17 replies to this topic

[tractor]

Hi all I’ve read the thread in FAQ about identifying what carb I have http://www.theminifo...0

It turns out I have a HIF carb, I measured the throat size and its 1 inch and 7/8 in diameter so a HIF7

Here it is









I have a 1275 engine that’s in standard spec with a stage2 LCB manifold and an 1.75 maniflow twin box side exit exhaust.

So is this carb too big for this spec? I do want to upspec the engine at some point in the future it’s just the budget didn’t allow me to do it this time round so is it a case of maybe putting a “thicker”? needle in the carb and when I come to up spec the 1275 (which won’t be anytime soon) I can just change to a finer needle, or am I better off shelving the whole carb until I upspec the motor?

In which case what size carb should I be looking for?

Thanks
Trac

Edited by tractor, 31 October 2012 - 11:11 AM.

[Tommyboy12]

Its basically one step up from a HIF44 which is pretty common on Minis. Thats a 1 3/4".

I would say its probably 'slightly' excessive with a pretty standard engine but I wouldnt say its a basis to bin it.

[Woreign]

I'm glad you posted a photo, as I have the same carb! It came with a doner engine and I was wondering what it was and it was used on?

And is it worth keeping for a Mini application, or would it be better for another make/model?

[Skortchio]

I'm glad you posted a photo, as I have the same carb! It came with a doner engine and I was wondering what it was and it was used on?

And is it worth keeping for a Mini application, or would it be better for another make/model?

All HIF carbs look alike, to know which size you have you need to unscrew the manifold on the end (2 nuts, easy peasy) and measure the hole.

38mm - HIF38
44mm - HIF44

Simples.

Onto the big boy:

An HIF7 is too big for damn near any mini engine, if we're talking optimums.

I can't find the reference now but it's roughly, HIF38 is good for about 65-70bhp and after that you should move to a 44 (only regarding HIF models here, not other carbs) for optimum results up to way beyond 120bhp. Around the 65-70bhp mark the 38 becomes too restrictive, choking the flow into the engine.

An HIF7 would give the opposite result, it will work. But you'll probably notice low end losses as the intake velocity is low due to the large diameter.

*Edited for clarity.

Edited by Skortchio, 31 October 2012 - 05:39 PM.

[tractor]

ah glad i asked now thanks skortchio, just had a quick look on ebay and prices vary but don't seem too bad

will i need to change the inlet manifold as well?

I'm glad you posted a photo, as I have the same carb! It came with a doner engine and I was wondering what it was and it was used on?

no worries wasn't too long ago i was new to all this and photgraphs helped loads :)

[Skortchio]

If you unbolt the manifold from the carb and measure the inlet size, again 44mm would be the normal. I'm not sure if there's larger models available, only know mini bits

May be worth throwing up a wanted ad on here for a 38 or 44 carb, eBay can be great but if the carb is a bit worn you might need another £40-50 of rebuild kit to make it work sweet.

Alternatively for the meantime you can use the HIF 7 with a correct needle, it won't be ideal but it will work, as Tommyboy says.

[smartie93]

I'm glad you posted a photo, as I have the same carb! It came with a doner engine and I was wondering what it was and it was used on?

And is it worth keeping for a Mini application, or would it be better for another make/model?

All HIF carbs look alike, to know which size you have you need to unscrew the elbow on the end (2 screws, easy peasy) and measure the hole.

38mm - HIF38
44mm - HIF44

Simples.

Onto the big boy:

An HIF7 is too big for damn near any mini engine, if we're talking optimums.

I can't find the reference now but it's roughly, HIF38 is good for about 65-70bhp and after that you should move to a 44 (only regarding HIF models here, not other carbs) for optimum results up to way beyond 120bhp. Around the 65-70bhp mark the 38 becomes too restrictive, choking the flow into the engine.

An HIF7 would give the opposite result, it will work. But you'll probably notice low end losses as the intake velocity is low due to the large diameter.

I'd say the problem would be fuel drop out rather than the actual air flow.

Going based on air alone it could be argued that a larger carb would increase the volume of air and therefore the mass of air in the intake. A greater mass would mean a greater momentum. This means at low engine speed the air continues to be drawn in (as it doesn't want to stop) despite the piston reaching BDC, increasing volumetric efficiency and therefore torque.

At higher RPM, the larger mass would also increase inertia. so the air would resist the fast acceleration needed to properly fill the cylinder at high engine speeds, reducing volumetric efficiency and torque.

But obviously this only works if you can get the fuel in in the first place :)

[dklawson]

I have never heard of an H7, HS-7, HIF-7, or the metric equivalent (HIF-48?).
Some large displacement early Jaguars used H8 carbs so there should be H8, HS8, and perhaps even HIF-8 carbs. Regardless, not very practical on even the biggest A-series.

[ACDodd]

You are measuring the wrong end. (see Skortchio answer)

The HIF44 does measure about 1 7/8" at the air filter end. The size is taken from the butterfly end. I think you will find this as 44mm.

AC

[tractor]

sorry guys you have one free pass to call me a goon, i was convinced i measured the engine side of the carb before i assembled it but when you mentioned the butterfly i questioned if i actually did.

just out here now and separated it from the manifold and it turns out i've got a hif6 1"6/8, is there any difference between this and a hif44 other than the 0.5mm throat size?

while i'm here whats the best way to take the needle out and check which one i've got? i'm guessing it'll be stamped on there some where

thanks
Trac

[Skortchio]

Needle out is by unscrewing the dashpot (shiny dome bit) by it's 3 screws, then lifting it off. You'll see the needle on the bottom of the cylinder as you lift it up.
On the side of said cylinder is another screw, undo this and then you can pull (with a little effort) the needle and it's small housing gizmo out.
The name should be stamped on the needle itself, at the thickest end.

[tractor]

quality thanks skortchio, done that and it came out relativly easy,

it's got B.D.L stamped around the thicker end, thats not a code i read about before whilst glancing over various other topics, what kind of needle is it? hopefully it'll be standard

Trac

[Skortchio]

There's no such thing, fella.

The needle code relates to it's profile, the shape of it. They're all of course thin at one end and thick at the other, but depending on engine it's attached to (and the air intake attached to it) will govern what shape it should be at it's 16 points or stations.

BDL is a pretty baseline needle. Stock ish 1275 engine, exhaust and K&N type thing.

The only way to get the absolute right needle is via a rolling road / dyno / AC Dodd tuning session, where they will reshape the needle to match the requirements of your engine.

Although, if you know roughly how your engine is running you could use something like:

http://www.mintylamb.co.uk/suneedle/

To compare different needle options but it's no comprimise for an expert job.

Something important to know, is that the mixture screw on SU carbs only effects the idle mixture anything else is needle.

Edited by Skortchio, 31 October 2012 - 09:59 PM.

[tractor]

awesom thanks skortchio, at first i thought yo menat there was no such thing as a BDL needle but i see what you mean theres no such thing as a standard needle.

i do plan on getting a rolling road seesion booked when the project is finshed and mot'd so i'll stick with what i've got untill then.

just googled ac dodd tuning, i've never heard of them before and they're bit of a treck for me but if they come recomended it'll proberly be worth the road trip

Thanks again for your help - this forum is brillaint how did novices like me do projects before the internet?

trac

[Skortchio]

Dude, he posted on this thread!

He's a legend, a real mini guru and damn helpful to boot! Ask him about his camshafts

Haha!

Edited by Skortchio, 31 October 2012 - 10:20 PM.