After doing headers and exhaust over the weekend, I've noticed my engine runs a bit different. Everything seems to point to the engine leaning out... hesitation off idle, lazy acceleration, hotter than normal running, etc...

Is is normal for a carb needing jetted up after changing out iron manifolds and stock exhaust for headers and good exhaust? The carb tune was just peachy and great before the exhaust work, but since has seemed to lean out.

Also... if it is normal, how much does a carb typically have to be jetted up? 2 sizes? 3?

--- This is a Holley 4160 (750cfm) btw, with dual metering blocks.

 

Try simply readjusting the mixture screws first. If that doesn't help, then rejet the carb. It is normal for the engine to run lean after switching to headers.

 

I did richen up the idle mixture a little bit, about 1/8-1/4 turn, and it helped a bit. I think it does need rejetting though.

Where is a good place to start with jetting? My carb has 69/76 right now. Going up 2 or 3 sizes sound ok?

 

Try two jet sizes per change.

 

Ok, thanks