SU carb dashpots, plus general carb blathering
Discussion
Although I have been driving assorted mouldy old death traps for years, it was not until this year that I acquired two cars that each have two SU carburettors (a slant four Dolomite and a straight six SD1). Indeed, none of my previous heaps had had dashpotted carbs of any variety, except for a Triumph Vitesse Mk 2 that had a pair of Strombergs, but that was decades ago and I can't recall if I had to fiddle with the carbs much.
Those who run cars with SUs on, how often do you find that you need to replenish the dashpots? I drive all of my old cars as cars, which means often and fast, so I find myself topping up the dashpots fairly often. I am using 3 in 1 oil at present, as it is light and easy to pop in. I fill only to the prescribed level. Maybe I should use engine oil instead. I dunno.
I was faintly dismissive of the SU setup on my Dolly Sprint at first, thinking "silly, budget oriented BL, WY U NO shell out for some Webbers or Dellortos?"*, but I have come to appreciate the simplicity of the SUs (compare Dellortos, which are fab, but which all have 947 jets to go wrong). They stay in tune, even though many say that Dollies are always in and out of tune.
Carb tuning is a black art. When I had a 1970s Alfa Spider with that lovely two litre twin cam and two Dellorto 40s, it never went out of tune. Same carbs on a Lotus 1600 twin cam - out of tune every time the wind changed. Dellorto 45s on a Lotus 912 engine - no tuning issues.
I still miss the woofly but mega thirsty single enormocarb on my old Jensen - a very cunning piece of kit with its four barrels coming into play de-ending on demand. The single Webber on a Lancia Beta's Lampredi twin cam is a cunning thing also. The second choke opens when you get to about 5000 RPM, and it feels like a poor man's blower cutting in. My Landy has one very utilitarian Zenith carb which never gives any problems and just chunters away on the remarkably smooth, tractable, and reliable 1950s Rover petrol engine that powers a 70s Landy. I briefly had a fancy-ass mid 70s Italian motorbike that had two tiny Dellortos, one for each cylinder, and they were a total pain in the butt.
That reminds me, I have a spare Carter (or is it Holley, I will check) four barrel lurking about if anyone wants one for a few quid. I could put it on eBay, but then would have to deal with eBayers, arrrrrgh!
Kindly share your joys and woes of carburettor craziness, including but not limited to dashpot disasters.
* because skint, obvs.
Those who run cars with SUs on, how often do you find that you need to replenish the dashpots? I drive all of my old cars as cars, which means often and fast, so I find myself topping up the dashpots fairly often. I am using 3 in 1 oil at present, as it is light and easy to pop in. I fill only to the prescribed level. Maybe I should use engine oil instead. I dunno.
I was faintly dismissive of the SU setup on my Dolly Sprint at first, thinking "silly, budget oriented BL, WY U NO shell out for some Webbers or Dellortos?"*, but I have come to appreciate the simplicity of the SUs (compare Dellortos, which are fab, but which all have 947 jets to go wrong). They stay in tune, even though many say that Dollies are always in and out of tune.
Carb tuning is a black art. When I had a 1970s Alfa Spider with that lovely two litre twin cam and two Dellorto 40s, it never went out of tune. Same carbs on a Lotus 1600 twin cam - out of tune every time the wind changed. Dellorto 45s on a Lotus 912 engine - no tuning issues.
I still miss the woofly but mega thirsty single enormocarb on my old Jensen - a very cunning piece of kit with its four barrels coming into play de-ending on demand. The single Webber on a Lancia Beta's Lampredi twin cam is a cunning thing also. The second choke opens when you get to about 5000 RPM, and it feels like a poor man's blower cutting in. My Landy has one very utilitarian Zenith carb which never gives any problems and just chunters away on the remarkably smooth, tractable, and reliable 1950s Rover petrol engine that powers a 70s Landy. I briefly had a fancy-ass mid 70s Italian motorbike that had two tiny Dellortos, one for each cylinder, and they were a total pain in the butt.
That reminds me, I have a spare Carter (or is it Holley, I will check) four barrel lurking about if anyone wants one for a few quid. I could put it on eBay, but then would have to deal with eBayers, arrrrrgh!
