HS6 carb death

[contractman]

Hi

Hope you can help with this

Had my 1500 1975 Spit since November and it has not been used much.

A few times I have used it there has been problems with acceleration, mainly underload.

A knowledgable mate has been round and confirmed I have HS6's Waxstat carbs on the car with ABT needles and K&N filters.

A quick test drive further to some more fettling, revealed average performance, the cars stop running and fuel pouring out the float over flow. ??)

Float is ok, but there is some sludge in the bowl, so a rebuild is on the cards.

Does this carb upgrade work with a possible standard head

If so what is the best needle to use, bearing in mind they are waxstat carbs, 4-2-1 manifold and twin exit exhaust pipes?

I am just concerned that I am going to re build these buggers and they are always going to be OTT

Cheers

[Clive]

are you sure they are HS6 carbs? did you change to them from the HS4's, as it is not a good idea. Measure the bore of the carb, hs4 1 1/2", hs6 1 3/4".
HS6 carbs always (AFAIK) fitted with 100 needles, as in they start "B" (A is 90 needles, used by HS4's)
Other way to check the carbs is the hs4's attach to the manifold with 2 bolts, the hs6's with 4, so would have 2 unused holes per carb.....
Seems a bit odd

If the float chambe is overflowing it is the needle valve, may need dismantling (easy) and cleaning or if worn replaced. Sludge not helpful, and may be this which has caused the problem, as in it has come through the needle valve to get into the chamber.

[andy thompson]

Are you sure they are HS6? If so too big.. you can get 140 bhp on HS4's if you know what you are doing.

[contractman]

Hi

I have not changed them, the opening out to the air filters in 1 3/4. Also can confirm secured with 2 bolts and have 2 unused, so pretty sure they are HS6 carbs.

Needle valve was cleaned and re fitted before flood happened, but will look again....

My main concern is this is a pants conversion........is it a silly idea by someone or a recognised upgrade?

Its pretty good on fuel consumption and seems to work well to a point but is unreliable?

[Richard B]

One HS6 would be fine, (John Kipping special!)

Two would I suspect be over carbed.

I'd suggest either a single HS6 SU, twin HS4 SU's (standard setup) or a single twin choke Weber/Dellorto.

To put it into perspective 2 x HS6 is considered an upgrade for a 2 litre MkII GT6 engine and standard spec for a 2500S Saloon.

[Clive]

Not a good conversion. A pair of HS4 is ideal and standard. HS6 will not improve anything, only make stuff worse.
BUT flooding is bound to be a needle valve problem. You may need a new one, or maybe a clean and a fuel filter fitting..................

[contractman]

Afternoon

It seems obvious by the replies that the HS6 carbs are not the best idea for a 1500 and they need changing back to HS4's.

I have been offered a set of 1.5'' HIF carbs quite cheaply.

Does anyone know if this is a straight forward enough swap, are there any major  difference with regard perfomance and linkages etc.

Cheers in advance

[Freek76]

I've got a pair of HIF4's on my 1500 Spitfire.
Bolts right on, only problem is the throttle shaft rotates the other way.
But that's fairly easy to sort.

Performance is identical as is the mileage.