Setting the Float on SU HD8
#1
07-15-2017, 09:37 PM
Setting the Float on SU HD8
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 carb 1 closest to radiator.
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 misadjusted based on this standard and was likely 9/16" about 1/8" larger than recommended.
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
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 carb 1 closest to radiator.
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 misadjusted based on this standard and was likely 9/16" about 1/8" larger than recommended.
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
#2
07-16-2017, 10:41 AM
#4
07-16-2017, 05:16 PM
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