Running too rich

[Hvilshoej]

Hi all. I am new to this forum but very exited to join.

I have a 1966 SWB 911 with a 1973 911E engine. The engine is in a pretty good shape and according to the previous owner - rebuilt app 12000 km ago (6-7 years).

The MFI has been renovated three months ago and ever since the car has been running rich.

When the engine is warm it starts to "pop" through the exhaust in the low rpm range (idle - 2500).

The air filter, sparkplugs and points are new. The cables from the distributor to the plugs are good. The timing is right.

I have checked the tube from the HE to the cold start thermostat - it is fine, but the thermostat is not warm even if the engine is at running temp.

I have read and followed the CMA to the best of my knowledge.

Any ideas?

Thanks in advance

['76 911S 3.0]

Originally Posted by Hvilshoej

The MFI has been renovated three months ago and ever since the car has been running rich.

I'd start there. What was changed/renovated?

[422flat6]

Take the tube off of the thermostat with the engine running at operating temp and see if hot air is coming out. If not you could have a leak or rusted out heat exchanger preventing the hot air from getting to the thermostat to lean it out.

If there is hot air, then search this forum for MFI thermostat threads. You can take it off, clean it (being careful to keep the washers in the correct order) and test it in hot water to verify it is extending all the way. IIRC there should be 25 washer pairs inside.

[tobluforu]

What do the plugs look like and which ones are you using? What do mean by the thermostat isn't warm, how are checking? Also, how do you know its running rich, are the plugs fouling?

[Hvilshoej]

Thanks for the answers.
To 422falt6 - I will try your idea tonight.
To tobluforu - I read somewhere on this forum that the thermostat normally would get so warm that you can't keep your hand there for at more than a couple of seconds because of the hot air from the HE. The reason I think it is running rich is because of the popping from the exhaust and also because the exhaust pipe end is black.
What plugs do you recommend?

[BSNMOE]

After the car is driven and warm, disconnect the tube at thermostat and blow hot air thru the thermostat with a heat gun or good hair drier. that should lean it out.

[bigel]

Who is Rich?

[Porboynz]

Originally Posted by Hvilshoej

Hi all. I am new to this forum but very exited to join.

I have a 1966 SWB 911 with a 1973 911E engine. The engine is in a pretty good shape and according to the previous owner - rebuilt app 12000 km ago (6-7 years).

The MFI has been renovated three months ago and ever since the car has been running rich.

When the engine is warm it starts to "pop" through the exhaust in the low rpm range (idle - 2500).

The air filter, sparkplugs and points are new. The cables from the distributor to the plugs are good. The timing is right.

I have checked the tube from the HE to the cold start thermostat - it is fine, but the thermostat is not warm even if the engine is at running temp.



Any ideas?

Thanks in advance

The thermostat housing should get too hot to touch comfortably, this will be your problem. You can either fix the thermostat in the lean position by packing it or fix why its not getting hot air from the heat exchanger, there needs to be a hose from the shroud to the lhs heat exchanger obviously. If these are all in place then the hose to the MFI must be blocked, they are supposed to be double skinned so maybe the inner has collapsed.
I have read and followed the CMA to the best of my knowledge.

[tobluforu]

There are two hoses, one that connects to the shroud and goes to the pump, another super thick hose under the car that goes from shroud to HE. Some have neglected to look under car for that hose. Some cars have been known to not even have the correct left side HE that has the port.
Plugs: 6 or 7 heat range ngk's.
If it was renovated and it runs worse, sounds like they might have effed up the thermostat.

[dicklague]

I had the same thing happen to me. I had the MFI "resealed" my mechanic installed it and all worked well until my first long drive. As soon as the car warmed up it was so rich that it was hardly driveable.

They had reset the MFI to "factory" settings. As you know from the above the stack of bi-metallic disks push in the rod to lean out the engine as it warms up.

I went to school on the MFI system and eventually took out the warm up stack and put in an adjustable screw arrangement so I could adjust the mixture there.

Of course I installed an AFR instrument so I could tell the AFR [air fuel ratio] all the time on the dash. And I did use the procedure to adjust the high and low adjustment.

