Fuel Regulator? Air Trumpets?

[Redman]

1. Am running through the list of basic service items and doing filters etc. In addition to the fuel filter in the boot, my LHD S3 has a fuel regulator in the engine compartment (RHS, just inboard the battery area) which in fact looks very similar to the fuel filter in terms of being a glass bowl with turn screw fastening nut underneath and also has a paper filter. SNGB do not list any fuel regulator and I cannot find reference to it or its filter in the forum(s). The filter appears to be - haven't opened it up yet - similar to the main fuel filter. Anyone able to advise?

2. The car does not have air trumpets fitted to the front of the intakes/air filter. Necessary / needed? If I get some, any advice of getting standard ones or going for a set with a bigger intake (and if so, where from)? And should I also look at installing the warm air hoses that run from the air filter body down to the inlet manifold?

Thanks.

Gordon

[MarekH]

Dear Gordon,

1/ This doesn't sound standard, so it's hard to advise. I can't think of a good reason to have two fuel filters in series. It's possible a charcoal canister would have sat here, so a picture would help as it is possible the item is simply misdescribed.
2a/ Air trumpets simply change the induction airspeed and thus the tone and volume of the noise.
2b/ The airboxes have a temperature sensor in them which controls the vacuum operated flaps you are thinking of reconnecting. The design aim here was to influence the inlet air temperature by mixing colder air from the end of the trumpet with warmer air which has come past the exhaust manifolds. The Owners Manual (blue booklet =UK spec; tan coloured booklet = US spec) gives details.

kind regards
Marek

[Redman]

1. On closer inspection it does look like a Filter King fuel regulator (difficult to see let alone take picture). Is this needed on an S3 with Stromberg's? Can I use a standard S3 fuel (paper) filter to replace within glass bowl? How best to check pressure output - the car runs fine at present though I do feel it starts to start "missing" over 3500 once hot.

[Redman]

2a. I have thoroughly confused myself on air intake etc by reading some of the (phenomenal) threads on the subject on this Forum. I'm a beginner with this car: so simply put, why would PO remove trumpets - and should I replace them? I'm not worried about noise but would be happier to do whatever might increase (or at least not reduce) power etc.


2b. The attached photo also shows the missing tube connection from manifold to air filter. Believe this helps with better initial running while everything is warming up but is if little or no benefit once up to temperature. True?

Photo also shows a circular body attached to the filter, with a short tube coming out if it. I cannot see this anywhere in my (blue) manual. What's it for and should it be connected to something?

Lastly, Marek seems to bring in other connections (vacuum?) to the filter. I don't seem to have anything like this, other than connections on the carbs themselves.

And thank you again for taking the time to help me!

Gordon

[Redman]

Marek:. 2b/ The airboxes have a temperature sensor in them which controls the vacuum operated flaps you are thinking of reconnecting. The design aim here was to influence the inlet air temperature by mixing colder air from the end of the trumpet with warmer air which has come past the exhaust manifolds. The Owners Manual (blue booklet =UK spec; tan coloured booklet = US spec) gives details.

What / where are these flaps you refer to? I cannot see these, either on the car or in my Blue manual. Thanks.

[MarekH]

Photo also shows a circular body attached to the filter, with a short tube coming out if it. I cannot see this anywhere in my (blue) manual. What's it for and should it be connected to something?

Inside the circular body is a rubber bellows which pulls the flap open or closed depending on vacuum applied.
The vacuum connection is the "short tube" and this goes into the airbox at the back and middle right in the middle of the air filter where it connects to a temperature sensor made by AC Delco. The other connection to that temperature sensor comes back out of the airbox at the back middle of the airbox and this then connects to the manifold. This way the air coming into the airbox is temperature regulated as coming from either the trumpet or via your "missing air tube" between the exhaust mainfold heatshield and the airbox. If you put your finger into the airbox here, you'll be pushing on the flaps inside the square section of the airbox tube that the "circular body" controls, halfway between the trumpet and the air filter.

This may all have been disconnected if it had failed due to corrosion or because the sensor is broken. Either would lead to a vacuum leak and a different idle speed condition.


The only reason to run a fuel regulator is because you maybe have a non standard fuel pump. You can check on the Burlen website for the correct twin back to back SU pump specifications. They are hidden in a pdf document somewhere on the site. The correct pump[ puts out ~3psi and would not need a regulator; a more powerful pump would make the carburettor float bowls leak fuel by forcing it out of the jets and into the carburettor bridge.


You should purchase the white 1974 Parts Manual book for the car or look at the one in this website's Knowledgebase to familiarise yourself with the components of the car. Most of the configurations are listed by chassis number and the Parts Manual gives an exploded diagram of how everything is put together. This will help you identify any non standard parts fitted to your car and so aid troubleshooting and understanding any advice given.

kind regards
Marek

[lowact]

Regarding the air intake/trumpets - don’t assume the V12 arrangement is somehow a cold air intake system due to the inlets being forward of the radiator. By design it is a “constant temperature intake”; target temp is 43 degC, this being the temperature at which the flap valves become fully open. This system, together with the temperature compensation valves on the stromberg carbs, is so that as far as possible the air fuel ratio doesn’t vary with the weather. The trumpets are ahead of the radiator to avoid any step change in air temperature every time the radiator fans start and stop.
And note the intake air temperature control is all of the time, not just during start-up.

[Redman]

Thanks both of you. I'm away this week but will get onto it on return. I've now seen the Parts links on the Members part of this forum (I've been using the SNGB Parts lists to explore what should / should not be on the car) and have in any case ordered the relevant parts book from Martin Tobey. More homework .......
Thanks again.

[Redman]

So: opened up air intakes to replace the filters. Temperature sensors have been deleted on both intakes so no connection to the circular body that in turn controls the flap. I assume this was as part of an overall removal of emissions control items. But it does mean that where the temp sensor was there remain tgec2 inlet/outlet tubes for the vacuum hoses (see photos). Should these not be capped iot prevent unfiltered air being sucked in?

[Redman]

To cap it not to cap, anyone? "But it does mean that where the temp sensor was there remain the 2 inlet/outlet tubes for the vacuum hoses (see photos). Should these not be capped iot prevent unfiltered air being sucked in?".

[Bob.]

As you say, they let in unfiltered air, so if you are not going to reinstate the air temperature control system they need blanking.