BJ8 Float Level

[saltiga]

When having set the float needle with the rod and assembled the float chambers, is it possible to check them by removing the piston cover and piston? With these removed, turn on the ignition, then lower the main jet with the choke lever, the fuel level can be observed, in the jet hole. Does anyone check this way and if they do, how far down is the level from the top of the jet outer sleeve? This is assuming the vehicle is on a level plane. Saltiga

[steveg]

Ignition should be off, as you don't want the fuel pump running.

There was a previous thread discussing this.

I tried it and was not able to tell exactly where the level was inside the jets. You can also remove the floats and observe with a caliper how far down the fuel level is in the float chambers. It should be as close to identical as you can get it.

[ozhealey]

Saltiga,

This topic generally draws out many opinions and is something I worked on for a long time to determine what worked best for me.

I have rebuilt my SUs in my many British cars a number of times and also had the “experts” to a full rebuild. Assuming the carbs are in good condition with no air/vacuum leaks, then tuning them and setting the fuel level is a pretty simple prospect.

To check or “set” the fuel level in the carbs I usually do the following (fuel level only, I’m not going to go through the whole setup of the carbs):
I have been told by many experts and passionate helpers totally conflicting information. However the best advice I ever received which has worked very well for many years is that regardless of everything else, the height of the fuel in the jet tube of the carburettors MUST BE THE SAME. This “may” mean the fuel bowl floats need to be set slightly differently to achieve this result.
(1) First follow the manual to set the float gap for the level of fuel in the bowls.
(2) When everything else is done, remove the carb tops, springs and pistons/needle.
(3) Turn on the ignition until the fuel pump stops the turn the ignition off.
(4) Observe the height of the fuel below the top of the bridges. THEY NEED TO BE THE SAME. If not, remove a fuel bowl lid and adjust one of the floats until you get the same level of fuel in the jet.

I am not sure if there is a “factory” setting, however I usually set mine to 4-5mm below the bridge as this was the advice from a very old guru. I usually use the choke to pull the jets down until they are at the level of the fuel. That way I can measure the height easier.

Over the years I have found the fuel bowl settings being the same does not always result in the same level of fuel in the jet. When I finally received the advice to adjust the floats as necessary to get the same height in the jet tube, tuning became significantly easier and my mixture settings tend to me much much closer to each other as a result.

This is only my own experience, there will be many others.

Cheers
Tony

[steveg]

Tony - thank you for the clarification!

I especially appreciate the suggestion to pull the chokes down the 4-5mm and adjust the fuel to that. That takes care of not seeing the fuel level down in the hole!

[red57]

Tony, I'm with Steve, thank you for a very clear description. I'm embarrassed to say that I routinely glance at the fuel height in the jets....but I never considered adjusting the floats to make them the same, relying simply on 7/16". Great trick and it matches my take on everything to do with multiple carbs - everything must be the same to our best ability. thanks again.
Dave

[saltiga]

Oz Healey Thanks for the information its exactly what I was looking for. Saltiga

[Michael Oritt]

I don't understand why the float bowls were not made with sight-glasses built into them so we could see the level of the fuel without having to take off the caps.
I also don't understand why distributor caps were not made out of a clear material so we could see what was going on inside--arc'ing, etc--while the engine is running.

I have several other Great Ideas for which I will be happy to release all rights for no consideration to anyone who wants to run with the ball.

[steveg]

Long as we're wishing, I'd like to wish for an adjustment screw for the float level so we could tune it to a gnat's eyebrow inside the jet tube per Tony OzHealey above.

[Michael Oritt]

Steve--

Just think of the fortune we can make with our New Improved SU's!

[steveg]

Healey tweaks - a get-rich scheme if I ever heard one!

[steveg]

Didn't want to trust the chokes to pull the jets down the exact same amount, so I used the mixture screws to lower each jet to 3/16" (.1875"). Seems counter-intuitive, but I had to bend the float arm upward to raise the float in order to lower the level in the jet. Was able to get them both to look like this. Blowing on the fuel further helps to make sure both levels are the same.

