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MG Midget and Sprite Technical - Fan to cool carb...?

Out and about loads in the hot sunshine yesterday and today. And was reminded that, although perfectly well behaved under idle when the weather (and under-bonnet temps) are cooler - when it gets really hot, idling drops about 200 rpm and really struggles to stay running. No other issues when hot or cold, and judging from performance and plug condition, set up is pretty spot-on.

So - is this vaporisation / a general heat-related condition? And if so - has anyone attempted to install a small electric fan (PC-sized) adjacent to carb(s)to keep them cooler? And does it work??

I have a single SU HIF44 on a Titan manifold.

Just curious.
Steve Clark

I doubt a small computer fan could shift enough air to make a difference. Do you have a heatshield between carb' and exhaust manifold and a cold-air inlet to your filter/airbox?
Nick Nakorn

where would the cool air supply come from for this, the under bonnet air is warm/hot for this to happen in the first place

check your all your cooling/heating system is fully function and clean inside, coolant elements of antifreeze wear out before the antifreeze parts so regular coolant changes on ordinary coolant

same with secondary cooling system, the oil

pays to have both pretty much topped in this very hot weather

then there's the engine and carbs tuning that might increase the heat but you say is pretty spot on

if you only have an engine driven fan then it's running at its slowest (and the water pump) exactly when you need it running at its most efficient

what do you mean by when it gets really hot, the ambient temperature or what the temp gauge is showing, is it about its usual reading
Nigel Atkins

The old Renault 5GT turbo has a fan like that to cool the carb as it sat right over the turbo and the fuel used to vapourise.



It had its own little duct that drew air from under the offside wheelarch and was activated by sensors in the carb base and the turbo heatshild.



Might be worth seeking one of those out.
SR Smith 1

wouldn't it be better to know why this car needs carb cooling when others with single carb'd souped-up engines don't need to use an additional fan
Nigel Atkins

I'm guessing it needs a heatshield.
Dave O'Neill 2

I'm thinking a photo might be helpful, they usually are
Nigel Atkins

Steve:

In the interest of keeping the fuel cool, I coated the fuel bowl of a single HS4 I used to run on my 1500 (don't run it now, throttle shaft wear too great) in Plasti-Dip (liquid plastic resin in a can), slowing down the inevitable warming of the fuel. Reasonably cheap, reasonably effective. the fuel lines to the carb were covered in thermal insulation as well.

Richard




Richard Reeves

Coolant, cooling system and oil all spot on. I meant the ambient temperature getting really hot. No belt driven fan - a Kenlowe which comes on when it should, does its job then turns off. And it's hardly 'souped-up' Nigel (there's a quaint old-fashioned phrase! ;-) - about 75 bhp I believe. About 2013-KERS-worth in fact.

I'm wondering if the simplest answer is the best (they usually are) - heat shield. You can see from the pic that there is one - but it's just in the 'vertical' plane. I have no idea what type of car the carb and heatshield came from. Would a heatshield fabricated so that it protects beneath the carb as well, do the job do we reckon? Wouldn't hurt I guess.

(And for the eagle-eyed, no that's not a Titan manifold. Pic was taken as I was about to swap).


Steve Clark

Hi, Steve, that heat shield looks like the standard one for a HIF44. As these are usually fitted to transverse engines and sit at a more extreme angle, the heat shield becomes more effective by protecting more of the carb, whereas on the midgets shallower angle and the angle of the exhaust (especially if a LCB is fitted) the float bowl is more exposed to the heat.

My car runs the same carb set up and I have found that it can get jittery if sat in stop start traffic for long periods of time.

I am in the process of fabricating an extension to the base of the heat shield that will protect the whole carb from the heat of the LCB manifold.
Will let you know how it goes once the car is back together.

Thanks
Mark
Mark Whitmore

Mark, I like the heat-shield extension idea.

Richard, I like the Plasti-Dip idea, good to know it can remain intact subject to under-bonnet temperatures. I'm assuming that's a brand name rather than a generic term?

