davidimurray
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 posted on 4/5/15 at 06:26 PM |
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Bike Carbs lean on acceleration
Right
Having finally thought I was just about there with my ZX6r carbs on the Duratec, I've been thrown another curve ball.
Having had this issue http://locostbuilders.co.uk/viewthread.php?tid=197720
Having had the car running just about perfectly under light throttle and cruise but running too rich under WOT I bought some smaller main jets. Before
I changed the mains I did a good 30 miles on the road with everything running fine. Changed them from the 1.5mm that were in for the Pinto to 1.4mm.
Fitted the new jets and fired the car up, but whenever I blipped the throttle the fuelling went off the scale lean. To be sure I took the car for a
quick spin and sure enough whenever accelerating it was going widely lean.
Back in the garage, I stripped the mains and pilots and soaked them in carb cleaner overnight, put the original 1.5mm mains back in, stripped and
cleaned the idle screws, checked the float levels, checked all slides are lifting when blipping the throttle, checked slide resistance, removed caps
and checked the O-rings, checked the carb balance and have sprayed all around the manifold with WD40 to check for leaks.
The only thing I have found is that no2 cylinder sparkplug is showing slightly leaner than the other 3.
All the above has made no difference to the running.
Has anyone got any ideas of things to try?
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
Gallery 5 http://www.facebook.com/media/set/?set=a.10150244028550325.366987.601005324&l=583fd5cd3a
Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
Duratec Engine Swap https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f " target="_blank"> https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f
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perksy
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| posted on 4/5/15 at 06:43 PM |
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Fuel pressure ok ?
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davidimurray
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| posted on 4/5/15 at 07:01 PM |
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Can't really check pressure, but have checked the flow and it is as good as it has always been (with zx6r bike pump). Forgot to say I have also
checked the filter just before the carbs and that was spotless.
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
Gallery 5 http://www.facebook.com/media/set/?set=a.10150244028550325.366987.601005324&l=583fd5cd3a
Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
Duratec Engine Swap https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f " target="_blank"> https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f
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stevepj
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| posted on 4/5/15 at 09:07 PM |
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Back in the good old days of Minis etc with SU carbs which operate in pretty much the same way as bike carbs ie a needle moving up and down in a jet
tuners would profile the needles by hand to produce the correct fuelling.
Using a standard tapering needle in a fixed size jet means there will be a compromise somewhere, what you can choose is where by changing the jet
size, the needle size and the needle height, unless you can find someone who can custom profile the needles for you.
Obviously the best place to have your compromise is where it will cause the least damage, a little rich at tickover isn't going to melt some
pistons as very lean at WOT will.
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davidimurray
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| posted on 4/5/15 at 09:24 PM |
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I agree with everything you say, but I don't think it applies to the issue I have. I had this setup with 1.5mm mains and needles in the same
position on the grooves running an idle afr of13, cruise/light accel afr of 13.8 and wot of 10.2. Changed the mains only to 1.4mm leaving everything
else untouched and light accel/ throttle blipping under no load gives an afr of 17-18+. Putting the 1.5 mains back in has no affect so the problem
Seems to be elsewhere.
quote:
Originally posted by stevepj
Back in the good old days of Minis etc with SU carbs which operate in pretty much the same way as bike carbs ie a needle moving up and down in a jet
tuners would profile the needles by hand to produce the correct fuelling.
Using a standard tapering needle in a fixed size jet means there will be a compromise somewhere, what you can choose is where by changing the jet
size, the needle size and the needle height, unless you can find someone who can custom profile the needles for you.
Obviously the best place to have your compromise is where it will cause the least damage, a little rich at tickover isn't going to melt some
pistons as very lean at WOT will.
[Edited on 5/5/15 by davidimurray]
Gallery 1 http://www.facebook.com/media/set/?set=a.116893465324.130778.601005324
Gallery 2 http://www.facebook.com/media/set/?set=a.245243755324.181913.601005324&l=a9831a9319
Gallery 3 http://www.facebook.com/media/set/?set=a.440671625324.232627.601005324&l=3f0d42c523
Gallery 4 http://www.facebook.com/media/set/?set=a.490098255324.297598.601005324&l=efb083b7df
Gallery 5 http://www.facebook.com/media/set/?set=a.10150244028550325.366987.601005324&l=583fd5cd3a
Gallery 6 http://www.facebook.com/media/set/?set=a.10150550640070325.430417.601005324&type=3&l=fe779b358c
Duratec Engine Swap https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f " target="_blank"> https://www.facebook.com/media/set/?set=a.10152527759580325.1073741828.601005324&type=1&l=40aae5e72f
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