72with mfi blowin blacksmoke

72 four door · 07-20-2008, 02:24 PM

When i start the car up it smokes blue for a couple of minutes,then goes away,[thats after sitting a couple of weeks] I've also noticed the idle is only at about 500rpm. after shes at temp i;ll hop on her and it blows black smoke out the pipe. I'm assuming this is a very rich condition? I also read that inside the pump when a govenor spring breaks it creates a rich condition. Any advice on this I do have the cma and other various threads pertaining to mfi. But would like any input thanks

Jeff Higgins · 07-21-2008, 10:23 AM

Not much to go on... How does it run otherwise? What condition is the motor in? The MFI system as a whole?

Some black smoke is normal with this system, at least the first time you get on it after puttering around for awhile. If it's been run at high rpm, and under load, up and down through the gears a few times, it should clear up. For the most part, anyway. There will always be more fumes coming out than with other induction systems.

Zeke · 07-21-2008, 10:46 AM

Blue, black white, we all have different definitions of these smoke colors. It could be a build up of oil in the HE's. What does it look like under there?

Yes, what little I know about the MFI pump (and I've torn one down), the spring breaking would not be a good thing for a number of reasons. You'd be running full RPM rich at all speeds. If you really suspect that, I think I'd remove the pump and investigate.

Maybe some of the MFI gurus like JC (not to take away from Jeff

)could tell you about an external test you could perform. That rack has to move, is all I know. The assembled disc thermostat holds the rack at rich until things warm up. That's a place to look as well. What some do to test that is to disconnect the hose from the left HE and use a hair dryer to heat and move the discs. No action is bad. They commonly get dirty and need service, which is a DIY project, IMO.

tmctguer · tmctguer's Garage

i would guess that the star up smoke is from the long period without driving the car.

The 500 rpm is about 1/2 of what it should be, and the black smoke is probably a rich condition.

I would remove the pump looking for the broken spring only after you have eliminated more simple fixes (e.g., points closed, timing wrong, rotor, cap, etc.).

Proper engine timing is critical in an MFI car.

tmctguer · tmctguer's Garage

i would guess that the star up smoke is from the long period without driving the car.

The 500 rpm is about 1/2 of what it should be, and the black smoke is probably a rich condition.

I would remove the pump looking for the broken spring only after you have eliminated more simple fixes (e.g., points closed, timing wrong, rotor, cap, etc.).

Proper engine timing is critical in an MFI car.

Rot 911 · 07-21-2008, 11:30 AM

My first question is how long has it been doing this? Assuming this is a recent occurence, prior to the smoking was everything in tune, both ignition and the MFI?

72 four door · 07-21-2008, 12:01 PM

The heat exchangers are new,well about 2 yrs old but the car only has 2000 miles on it with them it does have an oil leak small but does hit the exchangers. When i used to make right turns the cabin would fill with smoke. I just recently installed a k/n air filter,which shouldnt be a problem. The motor does idle at 500 should i bump up the idle screw or since its running rich also lean out the inrichment screw? What will make it idle better?

Jeff Higgins · 07-21-2008, 12:20 PM

Don't touch ANYTHING unless, and until, you are ready to go through CMA in its entirety. There is no "idle screw" per se that controls idle speed. Messing with the mixture screw in an attempt to adjust idle speed is a recipe for disaster. Again, do not touch anything until you are ready to go all the way. Study and fully understand CMA. Know how the system works, the theory behind it, and what each adjustment should do before diving into this. I cannot stress this enough. If going everything in CMA is beyond your abilities, even the "littlest" thing, bring it to some one who understands MFI. Or start on page one of CMA, posting your questions here as you go. No detail in CMA is insignificant, nor can any detail be skipped. It must be carried out in whole, in order, beginning to end. Please don't just start turning screws.

72 four door · 07-21-2008, 02:27 PM

Sounds like a smart idea. I was going to right down the adjustments i made,but will follow the procedure according to cma

fbarrett · fbarrett's Garage

Friends:

This was not uncommon with MFI. My '70 911E did this once in the pits at Woody Creek International Raceway (aka Aspen), and I recall taking a cover off the pump and simply replacing the spring. There was no need to remover the pump or disturb any settings. Since that was probably 30 years ago, though, that's about all the guidance this faded brain can provide.

Frank

304065 · 07-21-2008, 02:43 PM

Way to early to start cracking open the pump. Go to the "ultimate MFI resources thread" and read everything there, download a copy of CMA and start working systematically through it.

Any competent Porsche driver tracks faster if brakes come smoothly.

Air filter, compression loss, plugs, dwell, timing, fuel pressure, injectors, belt, correlation, smog.

Notice that the last one, "smog" or fuel mixutre is the last thing you check.

My money's on a stuck thermostat or a problem with the hoses from the heat exchangers but the only way you can tell is . . . are you ready for it. . . "CMA!"

There are a couple dozen guys here willing to help, post your questions as you go and you'll have it fixed fairly easily.

Good luck!