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Need carburation advice double SUs SH6

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Old Dec 31st, 2018, 13:08   #11
Derek UK
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I see where you are going there but you still need the dampers in place when balancing the flow. Once the flows are equal you shouldn't need to redo that for a LONG time. Adjusting the mixture via the jets comes afterwards and should really be done with the filters on.
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Old Dec 31st, 2018, 15:32   #12
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For me, the beauty of my system for adjusting the fuel mixture (measurement of the jets) when applied to the Volvo is that you don't need to remove the air filters.

To be honest, I developed that system on the MGA simply because I could not tune the carbs well enough using the lifting pin method. Air filters were not a factor because a) at first, I ran velocity stacks with no air filters and b) when I added air filters, my set up permits them both to be removed in about 8 seconds. Now the Volvo air filters are a different story …
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Old Dec 31st, 2018, 23:52   #13
Derek UK
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Quote:
Originally Posted by blueosprey90 View Post
For me, the beauty of my system for adjusting the fuel mixture (measurement of the jets) when applied to the Volvo is that you don't need to remove the air filters.

To be honest, I developed that system on the MGA simply because I could not tune the carbs well enough using the lifting pin method. Air filters were not a factor because a) at first, I ran velocity stacks with no air filters and b) when I added air filters, my set up permits them both to be removed in about 8 seconds. Now the Volvo air filters are a different story …
Agreed, but the carbs have to be treated separately by loosening the central clamp/clamps on the shafts to set the flows equally before locking down and adjusting the mixture. Yes, the jets should be set level with the bridge as a starting point with the dashpots off if you are being fussy, as just winding the jet nuts full up doesn't always set them equal. Not uncommon to find that one jet doesn't quite go fully up to the bridge so if that happens, match the other jets position to it. At that point turning the jets down 12 flats/ one 1/2 turns of the nut will give you a starting point but it is rare that they will end up with equal flats down after fine-tuning.
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Old Jan 7th, 2019, 23:53   #14
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Good evening, here I am going from bad to worst, tried to tune the carbs, went for a test and the first hill (fortunately close to home) the engine quit and could not get it started.
Towed the car home and went step by step on the rear carb and got it started for a few seconds, then a jet of fuel started spurting from an orifice below the float chamber of the rear carb, and the RPMs were about 3000, shut it off immediately to find out the source.
I don't understand the reason of the orifice (flooding relief?), especially that the front carb doesn't have one.
I have tried to identify the orifice in parts breakdown drawings, photographs of the float chamber, etc. to no avail.
I am on the verge of taking the whole thing apart and sent it for rebuild!
Ideas greatly appreciated
Thank you folks
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File Type: jpg Rear Carb Float Chamber.jpg (101.0 KB, 15 views)
File Type: jpg Front carb float chamber.jpg (96.6 KB, 15 views)
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Old Jan 8th, 2019, 03:19   #15
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Found the way to SW-EM.com SU carb service, and beñieve that I can inderstand a little better where the problem comes from, still puzzled by the lacking orifice in the dront carb.
Romorrow will be carb dissasembly and cleaning day!
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Old Jan 8th, 2019, 04:51   #16
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[QUOTE=adarvasi;2482641... then a jet of fuel started spurting from an orifice below the float chamber of the rear carb[/QUOTE]

The main reason fuel floods out the float chamber is caused by a sticking needle valve. Spare parts are available from Burlen Fuels in the UK and that also provide a rebuild service
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Old Jan 8th, 2019, 06:06   #17
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Sounds like your carb float chamber was overflowing. Agree you need to check the needle valve. But also check your float chamber, as it may have leaked.

https://www.youtube.com/watch?v=wLRFnTJ28oQ
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Old Jan 8th, 2019, 10:08   #18
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Can you remind us which carbs exactly are fitted. found it H6
http://sucarb.co.uk/float-chambers-s...le-valves.html
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Last edited by arcturus; Jan 8th, 2019 at 10:19. Reason: re read
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Old Jan 8th, 2019, 11:44   #19
Ron Kwas
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adarvasi;

It certainly sounds like we have two separate issues here...!

"fuel started spurting from an orifice below the float chamber of the rear carb"...that is not a problem with Bowl Valve (which when stuck open will result in fuel leaking from Bowl Vent on top), but a problem with Jet feed tube fitting and seal, a completely different issue from a stuck Bowl Valve!...see: http://www.sw-em.com/SU_HS6_Jet_Supply_Line_Seal.htm

...the fact that you don't see a venting hole on the top of front carb Bowl can be be explained by the fact that several styles of bowl venting, including (late model) to a fitting plumbed to a fuel evaporative canister exist, so from your description, it sounds like you have a non-matching pair installed (see also: http://www.sw-em.com/su_carbs.htm#Fuel_Bowl_Venting )not a huge problem per se, but one thing is certain, Fuel Bowls must be vented somehow to allow air to escape as it is replaced by fuel...it sounds your front carb may have a Bowl Lid with one of these vent fittings, and rear carb clearly has an older Bowl Lid fitted, with simple atmospheric venting...all should become clear once you disassemble and inspect (and I wonder where the Bowl Vent of from carb is routed too...?...please report what you find!...maybe just a picture showing the top of both Fuel Bowls...).

Good Hunting!

Last edited by Ron Kwas; Jan 8th, 2019 at 12:14. Reason: Spelling correction
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Old Jan 8th, 2019, 21:42   #20
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Arcturus, Thank you, I have SH6s in the car, and found the repairs kits in the USA at very reasonable prices
https://mossmotors.com/catalogsearch...cat=&q=375-578
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