Technical Questions - Fuel System
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Page last updated 7 January, 2009





Date asked

Question Answer

7th January 2009

By Frank Thomas

I own a '79 3000S which has the standard V6 with Weber 38DGAS carburettor. I want to change the original air filter and holder to a round/rectangular KN filter.

I"m not sure the correct replacement filter, and if its need an different base plate. Does anybody know the corrrect numbers ?

Please see below for a great choice of K&N filters for the DGAS carbs!

10th May 2008

By Paul Cheney

I have a 1977 2500M , with the standard Triumph 2.5 litre engine. Could I ask your opinion of using a lead additive, or is it safe just using unleaded fuel. I’ve heard different opinions….some say regular unleaded is fine, others have suggested the lead additive. I don’t know if this car has hardened valves, I suspect not. Just got the car recently, I live in Canada.


Reply by Paul on 10th May 2008

Thank you so much for your assistance. I did an internet search for the Miller’s product, and it may not be available here in Canada. But I did find results of fuel additive “tests” done on behalf of the Federation of British Historic Vehicle Clubs, and it looks like Red Line lead substitute may be a good alternative, and it is available here, so I’ll give it a go.

Many thanks for your email. Although hardened valve seats are preferred, I do know that the most popular additive over here is Millers VSP -

As far as I know this works well, some people have used it for years without need to get valve seats replaced.

I wouldn't recomment the fuel "catalysts" or inline systems as their marketing is written in such a way as to appear that they are fully tested, but most - if not all are unproven if you read the small print - I'm pretty sceptical about them.

Reply by M-Fix on 10th May

Yes redline is supplied here too - sure it will be ok as it's been in the local store for a while now (forgot that one)!

8th May 2008

By Mark Aspin

I have a sprint prepared 3000S.

Under heavy (!) cornering I get a fuel surge down the breather – which spills out onto road/paint.

Does anyone else have this problem or is anyone aware of a simple cure?

Currently I am utilising the rain drain pipe to prevent surge – but am considering rerouting a higher/longer pipe with restriction.

If anyone is aware of a good alloy tank replacement option – 8 gallons plus – would also be interested to hear.

Reply from Mark on 8th May 2008:

Will try David. Yes – definitely a few fumes on the last track day! So bad – I was black flagged a few times for dropping fuel.

Only solution I could come up with quickly was a reroute via the rain water drain and a ball point pen!!

Will keep you posted and provide you with a few pics in due course.

I do know there was a cannister fitted to the 3000M in the return piping which may well be to stop this, but could alternatively be a charcoal filter for fume filtering. Try David Gerald as they should keep the item in stock (see my links pages).

As for the Alloy fuel tank, I can put up a wanted ad. on the site for you, alternatively (again) David Gerald did have a batch of these made a few years back.

11th March 2008

By Rob Stanway

I'm sure I'm not the only one, but my car smells of petrol. It's fine when it's running but when you come back to it it smells strongly of petrol.

So I'm just going over the tank and replacing the old pipes and I have a question.
There is a breather pipe on the top of the tank, and another on the underside of the filler cap. These 2 points are connected and in the middle there is a 'T' with another pipe leading out of the car via a small hole in the rear skirt.

Is this all correct? I can't help feel that this other pipe from the T shouldn't be there, and also if I fill the tank surely it'll leak fuel...

Yes, all M series cars smell of petrol. A few things you can do are make sure the fuel sender gasket (cork or rubber) is present by undoing the bayonet ring. Be careful not to open it with a metal screwdriver as you don't want any sparks near the tank! The rubber type gasket is better & less likely to let any fuel smell leak into the car. Other areas to check are of course the carbs & fuel pipes in the engine bay, also the pipes you mentioned near the fuel tank. Also the filler neck (large diameter rubber pipe) - make sure the jubilee clips are tight. A place to check not often remembered is the grommet the fuel cap goes through in the bodywork. I use a dum dum type putty but even better is butyl tape - available from some specialist glazing suppliers. This won't fade paintwork like dum dum (which contains linseed oil & also smells).