I also have a push button installed on the dash to trigger the solenoid valve for cold starts. I do live in a warm climate, but I also enjoy being in control of warm up and start and not rely on the 50 year old parts and tech to do it for me. Of course the AFR gauge is the key so you know what is going on. I use a Daytona-Sensors Wego IV instrument that records up to 2 hours of data in addition to the digital real time readout.

The end result is that I have a great running 2.7 MFI system.

[Hvilshoej]

I have checked the thermostat and it seems to be working right. Now i am focused around the wiring of the micro switch, rpm transducer and stop solenoid. There goes a new wire from the three fuses box directly to the micro switch. See photo.
The red/Grey wire to the stop solenoid is taken off. I have replaced the blue wire with the red/grey wire with out any difference. Any ideas.
Thanks for all your replies.

[tobluforu]

that switch only works at a certain rpm when you let off the throttle. Unplug it and run it to see how it runs.

[Flieger]

Originally Posted by tobluforu

that switch only works at a certain rpm when you let off the throttle. Unplug it and run it to see how it runs.

This is correct, assuming the rpm transducer/speed switch is fully functional. Most of them have transistor leads broken after all the heat and vibration.

I like mine functional. No backfires while engine braking.

[tobluforu]

Take a few pics of your engine bay, its really hard to tell but it looks like you have some funky things going on in there. When you unplug the micro switch make sure you back off that screw which activates it. Some will adjust the screw too far in only to find that it hold the butterflies open.

[matthewb0051]

Make sure you check the pump is synced with the engine when belt is attached. Also don't forget to check your injectors. If those are not spraying right your adjustments will amount to nothing. I recently got an injector tester from mercedessource.com and after using it to test and clean my car was transformed.

[matthewb0051]

And in case you don't have this:

http://www.flatsixaddiction.com/pelican/MFI_Check_Measure_Adjust.pdf

[Porboynz]

Originally Posted by Hvilshoej

I have checked the thermostat and it seems to be working right. Now i am focused around the wiring of the micro switch, rpm transducer and stop solenoid. There goes a new wire from the three fuses box directly to the micro switch. See photo.
The red/Grey wire to the stop solenoid is taken off. I have replaced the blue wire with the red/grey wire with out any difference. Any ideas.
Thanks for all your replies.

The microswitch and RPM transducer only come into effect on overrun to cut the fuel and reduce backfiring, they play no part in how rich the system runs when accelerating or at steady throttle. Testing correct operation is simple, lift the revs to say 2500rpm and operate the microswitch, the engine should die until the revs drop when it will burst back to life and then die again as the revs rise.

You say the thermostat is working normally, does this mean it gets hot after 10 to 15 mins driving? If its not too hot to touch comfortably its not plumbed correctly to the hot air from the lhs heat exchanger. If in doubt, open it up and pack it in the fully closed position with washers, cold running will be impacted but once the engine is warm all should be well.

[cmcfaul]

How do you know its running rich? You really need an AFR to dial it in both at idle and at speed with load (hot, warm and cold).

The easiest way to make it leaner is simply to take a couple turns out of the linkage to the MFI pump. Could not be easier. However, you are completely blind and totally guessing with out an Air Fuel Ratio meter.

Chris
73 E

[tobluforu]

Originally Posted by cmcfaul

How do you know its running rich? You really need an AFR to dial it in both at idle and at speed with load (hot, warm and cold).

The easiest way to make it leaner is simply to take a couple turns out of the linkage to the MFI pump. Could not be easier. However, you are completely blind and totally guessing with out an Air Fuel Ratio meter.

Chris
73 E

Oh god, now you have written blasphemy in regards to not following the mfi commandments. How dare you not have that rod at 114mm.

[stownsen914]

Popping could be lean just as easily as rich.

As for the tailpipe being black, a couple thoughts:
1. Since there are adjustments for low, medium, and high RPM, keep in mind that if you are rich in one range but lean in another, you may still wind up with black on your tailpipe and mistakenly think you're rich in all ranges.
2. I've heard that pump gas these days may give misleading tailpipe color. But I am not sure of this, as I really only do such tuning on track-only cars that use leaded race gas.

As mentioned, having a good AFR meter will make your tuning MUCH easier. I'd be curious to hear if others agree with point #2, which might call into question the tailpipe color method of tuning.

Scott