HD8 carb issue

Technical advice Q&A
User avatar

PeterCrespin
Posts: 4334
Joined: Fri Mar 05, 2010 8:22 pm
Location: Gaithersburg, Maryland.
Contact:
United States of America

#21 Re: HD8 carb issue

Post by PeterCrespin » 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.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

MarkRado
Posts: 280
Joined: Fri Jan 26, 2018 9:13 am
Location: Graz
Austria

#22 Re: HD8 carb issue

Post by MarkRado » Thu Dec 12, 2019 4:25 am

:yeahthat:
Mark
1963 OTS 880436

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

mgcjag
Moderator
Posts: 5568
Joined: Fri Jul 09, 2010 6:15 pm
Location: Ludlow Shropshire
Great Britain

#23 Re: HD8 carb issue

Post by mgcjag » Thu Dec 12, 2019 9:01 am

Just sent a message to SNGB as there listing on their webpage does show SC needles....will let you know their response....Steve
Steve
1969 S2 2+2 & Building a C type replica

Link:
BBcode:
HTML:
Hide post links
Show post links


Topic author
cooper66
Posts: 75
Joined: Thu Jul 25, 2013 9:39 am
Location: France
France

#24 Re: HD8 carb issue

Post by cooper66 » Thu Dec 12, 2019 8:24 pm

Hi Steve,

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

Link:
BBcode:
HTML:
Hide post links
Show post links


Topic author
cooper66
Posts: 75
Joined: Thu Jul 25, 2013 9:39 am
Location: France
France

#25 Re: HD8 carb issue

Post by cooper66 » Thu Dec 12, 2019 8:52 pm

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
Pierre

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

PeterCrespin
Posts: 4334
Joined: Fri Mar 05, 2010 8:22 pm
Location: Gaithersburg, Maryland.
Contact:
United States of America

#26 Re: HD8 carb issue

Post by PeterCrespin » Fri Dec 13, 2019 2:54 am

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!
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

ralphr1780
Posts: 967
Joined: Wed Apr 11, 2012 4:29 pm
Belgium

#27 Re: HD8 carb issue

Post by ralphr1780 » Fri Dec 13, 2019 10:10 am

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
'69 OTS + '62 OTS - Belgium

Link:
BBcode:
HTML:
Hide post links
Show post links


christopher storey
Posts: 4886
Joined: Sun Mar 09, 2008 3:07 pm
Location: cheshire , england
Great Britain

#28 Re: HD8 carb issue

Post by christopher storey » Fri Dec 13, 2019 2:25 pm

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)

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

PeterCrespin
Posts: 4334
Joined: Fri Mar 05, 2010 8:22 pm
Location: Gaithersburg, Maryland.
Contact:
United States of America

#29 Re: HD8 carb issue

Post by PeterCrespin » Sat Dec 14, 2019 2:23 am

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 :oops:
Y
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

Link:
BBcode:
HTML:
Hide post links
Show post links


dal2.0litrefrogeye
Posts: 975
Joined: Fri Aug 06, 2010 10:48 pm
Location: sarf london
Contact:
Great Britain

#30 Re: HD8 carb issue

Post by dal2.0litrefrogeye » Sun Dec 15, 2019 12:43 pm

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
Its a way of life not a hobby
Darren . 64 4.2 modded 69 4.2

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

mgcjag
Moderator
Posts: 5568
Joined: Fri Jul 09, 2010 6:15 pm
Location: Ludlow Shropshire
Great Britain

#31 Re: HD8 carb issue

Post by mgcjag » Sun Dec 15, 2019 1:58 pm

Hi Darren....you had plastic ones made?....or plastic ones you purchased had different weights....Steve
Steve
1969 S2 2+2 & Building a C type replica

Link:
BBcode:
HTML:
Hide post links
Show post links


dal2.0litrefrogeye
Posts: 975
Joined: Fri Aug 06, 2010 10:48 pm
Location: sarf london
Contact:
Great Britain

#32 Re: HD8 carb issue

Post by dal2.0litrefrogeye » Sun Dec 15, 2019 7:21 pm

Hi they were brand new carbs ( webers ) with one of the 3 carbs float being 32 grams and the other two being 18 grams
Its a way of life not a hobby
Darren . 64 4.2 modded 69 4.2

Link:
BBcode:
HTML:
Hide post links
Show post links


Topic author
cooper66
Posts: 75
Joined: Thu Jul 25, 2013 9:39 am
Location: France
France

#33 Re: HD8 carb issue

Post by cooper66 » Sun Dec 15, 2019 8:33 pm

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
Pierre

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

ralphr1780
Posts: 967
Joined: Wed Apr 11, 2012 4:29 pm
Belgium

#34 Re: HD8 carb issue

Post by ralphr1780 » Mon Dec 16, 2019 9:41 am

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.
Ralph
'69 OTS + '62 OTS - Belgium

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

mgcjag
Moderator
Posts: 5568
Joined: Fri Jul 09, 2010 6:15 pm
Location: Ludlow Shropshire
Great Britain

#35 Re: HD8 carb issue

Post by mgcjag » Wed Dec 18, 2019 3:23 pm

Hi All...just heard back from SNGB....they have now revised their web calalogue to show the correct UM needles...Steve
Steve
1969 S2 2+2 & Building a C type replica

Link:
BBcode:
HTML:
Hide post links
Show post links


Topic author
cooper66
Posts: 75
Joined: Thu Jul 25, 2013 9:39 am
Location: France
France

#36 Re: HD8 carb issue

Post by cooper66 » Sat Dec 21, 2019 7:51 am

Hi Steve thanks will be better for the next ones !

Hi Ralph, interesting feedback thank you
Pierre

Link:
BBcode:
HTML:
Hide post links
Show post links


John ball
Posts: 26
Joined: Thu Jan 23, 2020 4:34 pm
Great Britain

#37 Re: HD8 carb issue

Post by John ball » Fri Jan 24, 2020 5:47 pm

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.
Jaguar XK120 FHC and Healey 100

Link:
BBcode:
HTML:
Hide post links
Show post links


christopher storey
Posts: 4886
Joined: Sun Mar 09, 2008 3:07 pm
Location: cheshire , england
Great Britain

#38 Re: HD8 carb issue

Post by christopher storey » Sat Jan 25, 2020 9:23 am

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.

Link:
BBcode:
HTML:
Hide post links
Show post links


John ball
Posts: 26
Joined: Thu Jan 23, 2020 4:34 pm
Great Britain

#39 Re: HD8 carb issue

Post by John ball » Sat Jan 25, 2020 1:22 pm

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.
Jaguar XK120 FHC and Healey 100

Link:
BBcode:
HTML:
Hide post links
Show post links

User avatar

mgcjag
Moderator
Posts: 5568
Joined: Fri Jul 09, 2010 6:15 pm
Location: Ludlow Shropshire
Great Britain

#40 Re: HD8 carb issue

Post by mgcjag » Sat Jan 25, 2020 2:23 pm

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
Steve
1969 S2 2+2 & Building a C type replica

Link:
BBcode:
HTML:
Hide post links
Show post links

Post Reply Previous topicNext topic