The breather pipe connects as you mention - and some cars have a fourth pipe which is the return from the carbs I have one but have blanked it off at both ends in case it's needed for future mods. The pipe from the 't' piece does vent to the underside of the car, and may spill a little fuel if the tank is full.

3rd March 2008

By Andrew Clark

bought a Taimar about 6 months ago which had been sitting for about 10 years. With not to much hassle I managed to get it through an MOT. I’ve replaced the fuel tank and all the fuel lines, the inlet manifold, the air filter, cooling header tank and pipework, 2 new 8” kenlowe fans and various other items have been dealt with. Just recently the car will not start and run. When I pump the throttle a couple of times and try to start again the engine fires and farts but doesn’t start. The engine only fires if fuel is added via the pump jets, but will not run. Previously to this the car was running but very badly sounded if it was misfiring. The carb has been refurbished but my concern is the fact that the car had been sitting for so long and the petrol galleries within the carb could be corroded slightly. But if this was the case I’m sure it would never have run at all. Do you have any other suggestions as to why this could be happening? By the way every item in the ignition system has also been replaced.

Follow up by Andre on 4th March 2008

Many thanks for you fast reply, I’ll have to give your suggestions a go. I like the idea of cooking my carb for 10 mins. Do you think it will need much seasoning?

Apart from the other obvious things like coil wires the right way round, ht leads and ballast resistor wiring etc, then I would suspect the carbs as they don't like to be left dry for too long. I attended a call out job last week for exactly the same problem (not a tvr). The car had been left for a year with no fuel in the carbs - basically all the pump jets had clogged up with deposits. After stripping them out and blowing through with compressed air, everything worked again but it took a while to clean them out.

Check the idle jets are clear too - without those working the car won't idle at all.

If you find the jet cleaning works ok but clogs up again, a trick I have seen before is to strip the carb right down to the bare casting and put in a saucepan of boiling water on a hotplate for about 10 mins! Sounds crazy, but worked by freeing out the deposits from the small fuelways and airways. This was followed by blasting with a can of carb cleaner, then drying with compressed air. Last resort option I think though...

4th January 2008

By Luke Sheffield

I see from your site that you have fitted triple 40DCNF's to your essex,i was wondering if you know the correct carb settings for triple 42DCNF's?i realise that the engine has to go on a rolling road to be properly set up,im trying to find out the rough set up,choke sizes etc, to start from.
   any help would be useful.
Thanks for your email. Not 100% sure myself for the 42's, although you could check here - some useful data for setting these up. 2 engines with 42's are covered in the Rolling Road, Power Charts section.

7th September 2007

By Dave

I have a small oil leak from the gasket of my fuel pump where it bolts to the engine of my 1600 cross flow is it easy to change the gasket by just unbolting the fuel pump renewing the gasket and bolting back on Yes that should be all you need to do - the pump may release some fuel when you take it off as the lever moves off the cam so make sure you have some rags handy.

16th July 2007

By Michael Ring

I have a 3.1 Essex with Stage Two Heads, HP Oil Pump, HD Con Rod Bolts, Steel Timing Wheel & a Kent V62 Cam. Currently It has the standard 38 DGAS Carb, K&N Filter & full stainless steel exhaust. I was wondering what would you recommend that I set the ignition timing too.

I have a 40 DFI Carb which I am planning on fitting but I discovered that I need to modify my existing throttle linkage. I have heard that these are heavy on fuel consumption but due to the little mileage the car covers it shouldn't be a problem. I have just come across a Holley 390 Carb & inlet manifold for sale which I maybe tempted to buy.

I was wondering which Carb would you recommend for the best increase in power & performance. 40 DFI or Holley 390.

