Stomber v SU

Talk about the E-Type Series 3

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Graham C
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#1 Stomber v SU

Post by Graham C » Tue Apr 10, 2018 2:38 pm

Hello,
I have a V12 fitted with Stromberg’s and it suffers with difficult starting from cold and hot. The main problem though is the stench of fuel when driving which poisons me the driver and my passenger as well as all passersby’s. Many have tried to tune the car and it is a lot better now and does not peter out whilst driving as it once did but still is far from good. Fuel consumption is staggering. I have been recommended to exchange the Stromberg’s for SU’s with the reason that the Stromberg’s cannot be maintained and SU’s are easier to set up. Has anyone else been through these issues and resolved them with SU’s?

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christopher storey
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#2 Re: Stomber v SU

Post by christopher storey » Tue Apr 10, 2018 2:53 pm

I'm not sure why you say that Strombergs cannot be maintained as, so far as I know, all spares are readily available from Burlens . The poor running and smell of fuel sounds like a. worn needle valves ; b. ruptured diaphragms ; c. possibly over pressure if you have non-standard fuel pump fitted such as a Facet . Any one of these would also explain the dire fuel consumption

here's an initial link : it's the on Zenith tab of the Burlen site

http://zenithcarb.co.uk/cf/vehicle/list ... ehicle=V12

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Whitact
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#3 Re: Stomber v SU

Post by Whitact » Tue Apr 10, 2018 5:38 pm

Hi Graham,
I have Strombergs on my OTS and SUs on my FHC (fitted by previous owner given similar advice to that which you have received). I rebuilt the Strombergs using the info in the knowledge base, or you can get Burlen to do them for you. The OTS starts better from cold, uses less fuel and has better pick up from idle to mid speed. The FHC is slow to start from cold, especially if it has been stood for a while, has a tediously heavy throttle pedal due to the return springs in the SUs and is generally not such a nice drive as the OTS. Both cars have identical gearing and the SNG ignition system and will return over 20 mpg on a good run. One thing well worth doing is fitting a vacuum advance capsule to the distributor. A great improvement to the mid range used for every day driving. In your situation I would be to get the Strombergs sorted and use the £1k or so saved for something else.
Cheers
Adrian Turner
S3 OTS & FHC
S1 FHC
XK140 FHC

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driver
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#4 Re: Stomber v SU

Post by driver » Tue Apr 10, 2018 8:20 pm

Hi Rob Gill here,
I reconditioned my strombergs with a kit from Burlens and changed all rubber fuel hoses has they were leaking etc ,all is ok now.Has for fuel consumption i dont check it yet as i have only recently started using the car
but it seems ok ,and every time i go to the petrol station the girls in the kiosk always ask me all about it and so does everyone else .................thats priceless, so i dont really care.
that my version of growing old disgracfully irresponcably or whatever :mrgreen: :bigrin: :swerve:
v12 etype 2+2

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JJC
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#5 Re: Stomber v SU

Post by JJC » Wed Apr 11, 2018 12:28 am

Hello there ! No difference in performance between SU's and Strombergs at all. I have had a Series 3 for 44 years. 20 or so years ago, a friend gave me a set of new SU's really cheap, and the Strombergs, although perfect with routine maintenance , and the occasional re-build , were just fine. But the SU's were new, and Strombergs were no longer in production, so what the heck. SU's.......just a bit, easier to adjust, but they run just fine...and easier to polish !!! LOL

Happy motoring !

John

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garrycol
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#6 Re: Stomber v SU

Post by garrycol » Wed Apr 11, 2018 1:33 am

Get someone who knows what they are doing - once the strombergs are set up they last for ever without adjustment - all you need to do is check the diaphragms, keep the oil in the dash pots topped up and occasionally check the wear on needles - all user items.

I have had my car for 36 years and in that time the carbs have only been looked at once and no adjustments were needed. The car had been laid up for nearly 10 years at one stage with no start - pumped fresh fuel through the carbs and it started first go and had a nice smooth 600rpm idle after a couple of minutes - starts hot or cold not issues.

The same for my Rover V8 with twin strombergs.

