The 'E' Type Forum

Not sure I follow the logic. The carb shouldn’t flood regardless of needle type, or even with no needle or piston at all.

Just sent a message to SNGB as there listing on their webpage does show SC needles....will let you know their response....Steve

Hi Steve,

I contacted already the french SNG Team about that, hope they can change it ...

PeterCrespin wrote: ↑

Thu Dec 12, 2019 3:05 am

Not sure I follow the logic. The carb shouldn’t flood regardless of needle type, or even with no needle or piston at all.

logic is very simple engine and piston movement create a intake under pressure, which generate piston displacement, the thinner is the needles the bigest is the gap with the jet

You are giving a (mixed up) account of how a CV/CD carb works, Pierre. However, your English is better than my French, so it is understandable that you say ‘pressure’ where you should say vacuum or negative pressure/depression.

None of which explains the flooding you said was happening in a non-running engine. For that problem, Christopher gave the full range of common possibilities in post 3

Neither incorrect nor badly-fitted needles have any connection at all with dead-engine flooding. Writing “Not sure I follow the logic’ is just me trying to be nice. Unfortunately, I know more about petroleum than politesse, so I’ll leave you in the capable hands of others. Bonne chance!

Well, please do excuse my ignorance, but I thought maybe wrongly, that with:
1/fuel supply disconnected
2/float bowls full
3/carbs pistons in but with no needles or thin needles
4/choke lever pulled

if you would then try to start the engine you would get enough depression in the carb throats to suck massively the fuel in and get a flooding.
Am I wrong in thinking this way?

Ralph : I agree with you . The whole point of the needles is to restrict flow of fuel sucked up by the venturi effect created by the air flowing between the bridge of the carburetter and the base of the piston . So, the bigger the annulus i.e. the circular gap between needle and jet, the greater the fuel flow and in an extreme case such as this where .100 needles have been fitted in a .125 jet, the greater the propensity for flooding when the engine is cranked over and/or running ( je suis desolee que je ne sais pas le Francais)

I agree too, Ralph. I thought from the first post pictures that Pierre’s engine flooded when stationary, and he’d taken the pistons out to watch it flood when switched on, pointing to pump overpressure or float valve setting or malfunction.

I’ll see myself out
Y

On the subject of floats , don't automatically go for plastic over brass , I've had plastic ones made That are of different weights ( by 50 percent difference )
And this then causes greif with multi carb tuning and a lot of head scratching to work out the problem

Hi Darren....you had plastic ones made?....or plastic ones you purchased had different weights....Steve

Hi they were brand new carbs ( webers ) with one of the 3 carbs float being 32 grams and the other two being 18 grams

So short update, the flooding was due the needles, after receiving the good UM needles from SNG, jet centering and it started up immediately !!!

I took the opportunity for rechecking the needle valves an seats, this is running perfectly. Next action I will replace the facel fuel pump by an electronic lucas one.

Thanks for all the advices

Good progress Pierre.
The Lucas electronic pump is a better choice than the Facet (which you can keep as a spare in the trunk), however you should check the pressure it delivers. Many posts relate excessive pressure tales resulting in needle valves failing to close properly and consequent flooding again.
Fitting a pressure regulator is a valuable recommendation.

Hi All...just heard back from SNGB....they have now revised their web calalogue to show the correct UM needles...Steve

Hi Steve thanks will be better for the next ones !

Hi Ralph, interesting feedback thank you

I am sorry, but cannot see the cause of the carb flooding to be because you have the wrong needle. Having the totally different wrong size needle is a completely different problem. As was said earlier in another post, the fuel level in the jet will be the same as the level on the fuel bowl. That will be set by the height of the float in relation to the shut off needle valve in the float chamber. Have a look at the diagram on the Burlen website of SU carbs for a full explanation.

Question - is MarkRado correct that the fuel level should be 5mm below the jet top when it is 2 1/2 turns down.

Comment - most engine tuners I know say the standard UM needle is too lean. It is too fat further down.

Note: virtually all the 0.125 needles are the same thickness on the top three stations, which are measured in approximately 1/16 of an inch increments from the top. So which ever needle you use the idle mixture will be the same but with needle raised by the piston those are the differences of some lean some rich.
Have a look at the SU needle charts.

John : you do not seem to have realised that these were .100 needles in a .125 jet! The stations were irrelevant because the needle was never going to regulate mixture strength at all ! And the proof of the pudding is in the eating, because with UMs fitted all is now well.

Chris: yes, of course I know the difference between the 0.125 and 0.100. I know I have 0.125 in my HD8’s in my XK120 and 0.100 in the H6’s in my Healey 100. But, the original photo on the forum showed the jets over flooding with no needle. I still maintain my comments about float level and shut off valve is the cause of flooding out of the Jet top in the carb. So, quite surprised the flooding has stopped, unless something is missing from the story ?

I am interested to still get an answer about how far down the jet the fuel should be seen and settle.
MarkRado say 5mm ? Is this correct ? Now you can see why I comment about needle thickness now relevant to the initial problem as described.

My comments about stations on the needles, was not in relation to whether they are 0.100 or 0.125, but my comments further down about the size of the standard UM needle as used on the 3x HD8’s on an E Type.

Hi John...there is no exact measurement to this......as your aware you have basic starting points to set up the carbs then adjust from there.......depending who you listen to you start 2 1/2 turns down(Jag manual).... or 2mm down or 0.06in down then with the piston/needle removed the fuel can be seen down the jet....how far down? I have been told by a very well known SU restorer that with 2 1/2 turns the fuel is approx 5/16 down the jet....I set my carbs initially with this and the car started and run quite well....but then some adjusting needed...useing the standard UM needles.....As far as im aware ideally with the needle fully in the jet the fuel would sit flush with the top of the jet.......are you just trying to discuss this or trying to set your carbs.....Steve