In answer to your questions, firstly about the ignition timing. This varies according to tune of car, type of distributor (eg standard or modified - eg Aldon, vacuum or non-vacuum) etc. Normally for these engines the ignition timing at max. is more important to make sure the engine doesn't have pre-ignition which can lead to engine destruction in certain conditions. For the best guide, take a look at these power charts provided by which show before & after results for engine work. What is relevant is the ignition timing which can be seen to be altered on the 2nd test (3.4L essex engine with triple carbs). As you can see the figures are all different so a guide is to set your max. timing to between 25º and 32º, then see what your idle timing figure is. Should be around 8º to 14º (14º is standard on 1976 Essex engines with standard vacuum distributor). Road testing will give you an idea of how the engine is in terms of correct tune once you have a rough timing setting. Don't forget the points gap varying also alters the timing, and also the idle speed will need to be altered during timing setup. The Holley carb is supposed to be great for street use, low end torque etc so I would say go for that - as it should be simpler to setup than triple webers. The engine will always use the same air/fuel ratio, that is to say one carb over another will only mean more fuel is being consumed if the airflow is greater. Therefore the 38 DGAS standard carb when setup correctly shouldn't use any less or more than a different carb on the same engine, EXCEPT that if another carb is used which increases the airflow available to the engine, then it would use more as the air/fuel ratio should be about the same. Expect a bit more fuel consumption, but also benefit from an increase in driveability and horsepower/torque.

12th February 2007

By Peter

Got a Taimar laid up in the garage with a fuel tank like a lace curtain - what was it off of ??? I take it you mean riddled with holes?? It was made by TVR and not from a donor can still buy them from David Gerald Sportscars Ltd (look on my links page).

24th October 2006

By Mark Da Silva

Im looking for some assistance in sourcing the supplier for a V6 Essex engine inlet manafold and triple weber carbs. I read the installation procedure on the site and would be very grateful for any further help you can give me. Try Ric Wood - - he can supply the manifold & linkages. Weber can supply the carbs although they are made to order now.

18th October 2006

By Tim Crake


I Ran 3 x Dellorto 40’s on my 1972 2500M without any clearance problems. Using short ram pipes and K&N filters.

It was a properly prepared “Racetorations “ engine using the early 150 bhp Injection single groove cam (best one for this engine unless you're racing) with lightweight roller rockers. We were getting about 170 bhp at the flywheel.

Biggest problem is the weight of the engine you need to replace all the bushes with hard powerflex, and seriously uprate the front springs use a quality shocker as well. Oh and if u do track days you WILL need some proper brakes.

Hope this may help.

Follow up by Troy Schmidt on 12th November 2006:

I performed this conversion on my 73 2500M. I did have to cut-out a small
portion of the heater box to make things fit. I was able to do this without
removing the heater box cover from the car and still maintain functionality of
the heater box. The best way to do this is actually mount up the manifold and
place the rear carb on and just fit and measure. I would advise making sure
your engine mounts are top notch and probably consider obtaining some of the
uprated type to prevent the engine from moving as much as this will necessitate
removing more material. The webers do benefit from velocity stacks, however. I
am currently using the K&N type filters 1 3/4 inch depth and have found some
'shorty' velocity stacks that fit inside. Any other??? please feel free to
contact me. (please email M-Fix and your questions can be forwarded to Troy).

Follow up by Bernard on 9th March 2007

I had 3-SK carb setup (=WEBER) on my '74/5 2500 M.
I used TWM manifold and I don't know what you are using, suspect this may make a difference.
I used TWM shorty air horns inside foam dome-shaped air cleaners and modified the rear air cleaner.
This involved re-shaping the base plate, foam and mesh retainer but left the footwell unmolested.

Many thanks for your information Tim!










Also thanks to Troy!

8th October 2006

By Stefan Kirschstein

I'm a German living in South-Africa, driving a Ford Ranger with a 3.0 V6 Essex , 1997.

Maybe you can help me with the carburator jetting from the original Weber carb.

To improve the fuel consumption on my Ford, I put bigger air floodvalves in, but now the car is jerking on low revs, when the engine is not on operating temperatur.

Maybe you guys in England have another idea to improve the fuel consumption. With my 80l fueltank, I drive 450 km.

