strangeling wrote on 12/31/69 at 16:00:04:Greg_650,
How do you actually know when you have the correct size jet installed ? Is the black soot or backfire caused by a jet that is too small or too large ?
Glenn
Backfires are generally caused by a lean mixture (small jet). Soot or blackish smoke would mean a rich mixture (large jet). The "sweet spot" is in the middle where it burns clean, sounds good, and has good power.
The other day, based on a guys exhaust color, very few backfires, and other stuff I opted to just change his main jet 1 size to a 147.5. We could have gone bigger, and may anyway, but black smoke is nothing more than wasted gas. So, we'll see (see note)...
If you have a stock exhaust you can simply go up one 1 size and change the spacer for a lot more fun and less noise. Then if you change other stuff for better flow, you can increase the jets even more just to keep that sweet spot.
Note: this was an unusual case too. The Stinger has a 2002, with only a small amount of bluing on his SuperTrapp (w/ 8 disks) and no bluing on his header. I didn't hear it running before this work but he swears it never backfires. Even better, all his jets were stock.
So, I thought it might be better to just try to just get more power without disturbing a good thing. 1/2 spacer and 147.5 is all we did. We cranked it before I left, but it wasn't ready for the street yet. Time will tell.