,
Craig.
As for dashpot oil Mike, I will do some experimentation once I get my steady state mixture sorted but if it is running lean with 20w50 then anything thinner is only going to make it worse if I understand correctly.
Thanks,
Craig.
Hello Craig,
The standard Lucas distributor will have fairly conservative advance, so unless the springs are completely shot the advance won't come in too early. With the cap off, turn the rotor and let it go,..it should spring back to the starting position. If it does not, or if it feels especially loose, then by all means replace the springs.
Everything else that you described sounds fine, so it would indeed appear that the needles themselves are the culprit.
The BBW needles may prove to be too rich in the top end, but they are not expensive should you need a compromise. The idle mixture points are very slightly richer, so you will likely need to make a slight adjustment there.
20W-50 engine oil in the dashpots is not a problem.
As far as ignition timing goes,..did you find that your engine idles most smoothly and with the highest rpm at 8 degrees BTDC?
Please let me know how you go with the BBW needles once installed.
Ron.
The standard Lucas distributor will have fairly conservative advance, so unless the springs are completely shot the advance won't come in too early. With the cap off, turn the rotor and let it go,..it should spring back to the starting position. If it does not, or if it feels especially loose, then by all means replace the springs.
Everything else that you described sounds fine, so it would indeed appear that the needles themselves are the culprit.
The BBW needles may prove to be too rich in the top end, but they are not expensive should you need a compromise. The idle mixture points are very slightly richer, so you will likely need to make a slight adjustment there.
20W-50 engine oil in the dashpots is not a problem.
As far as ignition timing goes,..did you find that your engine idles most smoothly and with the highest rpm at 8 degrees BTDC?
Please let me know how you go with the BBW needles once installed.
Ron.
4.6 Rover 3500 P6B
Hi Ron,
I will check the distributor in the way you suggest but I think it will be okay. I'm sure I would have noticed any slackness or binding in the mechanism when I cleaned it all out.
As for ignition timing, I actually tried a bit more advance (about 12 degrees BTDC) as this was recommended in a book (Des Hammill's book on RV8 tuning I think) and given I was running with super unleaded I thought it would take it okay. However, it sounded like it was pinking (sounded like something loose inside the exhausts making a tinkling sound under load which I hadn't noticed before). Of course a lean mixture would cause pinking to occur sooner I think so I might try some more advance once I install the BBW needles.
To be honest I need to get myself a few bits of tuning gear. I used to have a Gunsons carbalancer but I can't find it and I used to have a vacuum gauge which I also can't find. I do have a xenon timing light but for some reason it is very dim and I can't see my timing marks unless ambient light is very low. I also have no rev counter at present so I'm having to rely on the LED on the timing light which indicates when the RPM is equal to that set on the potentiometer next to it. A bit of a disaster really...
What would you recommend with regards to ignition timing? Do you just go for max RPM with smoothest running? The manual says 6 degrees BTDC dynamic and 3 degrees static which seems very low compared to Des Hammill's recommendations. Advice most welcome!
I'll let you know how the BBW needles perform once I get them.
Thanks again,
Craig.
I will check the distributor in the way you suggest but I think it will be okay. I'm sure I would have noticed any slackness or binding in the mechanism when I cleaned it all out.
As for ignition timing, I actually tried a bit more advance (about 12 degrees BTDC) as this was recommended in a book (Des Hammill's book on RV8 tuning I think) and given I was running with super unleaded I thought it would take it okay. However, it sounded like it was pinking (sounded like something loose inside the exhausts making a tinkling sound under load which I hadn't noticed before). Of course a lean mixture would cause pinking to occur sooner I think so I might try some more advance once I install the BBW needles.
To be honest I need to get myself a few bits of tuning gear. I used to have a Gunsons carbalancer but I can't find it and I used to have a vacuum gauge which I also can't find. I do have a xenon timing light but for some reason it is very dim and I can't see my timing marks unless ambient light is very low. I also have no rev counter at present so I'm having to rely on the LED on the timing light which indicates when the RPM is equal to that set on the potentiometer next to it. A bit of a disaster really...
What would you recommend with regards to ignition timing? Do you just go for max RPM with smoothest running? The manual says 6 degrees BTDC dynamic and 3 degrees static which seems very low compared to Des Hammill's recommendations. Advice most welcome!
I'll let you know how the BBW needles perform once I get them.
Thanks again,
Craig.
Hello Craig,
Yes having a good set of instruments is very important. I having a timing light, dwell tachometer and an SU carburettor air flow meter. As you know, each carburettor must have the idle screw carefully adjusted to ensure that both carburettors are flowing exactly the same amount of air.
It would be a good idea to ensure that this is indeed the case prior to installing the BBW needles.
