Twin H4 - questions for beginners

[timmy201]

Hi all,

I’m always on the lookout for parts and I’ve seen a couple of sets of twin H4 carbs around recently and had a few questions about them as I’ve never seen a set on a mini here in Aus:

Is there any main advantage to them over twin HS4 apart from them being more period correct for a Mk1?

Do they take the same range of needles as the HS carbs?

Apart from the fuel bowl, what else needs to be done to make them fit a mini?

Are the bodies LH & RH or is it just the position of the fuel bowl that changes?

Is there a specific choke lever that works & most mini engines just use the one choke?

Is the rebuild process about the same as HS carbs?

I’ve seen these 2 sets this week in the range of £100-150. What would be a reasonable price for a set in need of a rebuild? Has anyone ever used a set with 2 x RH fuel bowls like this? These sets both have 1159 fuel bowls, which is just listed as “fuel bowl short” on the Burlen website so I don’t know the angle of them

[timmy201]

Well this answers at least one of my questions - yes you can run 2 x RH fuel bowls
http://mk1-forum.net/viewtopic.php?f=3&t=14899&start=20

[greyghost]

I use a single H4 in my 850

they use the same needles as the HOME SAFE series, you have to remove the self centering bit of the needle (they are all the same under there)
and you will have to centre the needle, the process is the same as for the fixed needle HS2's
the rebuild process is similar

I would just set the choke up on one carb, it will work fine

the fuel bowls are handed, I use an H1 Float in my H4 to stop fuel starvation in hard cornering (pro tip from here, actually) rather than float-bowl extenders

I have lots of bits about in the shed, like a set pair of H1's and H2's, these are hard to get bits for

[timmy201]

So the fuel bowls are handed L & R for a mini but the bodies are all the same? Thats what I seem to have found from all the photos of pairs I've found

[Daz1968]

I fitted a pair from an mga on my mini, I fitted 30 deg bowls although some use the 20 deg ones ok, I also modified the throttle linkage by cutting it down and fitted correct choke levers, also bought the choke bracket from burlen, needles where same as in the hs2 as far as I remember I just fitted ones suitable from spec sheet on this site. Also my set had wrong bowl plungers for a mini so I changed those along with springs.
I also believe they are correct as they use same bolt pattern as hs2 and I don’t think in period a manifold was available for hs4 on mine, also I was led to believe the longer body helps torque. Never tried hs4 so can’t compare,
I just wanted them because I think they look better.

[timmy201]

Thanks Daz. That all sounds great, I like the look of them too and it's nice they were a period modification.

I was offered some H4 carbs from a fellow forum member (thanks Bill B). There is a pair of stripped AUC6020 bodies which I believe are the normal H4

IMG_5623.jpg

There is also a set on a manifold which are very similar to the H4 but slightly different. The bodies are stamped AUC7040 and 4031/. The main difference externally is the vent holes, which are not on the front air filter face. Would these just be an older version of the H4 or something different?

IMG_5631.jpg

The ones on the manifold are also about 1/4" longer & have a different top side. The damper and dashpot appear to be interchangeable and share the same bolt pattern

IMG_5636.jpg

Interested to see if anyone has seen this type before?

[mk1]

Is there any main advantage to them over twin HS4 apart from them being more period correct for a Mk1?
A little bit. In most applications people find that the longer body of the H4 gives a little more low end grunt. Whether you would ever notice this in the real world is questionable.

Do they take the same range of needles as the HS carbs?
Yes, needles are compatible across the range. As has already been said occasionally you may end up with a sprung needle & you will have to remove the spring & base before fitting

Apart from the fuel bowl, what else needs to be done to make them fit a mini?
Nothing

Are the bodies LH & RH or is it just the position of the fuel bowl that changes?
Yes & no. there is a threaded choke fitting on the right hand carb. On the left hand one, there is a boss, but it isn't drilled.

Is there a specific choke lever that works & most mini engines just use the one choke?
There are a few that work. My favourite is AUC4823, but others like the AUC4648 will work just as well. It is always better to use both choke levers, but the pull on the cable can be VERY HEAVY! My preference nowadays is to use both levers with a "T" handle choke cable. But if you want to retain the standard choke cable then you are probably better off using a choke on one carb. BUT IT WILL BE HARDER TO START.