Kindly share your joys and woes of carburettor craziness, including but not limited to dashpot disasters.
* because skint, obvs.
Edited by anonymous-user on Friday 6th November 10:20
I don't have any SU carbed cars now, but have had many - I always used engine oil and rarely had to top them up.
I now have both Webers (Lotus TC) and Dellortos (Alfas) and neither need much adjustment apart from occasionally balancing them, but even that is usually only after they settle on their mountings relative to one another if I've had them off. Webers always seem to leak a bit even after they've been reconditioned.
I've recently acquired a Citroen DS which I think has a solex - no experience of them but it seems to work OK...
I now have both Webers (Lotus TC) and Dellortos (Alfas) and neither need much adjustment apart from occasionally balancing them, but even that is usually only after they settle on their mountings relative to one another if I've had them off. Webers always seem to leak a bit even after they've been reconditioned.
I've recently acquired a Citroen DS which I think has a solex - no experience of them but it seems to work OK...
IIRC engine oil used to be considered too viscous, leading to slow response : but that was when 0W5 would have been unthinkable as engine oil.
Do you have a manual for any of the dashpotted wonders that mentions oil thickness?
I will ask Gerard the master tuner at work next week if I remember.
Do you have a manual for any of the dashpotted wonders that mentions oil thickness?
I will ask Gerard the master tuner at work next week if I remember.
998cc Mini with a single SU - probably every week or two. I just use 20/50 engine oil, easily dispensed with one of these:
http://www.toolstation.com/shop/p82913?table=no
Every SU I've ever owned has needed topping up. I think they're OK carbs - they'll never be the most powerful because of the lack of an accelerator pump, but when they're properly set up and any waxstat type crap removed they work well enough for me.
http://www.toolstation.com/shop/p82913?table=no
Every SU I've ever owned has needed topping up. I think they're OK carbs - they'll never be the most powerful because of the lack of an accelerator pump, but when they're properly set up and any waxstat type crap removed they work well enough for me.
I purchased a V8 landy with twin SU's...
Wasn't running quite right to start with.. and I didn't know much about carbs either.
It appears that some bellend had compensated / adjusted the carbs to run with the vacuum for the brake servo opened all the time (brake servo didn't work)
Now has correct servo, carbs adjusted to suit and running much better! Finding i'm topping up (not refilling) the carbs every few hundred miles I'd imagine
Wasn't running quite right to start with.. and I didn't know much about carbs either.
It appears that some bellend had compensated / adjusted the carbs to run with the vacuum for the brake servo opened all the time (brake servo didn't work)
Now has correct servo, carbs adjusted to suit and running much better! Finding i'm topping up (not refilling) the carbs every few hundred miles I'd imagine
N Dentressangle said:
998cc Mini with a single SU - probably every week or two. I just use 20/50 engine oil, easily dispensed with one of these:
http://www.toolstation.com/shop/p82913?table=no
Every SU I've ever owned has needed topping up. I think they're OK carbs - they'll never be the most powerful because of the lack of an accelerator pump, but when they're properly set up and any waxstat type crap removed they work well enough for me.
Coolio, I be shopping, cheers!http://www.toolstation.com/shop/p82913?table=no
Every SU I've ever owned has needed topping up. I think they're OK carbs - they'll never be the most powerful because of the lack of an accelerator pump, but when they're properly set up and any waxstat type crap removed they work well enough for me.