The compression ratio of your engine is quite high, so that will limit how much initial advance you can run combined with a factory set distributor as you found when trying 12 degrees BTDC.
Ideally the engine should idle as smoothly as possible, and there is nothing wrong with running at 8 degrees BTDC. With the factory set distributor, adding initial timing above standard adds that amount throughout the range, hence the onset of pinking with 12 degrees initial.
It is all a compromise really.
I look forward to hearing how the needles go.
Ron.
Yes having a good set of instruments is very important. I having a timing light, dwell tachometer and an SU carburettor air flow meter. As you know, each carburettor must have the idle screw carefully adjusted to ensure that both carburettors are flowing exactly the same amount of air.
It would be a good idea to ensure that this is indeed the case prior to installing the BBW needles.
The compression ratio of your engine is quite high, so that will limit how much initial advance you can run combined with a factory set distributor as you found when trying 12 degrees BTDC.
Ideally the engine should idle as smoothly as possible, and there is nothing wrong with running at 8 degrees BTDC. With the factory set distributor, adding initial timing above standard adds that amount throughout the range, hence the onset of pinking with 12 degrees initial.
It is all a compromise really.
I look forward to hearing how the needles go.
Ron.
4.6 Rover 3500 P6B
Got my needles today - guess what - they weren't BBW needles they were BAQ needles which are no use to me whatsoever. Have sent an email to the ebay seller but no reply as yet... He had BAQ needles advertised as well so I expect he got his envelopes mixed up.
So, looks like I'm unlikely to be able to test out the BBW needles this weekend as hoped but I have ordered a number of items from RealSteel.co.uk including a set of high performance ignition leads, rotor arm and dizzy cap. I've also got a set of dizzy springs and a sleeve to fit over my crank pulley to make timing marks easier to see. This lot should be here tomorrow.
Will update on the BBW needles once I get them. (If I ever get them...)
So, looks like I'm unlikely to be able to test out the BBW needles this weekend as hoped but I have ordered a number of items from RealSteel.co.uk including a set of high performance ignition leads, rotor arm and dizzy cap. I've also got a set of dizzy springs and a sleeve to fit over my crank pulley to make timing marks easier to see. This lot should be here tomorrow.
Will update on the BBW needles once I get them. (If I ever get them...)
Got some more needles delivered this morning but guess what....they were the wrong ones as well!! AAV this time. It beggars belief that I could be so unlucky as to get the wrong needles twice but there you go...
Been in touch with the company who will be sending me the right needles on Monday. I'll believe it when I see it really!
In the meantime I got a bunch of stuff from RealSteel as mentioned in my last post. Will get to work making up the ignition leads tonight I think!
Cheers,
Craig.
Been in touch with the company who will be sending me the right needles on Monday. I'll believe it when I see it really!
In the meantime I got a bunch of stuff from RealSteel as mentioned in my last post. Will get to work making up the ignition leads tonight I think!
Cheers,
Craig.
Hi Ron,
Sorry for not replying sooner but I've been pretty busy lately.
The BBW needles did arrive and I have fitted them along with a distributor advance recurve kit. The end result seems to be very positive but I'm still having cooling issues with my engine so I've not been able to fully realise the benefits. The engine seems very responsive now and my spark plugs are showing signs of brown deposits along with some black soot which is healthier than the super-clean white plugs I had before. It should be safer for the engine even if they are a bit rich. We'll see once I sort out the cooling.
As for the cooling, I have today fitted a larger expansion tank of the free flowing type where the tank feeds the bottom hose and is in turn fed via the high points of the engine and radiator. Unfortunately I've not had a chance to test it out yet but hope to do so tomorrow night. If I can sort out the cooling then I might be able to properly evaluate the engine performance.
I'll let you know how I get on - remind me if I forget...
Cheers,
Craig.
Sorry for not replying sooner but I've been pretty busy lately.
The BBW needles did arrive and I have fitted them along with a distributor advance recurve kit. The end result seems to be very positive but I'm still having cooling issues with my engine so I've not been able to fully realise the benefits. The engine seems very responsive now and my spark plugs are showing signs of brown deposits along with some black soot which is healthier than the super-clean white plugs I had before. It should be safer for the engine even if they are a bit rich. We'll see once I sort out the cooling.
As for the cooling, I have today fitted a larger expansion tank of the free flowing type where the tank feeds the bottom hose and is in turn fed via the high points of the engine and radiator. Unfortunately I've not had a chance to test it out yet but hope to do so tomorrow night. If I can sort out the cooling then I might be able to properly evaluate the engine performance.
I'll let you know how I get on - remind me if I forget...
Cheers,
Craig.
