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Keith Wallace
United Kingdom
367 Posts |
 Posted - 21/04/2009 : 12:31:01
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[size=3]Having just fitted new M6 needles and jets to my carburettors, making sure the shoulder of the needle is level with the bottom of the piston needle aperture as, the car now ticks over well but with the mixture nut screwed up as hard as it will go, surely the mixture should be so weak as to prevent the car from ticking over?
As bottom of both the pistons on each carburettor have a recess, should the needle shoulder be moved out from the aperture and a lined with the very bottom of the piston?
Any information would be very welcome
Keith[/size=3] |
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Keith Wallace
United Kingdom
367 Posts |
Posted - 22/04/2009 : 10:10:42
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Thanks Paul,
I Wanted to make sure other P owners also had recesses in the piston bottoms,
I have three x M6 needles, the one not being used, is much longer than the two I am useing. Maybe I am using the wrong needles and need the longer ones.
Keith |
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Mark Sellick
United Kingdom
56 Posts |
Posted - 22/04/2009 : 13:06:54
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Keith,
Probably stating the obvious so apologies, but have you checked that the new jets are the correct diameter (90thou?), and the needles really are M6 - I recently ordered a needle from Burlen and received something entirely different, although the label on the phial was correct!
Regards,
Mark |
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bahnisch
Australia
674 Posts |
Posted - 23/04/2009 : 13:40:47
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| Have you fitted new jets? These are often overlooked and the carbs will not respond unless the jets are OK. |
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Keith Wallace
United Kingdom
367 Posts |
Posted - 23/04/2009 : 14:59:07
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Yes, 2 x new jets have been fitted, (which were check for size against the originals and markings when fitted). The jets are now set flush with the inside of the carb body, but still giving a good tick over with no signs of over weak or rich mixture.
(Screwed up as far as they will go)
18 months ago, when I first checked the carbs, I noticed that the needles were differrent! (both stamped M6) and so I bought another M6 needle from Burlen and matched it with one of the originals of simular length.(Short one)
(By the by, All the diagrams I have ever seen do not apear to show the carb. pistons as having a receesed bottom, but flat -level with the needle aperture).
I will measure both needle lengths and perhaps some will be able to confirm which of the needle size is correct for the PB.
Thanks for all you help and advice.
Keith |
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Bruce Sutherland
United Kingdom
1565 Posts |
Posted - 23/04/2009 : 22:49:19
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Could it be that the jet is the wrong size? 1" SU OM carburettors should have 0.090inch bore size jets:
 
The jet should be marked "9": see photo (9 inverted)
The next larger jet bore size is 0.100inch which would/could incease the rate of fueling and hence the high idle speed with the jet screwed right up.
Could this be the problem?
Bruce. (PB0564) |
Edited by - Bruce Sutherland on 23/04/2009 22:51:51 |
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LewPalmer
USA
3244 Posts |
Posted - 23/04/2009 : 23:40:43
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Or simply try to insert a 3/32" drill bit into the jet (don'r even have to remove the jet from the carb). If it goes in the jet is either .100" or badly worn (thus a likely source of the problem). If it doesn't fit, it's a .090 jet.
Lew Palmer
Registrar, NAMMMR |
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Keith Wallace
United Kingdom
367 Posts |
Posted - 24/04/2009 : 09:59:24
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All jets (new + old) are stamped 9.
All three needles are of different lengths! but do not now think that this is the problem, as they all have the same girth at the point they meet the jet.
When I look again closely at the level of the jets, they are not flush with carb body, so will have to look at what's stoping the jets moving up level.
Thanks again
Keith
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DickMorbey
United Kingdom
3677 Posts |
Posted - 24/04/2009 : 13:41:38
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Keith,
It may be worth checking the choke setting. A couple of years or so ago my choke linkage was, unbeknown to me in tension, causing the jets to be pulled downwards and making the carbs over-rich - to the point where I had piston number 3 seize. At least I suspect that this was part of the cause.
I only discovered it one day when I happened to remove a clevis pin and the jet assembly jumped up into the "correct" location.
Regards
Dick Morbey, PA/B 0743 |
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