I've been looking around on here for about a couple hours and I still haven't quite found my answer. A buddy gave me a new header and after installing it my carb is running dogish. I can't get it to idle right. Right now its ideling below 1grand. When its running it almost sounds like there's something wrong with the a/f mixture. How do I change it(myself) in order to get it running right with the new header without going and dropping money. Any ideas would be greatly appreciated
Thanks

 

When you install a header your A/F ratio will change (lean) so you need to adjust your carb (enrich). You need to adjust your mixture adjustment screws on the carb so more fuel is added to the mixture at idle and you may have to change your carb jets because you could get real lean when running at higher engine RPM.

 

What do you mean when you say real lean. ?

 

A header allows the engine to breath better. Exhaust gases exit the cylinder faster thus allowing higher volumes of air/ fuel to enter the cylinders. Air is lighter than fuel thus air will move faster into the cylinders. At some point the fuel will not mix with the air fast enough (Idle mixture screw /jet size) and your air / fuel ratio will lean out. This is why your engine idle is off- it is lean. You will have to open the mixture screws more to allow more fuel into the A/F mixture. That is fine for idle and about 20% throttle opening but when you are above that your main mixture system cuts in and again, because of the engine breathing better with the new header, your A/F mixture most likely will lean out. If you have access to a Wideband Air / Fuel Ratio gauge you will see this happen as you advance the throttle towards open.

 

very well explained!!!!

 

with the throttle amost open and it leans out does it affect much or could I just let it lean out. I don't want to ask wrong questions but carbs are new to me. I have always been a efi fan but now that I have a carb'ed rig I m a big fan! Hello power!

 

Yes you could have serious problems if the mixture is real lean; burned valves, pistons, rings, etc. The only way to check the mixture is with an A/F ratio meter or gauge but you could use the old spark plug method. Install new spark plugs and drive the truck on the highway at normal speeds for awhile and then pull the spark plugs and look at their color. If they are all white then you are lean and if they are tanish / light brown you are okay. The EFI systems use an Oxygen sensor to adjust the A/F ratio while driving Carb systems do not have that capability.

 

This happened to me however I have a fuel injected 22re and I just put a cold air intake on it ran perfect after.

 

It ran perfect because your EFI system (oxygen sensor) compensated for the change and a cold air system does not have that much of an effect on A/F ratio compared to a well designed exhaust header.