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SU HS4 plastic floats


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For reasons best known to the DPO my Vitesse has been fitted with, what I believe to be, the manifold and SU HS4 carbs from a 2000 saloon or similar.

Now being at the stage of coaxing the beast back to life, I managed to get her started briefly until the rear carb dumping fuel out of the float chamber overflow stopped play.

Tonight I whipped off the float chamber lids to clean out the needle valve assemblies. Now, up until now, I have only ever worked on one carb at a time but, as there looked to be no danger of mixing up the front and rear assemblies as their fuel pipe arrangements are different, I had both on the bench side by side.

As you can see from the photos the float heights are significantly different front to rear.

The front float is the one with the extra hole close to the pivot pin. Apart from this hole all the other dimensions seem to match the rear float. The needle valve and its seat also are identical which only leaves the cover castings / pivot point. As an experiment I swapped the floats over and the heights remain the same.


Does anyone know if float height should be different front to rear?

I could see no way of adjusting the float height on these plastic floats. Does anyone know differently?

Is this discrepancy in float height anything to be worried about?






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Flooding often due to small wear marks on the float needle contact platform which will jam , look very closely they can lead you on a right song and dance contiually flooding,


the only way to adjust these orrible floats is to add washers under the needle .or fine file material off the float


I have a avid hate of these carbs and now have a 2000 with hs4 on pah !


there are coments around about fuel heights front to rear being diferent but I have never found any clies to back these ideas up,

the manuals give same fuel/float heights on front and rears to be the same

burlen do sel stay up floats supposed to be more reliable with modern fuels

having said that I have never come across a car yet with any ethanol degradation


it took a pair of new floats to stop su flooding on my 2000 the only visible change was the wear from needle contact,


of you lightly fettle the pad you change the height a lot ,finding a sealing washer thin enough to reset the heights is unlikley ... new float was the only compromise

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I came across a post on some website a while back re different float bowls front and rear on the vitesse/gt6 engine set up with SU carbs. The reason given is because these engines are not mounted horizontally (lower to the rear) and as the front bowl is forward of the carb body and the rear bowl is rearward the fuel levels at the jets, if all else is equal, will be different. (higher at the front jet and lower at the rear). Using a different bowls front and rear (I don't have the part numbers to hand but could look them up if needed) will level things up. 



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Hello Keith.


If you do go down the route of new floats (certainly worth considering), it will be worth your time giving Burlen Ltd a buzz to discuss your situation.


The link shows the new style floats on offer by the company and of course benefit from being ethanol proof / resistant.


Good luck.





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Thanks all for your replies.

DJN you are correct. On closer inspection I can see that the float bowls are different on both carbs. The mounting to the carb body is lower down the side of the bowl on the rear carb compensating for the engine angle. The float bowl covers appear identical and both covers have the same casting number.

As suggested by Pete and Richard, I have been in touch with Burlen and obtained a couple of 'Stay Up' floats. These arrived in Bonnie Scotland the very next day, a very impressive service. I fitted them today and set the float heights as per their instructions.

Things look encouraging, car is running and the petrol is staying in the float chambers.... so far!

Thanks again,



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