cd.thomson
|
| posted on 12/5/11 at 08:25 AM |
|
|
carb main jet diameters
Morning everyone,
just after a bit of education really. I discovered my zx9r carbs had 2mm main jets fitted, this made the car bog down and was giving a CO reading of
8%. I managed to track down a supplier of jets and purchased 1.6mm replacements, yet after fitting them the CO is still reading a little over 5%.
I've now bought a set of 1.3s but this seems very small compared to the recommendations I've seen on here and elsewhere online. Also am I
right in thinking that pousielles law applies to fuel flow through carbs and I may well overshoot into lean territory by going so narrow?
Is there anything else that could be richening out the mixture? There aren't any washers under the needles.
Also, is the non-cat emissions test performed at idle or fast idle? The mixture is spot on at 900-1k rpm, but just shoots up under any throttle.
thanks everyone
Craig
|
|
|
|
|
macc man
|
| posted on 12/5/11 at 09:04 AM |
|
|
What engine is it. I have a 2.0L zetec fitted with zx9R carbs. The mains are 1.6 which is about the right size. Might be worth getting it set up on a
RR. You can only get an approximation by trial and error.
|
|
|
cd.thomson
|
| posted on 12/5/11 at 09:10 AM |
|
|
hi macc man, its a 2.0l XE. It seems to run well at 1.6mm but is spitting a bit of fuel and I can't get it through IVA as it is.
I can't really afford a RR at the minute, just trying to get it below that golden 3.5% CO and then probably put the 1.6s back in!
Craig
|
|
|
britishtrident
|
| posted on 12/5/11 at 10:17 AM |
|
|
High CO would indicate lean mixture to me.
Lean Mixture -> poor, irratic or incomplete combustion or misfire -> High CO
Any misfire will cause high CO so check everything including manifold joints for air leaks, plugs and the ignition system
|
|
|
cd.thomson
|
| posted on 12/5/11 at 10:48 AM |
|
|
ah okay, thats confused me. I thought more petrol gave a high ratio of carbon to oxygen? 1:1 (CO) rather than 1:2 (CO2)??
I don't seem to be having any misfire and I've corrected an air leak on the exhaust side but I'll check that all over again this
weekend. Any tips for identifying leaks?
Ignition is megajolt running the basic map, not sure what advance its running.. Is it as simple as running more/less advance to decrease CO?
[Edited on 12/5/11 by cd.thomson]
Craig
|
|
|
coozer
|
| posted on 12/5/11 at 11:00 AM |
|
|
Try the air bleed screws under the carbs, they control the idle mixture. Main jet only come in wide open taking over from the needle. 1.6mm main
sounds about right.
Just a thought, have blocked the air bleed holes?
1972 V8 Jago
1980 Z750
|
|
|
cd.thomson
|
| posted on 12/5/11 at 11:04 AM |
|
|
cheers coozer,
I haven't blocked those airholes actually, I'd completely forgotten about them. Where are they again? inside the carb body?
I've got the mixture perfect on the meter at idle using those screws, but they don't seem to have any effect at 2-3k rpm
Craig
|
|
|
rusty nuts
|
| posted on 12/5/11 at 07:09 PM |
|
|
quote:
Originally posted by britishtrident
High CO would indicate lean mixture to me.
Lean Mixture -> poor, irratic or incomplete combustion or misfire -> High CO
Any misfire will cause high CO so check everything including manifold joints for air leaks, plugs and the ignition system
Sorry I don't agree, incomplete combustion/misfire will cause high hydrocarbons not high CO , the only thing that will cause high CO is a
rich mixture
|
|
|
jacko
|
| posted on 12/5/11 at 07:44 PM |
|
|
quote:
Originally posted by cd.thomson
cheers coozer,
I haven't blocked those airholes actually, I'd completely forgotten about them. Where are they again? inside the carb body?
I've got the mixture perfect on the meter at idle using those screws, but they don't seem to have any effect at 2-3k rpm
The air corection screws ajust the mixture at tick over .
the main neddles ajust the fuel/ mixture at higher revs
the air corection holes only come into play at high revs to stop the fuel/mix going week
NOT all engines need the air corection holes blocking
You need it setting up on a Rolling Road its the only safe way
Jacko
 
carbs on manifold
the brass ring / hole in line with the main neddles are the ones you block if needed
[Edited on 12/5/11 by jacko]
|
|
|
.jpg)