They are bullet proof and if there are issues it will be other items such as vacuum lines etc - check the diaphrams. oil level and that will be about it. Get someone who knows what they are doing.

Garry
1971 Series 3 E-type OTS

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lowact
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#7 Re: Stomber v SU

Post by lowact » Wed Apr 11, 2018 2:21 am

Hello Graham. I have the same problem, search “acrid smoke”. I suspect, based on side comments I read, that the fuel stench from carb’d V12s is fairly common and is mostly tolerated. It is not tolerable to me. I do not believe that the carb’s alone are the problem and I do not believe that changing the carbs from Stromberg to SU would fix the problem, I consider that any advice to change to SU’s to fix this problem is evidence of ignorance/incompetence, I would find another x-spurt.

The biggest difference between SUs and Stromberg is that the Stromberg has temp compensator valves and throttle bypass valves, both are emission control devices, both are instructed to be non-adjustable (on 175CDSE or 175CD-2) , both can be disabled/removed. The temp compensator is merely a bleed around the piston (not the throttle) and is insignificant, to check it, in UK you heat it up to see if it opens, in Australia we put it in the fridge to see if it closes – whoopee. The bypass valves are supposed to pop open on high vacuum to vent the space between the piston and the throttle plate. These bypass valves have metal on metal sealing so, unless perfectly matched, one may leak a bit all the time which on my car made carb balancing problematic. Couldn’t fix this by tightening the bypass valves, (spring compression, internal adjustment) so I removed the bypass valves completely, replaced them with blanking plates, thereby simplifying my strombies almost to SU level. Fixed the carb balancing and idling speed but didn’t reduce the stench. Based on this I suggest u investigate everything else before considering changing the carbs.

1st thing to ascertain, is the fuel stench from the engine bay or the exhaust pipe? In my case it is from the exhaust pipe.

2nd, are the Stromberg carbs in good condition? Mine are. Reconditioned, checked and double checked. Needles adjusted using a wide-band air fuel ratio meter. Still stank. Then modified as above. No change. Nevertheless, as Chris and Gary say, carb condition can be a cause, u need to eliminate this, if I was you (in UK) I would send my carbs to Burlen’s, to be fully reco’d as a starting point.

3rd, check yr vacuum. I read in the forum that a known issue with 6 cyl cars is fuel stench ultimately due to worn valve guides, maybe V12s also? Vacuum at idle is how to tell if you have worn valve guides. I have fuel stench and poor vacuum at idle (approx. -14 mm Hg, should be -20 mm Hg). Get a vacuum tests gauge, connect it temporarily, (eg. In place of the vacuum line to the brake booster (or any other vacuum source except carb throttle edge tappings) and measure the vacuum when idling.

If it IS low enough, I have nothing to suggest and my theory as to the problem with my car is blown out of the water. If it is NOT low enough, 1st check and double-check that there are no vacuum leaks, the following vacuum sources (if yr car has them) must not leak :
• The vacuum line to the brake booster,
• The small vacuum take-offs on each of the 4 manifolds (they face each other) and provide vacuum for the carb bypass valve actuation, gulp valve actuation, air inlet temperature control x2)
• The balance pipe between the left and right side manifolds.
• The carb bypass valves (diaphrams, test by trying to suck on the vacuum lines)
• the gulp valve (diaphragm, test by trying to suck on the vacuum line while blocking off the gulp valve connection to the balance pipe - important).
• The ignition retard port under the left rear carb (throttle edge tapping)
• The ignition advance port above the left rear carb (throttle edge tapping)
• The extra vacuum off-take that is next to the vacuum offtake of the brake booster
• All manifold, head and carb flanges (spray aero-start in these and check if vacuum is improved)

If all these are ok and vacuum is still not low enough, maybe, as I suspect, the problem is that you have leaking valve seals, changing carbs will not fix this!
Advice that everyone on this forum should be happy to endorse - If you have poor idle vacuum, fix this first?
Regards,
ColinL
'72 OTS manual V12

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71 V12
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#8 Re: Stomber v SU

Post by 71 V12 » Wed Apr 11, 2018 7:49 pm

Hi Graham,

This topic has come up before, info here:

viewtopic.php?f=6&t=10756&p=86425#p86425

I would recommend sticking with the Strombergs and replace all rubber fittings in the engine breather system.

