How are carbureted engines tuned?
01-31-2011, 02:53 PM
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How are carbureted engines tuned?
This is a curiosity question but how did people back in the day tune their carbureted engines when they added alot of mods and stuff to them? I know they didnt have the sensors and ECUs like we have today, but I'm sure there was still a bit involved like adding bigger fuel injectors and pumps. 
On older cars, do you not have to worry as much about AFR, like with newer ones?
On older cars, do you not have to worry as much about AFR, like with newer ones?
01-31-2011, 03:22 PM
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Well, you could use a wideband, but generally shadetree mechanics smelled/watched the exhaust, listened to the engine, and pulled the plugs to see if it was running too rich or lean.
When I was adjusting timing on most my carburated cars they also had a traditional distributor so you adjusted timing by turning the distributor. I always advanced the timing until it started knocking under load climbing hills. If that happened, I would hop out and retard timing a bit. Most people used a timing light though. I had great luck with my method though and as long as I didn't IGNORE the knocking I never hurt anything and generally made quite a bit more power than when timed "correctly".
You can adjust or change the main and secondary carburetor jets, accelerator pump, and power valve, also change carburetors. A lot of cars came with small 2 barrel carburetors, so we would swap in a new 4 barrel intake manifold and put on a bigger 4 barrel carb. That would take care of the intake and fueling side of things and the internals and exhaust were the same as today basically. Turbocharging was a bit different, and a supercharger usually sat on top of the engine and drew down air and fuel from a carb or carbs mounted on top of the blower.
To fine tune a carb's idle, you adjust the idle screw.
I may not be 100% on everything, I haven't rebuilt or tuned a carb since 1998.
When I was adjusting timing on most my carburated cars they also had a traditional distributor so you adjusted timing by turning the distributor. I always advanced the timing until it started knocking under load climbing hills. If that happened, I would hop out and retard timing a bit. Most people used a timing light though. I had great luck with my method though and as long as I didn't IGNORE the knocking I never hurt anything and generally made quite a bit more power than when timed "correctly".
You can adjust or change the main and secondary carburetor jets, accelerator pump, and power valve, also change carburetors. A lot of cars came with small 2 barrel carburetors, so we would swap in a new 4 barrel intake manifold and put on a bigger 4 barrel carb. That would take care of the intake and fueling side of things and the internals and exhaust were the same as today basically. Turbocharging was a bit different, and a supercharger usually sat on top of the engine and drew down air and fuel from a carb or carbs mounted on top of the blower.
To fine tune a carb's idle, you adjust the idle screw.
I may not be 100% on everything, I haven't rebuilt or tuned a carb since 1998.
02-01-2011, 03:01 PM
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along with what he said^^ most carbs have one or 2 mixture screws towards the base that let you control your fuel/air ratio.
What i would pay to swap the beta to a distributor/4bbl carb...
What i would pay to swap the beta to a distributor/4bbl carb...
