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McMuttley

Cooling the Carbs

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Good Morning Sages

Getting air to the carbs?
I believe I have a 4 engine with HS6’s and of course those mahoosive 'neighbour annoying' extractors sitting right underneath.
I have the standard cardboard air cowl, so water temps fine and cool when poodling, but it gets very wheezy when hot.
I don’t want to wrap/coat as the exhaust as it will be replaced in the nearish future.
How are you venting air to the carbs (if you are)?
I assume some sort of flanged intake then a hose directing air ?
Recommendations, materials? Dia of hose to be effective?
Demon weeks have these ?
Do these Moss heat carb shields work and are they simple to fit, ie, will i fup uck my carb settings by unbolting the carbs? (do I also need to add gaskets)
£46 seems a lot for a bent piece of tin !
I was going to slide this over the fuel lines as they sit v close to the extractors.

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Thanks Suart - any views on the best diameter to go for ?

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If you want ducting try:

http://www.ebay.co.uk/itm/Air-Ducting-Plastic-Flexible-Flexi-Air-Intake-Duct-Fittings-Induction-Hot-Cold-/190885529382?var=490189865485

and for heat reflective tubing to slip over fuel lines:

http://www.rallydesign.co.uk/product_info.php?products_id=1606

Certainly on late model Spitfires, Triumph introduced plastic insulator blocks between carb and manifold along with a heat deflector to help prevent fuel vapourisation. The original asbestos deflector tends to break up with age and I have found an alluminum plate does the job just as well. I attach to the lower carb mounting bolts (no need to remove carbs, just the lower bolt).

Jerry

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What exactly is happening to Olde Smokey, Austin? Wheezy when hot? Fine when poodling? Are you saying the engine is down on power at speed when it's warm?

 

I'd have looked at a number of other things around basic state of tune before I started adding ducting for cool air. Distributor advance, valve settings, fuel flow... probably many more and better ideas from folks smarter than I.

 

'Course, if the idea is to add some racy scoops and slots to go along with the roundels, well, have at it then.

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bonnet scoops there an idea !!!!

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Hi McMuttley ~

 

If you PM me your eMail address I'll send you photo's of my cold air system (which cost me nothing!).

 

Tom.

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Thanks Suart - any views on the best diameter to go for ?

I use the 76mm one.

Stuart.

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Is this a problem with extractors causing heat problems? I run twin HS6's in what is a TR4 Spec engine 2.2L with late 4a head but standard TR4 exhaust manafold, and have never had a problem in 30°C plus tempratures (36-37 last weekend )

 

Cheers

 

Alan

Edited by Kiwifrog

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Oui - mahoosive f off rally system stuffed in there (Not by me)

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I have a length of flexible hose (similar to that shown in the Revotec kits) of about 2" diameter, which I clipped to the lower right of the fibreboard inlet cowling, then carried upwards in an elongated S-shape to discharge in front of the air cleaner of the leading HS6.

It helps that I don't have the standard horn mounted in the way, but I can't say whether this makes any great difference - certainly can't do any harm.

I wrapped as much of the 4-branch manifold as possible when last I had all the exhaust system completely dismantled (several years ago), but it's difficult (impossible?) to wrap all of it. Were I undertaking this now, I would opt for the super coating advocated by Tony Sheach.

My engine is 2238cc and Rally spec, producing about 135+ BHP, so can produce quite a lot of heat.

Although the wings are vented, Tony seems to think that this has little effect at high speed, but without setting off a smoke bomb in the engine compartment whilst driving at 70mph, I don't know one would be able to check this!

Ian Cornish

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Austin

 

You need to think like an engineer here .... Offensive as that might be !

 

The job is to force cold air onto / into the air filters, so some ducty thing that sends air to the radiator is a good starting point, but doesn't answer the exam question.

 

The next step along from a good cowl is a duct on the RHS (drivers side) coming from the cowl back to the filters. This can't be direct induction as it unbalances SU's with differential air pressure (I know cos I've measured it, cos I'm an engineer) so it needs to be a nice insect free, icy blast from the front of the car into the area under the bonnet where the carbs can suck it up.

 

On BST82B I have such a device which shovels cold air from the rad cowl under pressure of forward speed, directly aimed at the BASE of the webers because hot air pushes cold air around and up. My big filters shovel this down the throats of the thirty things, and deliver a well mixed blend of finest M25 tinted atmosphere. This provides me with of the order several horsepower (!!) however and more importantly I have an audibly sweeter engine which behaves delightfully, even in traffic.

 

You're only South of me by a few junctions, so this should work.

 

Regards

 

Tony

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""

Do these Moss heat carb shields work and are they simple to fit, ie, will i fup uck my carb settings by unbolting the carbs? (do I also need to add gaskets)
£46 seems a lot for a bent piece of tin !