I find 3 in 1 or similar is too light and doesn't have the required dampening effect especially when regularly using full throttle 
. I use 20/50 engine oil in SU carbs. As long as the jets are centred correctly and the piston when raised with your finger makes a controlled drop and reassuring thud on the base all is well. Properly maintained SU's should stay in tune and as long as you stick to the correct order of setting them up will go for ages without requiring adjustment. Problems only really occur then the spindles and linkages are worn letting air in. Getting them re sleeved can turn a hesitant pig dog engine into a flying machine 
. I use 20/50 engine oil in SU carbs. As long as the jets are centred correctly and the piston when raised with your finger makes a controlled drop and reassuring thud on the base all is well. Properly maintained SU's should stay in tune and as long as you stick to the correct order of setting them up will go for ages without requiring adjustment. Problems only really occur then the spindles and linkages are worn letting air in. Getting them re sleeved can turn a hesitant pig dog engine into a flying machine Breadvan72 said:
I was faintly dismissive of the SU setup on my Dolly Sprint at first, thinking "silly, budget oriented BL, WY U NO shell out for some Webbers or Dellortos?"*, but I have come to appreciate the simplicity of the SUs (compare Dellortos, which are fab, but which all have 947 jets to go wrong). They stay in tune, even though many say that Dollies are always in and out of tune.
Way back when I was briefly in the Doli Sprint club, when I'd bought one for the ex. One of the guys there's day job was building F1 engines. His Sprint was a little non-standard to say the least. Anyway we swore by Dellortos on the Sprint rather than Webers. He said that the droplets from the Weber carbs were smaller and tended to condensate out more on the manifold lining... or some such... hey it was over 25 years ago.As to SU's I was always told to use engine oil in the dash pots. As others have suggested a pump can is the ideal way to fill them.
The 'correct' oil for SU dashpots is a straight 20 grade which if you like, you can buy in a labelled bottle for that purpose.
But you can buy 5 litres of Morris Lubricants straight 20 for £28.63 and I rather doubt even with the leakiest dashpots and a big fleet you would ever use that much in a lifetime!
http://www.morrislubricantsonline.co.uk/golden-fil...
for the cheap stuff.
Or if you are wealthy and like buying things...
http://sucarb.co.uk/dampers-caps-oil/damper-oil.ht...
£5.09 for a few cc's
But you can buy 5 litres of Morris Lubricants straight 20 for £28.63 and I rather doubt even with the leakiest dashpots and a big fleet you would ever use that much in a lifetime!
http://www.morrislubricantsonline.co.uk/golden-fil...
for the cheap stuff.
Or if you are wealthy and like buying things...
http://sucarb.co.uk/dampers-caps-oil/damper-oil.ht...
£5.09 for a few cc's
I have a few SU carbs under various old bonnets. Always used 20/50 engine oil in them. Its a good idea to take the dashpots off every so often and give them a good clean out with a rag soaked in brake fluid, or proper carb cleaner.
SUs are good, simple devices. The only trouble I've had with one was on my Dolomite 1500, one of the needle valves kept sticking open, just needed a clean out.
SUs are good, simple devices. The only trouble I've had with one was on my Dolomite 1500, one of the needle valves kept sticking open, just needed a clean out.
N Dentressangle said:
they'll never be the most powerful because of the lack of an accelerator pump, but when they're properly set up and any waxstat type crap removed they work well enough for me.
That is the whole point. The constant vacuum effect of the rising piston negates the need for an accelerator pump. The purpose of the acel pump is to prevent a flat spot when opening the throttle, as the carb goes from idle through to main jets.Anyway, SU's are pretty good things. As the man says replace those Waxstat jets with conventional ones, and fit the latest Ethanol proof floats and needle valves.
I use either 3 in 1 or a light engine oil.
I use 20/50 as well, some carbs seemed to need topping up more often than others (I had a Herald which I don't remember doing at all) . I once had 1ltr of cheapo 20/5o from Wilko own brand when I needed a top up. It was so watery that I didn't like to actually use it in the engine, so it sits on shelf and used in dashpots or any odd jobs that need a drop of oil.
I think it's been on the shelf now for 6/7 years and it's still 1/2 full. (along with the chainsaw oil and all the other specialised lubes)
Feeling the love for SU type carbs, great for the road use, simple to set up and repair. What's not to like.
I think it's been on the shelf now for 6/7 years and it's still 1/2 full. (along with the chainsaw oil and all the other specialised lubes)
Feeling the love for SU type carbs, great for the road use, simple to set up and repair. What's not to like.
I have triple SU HD8's on the Healey and I too use 20/50 which works just fine. They need topping up every ten days to a fortnight depending on use, but it gets driven hard when it does get driven as I use it to compete, so with normal spirited road use you may not need to as often as me.
