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Tuning Strombergs

Of course, tuning the carbs is only part of the process. The ignition needs to be spot on and OPUS amplifiers are now "Hopeless" amplifiers. Here's a new product that I found. I liked it so much that I'm now a distributor for the manufacturer. Click on the logo to check it out.


There's been some queries on Strombergs on various forums recently, so for V12 owners I have modified a very useful set of articles detailing exactly what to do with Strombergs and compiled it into a .pdf format document. It can be found here, or on my "Downloads" page.

I found the articles on the internet and I must credit this information to Steve Sutton. Although he has a twin carb Triumph Stag and I have a four carb V12 Daimler, the instructions were very useful to me. However, I have added quite a bit relevant to the V12 Jag engine (like vacuum diagrams) and I recommend you open it and save a copy to your computer.

Below are a few more of my thoughts on setting up Strombergs plus other material I have come across from various contributors. I used a Gunson "Carbalancer" air-flow meter when setting up the carb's but I don't know if they are still available. There are references to a Unisyn airflow meter which I have no experience with, but it is a similar device to a Gunson Carbalancer, or Crypton "Syncro-Check".

A great improvement was found after I sorted the carbs, but the most beneficial improvement was when I combined the carb work with changing the V12 vacuum retard system to a vacuum advance similar to the later XJ-S.

The difference in driveability after sorting the by-pass valves and the temp compensators was tremendous. Makes me wonder if SU's or fuel injection are that much better compared to properly set-up Strommies. My fuel consumption is virtually on a par with an HE V12 and with some timing mods I have done, possibly better than some, although final drive ratios and model weight come into the equation.

Balancing the airflow: A note from Roger Bywater of AJ6 Engineering

(Roger worked for Jaguar on the development of the V12 engine and now owns a tuning firm specialising in the V12 and other Jag engines - I strongly recommend you use the underlined link above to visit his web site, Paul.)

“…. the manometer idea is equally unsuitable as a means of balancing multiple carburettors. Indeed it is probably even worse than the old and discredited idea of trying to equalize the hissing noises of the carbs by listening to them with a length of pipe. Yes, I know that method is mentioned in various Jaguar workshop manuals, but those were just throwbacks to the days when they didn’t know any better. By the 1970s any raw fitter trying to do it that way in the Emissions Department at Jaguar soon had the folly of it demonstrated to him with the aid of a simple flow meter.

Crypton used to sell a useful little airflow meter called a ‘Synchro-check’ which is quite handy for quickly checking carbs on the car but I always found that the same equalisation method as for an EFI system worked as well as any, particularly with four carb V12s. It is just a matter of carefully assembling all the carbs on the bench top with float heights, etc., all exactly the same (actually if they are not all set exactly the same no method of balancing is likely to work) and the butterflies centred, set to 0.002'' clearance, then opened by exactly 2 turns on the screw for a basic idling condition.

Obviously all the mixture trimming ancillaries attached to the carbs must be in proper working order. Any subsequent adjustments are then applied exactly equally to each carb until the required idle speed and exhaust CO figures are obtained. Of course the throttle linkage must be so adjusted that the movement of all carbs is synchronised. Whatever tolerance differences there might be between carbs is always likely to be less significant than tolerance differences between individual cylinders.” ... End.

My thoughts on balancing the air flow

Roger is the Guru on V12s. I would go with the method he recommends. It's the modern professional's way of synchronising the butterfly throttles after sorting them on the bench. However, if the engine is running very rough and the carbs are staying on the car, then balancing with an air flow meter is a relatively quick way of improving things. If your carb's are already off the car, then do it Roger's way.

I used a Gunsons "Carbalancer" - a slightly poor quality air flow meter - but better than the hosepipe in the ear method. You'll have a merry dance round the front of the car trying to balance each bank! After you do one side, you'll find that it needs doing again when you've matched the opposite bank, and so on and so forth. It can take many attempts to get all four synchronised. This is another reason why I recommend Roger Bywater's method.

How I balanced the Temperature Compensation Valves by Paul Clarkson

This is all about the amount of air-flow through the valve and when each of them open. I wondered if I could work something more precise to balance the flow through each of the temp compensator valves on my Daimler V12's four carburettors. If the engine is hot enough for the valves to be open, then any throttle plate/butterfly valve synchronisation can be ruined if the temp compensator valves aren't also synchronised. Remember, they open to allow extra air in, so it's obviously better if they open together at the correct temperature. It's also good to check they all allow the same amount of air to flow through as they open further at higher temperatures. My method will do this for you.

It's nearly four years ago that I did this so use it as a guide and be prepared to experiment. I started by adjusting the bi-metal strip so it started to open in a large bowl of warm water (110F.). I placed a thermometer in the bowl to keep a check on temperature. With a short piece of hosepipe and a funnel fitted to the “nose” of the valve housing, I used a stopwatch and timed how long it took for 1 pint of warm water (taken from the bowl) to flow through. I kept the valve's bi-metal strip just below the surface of the bowl of water to keep it warm and I adjusted each valve to give the same flow time. The actual temperature isn’t too critical, as long as it is the same for each valve and enough to keep them all slightly open.

As this takes time, it's important to keep and eye on the thermometer in the bowl and kept it at the same temp for each of the valves. Then it was just a case of turning the adjustment screw on each valve by the same amount to produce opening of the valves at higher or lower temperatures than given in the above article.

I'm writing from memory here, but I adjusted mine to open at a slightly lower temp (110F.) than the author above to allow for the extreme heat build up in the V12 engine compartment. I then repeated the flow test using a bowl of water at a slightly higher temperature as a check. It worked perfectly. All four valves let the water flow through at the same rate. If they hadn't, I would have suspected a fatigued or bent bi-metal strip.

Using a Colourtune plug

I also used the Colourtune as described to check the mixture. I was actually holding the engine up to 4000 rpm. whilst doing this. BUT YOU MUST USE A MIRROR to check the colour of the flame. If the core of the plug gave way at that engine speed, or indeed any speed, it will be worse than a bullet, so make sure NOTHING is in it's path and wear safety goggles.

From Dan Siegel (SIII E-type Owner) Re: Flooding Strombergs.

This is what I did and it eventually worked for me. Let me say first, that you cannot use the factory float settings as set in stone. I say this because I found the the height of the needle shut-off valve {that I replaced} was not the same height as the original one.

Remove carb, drain the fuel, remove float cover. Since the carb is still leaking fuel, I would re-adjust the float height ever so slightly.

I would then attach an electric fuel pump with a benign fluid {I used windshield washer fluid} to the inlet side of the carb. I used a 5 psi pump [which is slightly higher psi that needed} and let the pump run for a 1/2 hour or so. If you are still experiencing leakage, you again need to re-adjust the float height so it closes earlier.

If after all this is not successful, I would most likely ship off the carb to someone professional like Joe Curto. If you want to just test whether or not the float valve is even shutting off the fuel, you can perform a similar bench test as follows:

Remove the float cover. Turn the carb upside down. Turn on the fuel pump with the same windhsield washser fluid, and observe if the needle valve is allowing any fluid past it's seat. The carb must be level.



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