 

 

 

 

Heat shields will prevent radiant heat from exhaust manifold and pipes from cooking the carbs. Aren't they standard fitment?

Peter

Edited by Peter Cobbold

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""

Do these Moss heat carb shields work and are they simple to fit, ie, will i fup uck my carb settings by unbolting the carbs? (do I also need to add gaskets)

 

£46 seems a lot for a bent piece of tin !

 

http://www.moss-euro...uk/-357876.html """

 

 

 

 

Heat shields will prevent radiant heat from exhaust manifold and pipes from cooking the carbs. Aren't they standard fitment?

Peter

Hi Peter - not standard on early TR4's with H6 carbs (although that's not the car under discussion and I can't comment on the HS6 set-up).

 

Austin - as Peter says, they restrict radiant heat and are a worthwhile addition (although maybe not the whole answer, as shown by other replies). I don't think your settings will change as a result of removing/refitting the carbs (but I'd expect to check mixtures and idle speeds etc. anyway) and yes, you should have gaskets either side of them - order 4 (unless they come in with the shield).

 

Cheers,

Tim

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You need 6 gaskets in all if you have heat shields and insulator blocks. Beware of heat shields fouling whichever throttle linkage you have on your carbs, they might need fettling to fit. I got an ARE shield for my HS6s from TRF and it needed some mods to clear everything, including the steering shaft. Also when it's in place it restricts access to the lower manifold nuts if you want to check them for tightness. You'll very likely need to rebalance the throttle butterflies when refitting. Finally you might run out of length on the lower mounting studs with the shields, extra gasket and throttle linkage in place.

 

Otherwise, no problems at all :rolleyes:

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Triumph never deemed it necessary to fit heat shields to any model TR from 2 to 6.That was however in the days of proper petrol and new cars with A1 cooling systems and blocks not silted up with 50 years of misuse.

Stuart.

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I would guess the HS6 tube from the float chamber and base of the jet are the most suscpetible to radiant heat. Especially at low fuel flows eg tickover. As a quick experiment try wrapping them in aluminium foil, shiny side out.

 

Ethanol is often accused of causing vapour locking. That's not strictly true as its own vapour pressure is rather low**. In order to compensate for that other more volatile hydrocarbons are added to bring the petrol's RVP up to BS specs. But we do not know what has been added. Butane is a cheap option. And I can well imagine butane in a hot HS6 jet tube bubbling away merrilly.

The only easy answer is to try fuels from different oil companies.

 

Peter

 

** High ethanol fuels are a big fire risk as its low vapour pressure doesn't displace air from the fuel tank headspace, leaving an explosive air-fuel mixture. E85 users beware !!

http://www.iafss.org/publications/fss/4/575/view

Edited by Peter Cobbold

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Keeping the carbs cool depends on a through put of air

All very well ducting cool air in but if there is no out flow from the engine compartment it will have back pressure : like blowing into a box.

Having wing vents allows the hot air out

The situation is worse if you run a sump guard as it stops flow out past the gearbox.

The situation is worse for road cars as they often have to sit in traffic so the whole engine compartment accumulates heat: the reverse is true of competition cars unless sitting on the grid

Cheers

Michael

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Austin

 

You guys are spoilt for choice. Here in Spain, nothing like that available, so I used 2 lengths of swimming pool hose starting right in the top corner of the air duct (aluminium in my case) and each one going to one carb so the back one got it´s share too. I had to change the mixture as the plugs went white showing too much air, so I directed the ends of the pipes slightly towards the inner wing.

I too have HS6´s to a TR4 manifold on my 3A but then I lagged the four branch stainless exhaust manifold nearly as far as the cruciform, so no other shields are necessary.

 

Dave

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Dave, I would rather have a pool than a Revotec !

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Austin

 

I am the opposite, I have cool carbs and NO pool, we had one years ago in S.Africa and I swore then that we would never have another one, too much cleaning and cost of chemicals, after all the Med. is just down the road!

 

Dave

 

 

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Did any one with H6 or HS 6 carbs try these offerings from the TR4/4A grille maker?

On TR4A I suspect they may foul the throttle rod bracket - but hey we are TR people with special hammers....

 

Peter W

 

https://www.ebay.co.uk/itm/MINI-HS6-1-3-4-TWIN-CARBURETTOR-HEATSHIELD/382250288208?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

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Peter

My swimming pool pipes are there to supply cold air from in front of the radiator. not to act as a heat shield to the carbs themselves. Once you install the air duct in front with the top plate as well, then ALL the air goes through the rad. to bring hot air to the intakes.

 

Dave

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