Nigel - cool air from front of car as in my set up or from the front to the intake tubes on a 1500 air cleaner case.
Nick Nakorn

I had one of those Renault GT Turbos and it was impossible to start hot until Renault finally retrofitted the carb fan. It ran from the moment the temp in the carb area reached a certain temp, whether the engine was running or not. It would run for a good 10 minutes after the car was shut down. Great car to drive, I am just glad I wasn't paying the bills as front tyres lasted 5000 miles and it needed a service every 3000! in two years and 60k miles it ate a valve, two turbos, three gearboxes, two snapped clutch cables, and it had electrics that Lucas would have been ashamed to sell - after a two hour drive the switches on the dash were too hot to touch more than a quick dab to switch off. But with 0-60 of 5.5 seconds, UNBELIEVABLE fun as a car for then 5500 GBP. A Nissan Sunny was available for the same price, or a MG Metro Turbo (which was a real dog) and a 205 GTi Peugeot was 500 more!

A lot of MGAs have the same problem (mine thankfully doesn't) and the best solutions are fitting a radiator with the correct spec. or for the others, fitting a bilge blower, which gives you an idea of the volume of air you have to move.
dominic clancy

Steve,
I'm with you a wider, bigger heat shield first

sorry but the info in your original post was a bit sparse and with no vehicle profile to look at options were covered

75 bhp is souped up from standard (only just sorted that phrase as written, yeap it's from when the cars were new)

a word of caution on that braided fuel line, hopefully not needed but just in case, keep your eye on them as you can't see if the rubber degrades under the braid and there a lot of rubbish rubber about, hopefully not yours but you never know for certain
Nigel Atkins

I think a bigger heat shild is your answer, the back side of the carb is really exposed to that exhaust header

Make the shield out of ally aluminum, other wise the heat will just soak into steel and act as an old wood stove...also if you can get it, some asbestous siding glued to the back side of the shild would be awsome souce Xs 33

Prop
Prop and the Blackhole Midget

I did my HIF conversion 8 years ago and have never suffered fuel vaporisation....until this year in le Mans in traffic.

I'm sure i've had it in hotter weather / heavier traffic and the only thing that had changed for this year is a replacement exhaust (not the manifold). I wondered if changing from a stainless long pipe + RC40 to a Maniflow mild steel system may just have changed the amount of heat that stayed in the engine bay a fraction.

I run a pusher electric fan which at no point struggled cooling the engine (and was installed at roughly the same time as the carb). But again maybe it just simply doesn't stir the air around the engine bay enough.

Or perhaps it was a tank of french supermarket fuel that was that bit different.

I too just have the std heat shield. I'm now collecting bits for a K conversion so wont spend too long trying to fix but I was considering :-

1) Change to a bigger puller fan (just to create more air movement in the engine bay)
2) Change back to engine fan for the same
3) A bigger more wrap around heatshield

With British weather its hard to test though ;-)
Dean Smith ('73 RWA)

Dean,
1) it'll have to be a very slim fan if you mean engine side of rad and fans put the warm air from the rad into the engine bay - I've got an uprated fan to fit so if you wait I'll let you know

2) engine fan goes slow at idle

3) would be my choice

let me know when you put the carb and manifold on ebay
Nigel Atkins

I agree with fitting an extended heat shield, and I also agree with Prop RE: adding some sort of insulation material to it. The US 1500s have a catalytic converter that runs very hot by nature (and hotter yet if the carb goes over-rich), so the larger shield was a must. Mine's still got the original heat shield, and it has some sort of foil-coated fiberboard on it, stood away from the steel panel with spacers to provide a slight air space.

Cheers,

-:G:-
Gryf Ketcherside

Could it be ethanol related?
Dave O'Neill 2

A puller would indeed need to be slim...but you can get a bigger diameter than a pusher due to the angle of the radiator housing in front of the rad.

Nigel - when I come to sell existing 1380 I will probably do some forum classifieds to include 1380, Aldon Yellow+Lumenition, HIFF44+Titan, Exhaust, Gearbox

Dean Smith ('73 RWA)

Id also consider a temporary solution...you will only have this issue 4-6 weeks iut of the year

The big problem is evacing the hot air out of the engine bay, do that and you can solve alot of heat related problems, currently air can easily get in, it just cant get out.

Prop
Prop and the Blackhole Midget

Dean,
fair enough, good idea, just note in a post when you do it please as I don't often look in classifieds (or ebay), cheers


ETA: good point by Prop about getting warm air out
Nigel Atkins

I had a talk to the boffins at work who where sorting out the jet pipe on a experimental aircraft about my heat shield and he said that it would be fine for the sort of temp we get . Made of stainless with air gap


mark 1500 on the road Preston Lancs

Stainless will work....but its a " bit#h" to work with, and not as efficient as aluminum

Prop
Prop and the Blackhole Midget

I have no idea if I actually needed to do it, but when I fitted my HIF44, I expanded the standard heatshield to the same width as the one used on twin su's. It seemed like a good idea.