JetFuelLevelCloseup.jpg

[John Turney]

At first glance, that looks like an alien eyeball.

[tahoe healey]

That jet setting looks way low to me.

[ozhealey]

Tahoe Healey,

I suspect Steve simply lowered the jet using the mixture screws to set the height of the fuel as I indicated in my discussion above. I’m sure he then adjusted the jet height back to achieve the correct mixture setting for his car.

Cheers
Tony

[steveg]

Apologies for lack of clarity. Tony is correct. After setting the floats for equal fuel level in the jets at .1875", I raised both jets back to .082"

[Legal Bill]

This is very interesting. I don't think I have ever done any of this. I always relied on setting the float height and that was that. I imagine this allows you to set the jets almost the same on both carbs.

[steveg]

In Feb 2018, in a thread: "Cold Start Problems", Martin Jansen, "Frameman", wrote:

".... On BJ8 carbs, the manual says to set float levels at 7/16ths, reset them at 5/16ths which will raise the fuel level in the float bowls. Next check to see if jet needles are located properly and make sure they are both set at same height, with the slides out look down into the jet orfis. Look at the fuel level , it should be 1/8 to 3/16th of an inch off the bridge of the carb body where the jet fits. The jet should be 1/16th of an inch from the carb body. I just finished doing a car that would not start in 60 degree weather after I did this fix the owner said he started the car no problem in -30 c. I have done this to many cars with complete success. Then tune carbs accordingly."

I can confirm this. When I adjusted my floats to give the 3/16" fuel level in the jets, as advocated by Tony "Ozhealey", the resulting float level is 5/16", not 7/16".

In addition, with Tom Bryant's line bored delrin bushings, the slow run screw becomes functional, allowing a range of idle adjustment without the previous cracking of the butterflies.
NFI. https://thosbryant.wordpress.com/cat...u-carburetors/

I have to conclude there was previously a little air leakage with my new stock bushings installed last year.

Where we differ is my jets are set to .083" down vs his at .0625" (1/16")

[John Turney]

Just a follow up on this thread, which I have printed out and saved in my SU tuneup files.

Although my float levels in both HD8s were the same at 7/16", the fuel levels in the jets were way different. The rear one was at about -0.191" below the top of the jet, but I couldn't see the level in the front one. The initial measurement was made using the depth gauge on the vernier caliper, but not lowering the jets.

After several tries, I ended up setting the rear float to 5/16" and the front float to 1/4". The fuel level in both is now 5 mm (-0.196"). These measurements were made by lowering the jets to -5 mm and adjusting the float levers so the fuel level was even with the jet. (See Steve's photo above.) After setting the fuel levels the same, I raised the jets back to -0.090". Having the fuel levels in the jets does make the rest of the tuneup go smoother and the idle is much better at ~700 RPM. It will even idle as low as ~300 RPM, but that's too low.

In summary - make sure the fuel level in both (or all) jets is the same. Although it seems like equal levels would result from having the same level in each bowl, it doesn't necessarily work out that way.

[Bob_Spidell]

"Although my float levels in both HD8s were the same at 7/16", the fuel levels in the jets were way different."

I'm curious as to why the fuel level in the jets would be so different if the fuel levels in the bowls are (presumably) the same. I suspect that violates some law of physics or hydraulics.

[steveg]

Bob - I'm with you - it's some kind of magic or cargo cult...It's amazing how complicated SUs really are!! Adjusting my float levels so the jet fuel level (per blowup pic above) is at 3/16" - I wound up with float levels at 5/16". Lucky me - both the same.

I also had a number of brass floats between my 2 original HD6s and my 3 HD8s - previous to the above adjustments, I weighed all the floats and picked two with identical weights.

I bought a 250ml graduated cylinder and some syringes with tubes - but haven't yet checked the float chamber volumes, which should be identical.

Still running the above setup. When I get my EGT probes installed , will be in a better position to go even further down the rabbit hole!

My jets are down approximately .060" at present as that shows values I like in my AFR gauges.

More to come.