28 replies to this topic

[iamweasel]

I'm keen to upgrade my carb from the standard single 1.5" SU. I've have minis before with twin 1 1/4 SUs (Also 998s) which were quick.

How does a single HIF 44 compare to twin 1 1/4"s? Obviously twin carbs look the business, but I want the best performance.

Are there other carb alternatives that don't require modification to the bulk head?

I'm pretty sure my 998 engine is standard - apart from an LCB.

One last question: after fitting a better carb, what is the next logical step in squeezing out a bit more power?

Cheers

[Dog]

If its a 998, I'd fit a HIF38...

This is around 38mm or 1.5" the design of the HIF carb is better than the HS4, that you I guess have?

you don't need a HIF44! IMHO, its too big!

[iamweasel]

Cheers mate.
So you'd recommend the HIF 38 over twin 1.25 SUs? Or is that just if I chose the go the HIF route?

Now that you mention it - how does over-carburetion effect performance? Do you just sacrifice fuel economy? I always thought 'more petrol, more power'...

[miniboo]

twin 1.25"'s will be very good for your 998

[Jammy]

The twin 1.25s will be more responsive, and I believe are slightly more torquey, but they are harder to set up initially (and so cost more to tune). They will also return less mpg than the HIF34. If you do go for twins, make sure you get ones meant for a mini. The carb should sit at an angle, with the float bowls either side sitting horizontally.

Dog is right in that you should get the HIF34 over the HIF44 though, if you don't go with twins.

After the carb, if you haven't already got it, get a decent exhaust system, the best for the 998 being the 1.5" RC40 (from MiniSpares or Maniflow), with the freeflow manifold. On from there you can either go for increased ratio rockers (1.3s or 1.5s), a new camshaft or modified head.

[Retro_10s]

i would recommend the HIF38

On verrrry hard cornering you don't get fuel starvation with these, and since you want performance I would go for this, also carbs cannot add 'power' as such, they can only take it away. A nice set of twin carbs would increase throttle response and probably make power very smooth through the revs... But so would an HIF38. And it's cheaper and easier to maintain.

[iamweasel]

Hi guys,
Thanks for all your input - I really appreciate it.
My mini's been with a mechanic recently and he's informed me that my single HS4 is quite badly worn, so it seems a carb change is now more of a necessity than a luxury

I'm gonna have a think about which option to go for: HIF 38 vs twin HS2s.
Fuel economy isn't an issue, as I only really use my car on weekends. Obviously twin carbs will be more expensive to buy, service and setup; so if they don't offer a significant power advantage over the HIF38 then maybe I should go with the HIF. However, if twin HS2s are worth the extra money then I'd rather spend a bit more hmmmmmmm Anyone selling an appropriate carb ?

How does the HIF38 compare with the standard HS4?

Thanks again for your input. After owning minis in south Africa it's such a pleasure to have the resources/parts/expertise that you do in the UK...

[Jammy]

What exactly does he mean by badly worn? You can get rebuild kits from Burlen.

Personally I'd go for the twins if this is an occasional use car you drive purely for fun. You can pick them up on Ebay for between £60-£140.

The HIF38 won't have much, if any performance advantage over the HS4. The main thing is that it has an internal float, which means it doesn't suffer from fuel starvation when going round right hand turns quickly.

If you find anything in the UK, and they won't send to SA, contact me and I'll act as a 3rd person if you want and send the stuff out to you.

Also, for future reference, could you fill out the 'Location' field of your personal information, it would help future advice given to you.

[iamweasel]

Cheers!
He didn't acutally say, where the wear on the carb is. I figure, seeing as I was thinking about upgrading my carb anyway, I might as well just do it now...

Sorry, I thought I had filled in my location. I'm in London - used to live in SA. Thanks for the middle-man offer though

I think the twins are what I'll go for. I've been watching carbs on eBay for a while actually, so I'll probably strt bidding. How important is it to get a set of carbs that were intended for a mini compared with a set from an MG or other BMC car? Are there certain AUD-type numbers to avoid? (eg. AUD69L&R or AUD104L&R) I have no idea what differences these signify

Miniworld have an article on servicing twin HS2s. So maybe it would be a good idea to strip them down first

[Jammy]

Its pretty important. I can't remember who it was who was having real problems with twin carbs. Just couldn't get them set up properly, until someone from ML Motorsport told him the carbs were sat at the wrong angle, one quick angled shim and everything was sorted!

[iamweasel]

interesting... thanks mate!

[iamweasel]

Sorry to ask a question which may seem obvious or may have been answered before, but how come two 1 1/4" carbs will work well on my 998 engine, but one 1 3/4" carb will be too much. Surely two 1 1/4 carbs will produce more air/fuel mixture than one 1 3/4". Or is this not what is implied by "too big"?

I ask this because a mini mechanic in SA once told me that one 1 3/4" would produce similar power AND be a bit more economical that two 1 1/4"s

Thanks again for the previous advice...

Edited by iamweasel, 16 October 2006 - 03:13 PM.

[Jammy]

Its because of how the SU carb works, using a venturi. I don't know exactly how it all works, but my understanding is that the fuel is sucked out the carb using the vacumm of the engine to create a venturi. Now, with a big carb like the HIF38 or HIF44 on a small engine like the 998, the engine doesn't create enough of a vacumm to suck enough fuel through the carb, where as the vacumm can work seperately on each 1 1/4 carb with twins.

This isn't quite correct. A HIF38 will still work on a 998, quite well in fact, but as you can understand, the vacumm can be used more efficiently in the throat of a 1 1/4 carb.

[iamweasel]

oh, so lobbing a bigger carb on the engine doesn't necessarily mean you'll get more fuel in the engine?
Quite the opposite, if I understand you correctly.

Cheers!

[fikus01]

got it spot on!! bigger isnt always better!! according to the vizzard tuning bible with a 1 1/2" su or hif 38 you're not restricting power til 90bhp even on a 1275+ and even then not by much and only at the very top end!!

i think the twin 1 1/4 carbs work better than a single big carb on a small cc engine(or even a big one) because the air speed thru the smaller diameter carb is much higher thus picking up the fuelling and putting it in the cylinders much nicer and in a better mix than a big wide carb taking the air slowly!!

1 of my minis had twin 1 1/4's and a cooper head and it made nearly 72bhp at the crank!! the twins sound nice but are really hard to setup properly!! really needed 2 rolling road setups per year!! 1 for winter and 1 for summer!! it never lost anyting but the sound when i changed it for a single 1 1/2" hs carb!!

Edited by fikus01, 16 October 2006 - 06:56 PM.