Float Setting on SU HD8

E-Type
1

Good Morning Experts,

I have a 1969 XKE Series II originally this car came with dual Stromberg carburetors.

I had this replaced in 1985 with triple SU carbs found on Series one cars and apparently several other cars.

Anyway this car has been in my garage under cover for the last 17 years and would not run for a variety of reasons.

I have been working to reverse this and had the car running very nice, however I noticed that fuel was leaking out of the overflow on carburetor 1 closest to radiator. ( don’t think the position is important potential fire risk is however )

I decide to refurbish the float chamber, so I got new floats and float chamber needle and seat the inlet valve, this time the type which have a ball bearing.

The new fuel valve came with a fiber washer which seemed to be a good idea.

I replaced the parts and the car would not even start, I am like oh crap…

So I decide to put back the original parts and see if that would point to the problem.
I also likely wrongly decided to leave the fiber washer, as the previous parts did not have one.

The car ran very poorly and so I was miffed. After doing some research I see that the exact level of the float is super important.

In the different resources I find it describes setting the float level using a 7/16" rod or drill bit so I decided to take it apart again and check I found that the float was badly adjusted based on this standard and was likely 9/16" about 1/8" larger than recommended or maybe even a bit bigger, it was way off.

I adjusted the float level and that did not help much although the car started. I decided that maybe he fiber washer was adding a dimension to this adjustment and so I removed it I was able to get the carburetors to run and balanced them but they are not running right, certainly not as they were before I started mucking around.

I did more research and find a few people describing a method to set the float and disregarding the standard recommended by the manuals.

Instead do whatever is necessary to get the fuel level set “to just cover the jet when it is fully retracted”

Similar advice was found recommending that “the fuel level is set at 0.120 to 0.200 inches below the bridge” and that “the preferable starting point for the depth of the jet is 0.070 inches below the bridge”.

The other thing I find on this subject is that the float level does not change by itself and so people like me mucking about cause the problem.

Since the carbs on my car were from some other car not sure what advice you can actually believe I do now it was from a Series one Jag anyway.

I also noticed that the three float levers are not all the same. I assume to an expert this may not make much difference but for a novice mechanic like me it is confusing.
I also read on a forum that there are two distinct float lever types one with the axial location offset by 1/8" from the center line of the lever and one a newer type which is in line with the center-line of the lever making the hole for the axial offset by 1/8 inch ! which rang all kind of bells with me.

I am wondering if this is why my float levels were miss-adjusted when I first started this refurbishment process.

That’s basically the story so far…
I would like to proceed confidently and get this right moving forward.

So in review all the original parts which were in there in the beginning are back in there a lot cleaner. the float chamber was adjusted back to the recommended at 7/16 of an inch.

I am planning to try the advice regarding the fuel level relative to the bridge and the starting point of the jet to the bridge I mentioned above.

I would appreciate some additional guidance and or acknowledgment of the advice I found in my research.

Best Regards
Jeff

SU_HD8 float lever.jpg2448Ă—3264 927 KB

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Set your floats at 7/16". Install, start/ run then check your fuel level in each bowl. Re adjust to get the level about equal in all three carbs. Go from there. You can’t set floats looking down the jet.

You can use a caliper to set needle heights in the pistons & jet drop (from the bridge) equally to the .001".
Try .080" jet height, IIRC.) That should get you in the ball park.
Dave

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Good Morning Dave,

I appreciate the prompt reply to my post.

Do you know anything about the two different float fork types and how this might affect the setting?

Best regards
Jeff

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Below is a picture of the two float fork types so you can see what I mean.

The math refers to the typical recommended setting of 7/16 inch

It appears to me that the setting would be different depending on the float fork selected.

Jeff

Float fork XKE SU HD8.jpg1703Ă—1730 2.12 MB

5

For the lever it’s the distance between the large curve and the bit which contacts the needle which you set to 7/16. Since the lids are the same the shape of the pivot end of the lever doesn’t matter.

I know this is a thermo carb, but look at this picture from the Burlen website:

http://sucarb.co.uk/mediafiles/su/tech_su_36a.jpg

Line 21 is the fuel level (it’s drawn lower than in reality).

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I had some trouble with a sticky float valve recently. I read that it’s important to align the fingers that contact the float so that they are precisely horizontal, or else the float and/or float fork might bind up. I found that mine weren’t quite right, although my problem turned out to be something else.

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Yes, I should have mentioned Wobbly Float Syndrome.

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Thanks Andrew and Robert…

I have seen the picture you posted and have been scouring the internet looking for a similar diagram for SU HD8 but no lock so far.

The thread on Wobbly Float looks like it is real interesting thanks !

It illustrates nicely the relationship between the float level and the fuel level at the bridge.

But as Dave mentioned I am not sure how you measure it accurately looking down the Jet

Has anyone ever seen one of these tool called JetSetter?

See below

Best Regards
Jeff

9

Jeff,

You don’t need to measure the fuel level at the bridge. Taking the bells off and looking down the jet tube is a quick and easy way of checking two things:

Are the jets at about the same height?
Is the fuel level in both carbs about the same height?

Taking the float chamber cover off is more bother, looking at the bridge gives you a quick visual check that the carbs are not wildly out of adjustment, and that the floats are more or less right.

I’m a tool junkie (about the only tap I haven’t got is left hand pipe), but the JetSetter looks to be little more than a Vernier that you can’t measure other things with.

Get a Uni-Syn if you want a carb adjusting tool - I’ve been adjusting SUs for about 40 years and I still can’t reliably adjust the balance by listening to the end of a hose.

That cross section diagram applies to the HD8 in terms of general arrangement. The basic function of an SU carb is pretty much the same, there are minor differences, but the HD family is always the same:

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Thank Andrew

I appreciate your advice, nice to speak to an expert

The answer to both of your questions is I am not sure at this point, but I will check.

I will look around for the left handed pipe wrench you are missing and let you know if I find one. :sunglasses:

Best Regards
Jeff

11

Jeff, I agree with Andrew about what you should try to do. That’s why I suggested using a Vernier caliper to set your needle heights in the dampers and getting the jet height all exactly the same. If your fuel level in all 3 carbs is close to equal…then you should be delivering about the same amount of fuel…IF your carbs are flowing nearly the same amount of air.

You may be a bit rich or lean but all 3 carbs should be exhibiting the same characteristics. You’ll be close
Then focus on the throttle shafts, to make sure they all start to rotate simultaneously. The connecting linkages are crude and fidgety to get adjusted just right. But they stay in sync once done.

Like Andrew I can’t set air flow (or SU mixture screws) by ear/hose either. I like manometers, (but I’m a motorcycle guy). I checked my notes I set jets at .080" and at .200" at full enrichment. Needles are set to the groove as per manual, but measured/set equal to the .001. Make sure the fast idle screw doesn’t touch the lever. My notes are dated 2010. Once you get SU’s right you just get to drive. My SU’s are 3.8 versions, FWIW. Good luck.

1 Like
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Hi David,

Thanks for the great information

I appreciate your advice !

Best Regards
Jeff