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MG Midget and Sprite Technical - Ideas for insulating fuel lines?

My Sprite has never had any problems with fuel vaporisation until this year.

I take my Sprite hillclimbing and on several occasions this year, when I have had a long wait for the start, or when I have run second after my son, although it revs freely with no load, it splutters and runs poorly for the first hundred yards or so before sorting itelf out and running properly. I haven't had any problems during normal runs on the road, including the occasional 30 mile motorway commute.

Over the winter I gave the cooling system a good going over, flushing it thoroughly and fitting a new pump and radiator. I also fitted a new, lower temp thermostat. As a result of the more efficient cooling system, it now takes longer to get up to its new working temperature which is several degrees below 'N'.

Although the engine is running cooler I think the under bonnet temperature must be higher causing vaporisation, probably to the rear carburettor.

Making sure that it doesn't get too warm before take-off seems to help avoid the spluttering. For the time being, I have wrapped the hoses in the engine bay with kitchen foil. I have done a couple of runs on a warm day with no problem.

The kitchen foil is not particularly elegant so I wonder whether anyone has any other ideas or suggestions for insulating fuel lines and keeping carburettors cool. Is there a better material for wrapping fuel hoses?

The car is a 1275 with 1 1/4" SUs, 'saucepan' air filters and a LCB exhaust manifold. The original steel heat shield is in place, not polished but painted with silver-grey exhaust paint.

I would welcome any suggestions.


Colin Mee


I remember your issue from a couple years back ... but I dont recall the various solutions offered at the time

I think the primary cause your battleing is the LBC aftermarket exhaust manifold

There is a material (asbetous ??) That wraps around the piping... BUT it creates condenstaion and will rust out your exhauste ... I have no experiance but those who make the claim are those that would be in the know and I trust them and there insight

What might be worth while and take a few minutes each time ... would be to get and use the exhaust wrap, then when your done for the race/day... remove the wrap, and avoid the condensation issue

A 2nd option would be some kind of wing heat vents... they CANT be just holes drilled into the wing side ... there has to be a lip around the hole to create a high/low air pressure area aka air moves faster over the vent then the air inside the engine bay... think of how an air plane wing works to create lift ... you want the same effect to SUCK the hot air out of the engine bay

Just a drilled hole / flat surface will create the opposite and the hot air will remain inside the bay at any speed above 5 mph because the air inside and out side the wing are moving at similar speeds and there is no lift

But I think those are your 2 best options, tempory heat exhaust wrap or funtional aerodanimic wing heat vents

Prop and the Blackhole Midget

I used to have this on my A series, generally after a thrashing then slowing down; which I guess is the issue you have when hillclimbing.

make the heat shield bigger is one option. Dad's done this on his and has fixed it.

modifying the carbs so there is a fuel return and running it back to the tank is another. keeps cool fuel running through everything - it's how they attempted to fix it on my big V8.

option 3 is making a hole in the bonnet above the carbs. I did that to mine and it fixed it.

Or holes in the wing (Prop the air is almost always going to be moving faster outside the car than in the engine bay, so you'll always have a sucky effect)

another amusing solution includes plumbing the washers so they point at the carbs, and fitting them with cut off socks to keep them cool in their own little water jacket (used on a P6 V8 touring Morocco to great effect)

Rob Armstrong


I love the water jacket, spray washer idea... classic, nice... ive not come across that before... im a fan

Because the holes in the wing are flat and no un even surface for the air to move across the moving air actually creates an invisable wall over the hole and that force field actually holds the heat in the bay... the faster you drive the harder the invisable wall... but if you put arounded lip over the hole then you create a suction effect andthe suction becomes stronger the faster you drive ... the lip creates a low pressure zone over the top of the hole in the wing ... or louvers in the bonnet top


Prop and the Blackhole Midget

Actually... im probably wrong, I know imagine the horror of that commint.. haha

By adding a rounded lip around the hole in the out side of the wing .... the air probably moves slower then the air inside the engine bay because the air has to cover more distance then the air inside the wing... so the air inside the wing is actualy moving faster then the air out side the wing because of the lip around the hole

Then there is that hole enstine realitivity of time travel of a train traveling east with the conductor walking west on the train and briefly meeting himself... EMC/2

I know... who new air had gravity and can warp time making negitive air a time traveler

Prop and the Blackhole Midget

At first I have used kitchen foil as well, it worked but not always in very hot weather (I will always remember a hot day in Paris uphill slow traffic, heater on).
I also tried a cool air duct to the carburettors. I abandoned that because it only worked when driving. Later I have re-routed the fuel lines away from the heat sources (outlet manifold and radiator flow). Replaced the mechanical fuel pump by an electric and placed double insulation blocks: between manifold and heat shield and between heat shield and carburettors. It works even with E 10 fuel in the south of France.


Flip Brühl


What carb set up is that... HIF ???

Prop and the Blackhole Midget

Adding a lip on a flat hole does help. As with louvres and similar. But a flat hole will work too.

The faster air blows over the hole, creating a low pressure area inside the hole, which creates net flow out of the hole (the sucking effect). A lip on the front of the hole creates a larger area of low pressure so therefore works better.

