I fitted some dynojet needles to my blackbird carbs (on 2.0L zetec engine) this evening. It has made a big difference to the mid range torque but I now have a rich spot at 1500-2500 rpm (AFR 9-10 to be precise). The Car bogs down as you pull off junctions etc. So do I lower the needle a clip position or lean the idle jets out 1/4 of a turn. AFR at idle is 12-13. I can't adjust the float level so that option is out.

It's always bin a bit of a black art to me

Does this help?


carb_tuning



[Edited on 12/9/06 by trikerneil]

Thanks, I have already diagrams like that. It seems that at the point I have the rich spot I could either lower the needle or lean out the idle jets. The car pulls fantastically everywhere else so I am more inclined to just lean the idle screws out a bit than mess with the needle height. I may call someone like Holeshot or TTS in the morning for their opinion. Then I guess I could also just add a little more ignition advance at that point in the map too?

I have the same problem. The first option is to lean off the mixture screw. If that fails, as it has for me, the only option appears to be to source smaller pilot jets.
This is as far as I have got because they seem very hard to get hold of!!
I am on R1 carbs, how about you.

cheers Tangoman

I have Blackbird carbs, the idle screws are currently 1 1/2 turns out on a 42 pilot jet. I have some 40's and 35's to change them to if I need to but I suspect that 1/4 to 1/2 a turn back in on the 42's should be enough. Mine were not hard to get hold of, all Honda Keihins from (97-99) seem to use the same type of pilot jets

Blackbird = 42's
Fireblade = 40's
CBR 600 = 38's or 40's
CBR400 = 35's

Allens Performance should be able to help you or a motorbike spares place (if you know what model of bike you want jets for)

http://www.allensperformance.co.uk/

not cheap though pilot jets are £5-7 each.

Solution found:

After talking to Bogg Bros and TTS, I lowered the needles a clip position to lean out the rich spot. This improved but didn't cure the problem. It also made the top end feel "flatter" than it had been. I ended up putting the OEM needles back in but with an extra 2 washers to shim them up and richen the mid range. The results are good the car pulls hard from 2000rpm right to the redline at 7000rpm. It doesn't feel like it is pulling quite as hard as when the dynojet needles were fitted, but I can't live with the car bogging down every time I pull off a junction. I think I may talk to Allens Performance about buying some needles with the same top end profile as the dynojet ones I have but with a slightly leaner profile at the lower end.

I will be driving past Allens tomorrow so I will drop in, if they are open, t see if they have some pilot jets for R1 carbs.
Going back to my SU days it was failry standrad practice to use a needle file to reduce the needle at any piont where a richer mixture was needed. Maybe you need to remove a washer and then file as required to thin the needle to richen up where required.
I am trying to use the TPS and MJLJ software while driving to plot how open the throttle is when rich so I can then remove the air filter to work out where the needle is at each of the plotted points. Not an exact science but near enough to give a good start for the rolling road.