New header, now too lean: advice?

[Kingme2]

I bought Marks header and exhaust formy '80 FI, very sexy...

Issue is the final stage of the setup after install is the "adjusting the air/fuel mixture"

My mechanic installed the header and exhaust, then gave me a blank look...

Locally, there are few Fiat pros left, so I'm resorting taking it to a "performance shop" that said they would try to tune the AFM, with a meter on the exhaust...they normally deal with Ferarris and BMW's...

Just to ensure I'm telling these boys the right thing, they are to pry open the AFM, turn a screw until they get the proper ratio... That's it? Read a bit on here about "tweaking your AFM" , sort of clear... I think.
That'll do it? Test the air mix while Under load (... Driving)

Any advice from others who've done this?

[narfire]

Nope... the air/idle screw is on the intake plenum, next to where the wires clip in to the throttle position sensor. (that set properly?)
The only time I'd be opening up the top of the AFM is if the car is stumbling at the lower RPM's, then one might want to adjust the two pins to a "cleaner" section of track.
I set the throttle plate just off where it is fully seated in the intake. A bit of slack in the cable and then adjust the screw to set the idle.

Give Mario a call at Ital motors in Edmonton for further help in setting these things up.
Chris

[So Cal Mark]

the air bypass on the AFM will alter the air/fuel mixture but it may not have enough adjustment range. When that happens the potentiometer in the AFM has to be moved. It's really important to use a CO meter and have the engine loaded (dyno!) when making this adjustment

[majicwrench]

I would bet that just installing a header is NOT going to alter the f/a ratio enough to have to adjust it. Does car run well?? if so, drive it and have fun. Opening up AF meter and tweeking stuff is something I would avoid if possible.
Like Mark said, minor adj can be done with screw on AFM
Keith

[So Cal Mark]

our header scavages so well that the mixture MUST be adjusted after installation. Overly lean mixtures cause super high exhaust temps.

[Kingme2]

Yes, Mark is correct. Wicked hot under there and have already damaged it... Now I want to get it tuned so I CAN race around and have fun.

One of the local performance places has agreed to try... I will call Ital Motors, as well. Spent lots there, have yet to find them friendly or helpful, but...

Considered driving up Saturday, but would have to drive up, leave it, then drive up following weekend (wife agree to 2nd 3hr each way driver he day before honeymoon? Unlikely...)

[narfire]

Just a question... Mark's header for the fi cars do have the port for a O2 sensor? If so, would not the sensor pick up the exhaust "lean" and send a signal to compensate?

Just wondering

[majicwrench]

Bear in mind this is all theory, BUT just cause it scavenges well, that should not change the mixture. If system is getting more exhaust gas out, it will be replace on intake stroke with air that goes thru AFM and thus gets proper fuel injected from injectors. Or please explain how it would alter mixture. I'm an old guy but still have lots to learn.
' Ive put headers on untold nubers of cars (not fiats) and never had to mess with the mixture.
' Certainly running it richer could cool exhaust.
' Keith

[timinator]

Now I want to get it tuned so I CAN race around and have fun.

What you are experiencing with Mark's header is pretty common with a good header and exhaust. With the stock exhaust manifold, and a restrictive head pipe and muffler, there is a certain amount of exhaust gas that does not make it out of the cylinder before the exhaust valve closes. You can consider this as an egr system. The purpose of an erg is to lower the cylinder temp during combustion to limit the formation of NOx. By adding a good header and exhaust you are raising the cylinder temp considerably because of exhaust scavenging. Now there is nothing in the cylinder taking up volume when the next batch of air and fuel arrives. Adding more fuel will help to lower the cylinder temp. You might find that the engine may need less advance for best power. Retarding the timing will make the mixture leaner. So more fuel needs to be added. I have seen plenty of ceramic coated headers with the coating burned off from running to lean. Ceramic burns at over 1100F. You should not run a stock motor at that high of an exhaust temp. Burned or cracked valves, valve seat wear, over heated pistons are sure to occur. So get it tuned and have fun.

[Kingme2]

Awesome, thank you.

Into shop soon, hope to put a few Kms of big-grin driving before I wrap it up for the season.