1971 MGB GT - Fuel tank brimmed, new MPG reading calculated - see page 39

[danthecapriman]

I’m not sure how it’s plumbed together on the B, but is there any rubber fuel pipe at the back near the tank? 
Just a thought, but could a filer be fitted in at the tank end anywhere as then it’ll filter fuel directly out of the tank and help stop dirt getting into the pump as well as the carbs. Might not be possible though.

[chadders]

4 minutes ago, danthecapriman said:

I’m not sure how it’s plumbed together on the B, but is there any rubber fuel pipe at the back near the tank? 
Just a thought, but could a filer be fitted in at the tank end anywhere as then it’ll filter fuel directly out of the tank and help stop dirt getting into the pump as well as the carbs. Might not be possible though.

It could but you'd be scrabbling around on the ground to check or change it.

It's bad enough hitting the pump with a hammer when the points stick, which I once had to do on the Tinsley Viaduct with HGVs storming past a few inches from me, fortunately in daylight.

[Rusty_Rocket]

I change that awful braided hose a lot at work.  It will leak underneath the braid sooner or later and ruin your day.  It's also totally pointless and cuts your fingers when it starts to fray.

Replace everything with Gates Barricade, nothing else is good enough, and I usually put a clear plastic filter on the bulkhead at the top where the hard line comes up.

That small black thing that caused the running issues is almost always a bit of rubber hose, that's been shaved off the internal diameter when you fit the hose to the float chamber.  It then gets stuck in the needle valve and causes mayhem.

Once I've fitted new hoses and a fresh filter, I leave well alone and then the system is much more reliable.  An upgrade to a pair of HiF carbs would make it better still, but they're very expensive now!

[danthecapriman]

19 minutes ago, Rusty_Rocket said:

I change that awful braided hose a lot at work.  It will leak underneath the braid sooner or later and ruin your day.  It's also totally pointless and cuts your fingers when it starts to fray.

Replace everything with Gates Barricade, nothing else is good enough, and I usually put a clear plastic filter on the bulkhead at the top where the hard line comes up.

That small black thing that caused the running issues is almost always a bit of rubber hose, that's been shaved off the internal diameter when you fit the hose to the float chamber.  It then gets stuck in the needle valve and causes mayhem.

Once I've fitted new hoses and a fresh filter, I leave well alone and then the system is much more reliable.  An upgrade to a pair of HiF carbs would make it better still, but they're very expensive now!

Is Gates Barricade the marine grade stuff?

Ive been using marine hose on my cars. There’s a certain standard it’s got to meet or exceed with regard to ethanol so if it’s good enough for boats! So far I’ve not found any of it cracking, hardening or degrading. The cheap crap hose I got from a car spares place didn’t even last a year before it started perishing.

[vtec-e]

Found this image as a suggestion for possible routing of the new pipes and filter.

[Zelandeth]

Problem with Gates Barricade is trying to bloody get it.  

This is the only stuff I use these days, from this source as I'm reasonably confident that it is actually what it says it is.

https://www.glencoeltd.co.uk/cohline-fuel-vacuum-hose/

Rather than the 80% or so it seems that on eBay etc these days is counterfeit or has been sitting on a shelf for 20 years.

[busmansholiday]

1 hour ago, vtec-e said:

Found this image as a suggestion for possible routing of the new pipes and filter.

That's where I fitted the filter on mine.

[Matty]

7 hours ago, Rusty_Rocket said:

An upgrade to a pair of HiF carbs would make it better still, but they're very expensive now!

They certainly are. I really wanted one but ended up with a HS6 after the money people wanted for a rebuilded unit reduced me to tears.

[Peter C]

Gents,

Thank you for your advice about the installation of a fuel filter and new fuel lines.

I have an idea of what needs doing, I just need to procure the right materials.

Watch this space. 

[Peter C]

For sometime now I wanted to fit an amplifier to power the MGB’s speakers.