I have toyed with converting to Webers, but to be honest I like the simple reliability of the SU's and the fact they are more flexible in use across the rev range and in a variety of circumstances, whether it be thrashing it up a hill climb, or doing a regularity. Horses for courses, but 20/50 does it nicely for me.
I have toyed with converting to Webers, but to be honest I like the simple reliability of the SU's and the fact they are more flexible in use across the rev range and in a variety of circumstances, whether it be thrashing it up a hill climb, or doing a regularity. Horses for courses, but 20/50 does it nicely for me.
I used to think that SUs were a bit cheapo and naff, but I can now see their simple virtues. Mine can't be too bad, as when a 435i ahead of me attempted to show me its heels this afternoon, I did not do a bad job of keeping in Sidewinder range for a couple of miles of A road with a few swoopy curves. I do believe that my Dolly lifted her skirts, so to speak. To be fair, the BM was not on full War Emergency Power, perhaps mindful of the local speed limits and relatively high number of police vehicles in the area, but he was still cracking on at a brisk pace. Then he stormed up a long and twisty hill covered with wet leaves, so discretion became the better part of valour, and I saw him no more.
Breadvan72 said:
I used to think that SUs were a bit cheapo and naff, but I can now see their simple virtues. Mine can't be too bad, as when a 435i ahead of me attempted to show me its heels this afternoon, I did not do a bad job of keeping in Sidewinder range for a couple of miles of A road with a few swoopy curves. I do believe that my Dolly lifted her skirts, so to speak. To be fair, the BM was not on full War Emergency Power, perhaps mindful of the local speed limits and relatively high number of police vehicles in the area, but he was still cracking on at a brisk pace. Then he stormed up a long and twisty hill covered with wet leaves, so discretion became the better part of valour, and I saw him no more.
SUs are fine, once properly set up and balanced. The joys of adjusting the slightly worn linkage with one end of a rubber tube in your ear and the other in the carb. And adjusting valve clearance, dwell, points, timing...
Having had many Triumphs I've experienced Strombergs and SUs. Old Strombergs often use dashpot oil as the chamber is actually an open tube with the needle at one end. The needle tuning adjuster has an "O" ring that degrades over time thus allowing the oil to be sucked out.
In SU's, the needle is fixed and the jet is adjusted for tuning, so the dashpot chamber is closed at the needle end ergo no loss of oil.
Strombergs also have nasty rubber diaphragms whereas the SU vacuum is formed using a solid diaphragm that is part of the piston.
Strombergs have a lower profile, so good on the top of V8's (like my Stag) but I loved the 2" SU's that I put on the wife's Sprint.
PS The SU workshop manual states SAE20 oil for the dashpots, ie 20W50. That's what I've always used.
In SU's, the needle is fixed and the jet is adjusted for tuning, so the dashpot chamber is closed at the needle end ergo no loss of oil.
Strombergs also have nasty rubber diaphragms whereas the SU vacuum is formed using a solid diaphragm that is part of the piston.
Strombergs have a lower profile, so good on the top of V8's (like my Stag) but I loved the 2" SU's that I put on the wife's Sprint.
PS The SU workshop manual states SAE20 oil for the dashpots, ie 20W50. That's what I've always used.
Edited by LoudV8 on Friday 6th November 18:50
As I recall, if there's too much oil in the dashpot then the excess is expelled through the breather hole in the plastic cap when the piston rises to the top of its travel. So it may well be that the amount of oil that's left is actually the correct amount. I certainly can't recall having to add much oil to the SUs of any car I've owned with them on.
As others have said, engine oil of the correct viscosity is the way to go. 3 in 1 is far too thin and actually allow the piston to rise too quickly as the throttle is opened suddenly, causing the mixture to go lean momentarily and making the engine hesitate for a moment or two.
As others have said, engine oil of the correct viscosity is the way to go. 3 in 1 is far too thin and actually allow the piston to rise too quickly as the throttle is opened suddenly, causing the mixture to go lean momentarily and making the engine hesitate for a moment or two.
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