It sounds like you have tried the air corrector jets (that are at the top of the emulsion tubes)....which is the best way to get a bit better fuel economy out of the standard main jet size. Don't forget that the idle jet will also control the engine when running below about 3000rpm, and so I would suggest you concentrate on this area, as you are more likely to be losing out at these lower engine revs when cruising below 50 or 60 mph (100kmh). Put back the original jets for the air correctors and try below:

The Idle mixture screw also adjusts the mixture for progression up to 2800/3000rpm, so maybe you could start by turning the idle mixtire crew in a bit (perhaps 1/4 of a turn on each side of the carb) to see if it will run ok like that. If you have access to a CO meter then you will see what your adjustments are and can track them to see which is best. the lower the CO the better, but don't forget at low rpm's to 3000rpm the engine has to be smooth. If it hesitates then you have gone too lean and need to open the idle mixture screws a bit at a time until it runs ok.

Good luck & I hope this helps you - let me know how you get on! Don't forget also (I think) that some parts of South Africa are quite high up above sea level if I remember my geography - your jets over there will be different to those in europe to allow for altitude!

9th August 2006

By Amy Butcher

On an essex engine on the middle section where the carbs go there is a pipe air i think where does this attach to???? If it's on the bakelite spacer under the carb then it's for the distributor vacuum - this is split by the PVS (parted vacuum switch) which also controls the original air filter cold/hot air intake flap.

There is a second larger breather pipe which connects to the rocker breather system - this helps to recycle oil vapour by sucking it out of the rocker cover and back into the engine.

18th May 2006

By Jonathan Garton

I have a 28 year old Taimar with V6 2994cc Essex engine, Webber carb. Generally OK but it has developed problems restarting if well warmed up then stopped for say 30 mins. Starts OK if only left for 5 mins, or when cooler (an hour or more). Start OK when cold. When it fails to restart engine turns well, but does not fire. Will eventually start reluctantly, then run fine. Condenser
and coil have been replaced, but has not changed or solved the problem. Could it be carb jet settings? or plugs?







Follow up on 24th May 2006

Spark plugs are correct spec.

I changed the air intake for a K&N some time ago, so OK on warm air flap.

Choke is manual on mine (perhaps someone gave up on the automatic in the past), but I need to check
that it is fully opening when knob is pushed in.

I will also check spark and fuel level in float chamber if I can replicate the problem in the
workshop. Chamber certainly does drain when car left - eg a week between starting will need 3 or 4
seconds on the starter motor before it fires, but I have not had this problem restarting within a
few hours if engine cold. I only get the restart problem when engine is hot, and it would be odd if
chamber is low after 30 mins, but OK after 2 hours!?

There are a couple of things to check, the first being the plug grade. Make sure they are
as per specification - the wrong heat grade or incorrect shape plugs won't works as well as the correct ones.

Also check the fuel system - especially whether the choke is fully off. This is controlled by a bi-metallic coil
and heated by coolant, and a fault here either with the operation or with the position of the mechanism could
mean the choke isn't fully off oncet temperature. When warmed up fully, remove the air filter cover and make sure
the choke flap is fully open. If not the adjustment/mechanism needs looking at.

If all is ok here check the float level in the carb at the time the problem is occurring - it may be that the level is too low.

Other things could be ignition coil breakdown (when hot) - not an unknown problem.

Also fuel vaporisation - check to make sure bakelite type carb spacer is fitted...without it the fuel will boil and run into the cylinders - flooding the engine so starting will be difficult (check for smoke when it does fire up).

If standard air filter is fitted perhaps the hot air flap is not moving to the cold air intake position (parted vacuum switch on inlet manifold controls this using vacuum from carb and heat waxstat).