Kind regards,

Kevin

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Woolfi
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#9 Re: Stomber v SU

Post by Woolfi » Thu Apr 12, 2018 11:37 am

Hello John,
you wrote in a former post: Hello there ! No difference in performance between SU's and Strombergs at all.

I think, that there can be a small difference in power between the Stromberg carbs and the bigger SU HD8. But maybe the difference is smaler , than you can detect / feel when driving. Maybe a dyno shows a difference in power above 5000 rpm.
I was searching a long time, to find a reliable post about a dyno test of these two carbs on a EV12, but have not been able to find.
Regards Wolfgang Gatza

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#10 Re: Stomber v SU

Post by Whitact » Thu Apr 12, 2018 5:12 pm

Hi Woolfi,
I believe that the SU conversion for the S3 E-Types is generally four SU HIF44 carbs. That's certainly what my FHC has. When I had it on a rolling road it made 272 bhp and the guy testing it remarked that with Strombergs it would have made a little more. The Strombergs are 1.75 inch compared to the 1.73 inch of the HIF44. I've not had my OTS on a rolling road so do not have comparative figures to verify that suggestion.
Cheers,
Adrian Turner
S3 OTS & FHC
S1 FHC
XK140 FHC

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JJC
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#11 Re: Stomber v SU

Post by JJC » Thu Apr 12, 2018 11:54 pm

No difference in day to day driving....none. One has a bit more on a dyno ? Could be....years ago, after I switched to SU's , I ran on a dyno just for fun and giggles, but it does not represent real world driving, so whatever your using, keep 'em in good shape, and just enjoy !!

John

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#12 Re: Stomber v SU

Post by Woolfi » Fri Apr 13, 2018 9:55 am

"The Strombergs are 1.75 inch compared to the 1.73 inch of the HIF44."

This is not correct. The entrance of the Stromberg has only roundabout 41 mm instead of 1,75 x 2,54 = 44.45 mm. I was wondering, when I realised this the first time.
The SU HD8 has 2,54 x 2, 00 = 50,8 mm.
I don't know, why the Stromberg with a "mouth" diameter of roundabout 1,62 inch is called a 1,75 inch carb.
A have grindet the entrance of the carb a little bit like a trumpet, to reduce flow turbulence, which leads to a dynamic reduction of the "real" diameter at WOT.
Regards Wolfgang Gatza

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Graham C
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#13 Re: Stomber v SU

Post by Graham C » Wed Apr 18, 2018 10:03 am

Thank you to everyone who responded to my post. The consensus was unanimous that the Stromberg’s need not be changed and instead should be overhauled. A new expert has been found and has fitted new diaphragms and tuned the Stromberg’s with better results. Certainly the car does not peter out or hunt as it did whilst driving. Hot starting is only an issue when the car has been turned off for a period of time. Immediate hot starting is not an issue. I agree that the fuel stench must be coming from another source other than the carbs. New tank fitted and some but not all fuel lines. The smell is greatly reduced by keeping the roof on and the windows closed which is a shame considering the car is a convertible. Many more things to try as explained to me in your responses.

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Graham C
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#14 Re: Stomber v SU

Post by Graham C » Wed Apr 18, 2018 1:11 pm

lowact wrote:
Wed Apr 11, 2018 2:21 am
Hello Graham. I have the same problem, search “acrid smoke”. I suspect, based on side comments I read, that the fuel stench from carb’d V12s is fairly common and is mostly tolerated. It is not tolerable to me. I do not believe that the carb’s alone are the problem and I do not believe that changing the carbs from Stromberg to SU would fix the problem, I consider that any advice to change to SU’s to fix this problem is evidence of ignorance/incompetence, I would find another x-spurt.

