MFI Load mixture setting

1972_911T · 07-25-2005, 12:34 PM

Im going for my smog test tmrw and im pretty sure my engine will need adjusting as it just been re installed after an engine fire! In my book it says the load mixture should be done in second gear at 2000rpm on a dynamo is this the only way or just the best way? as the garage im going to dosent have a rolling road. Is it possible to get it near by just revving the engine to 2000rpm with no load?

Thanks Steve

jluetjen · jluetjen's Garage

Who is still smog testing '72's??? I thought most states didn't even bother testing the early '70's car since they are more then 25 years old.

1972_911T · 07-25-2005, 01:28 PM

Im in the UK and unfortunatly even been 33 years old it still has to pass the emissions. Any way its not this that concerns me tweeking the mixture to get it through the test is no problem but while hes got it hooked upto a co2 meter its the perfect opertunity to get the mixture set right as ive been doing some tinkering with it recently to try and sort out my cold running issues!

Zeke · 07-25-2005, 03:45 PM

As the description indicates, it is a part load, or part throttle under load adjustment. simply reving to 2K with no load does not open the butterflies and, hence, the pump arm much; you would be adusting to just off idle. No, you need the arm to be in a more open state. Some do it while driving using an O2 sensor and stopping periodically to make each increment of the adjustment. For a quick check after you think you have it dialed in, you could slip tshe clutch while sitting. Obviouxly that is crude, but it would give you a qucik look at your instrument.

Eagledriver · 07-25-2005, 05:12 PM

As you probably know the best way to do this is to go through Check Measure and Adjust step by step. Having said that if you want to try to pass smog and want to try it the quick and easy way you can just experiment with leaning the main rack 2 clicks at a time and checking for drivablily with the engine warmed up. When you get too lean the engine will tend to feel sluggish and not want to take throttle. It will pop and lurch at part throttle settings. You then can richen up 2 clicks to where these symptoms just fade away. Most smog failures on MFI cars are from too rich a mixture so err to the lean side to pass the test.

Having said all this be sure to take notes on exactly how much you have changed things to you can put them back if you make it worse.

-Andy