This is because:

• Of all the tinkering jobs that I do on my cars, installing ICE is my favourite. 
• I've had upgraded ICE in dozens of cars over the years but I've never had an external amplifier powering the speakers (just subs).
• I had everything I needed in the garage.

I started by re-wiring the six speakers - two tweeters on the A posts, two speakers in the front doors, two speakers in the rear 3/4 panels. I extended new cables towards the footwell behind the passenger seat.

I connected a new +12V supply to the battery and a new earth connection for the amplifier. 

I connected the new cables to the amplifier and extended the RCA and remote cables alongside the passenger seat, to where the head unit is perched.

So far so good.

I removed the head unit and at that point I hit a big stumbling block - the head unit only had one pre amp output. The head unit has front and rear high pass filters and on that basis, I could have sworn that it also had two pre amp outputs. This was a significant issue because the amp's high pass filter allows too much bass to the speakers, which means that I needed the input signal into the amp to provide just high and mid tones. However, as I also need the head unit to provide a through (full range) signal to the subwoofer's amplifier, which has a built in low pass filter, I couldn't split the head unit's single output. 

Bugger.

I ended up buying a replacement head unit. So much for having everything I needed in the garage.

The spec of this unit is identical to the one I had, other than it has the all essential two pre amp outputs.

Fitting the new unit was a doddle.

The sound quality with the Sony amp powering the six speakers is great. I still have to fiddle with the gain settings as at the moment I can crank the volume up on the head unit to around 50 (62 being max - why not 60 or 100?), which is a bit high. The gain setting on the Sony amp is at approx 30% and 50% on the sub's amplifier. I can't crank the gain setting on the Sony amp too high as it is a bit too powerful for the speakers, although if I understand matters correctly, bass tones do most damage to speakers and my speakers only produce mid and high tones. 

I really like the idea of a ridiculous sound system in an MGB and I still have a very nice Alpine amp in the garage, which could easily power four more speakers. By removing the passenger side map pocket, I can make space for a speaker that could be fitted to point towards the cabin. There is already space on the driver side for installation of a matching speaker. I just need to figure out where to put the other two speakers. 

If anyone is interested, I am roffling the old head unit:

More soon.

 

[Peter C]

Due to a nasty sinus infection I've stayed away from the garage for a few weeks. I'm feeling better, well enough to spend a day in the garage installing more ICE into the MGB.

I had a nice Alpine 3523 amp that needed a home as well as a couple of MDF enclosures ready to receive some 6x9 speakers. 

The plan was to fit the additional speakers behind the front seats, alongside the subwoofer. 

Before buying the speakers, I did a bit of research and settled on these Pioneers. They have a relatively small magnet, which means that they would fit into the enclosures ok and they mostly have good reviews. The positive reviews referred to crisp mid and high tones whilst the less favourable comments referred to insufficient amounts of bass. My plan was to run these speakers off the same signal as the Sony amp and speakers, which is set to only produce mid and high tones, so I wasn't fussed about the quality and quantity of bass tones. 

I mounted the Alpine amp behind the driver's seat. As before, I connected the +12V supply directly to the battery (fused at the battery end). I made use of the same earthing connection and I connected the remote cable to the Sony amp's remote terminal. As the head unit only has two sets of pre-amp outputs, one of which is for the subwoofer amp, I had to split the other output with adaptors that I had from a previous project. 

The 6x9 speakers fitted just fine. The enclosures are mounted on hinges, which allow the enclosures to tilt forward, the same as the subwoofer enclosure, which is necessary to enable access to the battery. 

With the front seats in reclined position, the amps and wiring are fully concealed. 

I also fitted a pair of tweeters on the B posts, which are positioned high enough to be heard up front.

The luggage compartment carpet set that I bought at Beaulieu last year contained a piece of material destined for the back of the rear seat. It was surplus to requirements so I cut it in half and lined the tops of the speaker enclosures with it. It works well as the carpet and vinyl edgings match the rest of the interior. 

 

 

I am pleased with the way the installation turned out. I only had to pay for the speakers and they weren't particularly expensive. The enclosures fill the two voids that didn't serve any purpose and don't impede on luggage space. 