Is the rebuild process about the same as HS carbs?
Yes. The centring of the jet is MUCH more difficult & will take you a few attempt for each carb. Where as sorting the linkages & choke out is a lot easier. I have done 100's & find the whole process quite relaxing.

I’ve seen these 2 sets this week in the range of £100-150. What would be a reasonable price for a set in need of a rebuild? Has anyone ever used a set with 2 x RH fuel bowls like this? These sets both have 1159 fuel bowls, which is just listed as “fuel bowl short” on the Burlen website so I don’t know the angle of them

If you can get a decent set for 100 - 150 you are doing well. All LHD cars have 2 Right Hand float bowls, or should have. I have no idea what the bowl is.

Finally. Don't get too hung up on finding 2 x 30° float bowls. They are very expensive or hard to find & the much more common 20° ones work JUST AS WELL!

[timmy201]

Thanks for the detailed response Mark!

I don’t suppose you had any idea on the set above on the manifold?

[mk1]

Can't really comment on them, as they are just a pair of H4's. As long as they are not corroded or very warn, they will almost certainly be fine.

[underkut]

Has anyone fitted or tried to fit a pair of HD4s onto a mini?(stupid question , someone would have for sure) but i see these come up quite often sub £100 and wondered if there is any reason why they are relatively cheap , if they could be used on a mini.
cheers

[mk1]

They "could" be used on a Mini. But most people go for the H4 as it's the carb that was used by the famous race & rally cars of the 60's. There could also be a clearance issue between the bottom of the carb & the bulkhead.

Rather than use HD4 carbs, you'd be better off going for a good old pair of HS4's.

[underkut]

Thanks Mark
I am currently running a 45 dcoe but on my old mk 1 i had H4s and obviously easier to set up , but looking at the Hd4s i thought there could be a couple of quid to be made , but i think i will stay well clear.
thanks for your advise (as always)

[timmy201]

I was missing a few parts from the carbs I had, like a fuel bowl lid, choke linkage and the brass damper caps. I found these on eBay today and made an offer (eBay also had a $5 voucher for some reason) and I managed to get them for $75 (40 GBP). I'm hoping this should leave me with sufficient parts now to make up one good set!

[mk1]

BARGAIN!

[timmy201]

Thanks Mark, it was a good score on eBay for a change. They had a pretty generic title so it was lucky I found them

Is there any other general advice for stripping them down and checking for wear in the throttle shaft? When they are assembled they seem nice and tight but obviously this will need a closer look once pulled apart.

I’ve got a set of T2 and T3 floats, is it worth swapping to the smaller floats like the historic racers use?

[mk1]

It is very rare to find a set that don't have worn spindles. They ALWAYS benefit from new bushes. These can be done at a reasonable cost by a firm like SUMidel in Aus. https://www.sumidel.com/

Me in the UK or Joe Curto in the states.

[timmy201]

It is very rare to find a set that don't have worn spindles. They ALWAYS benefit from new bushes. These can be done at a reasonable cost by a firm like SUMidel in Aus. https://www.sumidel.com/

Me in the UK or Joe Curto in the states.

Ok thanks Mark.The newest set I bought seem OK, one spindle isn't worn at all but the other has some slight wear. I bought a full rebuild kit from Midel, the new teflon bushes don't seem to be that tight of a fit, do they shrink up a bit once you press them into the carb body?


My collection of them has grown! Is there a guide on how much to modify the standard manifold to suit the H4?

Little things left to sort out now, like the throttle and return springs, and find the missing choke parts.


Interestingly I have a R/L pair of 30 degree T2 bowls, I wonder what they would have come from originally?

[mk1]

I don't use the teflon ones, I use the bronze ones supplied by Joe Curto.

[Peter Laidler]

I have machined the 1/4" dia shaft at a point half way through the bushes and inserted neoprene O rings. Rubber greased shaft outboard of the neoprene rings. Shafts are absolutely air tight, the minutest bit of extra friction but a perfect fit.

[LuisM]

Resurrecting this topic with a question,
in most of the cases I see H4 sets in mini applications using throttle return springs similar to the ones from HS carbs ( a shaft lever and long spring pulling from an anchor point ), but MG , Volvo H4’s use shaft fitted springs ( similar to HIF carbs ).
Any reason for this ? Or just availability/cost of parts ? As a shaft centric spring should cause less shaft wear .

Thahks
Luís