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Need carburation advice double SUs SH6

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Old Jan 10th, 2019, 04:32   #31
adarvasi
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Quote:
Originally Posted by blueosprey90 View Post
I think Ron will say yes.

See this link, first 3 or 4 pictures. They may help you visualize the situation.

https://sites.google.com/site/fifers...wPrintDialog=1
In addition to everything else that has been mentioned about what might cause the carburetor to overflow, It also may be possible for the fuel pump to have too much pressure. The SU carbs only require about 3 psi of fuel line pressure. If you have an aftermarket fuel pump it might be rated at too high a pressure.

My money (of course, I never bet more than $1) is riding on a leaking float as your cause of overflow. Initially you did not seem to have this overflow problem. My guess is that it took a few days of gasoline sitting in the float chamber for the float to slowly fill with fuel and sink to the bottom - or at least to the point where the float wouldn't rise high enough to shut the needle valve.
Very interesting points, will check both
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Old Jan 11th, 2019, 00:50   #32
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Took both carns out today, they were in a filthy state, and had a surprise, in the manifold connection for the rear carb, there was a piece of folded metal, see picture.
Also the interior of the manifold is quite black, except where I imagine that the fuel flow has kept it cleaner, is this normal?
The piston on the rear carb has some rough edges, is this a problem?
I do not cease to be amazed as the poor maintenance and aberrant things that some people so to their cars, like painting all the carb linckage with aluminum paint.
As usual, grateful for your kind advice.
Andres
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Old Jan 11th, 2019, 06:00   #33
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I think you were very lucky not to have that piece of metal ingested into the engine. Is it a piece that was part of the air filter canister assembly?

Use carburetor cleaner to clean the carburetors as best that you can.

You can try smoothing the piston with 0000 steel wool of maybe 1500 wet/dry sandpaper, but don't mess with the top lip interface between the piston and the dashpot dome. The piston interface is supposed to be machined to match to the dashpot.

https://youtu.be/IfU47Oqq9wA

It almost looks like the black are oil deposits. Does your car have an crankcase ventilation system where there is a hose running from the block to the carburetors.

Last edited by blueosprey90; Jan 11th, 2019 at 06:06.
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Old Jan 11th, 2019, 12:31   #34
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adarvasi;

Remove Foreign Object Debris from intake track (obviously, and check for secondary damage), and clean using carb cleaner and rags, and don't let a little remaining soot bother you too much...you can clean up what looks like a poor casting edge (possibly FOD) at the guide groove in the Dashpot with a file as it is not part of the many other precision machined and matched surfaces of an SU carb**...otherwise observe the rule to remove no metal and USE NO ABRASIVES on any part of the Dashpot or Dome or their Centering Guidetubes...ever!

Notes and recommendations here: http://www.sw-em.com/SU%20Carb%20Service.htm ...take particular note of Contact/Non-Contact area Graphic located there.

** While they are apart, perform 5-7 sec test to check matching. See: http://www.sw-em.com/su_carbs.htm#Da...20of%20Dashpot

Cheers
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Old Jan 11th, 2019, 13:45   #35
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Great advice and info Ron, most grateful for your help.
There is no secondary damage to the intake manifold, the FO was lodged at the entrance, and I remove it as soon as ai discovered it.
The car has a cranckcase ventilation hose from the oil filler cap to the carb
Have a great weekend
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Old Jan 11th, 2019, 14:15   #36
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The guide groove is there to stop the piston rotating but if damaged can cause the piston not to rise and fall smoothly. File with care. The piece of folded metal may well have been causing the fuel flow to be biased into one of that pair of intakes so there may be an improvement in running with it out of the way. Carbs look as if they need a rebuild but the essential thing to look at is how worn the throttle shaft bushes are. If there is any wear at all they really need replacing along with the shafts if you are to get good idle and low speed running, as the air leaks make tuning impossible.
If your engine is a B20 and the breather pipework is all correct the hose from the filter to the cap will be flowing air from the filter into the engine so there should be no problem with oil coming into the engine via the filters. Carb cleaner or cellulose thinners plus an old toothbrush should make the carbs look a lot better. A basic gasket service kit isn't expensive.
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Old Jan 11th, 2019, 14:46   #37
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What is the object indicated in Picture 4?
Attached Images
File Type: jpg carb3.jpg (153.5 KB, 16 views)
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Old Jan 11th, 2019, 15:23   #38
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Arcturus;

...it's the bottom end of screw(4) which holds the anti-rotation pawl(3)...(which incidentally rides in that slot of Damper Piston(12)).

Last edited by Ron Kwas; Jan 11th, 2019 at 15:29. Reason: Edit: Added Graphic
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Old Jan 11th, 2019, 16:20   #39
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Thank you Derek, Monday I am receiving a rebuild kit and new needles (HF) that wre recommended by Joe Curto for higher altitude.
I will carefully clean as best as possible the carbs, change the bushingsand shafts and replace all gaskets.
The metal piece definitely was causing a flow disturbance.
My engine is a B18D.
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