So, how does the system sound? Nice! You can definitely hear the extra sound coming from the rear. I still need to balance the amps to ensure that each amp and associated speakers are performing at their optimum but I will leave that for another day. 

I'm pretty sure that the installation is now finished. I don't have any more equipment to install and there isn't much more available space inside the MGB for more speakers. 

As matters stand, the new Pioneer head unit is located in the passenger footwell, the Sony amp is powering a pair of tweeters fixed to the A posts, a pair of Pioneer 4 inch speakers in the front doors and a pair of Alpine 4x6 speakers located in the rear quarter panels, the Alpine amp is powering the new 6x9s and the tweeters fixed to the B posts and the integral amp is powering the subwoofer. In total, that's 11 speakers. Not bad, if you consider that the original MGB had just the one.

All being well, the MGB will be making an appearance at the Flower Farm place next Sunday.

See you there?

 

 

[High Jetter]

1 hour ago, Peter C said:

See you there?

I reckon we'll hear you coming! 🤣

[Peter C]

10 minutes ago, High Jetter said:

I reckon we'll hear you coming! 🤣

Not my style, I’m too old for such shenanigans!

[vtec-e]

Nicely finished, looking forward to hearing it soon.

[Peter C]

I took the MGB to the AS Flower Farm meet today. That's the furthest that the MGB has travelled in my ownership.

it made the 100 mile there and back journey without any issues. On route there I didn't take it past 60MPH but on route home, the B-series seemed to have developed more poke and on a few occasions I got the MGB up to and a little over 70 MPH. @vtec-e was following me in his Renault Clio and at times couldn't keep up. Ha ha! 

I took a few photographs with some other old motors.

These are my favourite photos, battle of the van engined sports cars. Germany v England, it was 1966 all over again. England won, of course. 

I told @inconsistant that I had a Porsche 924 when I was in my early 20s. Here it is.

WLN90X. I've checked, it's been dead for a long time. 

Finally, huge thank you to @LightBulbFun for letting me sit in his incredible AC Invacar. 

Proof that you don't need a sexy red sports car to look cool.

 

[vtec-e]

3 hours ago, Peter C said:

I took the MGB to the AS Flower Farm meet today. That's the furthest that the MGB has travelled in my ownership.

it made the 100 mile there and back journey without any issues. On route there I didn't take it past 60MPH but on route home, the B-series seemed to have developed more poke and on a few occasions I got the MGB up to and a little over 70 MPH. @vtec-e was following me in his Renault Clio and at times couldn't keep up. Ha ha! 

 

Not only the Clio, but also the BMW M140 between us at one point struggled to keep up with you 😄

[Peter C]

3 minutes ago, vtec-e said:

Not only the Clio, but also the BMW M140 between us at one point struggled to keep up with you 😄

Makes sense, the B’s motor felt very eager on route home. 

[Peter C]

I had plans to go for a day trip with my wife and son today but the sixteen year old (son, not wife) wasn’t well this morning so we postponed the outing.

My wife went to the gym and I decided to take advantage of the lovely weather and ended up taking the MGB for a road trip.

First stop, obtain a full tank of Esso’s finest.

Regular readers will be familiar with my route to Silverstone via the A413.

Looking good by Stowe Gate.

And by a postbox in Dadworth. Two red British icons?

It was a bit busy outside Silverstone due to Japfest being on. Plenty of people on the big roundabout outside the circuit taking photos of powerful rear drive sports cars passing by. And my MGB.

I’m now parked a mile up the road and I was enjoying a cuppa and some BBC Radio Live 5 on the old radio cassette unit until….

…. some twat in a Nissan Skyline turned up and started revving the fuck out his engine, spitting flames from the exhaust, generally doing what I would have done 25 years ago.

Hopefully the journey home will be as peaceful as it was getting here.

[Peter C]

I got home without any issues, however the fuel gauge reading caught my attention. 

I brimmed the tank shortly after I left home and my return journey to Silverstone via the A413 was about a 100 miles.

