givemethebighammer
|
| posted on 26/4/06 at 10:15 PM |
|
|
slight popping on the overrun
My 2.0L zetec (blackbird carbs / gems 3d ecu) pops a little at only a couple of ignition load sites (quite quiet not loud bangs, I probably
shouldn't worry really)
2000 rpm @ 0% load to 2500 rpm @ 0% load. The LC1 wide band confirms that the mixture is slightly lean at these points (15-16AFR).
(0% = throttle fully closed)
advance at these sites is
2000rpm @ 0% 24.61 degrees
2400rpm @ 0% 26.02 degress
Apart from these two sites the car runs very well which is confirmed by the LC1 wideband showing good AF ratios everywhere else so I am loathed to
adjust the fueling. So can I just reduce the advance at these two sites to stop the popping. I was thinking something
like
2000rpm @ 0% 20 degrees
2400rpm @ 0% 22 degrees
Or should I just enjoy the popping
|
|
|
|
|
Jon Ison
|
| posted on 26/4/06 at 10:18 PM |
|
|
Popping on overun is/can be an air leak on the exhuast side of things, most tuned cars "pop" on overun though, if the exhaust is short
enogh nice flames come with it.
|
|
|
givemethebighammer
|
| posted on 26/4/06 at 10:52 PM |
|
|
Thanks Jon, but the popping only happens at the specific load sites above. If the exhaust was leaking air wouldn't it pop in other places too ?
Mixture is definitely slightly lean when it does it.
[Edited on 26/4/06 by givemethebighammer]
|
|
|
Danozeman
|
| posted on 27/4/06 at 09:26 AM |
|
|
Id make it worse. A pop sounds good.
AS Jon said its usually an air leak.
Dan
Built the purple peril!! Let the modifications begin!!
http://www.eastangliankitcars.co.uk
|
|
|
C10CoryM
|
| posted on 27/4/06 at 02:02 PM |
|
|
Popping after letting off the gas comes from being lean. You hear it a lot on dyno pulls where a car is running out of fuel on the top end. If you
were injected Id suggest fattening it up a little, but if the A/F is good everywhere else just leave it alone. Some engines just do that and its more
noticable with louder exhaust. As long as its just a couple little pops its fine. Louder bangs are hard on valves .
And yes, an exhaust leak can introduce air into the gases making them lean as well.
Cheers.
"Our watchword evermore shall be: The Maple Leaf Forever!"
|
|
|
givemethebighammer
|
| posted on 27/4/06 at 10:34 PM |
|
|
thanks for the replies. One of the westy people suggested that I increase the advance at the sites in question. Two degrees of extra advance seems to
have reduced the popping to a quiet burble. I guess this may change if the engine / exhaust gets really hot. But I'm happy with it.
|
|
|