The biggest difference between SUs and Stromberg is that the Stromberg has temp compensator valves and throttle bypass valves, both are emission control devices, both are instructed to be non-adjustable (on 175CDSE or 175CD-2) , both can be disabled/removed. The temp compensator is merely a bleed around the piston (not the throttle) and is insignificant, to check it, in UK you heat it up to see if it opens, in Australia we put it in the fridge to see if it closes – whoopee. The bypass valves are supposed to pop open on high vacuum to vent the space between the piston and the throttle plate. These bypass valves have metal on metal sealing so, unless perfectly matched, one may leak a bit all the time which on my car made carb balancing problematic. Couldn’t fix this by tightening the bypass valves, (spring compression, internal adjustment) so I removed the bypass valves completely, replaced them with blanking plates, thereby simplifying my strombies almost to SU level. Fixed the carb balancing and idling speed but didn’t reduce the stench. Based on this I suggest u investigate everything else before considering changing the carbs.

1st thing to ascertain, is the fuel stench from the engine bay or the exhaust pipe? In my case it is from the exhaust pipe.

2nd, are the Stromberg carbs in good condition? Mine are. Reconditioned, checked and double checked. Needles adjusted using a wide-band air fuel ratio meter. Still stank. Then modified as above. No change. Nevertheless, as Chris and Gary say, carb condition can be a cause, u need to eliminate this, if I was you (in UK) I would send my carbs to Burlen’s, to be fully reco’d as a starting point.

3rd, check yr vacuum. I read in the forum that a known issue with 6 cyl cars is fuel stench ultimately due to worn valve guides, maybe V12s also? Vacuum at idle is how to tell if you have worn valve guides. I have fuel stench and poor vacuum at idle (approx. -14 mm Hg, should be -20 mm Hg). Get a vacuum tests gauge, connect it temporarily, (eg. In place of the vacuum line to the brake booster (or any other vacuum source except carb throttle edge tappings) and measure the vacuum when idling.

If it IS low enough, I have nothing to suggest and my theory as to the problem with my car is blown out of the water. If it is NOT low enough, 1st check and double-check that there are no vacuum leaks, the following vacuum sources (if yr car has them) must not leak :
• The vacuum line to the brake booster,
• The small vacuum take-offs on each of the 4 manifolds (they face each other) and provide vacuum for the carb bypass valve actuation, gulp valve actuation, air inlet temperature control x2)
• The balance pipe between the left and right side manifolds.
• The carb bypass valves (diaphrams, test by trying to suck on the vacuum lines)
• the gulp valve (diaphragm, test by trying to suck on the vacuum line while blocking off the gulp valve connection to the balance pipe - important).
• The ignition retard port under the left rear carb (throttle edge tapping)
• The ignition advance port above the left rear carb (throttle edge tapping)
• The extra vacuum off-take that is next to the vacuum offtake of the brake booster
• All manifold, head and carb flanges (spray aero-start in these and check if vacuum is improved)

If all these are ok and vacuum is still not low enough, maybe, as I suspect, the problem is that you have leaking valve seals, changing carbs will not fix this!
Advice that everyone on this forum should be happy to endorse - If you have poor idle vacuum, fix this first?



Many thanks for your detailed reply Colin.
Have you managed to resolve your fuel smell now by doing the thigs you mentioned?

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#15 Re: Stomber v SU

Post by mgcjag » Wed Apr 18, 2018 2:17 pm

Hi Guys...you dont have to quote everything back in your reply....it does take up valuable server space...if needed just a sentance or so.....thanks.. Steve
Steve
1969 S2 2+2 & Building a C type replica

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#16 Re: Stomber v SU

Post by lowact » Thu Apr 19, 2018 1:23 am

Hi Graham, no I haven't resolved the smell, which is worse when stationary so nothing to do with aerodynamics. I have a master plan, Convert engine to HE, efi, at the same time that I convert to RHD at the same time that I install an LdN overdrive unit. I have collected everything I need for this except new synchro (balk) rings for my gearbox, apparently there is a galactic shortage of these until mid-May. In the meantime I had thought to entertain myself by playing with the existing carbs and the ignition off the HE. But I've been stymied by the issue I have with low vacuum, as earlier I have convinced myself that this and the acrid smell are due to the same cause, worn valve guides, so for now I'm just putting up with it ...
Regards,
ColinL
'72 OTS manual V12

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