Lawrence Slater

Just a thought, would there be any mileage in polishing carbs or heatshield to reflect heat rather than absorbing it?
Colin
C Martin

Lawerance,


Watch out for iccying .... haha

Actually.. it could in the dead of winter, ive never heard of that happening on a midget, on a B2000 mazda I had once , it was notorious for the carb packing on ice in 1/2 hour drive

And a guy I knew way back in the day had a VW bettle do the same

So if the carb is over cooled, it could ice up, but easy to fix....WD40 and a screwdriver ... ive heard ice melt works good to but not inside the carbs

Collin, probably very little and hard.to measure but they sure look good... moss sold a polished dashpot with that claim....id think wraping in foil would get better results

Prop
Prop and the Blackhole Midget

It'll never run properly with the vacuum pipe off, Steve.
Nick and Cherry Scoop

Been meaning to take some photos of my extended heat shield for the HIF and finally got round to it!

It just bolts onto the original HIF shield which has been bent back a bit first. Heat shield is titanium (hence the stop drilled cracks!) and covers most of the manifold. Never had any problems with heat.




john payne

Another:




john payne

Apologies for the upside down pic!
john payne

A good solution John!
Nick Nakorn

As Prop said, the problem is unlikely to last long, so how about using the choke control to temporarily increase the idle revs when it's very hot - without enriching the mixture, of course.
Peter Blockley

Chaps

To revert to Steve's problem, I do not believe the root cause is vapourization. Hot air is less dense and carries less fuel, thus the thing stalls when hot.

All other things being equal, enrichen the mix v. slightly to reduce running temperature and thus keep mix ratio constant at elevated temperatures.

Regards

Mark
Mark O

Quite a valid point as both Dean and I sat in heavy traffic on the way to Le Mans this year. With very similar set-ups (single Hif44 etc), Dean's was suffering fuel vapourisation while mine didn't. Apart from bad panel gaps which may allow more heat to escape, my car was tuned slightly rich after a recent burned no.3 piston.
G Lazarus

Yep - very slight choke is what I've been doing! Will try and fabricate a larger heat shield as a winter project. Thanks chaps.
Steve Clark

...but using the choke on a HIF44 does enrich the mix as well as increasing the idle speed. My point being that using the choke masks the root cause - a slightly weak mix.
Mark O

Or you can manage the hot air in and out.Vents above the carbs would allow stagnant hot air to escape so that underbonnet temperatures don't build, and they also help to pull air through the radiator once on the move. With this I find I don't need to run a fan at all.


Fergus Pollock

er, you've also got side vents
Nigel Atkins

I was running the Midget in the garage yesterday for about 1/2 hour at 3000 rpm, just to see where on the wings and bonnet the hot spots occur. And they are 'exactly' where Fergus has his vents.

I also felt around the gap between the inner and outer wing, at the top and rear of the wheel arch. You can feel a slight hot draft emanating from there. Other than that, once the hot air is trapped at those positions, there is no escape.

But not all cars suffer from hot air syndrome.

The side vents look good though.
Lawrence Slater

What I first have found running a turbo with Hif44 was the heat was building in between inner and outer wing stuck at the end with nowhere to go, I used a laser temperature probe to pin point this that I use at work, it was causing the fuel to vaporize (in carb or fuel line leading to carb)) when stationary, holes/vents put towards the end of the wing sorted the problem perfectly, the funny thing is the build up of heat was still there when stationary and no fan on, as soon as the kenlowe kicks in it dispersed the heat through the vents in an instant and the temperature dropped.
So I would not suggest fitting a carb cooling fan, just concentrate on finding somewhere for the heat to go, as you already have a fan manual or electric as others have already suggested.
hope my findings may help
Cheers


Rob Newton

Chaps

I must be missing something ...surely the question to ask is why does it overheat in the first place? If running right, it should get nowhere near hot enough for fuel vapourization - which I think is a red herring anyways. Mucking about with choke enriches the mix, which means the engine runs cooler and thus the stall disappears as the engine and surrounding air cools, becomes more dense, and carries enough fuel to enable a stable idle.

Mark O

This thread was discussed between 12/07/2014 and 06/08/2014

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