Backfire A/F Ratio Drop on MPI Nytro

[morrisond]

I'm helping a friend dial in his Supercharged Nytro. When he is cruising and gets on at 5-6,000 rpm his A/F ratio will go down to 10:1 from 11.5-1 and I can hear a backfire when I'm behind him and the sled hesitates for a second before before going again.

Is this something to do with the boost coming in? He is using RB3 and there are no obvious lean spots. Is there a way to add or take away fuel when the boost comes in right at that point?

Thanks

 

[Agman 57]

Is he running a Gems box for his fuel settings, I would think he is if he has a MPI unit. Mine would cough like that when I would nail it. It was running to rich on mode 4, which is the extra fuel on boost, I dropped down 2 lights and it made all the difference in the world.

 

[morrisond]

He is using rapid bike 3

 

[backcountrymafia]

if his a/f is leaning out a bit like you said when he punches it, i understand that the rb3 uses a accelerator pump feature. it sounds like theres a surge in air volume when he punches it and maybe you could try adding some fuel in that rpmand tps range to fatten up the mixture, is the sled bogging slightly when he gets on it or is it smooth? with a supercharger the boost deliverly should be fairly linear at that rpm and if it has a little surge then you should be able to give it fuel and smooth it out.

 

[morrisond]

According to the A/F Ratio it's going rich, down to 10:1 then recovers to 11-11.5:1 There is a bog. We added fuel in the middle and didn't get rid of it.

 

[rxrider]

At 10.0 AFR his sled is not going to run right, it's about to drown in fuel, and it will bog and miss and pop and not good. Try to lean out the part of the map causing the 10.0 AFR

 

[Nitrousman1]

Is this an MPI Stage 1,2 or 3? Some guys on here have maps for the different stages so maybe he could try one of them. You could even check the RB3 forum on here for one to download.

 

[gsxr]

rb3

Go to the rb3 map and Lean out the middle to see 12.5 / 13.0 a/f , It will run much better.

 

[spddmon]

check the rpm range where it goes rich and take fuel out of the map in the coresponding rpm range on rb3