It's helped by the higher pressure in the engine bay as well, which helps push the air out. It's higher pressure because it's been rammed in there from the front and has nowhere to go except down and out.

Interestingly, after cutting the hole in my bonnet, my Midget no longer lifts the front end at speed. Must be because I've reduced the high pressure under the bonnet.
Rob Armstrong

Best putting a hole in both wings to prevent the car veering to the right on that theory Rob
Graeme Williams

How about this stuff (see picture)


I had terrible problems with vapour lock,
ended up changing to elec fuel pump at the back, replaced the entire fuel line with a nice thick rubber hose, big vent in top on bonnet and side vents also...

No trouble now and its always at least 30 degrees C when ever i drive, normally more like 34 deg (94F)

Andy Phillips (frankenfrog)

Rob, do you have a picture of your bonnet vent ?
Andy Phillips (frankenfrog)

Thermal barrier coating on the exhaust manifold (not wrap). Thermal barrier coating on the inlet manifold. Thermal barrier coating on the float bowls.
Daniel Stapleton

made out of a bit of gas fire. Holes drilled in the edges, then curves cut with jigsaw.

Bits bent round and screwed into hole in bonnet. Bit of filler to finish and a spot of paint.

Rob Armstrong

What happens if you get caught in one of those monsoon like rain showers you get there? Doesn't the engine flood?
Lawrence Slater

Would removing the nearside splash panel (assuming it's not been removed already) and ducting cooler air to the carbs help or is that wistful thinking?
Daniel what do you recommend as a thermal barrier coating?
Jeremy Tickle

water goes in, hits exhaust manifold, comes back out as steam.
Rob Armstrong

Here is an interesting idea I found out about recently. Its mainly for hard fuel lines where they run near heat sources. Its the seal that goes on an oven door. There is a piece of woven wire for support inside. You just pull it out and then slide the outer, insulating part over the fuel line. Don't know if it works, but looked interesting!

Jack Orkin

would this be any good used it to protect cables on an aicraft
mark 1500 on the road Preston Lancs

Jack that is braided fibreglass sleeving available from electronics or electrical parts suppliers
R W Bowers

Well, as such, does it provide any insulation qualities? I got it from someone who was handing them out at a recent MG V8 meet, where they seem to have more problems with fuel and heat. Probably due to the fact that they have hot exhaust on both sides. He had a box full and was handing them out and said they were from oven door seals. May be the same product with multiple uses. Some of the sleeves Andy mentioned may be better, though more expensive.
Jack Orkin

V8s have big issues with it. Mine stranded me after a service stop - set off back onto the motorway, used up all the fuel in the dashpots then died... Fitted an electric pump under the tank at the back to force feed the mechanical one and it's all better now!
Rob Armstrong

or this?
Reasonably inexpensive - looks like the metal braiding on some fuel lines but presumably fibreglass has better heatshielding properties than steel?
Jeremy Tickle

Thank you for all the suggestions - plenty of food for thought.

For the time being I'm ruling out hole cutting but, if I fit a fibre glass bonnet at some stage, I'll definitely add some holes - some sort of hole or slot towards the rear for hot air to exit and another, with suitable ducting, to feed the carburettors.

I like the look of the CBS temp sleeve and will investigate further as the online shop only seems to want to sell it in long lengths and I only need less than a metre.

I also like the look of your heat shield Flib - that's definitely on the To Do list.

Daniel, can you provide any more details of the Thermal Barrier Coating - is it a DIY product? My exhaust manifold will have to come off over the winter for a repair or replacement so a dose of thermal barrier might be added to the job list.

Your posts reminded me that I had a roll of self-adhesive foil tape left over from insulating the extension. As a short-term measure I have wrapped the fuel lines with it and jacketed the float chambers. It's not the most elegant but it looks neater than kitchen foil!

I'm hill climbing again this weekend so it should give the new foil a good test, especially if it's warm, though that's unlikely as it's a bank holiday weekend.

Many Thanks

Colin Mee

Hi, For the more thrifty amongst us, I have used an old ironing board cover (Reflective silver rather than flowery) as a very flexible heatshield around the bulkhead.
The foam backing was falling off, but if not I'd remove it due to its likely flammability. The cloth left over looked like something astronauts wore on Apollo 14!
G Waite

I like it Gary!
Colin. You do have an electric fan don't you?
I have an override switch in parallel to the radiator switch, to keep air circulating when standing still.
I recently also fitted a kit from maplins to run fan on for 5 mins when required
Dan Cusworth

If you are replacing the exhaust manifold then getting it coated with an anti heat system like Zircotec is another option. Its not that cheap but it does work in my experience as well as protecting the manifold from corrosion etc and looking good!
Bob Beaumont

Hi Dan
It was supposed to have an electric fan by now but that winter project went a bit awry and ended up just being a thorough clean out plus new pump and radiator. An electric fan is still on the wanted list but it just took a step back when a half shaft broke at the weekend!

Thanks for the Zircotec recommendation - I'll certainly investigate that one.


Colin Mee

This thread was discussed between 24/08/2015 and 02/09/2015

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