I paid £45 for fuel, at £1.80/litre of super unleaded means that I filled the tank with 25 litres, which equates to 5.5 gallons. 

When I got home, the fuel gauge was showing just over half a tank, the same as before I got fuel.

100 miles divided by 5.5 gallons = 18MPG!

Fuck that, that's insane. I took it so easy all the way, never went past 3,000 revs and there was virtually no traffic on route. 

There are no fuel leaks that I am aware of. When I had an issue with a sticky carburettor float valve and fuel was pissing out, you could smell it from a mile off. I'm not getting any nasty whiffs now.

I knew that the engine was running rich because it would start with the choke briefly pulled out and then it would idle and run ok with the choke immediately pushed back, rain or shine, hot or cold. And you could hear the powerful idle when standing by the tailpipe. 

I'm going to have a fiddle with the carburettors and lean out the mixture bit by bit. I would be happy with 30MPG.

Just as well fuel is cheap nowadays. 

[Mr Pastry]

2 minutes ago, Peter C said:

I got home without any issues, however the fuel gauge reading caught my attention. 

I brimmed the tank shortly after I left home and my return journey to Silverstone via the A413 was about a 100 miles.

I paid £45 for fuel, at £1.80/litre of super unleaded means that I filled the tank with 25 litres, which equates to 5.5 gallons. 

When I got home, the fuel gauge was showing just over half a tank, the same as before I got fuel.

100 miles divided by 5.5 gallons = 18MPG!

Fuck that, that's insane. I took it so easy all the way, never went past 3,000 revs and there was virtually no traffic on route. 

There are no fuel leaks that I am aware of. When I had an issue with a sticky carburettor float valve and fuel was pissing out, you could smell it from a mile off. I'm not getting any nasty whiffs now.

I knew that the engine was running rich because it would start with the choke briefly pulled out and then it would idle and run ok with the choke immediately pushed back, rain or shine, hot or cold. And you could hear the powerful idle when standing by the tailpipe. 

I'm going to have a fiddle with the carburettors and lean out the mixture bit by bit. I would be happy with 30MPG.

Just as well fuel is cheap nowadays. 

I wouldn't rely too much on the fuel gauge, they are not super accurate - maybe brim the tank again and see how much it takes?

[Peter C]

9 minutes ago, Mr Pastry said:

I wouldn't rely too much on the fuel gauge, they are not super accurate - maybe brim the tank again and see how much it takes?

I hear what you’re saying but I know that the ‘B is running rich.

[LightBulbFun]

17 minutes ago, Mr Pastry said:

I wouldn't rely too much on the fuel gauge, they are not super accurate - maybe brim the tank again and see how much it takes?

this! 

 

dont rely on the fuel gauge for MPG calculations, I always calculate it by brimming tank and just seeing how many miles I have done since I last filled up, the amount of fuel that goes into the tank vs the distance covered since the last fully brimmed fill up, gives you your MPG

heres a handy website that does all the maths for you  

https://www.mpg-calculator.co.uk/

[Matty]

On 12/04/2026 at 15:41, Peter C said:

I took the MGB to the AS Flower Farm meet today. That's the furthest that the MGB has travelled in my ownership.

it made the 100 mile there and back journey without any issues. On route there I didn't take it past 60MPH but on route home, the B-series seemed to have developed more poke and on a few occasions I got the MGB up to and a little over 70 MPH. @vtec-e was following me in his Renault Clio and at times couldn't keep up. Ha ha! 

I took a few photographs with some other old motors.

These are my favourite photos, battle of the van engined sports cars. Germany v England, it was 1966 all over again. England won, of course. 

I told @inconsistant that I had a Porsche 924 when I was in my early 20s. Here it is.

WLN90X. I've checked, it's been dead for a long time. 

Finally, huge thank you to @LightBulbFun for letting me sit in his incredible AC Invacar. 

Proof that you don't need a sexy red sports car to look cool.

 

Brilliant. Wish i lived in an area where theres more of us in it.

