Carburettor options

[andrew.searston]

Hi everyone
I’m considering some carburettor options for my 1098 with a 1275 head and a full mani flow system. Currently running a worn hif38 having changed needles rolling road and many hours spent I’m considering other options like twin carbs, Weber ect. My question is what benefits would these have over a rebuilt hif38 to make the most of the engine I have

[philthehill]

These are my opinions for what they are worth.

Twin 1 1/4" SU HS2 carbs are not worth the trouble and expense. Whilst looking good there are no real benefits against cost.

Twin 1 1/2" SU H4 carbs - well worth the money and will give a real benefit to engine breathing. Downside - a good pair is expensive.

Twin 1 1/2" SU HS4 carbs - similar performance gains to the H4 but less expensive.

Weber 28/36 DCD carb - will give a good performance benefit but fuel thirsty.

Weber 40DCOE carb - best all round performance but again expensive to install.

Weber 45 DCOE - too big for a 1098cc even with the performance additions you have.

There are other carbs you could consider but they are not run of the mill types and finding spares may be a problem.

Overall I would suggest that you obtain a reconditioned or serviceable Hif38 to replace your worn carb but there again not cheap

http://sucarb.co.uk/hif38-carburettor-f ... 27227.html

Here is a reconditioned Hif38 for sale on 'e' bay
https://www.ebay.co.uk/itm/MANUAL-CHOKE ... SwydRbia0D

Phil

[andrew.searston]

That’s brilliant thanks, what about a hif44?

[philthehill]

I would suggest that a hif44 at 1 3/4" choke is too big for a 1098cc engine even though fitted with the 1275cc head.

The hif38 with 1 1/2" choke will give a much better gas flow at the engine revs you expect to use - bigger is not always better.

[andrew.searston]

I do have a 1275 that I plan to rebuild one day and swap in, so ideally I’d like a good all round carb that would work on both of the engines

[andrew.searston]

I do have a 1275 that I plan to rebuild one day and swap in, so ideally I’d like a good all round carb that would work on both of the engines

[philthehill]

The hif38 will work well on both your existing 1098cc engine and the 1275cc engine you propose to fit at a later date.
Only if you gas flowed the 940 head and fitted a performance camshaft will you gain any real advantage with a hif44 SU carb.

[Chipper]

Another option would be a single 1.5" HS/HS4 SU, as used on many 1970s (and early 1980s) BL A-series engined stuff, such as Mini, Marina, Alllegro, etc.

These were the defacto carb fitment for some years prior to the HIF carbs coming along.

I tried one many years ago on my standard 1098cc, and it gave a noticeable gain over the original single 1.25" SU.

The main benefit with the HIF, is far smoother throttle control in traffic, due to the cam operated progressive linkage.

[alawrence10360]

This might squeeze in ..
https://www.ebay.co.uk/itm/333521103768

[philthehill]

The 45 DHLA is too big and the inlet manifold is too long.

Both carb and manifold would be suitable for big bore engines with large valve/gas flowed head, performance camshaft and turning at high revs.

The longer the inlet manifold the better the ram charge at high revs. That is - the mixture keeps flowing pushing the mixture before it towards the inlet valve - helps reduce/eliminate any pulsing of the mixture.

If you must go the Weber route this is a more suitable application:-

https://www.ebay.co.uk/itm/Weber-40-DCO ... SwbuJech8v

[andrew.searston]

That Weber setup does look nice. Would it be as reliable as a hif? And much more performance to be had with it

[philthehill]

On a cost/benefit analysis you will not get a suitable return for your money.
You may have to re-jet etc to get it running right and Weber spares are not cheap.
I would stick with your hif38.

[alawrence10360]

https://www.ebay.co.uk/itm/143576581731

[ampwhu]

Good choice

[alawrence10360]

or something more exotic
https://www.ebay.co.uk/itm/193419010440

[philthehill]

I may have miss read this advert. It looks as if the carbs are included.

Phil