5 replies to this topic

[grizzler73]

Hi Guys

I'm looking at getting a set of Twin 1.5" SU's in either H4 or HS4, can I buy 2 singles and build a set of twins out of them?

This is for a rear engined GTM so don't need the angled float or any of that stuff. Twin 1.5" SU's are so expensive these days!

 

Cheers

Simon

Edited by grizzler73, 07 December 2021 - 01:33 PM.

[Gilles1000]

There is one guy in Germany building a Broadspeed GT replica, and I think he is using two single H4s as for the LHD the brake master cylinder comes in the way of the fuel bowl.

[imack]

My twin hs4's are built from a pair of hs4's I put together in the late 80's.
It wasn't easy even then to find a left hand and right hand carb.
Linkages and cupped bolts are shortened twin hs2 ones. Still on the car today.

[coopertaz]

anything is possible but carbs are handed, can buy adaptors for float bowl for corrct angle seperately

[timmy850]

The bodies on H4 carbs are essentially all the same, and you just change the fuel bowls to be LH or RH. If you were using them without angled fuel bowls then you could simply flip them 180 degrees

[mvahora]

Hi Guys

I'm looking at getting a set of Twin 1.5" SU's in either H4 or HS4, can I buy 2 singles and build a set of twins out of them?

This is for a rear engined GTM so don't need the angled float or any of that stuff. Twin 1.5" SU's are so expensive these days!

 

Cheers

Simon

 

I've just gone through this so can help, 

 

You can pair them but you will have to thoroughly inspect each carb to determine exactly what vehicle it came off (in the absence of identification tags). Either way I would still suggest opening them up and having a look at every part in them. Likely that someone down the line had changed something incorrectly. Likely that parts will be worn as well.

 

Your need to baseline/match/refurb them first in order to get them close to factory conditions. You need to be careful. 

 

Open each carb and read the codes on each item (dashpot, piston, damper, needle, springs, jets, body's, float bowls, float bowl lids etc.) Then email Burlen the codes and they will advise what vehicle the carbs originally came from. This will allow you to know the correct replacement parts to purchase if any, and any incorrect parts that are inside. 

 

For example your findings may tell you that you have a front and rear hs4 from an MG Dolomite. One from 78, one from 79. Burlen will tell you the original identification code of the entire unit (e.g. FZX3001) and with that information you could use their SU manual handbook to find exactly what parts should be in each of your particular carb. 

 

Within each individual SU carb there are both generic parts which can be mixed and matched e.g. carb body, as well as carb specific parts such as the needles, jets, dampers etc. which should not be different or mixed.

 

Then when paired with another carb; certain parts in both carbs will need to match. For example on Twin HS4s; both dampers should be AUC8114s however some single HS4s come with AUC8103s. So you would need to purchase AUC8114s if one (or both) of your HS4 carbs have an AUC8103.

 

You want them to work for their intended purpose. Otherwise you'll end up having worn, out of sync, mismatched hs4s with mismatched parts within each carb. And you don't want to go down that road at all.  

 

Do the drop test on each piston and dashpot to see if they are worn. E.g. HS4s should drop between 3-6s according to the David Vizards yellow manual and others. In the case of twins you would want them both dropping at almost the same rate. I've seen some that drop in 1s which indicates a unsalvageable dashpot or piston (you would have to check which one it is by swapping the piston into another dashpot). If its drops in 1 or 2 seconds it cannot be used. I've seen people put them on their minis without knowing and then have constant issues with tuning. You will also need to check the floats, as well as the needle valves, best to change them over to the new black floats with the Viton tipped valves. 

 

You can use burlens twin hs4s full refurb kit to service them both. You will also need to purchase any other generic or specific parts required to bring them up to spec and match them as a set. You will also need all the linkages etc.

 

If the carbs are dirty and you want to clean them make sure to use a proper carb cleaner. NEVER grind or sand the internals e.g. inside of a dashpot or piston or you will ruin them. 

 

There is a good video series on youtube:

 

 

Hope that helped

Edited by mvahora, 13 December 2021 - 04:45 AM.