16th May 2006

By Hubert Leferink

My name is Hubert Leferink Membernr. **** and I live in Holland. Sorry when my English is not perfect. About 4 years ago I finished a restotation projekt of a T V R 3000 M after 7 years work, see also a Sprint Magazine of 2002 of the Mellow Yellow T V R 3000 M. The car is running wonderful since then but since a few month's I have a starting problem when the car hasn't run for more than a week the car doesn't start. When I do some petrol in the carburettor the car is starting immediatly and the problem is gone until the car isn ' t for more than a week. In the meantime I have already replaced the fuelpump for a new one but without the wishful succes. Can you can me the solution for my problem? In advance thank you very much. Best regards: Hubert Leferink Julianastraat 35 7511 KB Enschede Holland E-mail:
Ok sounds like it's a fuel related problem for sure.

It sounds like fuel is either slowly draining back into the fuel tank (perhaps due to a small air leak in a fuel pipe), or perhaps the float valve in the carb isn't sealing properly alowing fuel to slowly return to the tank. I had this problem once and traced it to a perished rubber fuel hose which meant that starting after 2 days was difficult - even the pump didn't suck fuel straight away.

As you have already tried a fuel pump then it can't be a leaking pump allowing fuel to drain into the engine sump.

To trace the fault take the fuel pipe off the fuel pump (tank side), and also off the tank. Plug the pipe at the tank, then get a vacuum pump/gauge and suck a vacuum in the fuel pipe, and then wait to see if the gauge shows a pressure loss. If so you will need to carefully check the whole supply pipe to find the leak. If there is no problem here (i.e. no pressure loss), then open the carb top, to see if there is enough fuel in there. If not, check the float for damage, the float valve seat (by removing the valve), and also check the float level (after running the engine) to make sure it's correct.

Hope that helps, if still having problems please feel free to email me again.

3rd May 2006

By Paul

I have a 1985 280i that has a misfire problem. The car will be running fine and then begin to misfire, just a little at first then more and more frequently until so often the car is not driveable. If I wait a few minuets the car will start and run fine for awhile then start to misfire again. If this should happen on the open road I have found if I shift to neutral, and coast, turn the ignition key off, wait about 5 seconds , turn key back on ,put back in gear the misfire disappears. I am not the best mechanic but have looked at what I know. Could this be related to the fuel injection system? Any ideas? It's very possible it could be fuel injection, but also could be something like the ignition coil - these when breaking down can give intermittant problems. Not sure on that engine if it has a coil module - best think would be to take the coil & amplifier (if fitted) to your local auto electronic repair centre and get them to check the coil. If ok, you can then have a look elsewhere. I looked at a VW polo recently which had a similar problem and it stumped me until I went to my local centre - even with all the test equipment I have at work, nothing could sucessfully prove whether it was the coil or the module that was at fault (this was after someone else put a new injection computer on the car which was a wasted £450!).

Looking at the fuel injection - it may be related to the enrichment for cold starting. Once the engine warms up it may be over fuelling and therefore running badly....could well be that. In the haynes manual it's called the warm up regulator, and uses a bi-metallic strip to alter the mixture - definately worth a look. Secondly the start valve sprays fuel into the inlet manifold on cold starting - make sure it's not always working - if faulty that would cause a similar problem...a fault here could be caused by the thermotime switch being faulty - it is screwed into the engine next to the warm up regulator.

3rd May 2006

By Jakub Kouril

Hello, have a 3.0 Essex lump and bought Swaymar inlet manifold and Holley 390 carb. Engine has Burton stage 3 heads, fast road cam, big bore exhaust system, Lumenition ignition. Can you advice the carb jetting and setting of the ignition timing ? I have no holley info I'm afraid regarding jetting guidelines - however you may like to email Ric Wood - who will probably know off the top of his head and may keep them in stock.

26th August 2005

By Wim Boon

Being the happy owner of a TVR 3000M for a couple of weeks now I have a
question for you about the fuel system.
When I don't start my engine every day, its takes a very long time before
the fuel is available at the right place. A bad thing for my battery and
starter motor.
I have fitted already a valve to block fuel return to the tank, but since
there is a return fuel hose this does not help.

