MFI, High idle, low idle..sticking idle.

[GRMPer]

I've got our 69 911E running pretty well, but the idle seems to catch around 2500 rpm, despite not appearing to have any throttle linkage issues. took a look inside the distributor and the weights are free, not sticking.

Coming to a stop light, it will catch high, but you can "drag" it down using the clutch and a higher gear.

All of the air correction screws are adjusted to approximately the same amount "out" 5 half turns, per the book. Air flow at that is actually pretty close on all cylinders at 3k.

Is there something I'm missing?

The MFI does need to be adjusted, it's rich at idle, and I'm using the "baseline" settings that I got from when it came back from Jerry Fairchild. Essentially, I'm trying to iron out all of the "easy" issues before I take it to someone with a 4-gas for final tuning.

Thanks!
Per
http://www.classicmotorsports.net/911.html

[Tim Walsh]

This may sound obvious but is the hand throttle all the way down?

[Rot 911]

Are the butterflies in the throttle plates closing properly? Sometimes when the throttle plates get older and used more the butterflies will actually create a lip from opening and closing so much and the butterfly on one or more of the plates with catch on that lip. Or the throttle bodies become worn and there is play in the butterflies. Or you have not correlated the throttle stops and the butterflies are not completely closing. Or it is something else.

[304065]

I have the same problem, I think the thermostat discs are sticking. The idle is high until they heat up and move the actuating rod for the rack. Take it apart and clean it with Chemtool, there are detailed instructions in the archives here for the correct order of the discs on the shaft.

VIVA MFI

[Rot 911]

Originally posted by john_cramer
I have the same problem, I think the thermostat discs are sticking. The idle is high until they heat up and move the actuating rod for the rack.

John good thought! That one slipped right by me. Not having the thermostat hose hooked up or sticking thermostat discs would definitely give you a high idle and leave the engine running rich all the time!

[GRMPer]

I'll check the throttle plates, the thermostat does have it's pipe.

What gets me is that you CAN "drag" the idle down using the clutch/transmission, back to its "normal", low, fat idle (700 w/ lots of gas fumes, currently)..that makes me think distributor, even though it's smooth as silk.

I'll pick up a little mirror so I can see down the 2,3,5,6 stacks.

thanks for the suggestions.

Per

[GRMPer]

Oh, and the hand throttle appears disconnected...up or down doesn't change a thing.

I'll need to figure that out at some point.
Per

[RichMason]

I had the same problem on my 69 E. The TBs were worn out and sticking. I could never get the idle below 1300 but when it stuck higher, bumping the clutch would bring it down from say 2500 to 1300-1500. I sent my TBs to Eurimetrix last week so he can rebuild and resell them so I know he has a set available.

[GRMPer]

Hmm, I wonder if the sticking is more because of a decade of grunge from not running or if it's from wear. I'll get one of those inspection mirrors on a stick and see if I can see what's going on.


Per

[GRMPer]

Ok..some more digging (and a lot of learning) and here's what I've figured out.

A) the adjuster for the speed switch was actually keeping the throttles from closing completely. When I backed this off, the idle became very, very, very low...cough cough quit.

B) hooked up the hand throttle (using a link I made from a $.67 "Mirror Clip" from Lowes) and could then pull the idle back up enough to drive around..but it would still be kind of weird..up and down.

C) After reading a few of the MFI articles (and Check-Measure-Adjust), I disconnected the link between the throttle bodies and the pump....pushing the link forward (richer) instantly cleared up the idle...nice and smooooth. Had to push it nearly 1/2" for it to really idle well....past that and it would start getting smokey and stumbly.

so, I guess that's the next step. I've got the MFI tools ordered and I can start fine tuning the mixture when they get here. I'd like to get it close before I waste mechanic and/or chassis dyno time.

Pics have been updated on the website:

http://www.classicmotorsports.net
(click on project car updates)

Per

[Paul Thomas]

Per,
Make sure before you fiddle too much with the mixture that you measure the length of the rod from the cross shaft to the pump. If it is too short it could cause the condition you described.

Paul

[GRMPer]

Yea, I was wondering about that, it measured out correctly, but I noticed elsewhere on Pelican, someone mentioned something about the shafts going from the crossbar to the tbs themselves needing to be the right length as well...I'll check those.

Love that "search" feature on the Pelican board.

Per

[Mr Beau]

Per,

Where did you get the MFI tools from??

[GRMPer]

From our host:

They're listed under "tools" in the early 911 store..I think something like 41 bucks for the three widgets.

Per

[Halm]

Per,

I had EXACTLY the same problems with mine. P-Thomas helped me out by doing 2 things. First the linkage was way out of spec and he set that. Then he used a Gunston Gas Analyzer and got my way too rich mixture down to where in needed to be. About 12 - 13 clicks as I remember.

Now the car runs very well, especially around town and gas mileage went from 16 mpg on the highway to almost 24 mph on the last trip.

[GRMPer]

Yea, I'm eagerly awaiting the tools from pelican so I can actually adjust. I've got a friend that has a 4-gas that we can use to fine tune. I was surprised that my mixture was lean...but that's why its bad to assume things.

Per