[vtec-e]

Any indications last week on the run to and from Godstone that the mpg was that bad ? That day out must have been a similar journey length. I would certainly do another brim fill-up before fiddling with the carbs.

Those B series engines always sounds to me as though they are hunting a bit, so I wasn't surprised when yours did when you were manoeuvring into place to take the pictures at the end. I would also whip out all 4 plugs and see if any are sooty. Maybe the carbs are out of balance, but that would lead to more general bad running.

 

[Tommyboy12]

I never got much more than it 25mpg out of my MGB. It's definitely running rich if it runs without choke when cold but you'll struggle to get 30mpg regularly unless you only do motorway driving at 50mph 😅

[chadders]

1 hour ago, Tommyboy12 said:

I never got much more than it 25mpg out of my MGB. It's definitely running rich if it runs without choke when cold but you'll struggle to get 30mpg regularly unless you only do motorway driving at 50mph 😅

Overdrive can make a 10 to 20% improvement on dual carriageways and motorways in my experience. Mine does about 25mpg on my Sunday Morning Runs down the coast road and inland where I can't use the O/D much.

 

[Dj_efk]

Yep sounds like you need a carb tune and balance - whilst there I’d advise double-checking all other settings (rockers, ignition timing etc.) are spot on.
 

For more MPGs beyond that I think about the following upgrades:

- Overdrive is defo worth having for faster roads as above

- Can’t remember if you have upgraded the ignition system already, but if not then 123 distributor with similarly upgraded plugs coil and leads, you’ll never have to touch the timing again once working correctly.

- Then I’d look at a freer flowing exhaust and possibly an econotune head to give it a bit more pep - but these would require a rolling road tune though I’d have though as you’ll then need different needles

[Marina door handles]

When I daily'ed my BGT back in the late Nineties, I was getting 25mpg out of if and that was hooning around like an idiot (because I was!) . 18 does seem a bit low unless you have a V8.....

[Peter C]

@vtec-e The previous time I had a full tank was when we visited the Flower Farm and that was about 100 miles return and I was left with just over half a tank, the same as yesterday.

@Tommyboy12 All noted, under the circumstances I could cope with 25MPG.

@chadders My 'B has a fully working overdrive and I use it as and when necessary.

@Dj_efk I had the engine fully tuned up (carbs and ignition) by a specialist last year. I fiddled with the carbs because on motorway runs to London I the engine wasn't firing properly on two cylinders - I suspect one carb was making the cylinders run too lean. I believe that the ignition (proper Distributor Doctor parts) are all ok. Considering how little I drive the MGB, I don't want to invest in (expensive) electronic ignition or fancy exhaust systems.

@Marina door handles I can't imagine you hooning around in an MGB!

So, update.

I decided to whip out the plugs. It's a difficult job on an MGB but I managed.

Access to the plugs is impossible. 

Plugs removed and it looks like cylinders 3 and 4 are running richer than 1 and 2, although all four plugs looked sooty. 

I cleaned up the plugs and put them back in - another horrendous job.

I marked up the carburettor mixture adjustment nuts with blue paint, so that I know what point I am starting from.

I adjusted the front carburettor (clockwise - from underneath) to make the mixture leaner by 3/4 turn. Based on my inspection of the plugs, I did the same on the rear carburettor but by one full turn. That sounds a lot but I must confess that I turned them the other way a similar amount when I fiddled with the mixtures last year.

I started the engine, which ran fine, at much lower RPMs and without chugging, which it did before. Sounded ok and it idled better than before.

The plan is to take it for a long drive as soon as possible and see how it's running.

More soon.

 

[vtec-e]

Glad to see you got round the access problems!

Clockwise sounds right to me, to raise the base part that the needle slides in/out, but it has been 40 years since I messed with SU's. Gunsons still make a Colortune to help set the correct mixture, but they are about £100 the last time I looked. Maybe someone local on the forum has one you could borrow, if you dont have one.

I can dig out my old Gunsons Carbalancer, and drop it off next time I'm passing your way if it helps in the future, although a piece of tube is just as good.