I am thinking now about a electric fuelpump. Can you tell me if that is a
right solution and if yes, do you know a suitable type or brand? Should I
use a impeller type, a membraan type or something else?

Furthermore I wonder if what to do with the existing mechanical pump. Bypass
it, dismantle it, or leave it in the system?

I am assuming you have checked the fuel's position and found it's not being
pumped correctly? Without a non-return valve the fuel may creep back to the
tank, especially if the fuel pump is faulty. With a non-return valve the
fuel shouldn't creep back - strange that it's doing this now.

An electric fuel pump also will allow the fuel to creep back (as it does on
my car), but I simply let the pump stop "clicking" fast then I know the fuel
is up to pressure. Sure, fit an electric fuel pump - I use a facet fuel pump which
works fine (i also use a fuel pressure regulator/filter), however the
fuel pump clicking could be annoying to some people.....the choice is yours!

As for the old mechanical pump, you could leave it in place, but it would be
better to remove it and fit a blanking plate made from a piece of steel
plate, and a gasket to seal it to the block. This would also very slightly
reduce the friction on the engine (which is a good thing).

19th July 2005

By Paul Bennett

Have you any infomation on stripping and rebuilding the Weber 38dgas as fitted to 3000m?
Not as yet, however I will see what I can do when I get a spare moment!

Follow up on 12th November 2006: Weber 38DGAS stripdown now available in the members area.

3rd June 2005

By Mike Garcia

Curious to know if anyone has made a Fuel Cell replacement for the Tamair? My gas tank area has strong fumes. I have replaced all hoses and connectors. I am thinking about pulling the old tank. I may find that it is sweating gas.

I have seen the plastic fuel cells for other cars made. Do you know of any manufactures that would make one. Fuel cells are safer and wont snap in the event of a rear end collision.

Yes the fuel tanks do eventually leak - and I always feel they are a serious problem in the event of an accident as they are in the car with you...

No-one makes a tailor made fuel cell for the TVRs as far as I know, but over here the ATL Fuel Cells seemed to be the popular make stocked in the biggest motorsport retailer. Try the ATL website:

They can tailor make one for you - but I guess it's going to be expensive!

If anyone knows a supplier of a suitably sized tank for the M-Series please send me an e-mail.

1st April 2005

by Paul Bennett

I need to replace the inner throttle cable on my 1977 tvr 3000m.

My throttle cable does not seem to be as per the tvr parts manual. I noticed that your cable on the "changing to roller rockers" seems to be the same as mine. Could you let me know what car the cable is from so that I can try and find one?

I have attached a picture of my cable:

The cable I used to match the original is identical at the carb end - (for Ford's Fiesta XR2 MKII approx 1987), but longer than needed so a wire grip at the pedal end after cutting the outer cable to suit can be used to keep the cable in place on the pedal.

5th Septmeber 2004

By Mick B

Will I need to remove the rear screen in order to remove the fuel tank?
Yes I would recommend it! Much easier to lift out from above....and can't say I've even bothered to try it without removing the glass.
Rear screen is simple to get out really - just nerve wracking trying not to drop it!

18th December 2003

by Stuart Morgan

Hi Mark - Reading your article about fitting triple carbs (I've found a manifold and 3 x 42 DCNFs). Can you please reiterate what you did about the choke linkage? - It appears from your pictures that it grabs somewhere around the middle carb, but I can't tell for sure.

Also, I assume it doesn't matter which way round you put the carbs?

Stuart replied following my answer with this:

Mark - For your info, I've asked some Maserati owners what they think, and the consensus is that it doesn't really matter which way round you have them - just set them up to suit the throttle and choke linkages. To be honest, I think the way you have them is better so I'll probably do them the same as you.
I since found out that chokes are unnecessary - so have disconnected the cable (easy one)!

Apparently the carbs were meant to be round the other way, buton my manifold wouldn't clear the distributor that way round. Also the throttle cable was shorter as a result, and didn't need a 180 degree loop (the other way it would have to pull to from the direction of the front of the car.